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Learn by comparing

A good number needs a good question.

Explore 32 decision labs spanning measurement, error correction, networking, control and sensing. Compare complete input regimes, follow the calculation and discover which assumption changes the answer.

Evidence and experimental design

Evidence and experimental designA fair control experiment can start with the pairingWhat changes when two implementations experience the same batch disturbance?

Imagine comparing two pulse implementations during a day when a laboratory drifts between warmer and cooler operating conditions. Running all of A first and all of B later confounds implementation with time. Even if the total number of shots is large, a difference between the batches can masquerade as a difference between the methods. The experimental unit must be identified before the error bar is chosen.

A matched design asks A and B to encounter similar conditions and records their difference within each match. A disturbance shared by both measurements can then cancel. The relevant variation is the variation of the differences, rather than the sum of two variances treated as unrelated. Pairing earns this benefit only when the correspondence is real. Pairing unrelated records after inspecting their outcomes is not the same experiment.

This laboratory constructs ten matched batches with a shared disturbance and smaller difference noise. Its calculation shows the exact standard-error consequence of retaining or discarding the match. The learning goal is to ask what was randomized, what was repeated, and which conditions were shared. A quantum benchmark can have thousands of circuit shots while still having very few independent calibration batches.

Synthetic decision model

Start with the assumptions

  • Each pair shares the declared disturbance.
  • Difference-noise values are constructed, not sampled from a fitted distribution.
  • The sample standard deviation uses denominator n - 1.

d_i = B_i - A_i; mean difference = sum(d_i)/n

SE_paired = sample_SD(d)/sqrt(n)

SE_unpaired = sqrt(sample_Var(A)/n + sample_Var(B)/n)

Synthetic a fair control experiment can start with the pairing plot: Illustrative response versus Matched batch.
Synthetic baseline case. Horizontal axis: Matched batch. Vertical axis: Illustrative response. Curves show A, B. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Common disturbance scale
0.5
Difference noise scale
0.5
True shift
1.2
Response baseline
50
Shared disturbance pattern
-3, -2, 0, 2, 3, 1, -1, 4, -4, 0
Difference-noise pattern
-1, 0, 1, 0, -1, 1, 0, 1, -1, 0
  1. Compute ten matched differences B_i - A_i. Their mean is 1.2 and their sample standard deviation is 0.408248.
  2. Divide the difference standard deviation by sqrt(10), giving 0.129099. Treating the same observations as unpaired gives 0.632456.
  3. The paired calculation retains the shared disturbance as covariance; it cancels in each difference. The unpaired expression discards that relationship.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Batch pairs10
Mean B minus A1.2000000000000028
Paired standard error0.12909944487358055
Unpaired standard error0.6324555320336759
Unpaired / paired variance24.000000000000004
All ten matched synthetic observations
PairABB − A
148.549.20.7000000000000028
24950.21.2000000000000028
35051.71.7000000000000028
45152.21.2000000000000028
551.552.20.7000000000000028
650.552.21.7000000000000028
749.550.71.2000000000000028
85253.71.7000000000000028
94848.70.7000000000000028
105051.21.2000000000000028

The variance ratio is 24 in this constructed batch. Matching is useful because the common disturbance is genuinely shared. These ten deliberately chosen observations do not validate a population distribution or establish a significance level.

Comparison regime
Complete inputs
Common disturbance scale
2
Difference noise scale
0.62
True shift
1.95
Response baseline
50
Shared disturbance pattern
-3, -2, 0, 2, 3, 1, -1, 4, -4, 0
Difference-noise pattern
-1, 0, 1, 0, -1, 1, 0, 1, -1, 0
  1. Compute ten matched differences B_i - A_i. Their mean is 1.95 and their sample standard deviation is 0.506228.
  2. Divide the difference standard deviation by sqrt(10), giving 0.160083. Treating the same observations as unpaired gives 2.367902.
  3. The paired calculation retains the shared disturbance as covariance; it cancels in each difference. The unpaired expression discards that relationship.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Batch pairs10
Mean B minus A1.9500000000000028
Paired standard error0.16008331164323922
Unpaired standard error2.36790202500019
Unpaired / paired variance218.79396462018917
All ten matched synthetic observations
PairABB − A
14445.3300000000000051.3300000000000054
24647.951.9500000000000028
35052.572.5700000000000003
45455.951.9500000000000028
55657.3300000000000051.3300000000000054
65254.572.5700000000000003
74849.951.9500000000000028
85860.572.5700000000000003
94243.3300000000000051.3300000000000054
105051.951.9500000000000028

The variance ratio is 218.793965 in this constructed batch. Matching is useful because the common disturbance is genuinely shared. These ten deliberately chosen observations do not validate a population distribution or establish a significance level.

Extended regime
Complete inputs
Common disturbance scale
3.8
Difference noise scale
0.86
True shift
2.8499999999999996
Response baseline
50
Shared disturbance pattern
-3, -2, 0, 2, 3, 1, -1, 4, -4, 0
Difference-noise pattern
-1, 0, 1, 0, -1, 1, 0, 1, -1, 0
  1. Compute ten matched differences B_i - A_i. Their mean is 2.85 and their sample standard deviation is 0.702187.
  2. Divide the difference standard deviation by sqrt(10), giving 0.222051. Treating the same observations as unpaired gives 4.467241.
  3. The paired calculation retains the shared disturbance as covariance; it cancels in each difference. The unpaired expression discards that relationship.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Batch pairs10
Mean B minus A2.8500000000000005
Paired standard error0.2220510451825581
Unpaired standard error4.467240759126376
Unpaired / paired variance404.73715521903904
All ten matched synthetic observations
PairABB − A
138.640.591.990000000000002
242.445.252.8500000000000014
35053.713.710000000000001
457.660.452.8500000000000014
561.463.391.990000000000002
653.857.513.710000000000001
746.249.0500000000000042.8500000000000014
865.268.913.7099999999999937
934.836.791.990000000000002
105052.852.8500000000000014

The variance ratio is 404.737155 in this constructed batch. Matching is useful because the common disturbance is genuinely shared. These ten deliberately chosen observations do not validate a population distribution or establish a significance level.

Try the reasoning: Before calculating an error bar, identify the independent experimental unit. What evidence justifies the correspondence within each pair?

Sources and model boundaries
  • Two-Sample t-Test for Equal Means ↗

    A paired comparison has a one-to-one correspondence between observations, allowing analysis of within-pair differences. The lab does not reuse NIST data or claim a significance test for its deterministic records.

  • Combining uncertainty components ↗

    Uncertainty propagation includes sensitivities and covariance; independent terms simplify the variance sum. Covariance, bias and distribution assumptions in the teaching models are declared separately; no NIST endorsement is implied.

Evidence and experimental designA better result in every workload can lose the combined scoreCan a changing workload mix reverse a performance comparison?

A benchmark suite is a distribution of questions. If a provider runs mostly easy instances while another tackles mostly hard ones, their overall completion percentages answer different questions. Neither percentage is wrong as a description of its own workload. The mistake occurs when the two denominators are treated as interchangeable evidence about the methods.

The constructed example contains only two strata, easy and hard. Method B improves the stipulated success probability in both. It is nevertheless possible to make B look worse overall by allocating more hard work to B. The reversal comes entirely from the weights. There is no hidden quantum effect and no arithmetic paradox once those weights become visible.

Standardization chooses one reference workload and evaluates both methods against it. That requires a defensible reference: the published challenge set, a fixed deployment distribution or a clearly labeled teaching mixture. A fair comparison keeps both the observed mix and the standardized comparison. Discarding the operational mix can erase useful information about what a service actually handled; discarding standardization can reward an easier test.

Synthetic decision model

Start with the assumptions

  • Within-stratum rates are known synthetic probabilities.
  • Easy and hard are fixed categories with comparable meanings.
  • No uncertainty intervals are attached to stipulated rates.

Mixed success = easy_fraction × p_easy + (1-easy_fraction) × p_hard

Standardized success uses the same easy_fraction for both methods

Percentage-point difference = 100 × (p_B - p_A)

Synthetic a better result in every workload can lose the combined score plot: Success (%) versus Comparison.
Synthetic baseline case. Horizontal axis: Comparison. Vertical axis: Success (%). Curves show A, B. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
A easy success
0.93
A hard success
0.47
B within-stratum gain
0.02
A easy workload fraction
0.55
B easy workload fraction
0.4
Reference easy fraction
0.2
  1. A is weighted using 55% easy work; B uses 40%. Those are different test distributions.
  2. Use the shared 20% easy reference for both: A = 0.562, B = 0.582.
  3. The raw difference is -4.9 percentage points. The shared-workload difference is 2 percentage points.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
A mixed success (%)72.30000000000001
B mixed success (%)67.4
Raw B minus A (percentage points)-4.900000000000004
A standardized success (%)56.2
B standardized success (%)58.20000000000001
Standardized gain (percentage points)2.0000000000000018

The direction reverses after standardization. B was defined to improve both strata by 2 percentage points. Aggregation cannot identify that fact without the workload mix. These rates are stipulated probabilities, not estimates with sampling intervals.

Comparison regime
Complete inputs
A easy success
0.93
A hard success
0.47
B within-stratum gain
0.03
A easy workload fraction
0.7000000000000001
B easy workload fraction
0.325
Reference easy fraction
0.45
  1. A is weighted using 70% easy work; B uses 32.5%. Those are different test distributions.
  2. Use the shared 45% easy reference for both: A = 0.677, B = 0.707.
  3. The raw difference is -14.25 percentage points. The shared-workload difference is 3 percentage points.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
A mixed success (%)79.2
B mixed success (%)64.95
Raw B minus A (percentage points)-14.249999999999996
A standardized success (%)67.7
B standardized success (%)70.7
Standardized gain (percentage points)3.0000000000000027

The direction reverses after standardization. B was defined to improve both strata by 3 percentage points. Aggregation cannot identify that fact without the workload mix. These rates are stipulated probabilities, not estimates with sampling intervals.

Extended regime
Complete inputs
A easy success
0.93
A hard success
0.47
B within-stratum gain
0.041999999999999996
A easy workload fraction
0.88
B easy workload fraction
0.23500000000000004
Reference easy fraction
0.75
  1. A is weighted using 88% easy work; B uses 23.5%. Those are different test distributions.
  2. Use the shared 75% easy reference for both: A = 0.815, B = 0.857.
  3. The raw difference is -25.47 percentage points. The shared-workload difference is 4.2 percentage points.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
A mixed success (%)87.48
B mixed success (%)62.01000000000001
Raw B minus A (percentage points)-25.46999999999999
A standardized success (%)81.5
B standardized success (%)85.7
Standardized gain (percentage points)4.200000000000015

The direction reverses after standardization. B was defined to improve both strata by 4.2 percentage points. Aggregation cannot identify that fact without the workload mix. These rates are stipulated probabilities, not estimates with sampling intervals.

Try the reasoning: Choose a second common workload distribution. Does the within-stratum improvement change, or only the aggregate score?

Evidence and experimental designA shot budget is also a time budgetHow should measurement effort change when groups take different amounts of time?

The most variable contribution to an observable may deserve extra measurement effort, but that is not the complete allocation question. Some settings take longer to prepare, some require a costly basis change, and others produce information much more cheaply. A fixed number of shots and a fixed amount of laboratory time impose different constraints.

This lab combines observable coefficients, group variances and per-shot time. The continuous calculation has a closed-form optimum under its assumptions. Converting it to integer shot counts then introduces a small implementation problem: rounding can waste time or slightly change the optimum. The worked answers expose both the lower bound and the rounded schedule instead of hiding the distinction behind an allocation score.

The model assumes the groups are independently estimated and their variances are known. A real pilot experiment spends part of the budget learning those variances. Calibration and circuit switching may add costs that depend on how measurements are grouped. Increasing one time cost while holding its physical variance fixed changes the preferred allocation. The resource tradeoff is conditional on these assumptions; different Hamiltonians and acquisition workflows can require different schedules.

Synthetic decision model

Start with the assumptions

  • Group estimates are independent.
  • Variances, coefficients and per-shot costs are known and stationary.
  • The rounded greedy schedule is compared with a continuous bound, not certified as the integer optimum.

V = sum_i (a_i sigma_i)^2 / n_i; sum_i c_i n_i <= T

n_i* = T |a_i| sigma_i / (sqrt(c_i) sum_j |a_j| sigma_j sqrt(c_j))

Continuous lower bound V* = (sum_i |a_i| sigma_i sqrt(c_i))² / T

Synthetic a shot budget is also a time budget plot: Shot count versus Measurement group.
Synthetic baseline case. Horizontal axis: Measurement group. Vertical axis: Shot count. Curves show Rounded allocation, Equal time. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Time costs per shot
1, 2, 5
Group standard deviations
1, 1.4, 0.6
Observable coefficients
1, -0.5, 1.2
Time budget
1200
  1. The continuous solution allocates 333.340886, 164.99532, 107.333695 shots. It minimizes variance under the time constraint before integer rounding.
  2. Round down, then spend affordable remaining units by the largest immediate variance reduction per unit time. The resulting counts are 335, 165, 107. This greedy rounding is not claimed to solve every integer allocation problem exactly.
  3. Variance is sum((coefficient × standard deviation)^2 / shots) = 0.0108. Equal time across groups yields 0.01143.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Allocated shots, group 1335
Allocated shots, group 2165
Allocated shots, group 3107
Used time1200
Allocated variance0.010799631409646753
Equal-time variance0.01143
Continuous lower bound0.010799510630309797
Measurement-group allocation
GroupContinuous shotsRounded shotsEqual-time shots
1333.3408855913823335400
2164.99532045387687165200
3107.3336947001727710780

The rounded allocation uses 1,200 of 1,200 time units. Its variance is 0.001118% above the continuous lower bound. The calculation shows why a costly measurement may deserve fewer shots even when its contribution is noisy.

Comparison regime
Complete inputs
Time costs per shot
1, 3, 7
Group standard deviations
1, 1.7999999999999998, 0.8
Observable coefficients
1, -0.5, 1.2
Time budget
2700
  1. The continuous solution allocates 529.53979, 275.156946, 192.141339 shots. It minimizes variance under the time constraint before integer rounding.
  2. Round down, then spend affordable remaining units by the largest immediate variance reduction per unit time. The resulting counts are 531, 275, 192. This greedy rounding is not claimed to solve every integer allocation problem exactly.
  3. Variance is sum((coefficient × standard deviation)^2 / shots) = 0.009629. Equal time across groups yields 0.011011.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Allocated shots, group 1531
Allocated shots, group 2275
Allocated shots, group 3192
Used time2700
Allocated variance0.009628693716829308
Equal-time variance0.01101111111111111
Continuous lower bound0.009628675841389512
Measurement-group allocation
GroupContinuous shotsRounded shotsEqual-time shots
1529.5397902499327531900
2275.1569464026749275300
3192.1413386488632192128

The rounded allocation uses 2,700 of 2,700 time units. Its variance is 0.000186% above the continuous lower bound. The calculation shows why a costly measurement may deserve fewer shots even when its contribution is noisy.

Extended regime
Complete inputs
Time costs per shot
1, 5, 7
Group standard deviations
1, 2.28, 1.04
Observable coefficients
1, -0.5, 1.2
Time budget
4500
  1. The continuous solution allocates 656.836967, 334.870921, 309.829776 shots. It minimizes variance under the time constraint before integer rounding.
  2. Round down, then spend affordable remaining units by the largest immediate variance reduction per unit time. The resulting counts are 662, 335, 309. This greedy rounding is not claimed to solve every integer allocation problem exactly.
  3. Variance is sum((coefficient × standard deviation)^2 / shots) = 0.01043. Equal time across groups yields 0.012277.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Allocated shots, group 1662
Allocated shots, group 2335
Allocated shots, group 3309
Used time4500
Allocated variance0.010430443022618991
Equal-time variance0.012276722741433023
Continuous lower bound0.010430312959808825
Measurement-group allocation
GroupContinuous shotsRounded shotsEqual-time shots
1656.83696711281996621500
2334.8709207605855335300
3309.8297755834646309214

The rounded allocation uses 4,500 of 4,500 time units. Its variance is 0.001247% above the continuous lower bound. The calculation shows why a costly measurement may deserve fewer shots even when its contribution is noisy.

Try the reasoning: Which group gains most from the next affordable shot? Compare its variance reduction per unit time with that of the other groups.

Sources and model boundaries
  • Combining uncertainty components ↗

    Uncertainty propagation includes sensitivities and covariance; independent terms simplify the variance sum. Covariance, bias and distribution assumptions in the teaching models are declared separately; no NIST endorsement is implied.

Evidence and experimental designCorrelated measurements can call for an unexpected weightWhen is averaging two estimates less useful than combining their shared noise explicitly?

Two instruments can agree because both see the same disturbance. Agreement then contains less independent information than it appears to. Conversely, carefully combining correlated signals can sometimes cancel a disturbance. The deciding object is the covariance matrix, which records how the errors move together as well as how large each error is.

For two unbiased estimates, any weights that sum to one preserve the common mean. The variance is a quadratic function of one remaining weight. Minimizing it can produce an ordinary weighted average or a coefficient outside the interval from zero to one. A negative weight subtracts a correlated contribution; it is not a negative probability. Such cancellation also makes the answer more dependent on the validity of the error model.

The cases compare three choices: equal weights, an independence-based weighting, and a covariance-aware weighting. All three are evaluated using the same actual covariance. That last step matters: an algorithm should not be rewarded by calculating its uncertainty under the very assumption being questioned. Varying the correlation while keeping both individual uncertainties fixed isolates the role of shared noise.

Synthetic decision model

Start with the assumptions

  • Both estimates are unbiased for the same quantity.
  • The covariance matrix is positive definite in the tested regimes.
  • Weights are chosen from known uncertainty inputs, not from favorable observed outcomes.

Var(wA+(1-w)B) = w² v_A + (1-w)² v_B + 2w(1-w)c

w* = (v_B-c)/(v_A+v_B-2c)

c = rho × s_A × s_B

Synthetic correlated measurements can call for an unexpected weight plot: Combined uncertainty versus Weight on A.
Synthetic baseline case. Horizontal axis: Weight on A. Vertical axis: Combined uncertainty. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Sensor A standard uncertainty
1
Sensor B standard uncertainty
1.8
Correlation
-0.3
  1. Covariance = correlation × s_A × s_B = -0.54. Insert it in all three variance terms.
  2. Differentiate the variance with respect to A’s weight, with B’s weight fixed to 1 - w. The stationary point gives w = 0.710526.
  3. The standard uncertainty is sqrt(0.554211) = 0.744453. An independence-based weight is 0.764151, but its real variance must still include covariance.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Optimal A weight0.7105263157894737
Optimal B weight0.2894736842105263
Combined standard uncertainty0.74445317268166
Equal-weight uncertainty0.8888194417315589
Ignore-correlation weight, evaluated correctly0.7546580165645312

Both weights lie between zero and one in this regime. The estimate is unbiased only because both inputs were assumed unbiased and the weights sum to one. A gain error or wrong covariance can reverse this result.

Comparison regime
Complete inputs
Sensor A standard uncertainty
1.25
Sensor B standard uncertainty
2
Correlation
0.2
  1. Covariance = correlation × s_A × s_B = 0.5. Insert it in all three variance terms.
  2. Differentiate the variance with respect to A’s weight, with B’s weight fixed to 1 - w. The stationary point gives w = 0.767123.
  3. The standard uncertainty is sqrt(1.315068) = 1.146764. An independence-based weight is 0.719101, but its real variance must still include covariance.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Optimal A weight0.7671232876712328
Optimal B weight0.23287671232876717
Combined standard uncertainty1.1467643581619917
Equal-weight uncertainty1.2808688457449497
Ignore-correlation weight, evaluated correctly1.1513427826920897

Both weights lie between zero and one in this regime. The estimate is unbiased only because both inputs were assumed unbiased and the weights sum to one. A gain error or wrong covariance can reverse this result.

Extended regime
Complete inputs
Sensor A standard uncertainty
1.55
Sensor B standard uncertainty
2
Correlation
0.8
  1. Covariance = correlation × s_A × s_B = 2.48. Insert it in all three variance terms.
  2. Differentiate the variance with respect to A’s weight, with B’s weight fixed to 1 - w. The stationary point gives w = 1.053726.
  3. The standard uncertainty is sqrt(2.398336) = 1.548656. An independence-based weight is 0.624756, but its real variance must still include covariance.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Optimal A weight1.0537261698440212
Optimal B weight-0.05372616984402123
Combined standard uncertainty1.5486562632931455
Equal-weight uncertainty1.6854153790683175
Ignore-correlation weight, evaluated correctly1.6321086060481949

The optimal solution uses a negative weight, which subtracts shared noise while increasing sensitivity to model error. The estimate is unbiased only because both inputs were assumed unbiased and the weights sum to one. A gain error or wrong covariance can reverse this result.

Try the reasoning: Find the regime with a weight outside zero to one. Which covariance assumption makes that subtraction useful, and which calibration error could invalidate it?

Sources and model boundaries
  • Combining uncertainty components ↗

    Uncertainty propagation includes sensitivities and covariance; independent terms simplify the variance sum. Covariance, bias and distribution assumptions in the teaching models are declared separately; no NIST endorsement is implied.

Evidence and experimental designOne campaign can ask enough questions to manufacture a surpriseHow does searching many comparisons change the chance of a false alert?

A benchmark campaign may compare dozens of circuits, calibrations, devices and parameter choices. Even if every individual statistical test has a small false-positive probability, the chance of at least one apparent surprise can become large. Selecting the most flattering comparison after the search conceals the size of that campaign.

This lab assumes all tested null hypotheses are true and computes the exact independent-test probability of at least one false alert. It then introduces a simple family-wide bound by dividing the desired total error allowance among the tests. The exact probability uses independence. The union-bound guarantee does not, provided each individual false-positive bound is valid. Keeping those two claims separate is the main mathematical lesson.

A correction is not a complete scientific analysis. It can reduce the power to detect a real effect, and it does not repair data leakage, a biased estimator or an inappropriate null model. The number of comparisons therefore belongs in the experiment plan. Predeclared endpoints and a fresh validation set can make the campaign easier to interpret than a long list of selected p-values.

Synthetic decision model

Start with the assumptions

  • Every null hypothesis is true in this scenario.
  • Exact family probabilities use independent tests.
  • Each individual cutoff is a valid false-positive probability bound.

P(at least one false alert) = 1-(1-alpha)^m under independence

Expected number of false alerts = m alpha

Bonferroni per-test cutoff = desired_family_bound/m

Synthetic one campaign can ask enough questions to manufacture a surprise plot: Chance of at least one false alert versus Number of independent tests.
Synthetic baseline case. Horizontal axis: Number of independent tests. Vertical axis: Chance of at least one false alert. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Tests in campaign
20
Per-test false-positive probability
0.01
Desired family upper bound
0.05
  1. All 20 null hypotheses are assumed true. Independence gives the probability of no alert as (1 - 0.01)^20.
  2. Subtract from one: the campaign alert probability is 0.182093, even though each test uses 0.01.
  3. Dividing the desired family bound 0.05 by 20 gives 0.0025. The union bound does not require independent tests; the displayed exact corrected probability does.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Expected false alerts0.2
Chance of one or more false alerts0.18209306240276915
Bonferroni per-test cutoff0.0025
Bonferroni family upper bound0.05
Independent-test family probability after correction0.04883012474683423

At least one false alert occurs with probability 18.209306% under the independent all-null scenario. The correction is a declared campaign rule, not a substitute for replication or a complete analysis of statistical power. A laboratory must count the comparisons actually searched, including hidden tuning decisions.

Comparison regime
Complete inputs
Tests in campaign
120
Per-test false-positive probability
0.01
Desired family upper bound
0.05
  1. All 120 null hypotheses are assumed true. Independence gives the probability of no alert as (1 - 0.01)^120.
  2. Subtract from one: the campaign alert probability is 0.70062, even though each test uses 0.01.
  3. Dividing the desired family bound 0.05 by 120 gives 0.000417. The union bound does not require independent tests; the displayed exact corrected probability does.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Expected false alerts1.2
Chance of one or more false alerts0.7006196086876684
Bonferroni per-test cutoff0.0004166666666666667
Bonferroni family upper bound0.05
Independent-test family probability after correction0.048780486840748906

At least one false alert occurs with probability 70.061961% under the independent all-null scenario. The correction is a declared campaign rule, not a substitute for replication or a complete analysis of statistical power. A laboratory must count the comparisons actually searched, including hidden tuning decisions.

Extended regime
Complete inputs
Tests in campaign
240
Per-test false-positive probability
0.012
Desired family upper bound
0.05
  1. All 240 null hypotheses are assumed true. Independence gives the probability of no alert as (1 - 0.012)^240.
  2. Subtract from one: the campaign alert probability is 0.944835, even though each test uses 0.012.
  3. Dividing the desired family bound 0.05 by 240 gives 0.000208. The union bound does not require independent tests; the displayed exact corrected probability does.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Expected false alerts2.88
Chance of one or more false alerts0.9448346089590153
Bonferroni per-test cutoff0.00020833333333333335
Bonferroni family upper bound0.05
Independent-test family probability after correction0.04877553049450735

At least one false alert occurs with probability 94.483461% under the independent all-null scenario. The correction is a declared campaign rule, not a substitute for replication or a complete analysis of statistical power. A laboratory must count the comparisons actually searched, including hidden tuning decisions.

Try the reasoning: Which comparisons would a complete campaign register need to count, including tuning choices that never became a published test?

Evidence and experimental designAn outlying batch changes the question behind an averageWhat do robust summaries protect, and what can they stop estimating?

A single disturbed acquisition can dominate the arithmetic mean of a small batch. That influence is sometimes a reason to inspect equipment and repeat the acquisition; it is not automatic permission to delete the inconvenient record. An analysis rule should say what kind of contamination it addresses and which physical quantity remains the target after the rule is applied.

The constructed record compares an arithmetic mean, a median and a precisely defined trimmed mean. The extra disturbance is visible and synthetic, so its influence can be calculated exactly. The exercise does not argue that the median is universally superior. For an observable whose physical definition is an expectation value, replacing the mean with a different statistic can change the estimand rather than merely improve the estimate.

The explicitly supplied observations show how changing one point affects each summary. A real contamination model needs independent evidence. Documenting saturation, a known synchronization fault or a predetermined rejection rule is stronger than choosing whichever summary makes a desired conclusion look stable.

Synthetic decision model

Start with the assumptions

  • Eleven observations are explicitly constructed.
  • The disturbance is added to one known record.
  • No sampling distribution or confidence interval is inferred.

Mean = sum(x_i)/n

Median = the middle ordered observation for odd n

One-per-tail trimmed mean averages x_(2) through x_(n-1)

Synthetic an outlying batch changes the question behind an average plot: Illustrative response versus Acquisition batch.
Synthetic baseline case. Horizontal axis: Acquisition batch. Vertical axis: Illustrative response. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Ordinary noise scale
1
Target level
10
Single-batch disturbance
5
Ordinary noise pattern
-2, -1, 0, 1, 2, -1, 0, 1, 0, -2, 2
Disturbed observation, one-based
11
Observations trimmed from each tail
1
  1. The constructed eleven observations are 8, 9, 10, 11, 12, 9, 10, 11, 10, 8, 17. Only the final entry receives the declared extra disturbance.
  2. The arithmetic mean uses every magnitude and gives 10.454545. The median is the sixth sorted value, 10.
  3. Remove one observation from each sorted tail and average the remaining nine to obtain 10. This is a specified transformation, not permission to discard inconvenient measurements after seeing a result.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Arithmetic mean10.454545454545455
Median10
One-point-per-tail trimmed mean10
Mean minus target0.45454545454545503
Median minus target0
Trimmed mean minus target0
All eleven constructed observations
BatchResponse
18
29
310
411
512
69
710
811
910
108
1117

The disturbance shifts the mean by 0.454545 from the stipulated target. The comparison demonstrates influence, not a claim that a median estimates every physical observable correctly. For an expectation value defined as a mean, robust summaries can change the estimand and must be justified by a contamination model.

Comparison regime
Complete inputs
Ordinary noise scale
1.5
Target level
12.5
Single-batch disturbance
20
Ordinary noise pattern
-2, -1, 0, 1, 2, -1, 0, 1, 0, -2, 2
Disturbed observation, one-based
11
Observations trimmed from each tail
1
  1. The constructed eleven observations are 9.5, 11, 12.5, 14, 15.5, 11, 12.5, 14, 12.5, 9.5, 35.5. Only the final entry receives the declared extra disturbance.
  2. The arithmetic mean uses every magnitude and gives 14.318182. The median is the sixth sorted value, 12.5.
  3. Remove one observation from each sorted tail and average the remaining nine to obtain 12.5. This is a specified transformation, not permission to discard inconvenient measurements after seeing a result.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Arithmetic mean14.318181818181818
Median12.5
One-point-per-tail trimmed mean12.5
Mean minus target1.8181818181818183
Median minus target0
Trimmed mean minus target0
All eleven constructed observations
BatchResponse
19.5
211
312.5
414
515.5
611
712.5
814
912.5
109.5
1135.5

The disturbance shifts the mean by 1.818182 from the stipulated target. The comparison demonstrates influence, not a claim that a median estimates every physical observable correctly. For an expectation value defined as a mean, robust summaries can change the estimand and must be justified by a contamination model.

Extended regime
Complete inputs
Ordinary noise scale
2.1
Target level
15.5
Single-batch disturbance
38
Ordinary noise pattern
-2, -1, 0, 1, 2, -1, 0, 1, 0, -2, 2
Disturbed observation, one-based
11
Observations trimmed from each tail
1
  1. The constructed eleven observations are 11.3, 13.4, 15.5, 17.6, 19.7, 13.4, 15.5, 17.6, 15.5, 11.3, 57.7. Only the final entry receives the declared extra disturbance.
  2. The arithmetic mean uses every magnitude and gives 18.954545. The median is the sixth sorted value, 15.5.
  3. Remove one observation from each sorted tail and average the remaining nine to obtain 15.5. This is a specified transformation, not permission to discard inconvenient measurements after seeing a result.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Arithmetic mean18.954545454545453
Median15.5
One-point-per-tail trimmed mean15.5
Mean minus target3.4545454545454533
Median minus target0
Trimmed mean minus target0
All eleven constructed observations
BatchResponse
111.3
213.4
315.5
417.6
519.7
613.4
715.5
817.6
915.5
1011.3
1157.7

The disturbance shifts the mean by 3.454545 from the stipulated target. The comparison demonstrates influence, not a claim that a median estimates every physical observable correctly. For an expectation value defined as a mean, robust summaries can change the estimand and must be justified by a contamination model.

Try the reasoning: If the physical quantity is an expectation value, what contamination model would justify replacing the arithmetic mean with a median?

Error control and measurement

Error control and measurementThe useful mitigation threshold is an error-budget crossoverHow many shots make a reduction in bias worth its extra variance?

An error-mitigated estimate can move closer to a reference on one run and farther away on another. That variation is expected when the procedure amplifies sampling noise. Judging the method by a single favorable estimate confuses chance with a repeatable improvement. A planning calculation needs a loss function that accounts for both the systematic offset and the spread.

Mean squared error supplies a simple choice: variance plus squared bias. This lab stipulates a raw bias, a smaller residual bias after mitigation and a variance multiplier. With few shots, the added variance can dominate. With enough shots, a reduction in persistent bias can become more valuable. Equating the two expressions gives a transparent crossover rather than an unconditional claim that mitigation helps or hurts.

The assumed biases are the difficult inputs. They cannot normally be read directly from an unknown quantum answer. A trusted smaller problem, a controlled noise study or an independently justified model may provide evidence about them. The example therefore belongs beside a discussion of validation. It explains what would have to be known to choose a sample budget, while keeping the synthetic crossover separate from an experimentally established accuracy gain.

Synthetic decision model

Start with the assumptions

  • The multiplier gamma applies to variance, not standard deviation.
  • Biases and shot variance are constant over the campaign.
  • Both estimates target the same observable.

MSE_raw = b² + v/N

MSE_mitigated = b_m² + gamma v/N

N_cross = (gamma-1)v/(b²-b_m²), when the denominator is positive

Synthetic the useful mitigation threshold is an error-budget crossover plot: Mean squared error versus Total shots.
Synthetic baseline case. Horizontal axis: Total shots. Vertical axis: Mean squared error. Curves show Raw MSE, Mitigated MSE. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Raw bias
0.05
Residual mitigated bias
0.01
Per-shot variance
0.25
Variance multiplier
2
Total shots
100
  1. Raw MSE = bias squared + sampling variance = 0.0025 + 0.0025.
  2. Mitigated MSE = residual bias squared + inflated sampling variance = 0.0001 + 0.005.
  3. Equating the MSEs gives N = 104.166667. Integer shot counts above that value favor mitigation in this model.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Raw mean squared error0.005000000000000001
Mitigated mean squared error0.0051
Raw root mean squared error0.07071067811865477
Mitigated root mean squared error0.07141428428542851
Continuous crossover shots104.16666666666664

At 100 shots, the raw estimate has lower modeled MSE. This is an accuracy comparison over repeated hypothetical experiments, not a judgment based on whichever single answer looks closer to an expected result. Biases must be independently characterized before using the model to plan an experiment.

Comparison regime
Complete inputs
Raw bias
0.05
Residual mitigated bias
0.02
Per-shot variance
0.25
Variance multiplier
2
Total shots
3200
  1. Raw MSE = bias squared + sampling variance = 0.0025 + 7.8125e-05.
  2. Mitigated MSE = residual bias squared + inflated sampling variance = 0.0004 + 0.000156.
  3. Equating the MSEs gives N = 119.047619. Integer shot counts above that value favor mitigation in this model.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Raw mean squared error0.0025781250000000006
Mitigated mean squared error0.00055625
Raw root mean squared error0.05077524002897476
Mitigated root mean squared error0.02358495283014151
Continuous crossover shots119.04761904761904

At 3,200 shots, mitigation has lower modeled MSE. This is an accuracy comparison over repeated hypothetical experiments, not a judgment based on whichever single answer looks closer to an expected result. Biases must be independently characterized before using the model to plan an experiment.

Extended regime
Complete inputs
Raw bias
0.05
Residual mitigated bias
0.032
Per-shot variance
0.25
Variance multiplier
3
Total shots
204800
  1. Raw MSE = bias squared + sampling variance = 0.0025 + 1.2207e-06.
  2. Mitigated MSE = residual bias squared + inflated sampling variance = 0.001024 + 3.66211e-06.
  3. Equating the MSEs gives N = 338.753388. Integer shot counts above that value favor mitigation in this model.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Raw mean squared error0.0025012207031250007
Mitigated mean squared error0.0010276621093749999
Raw root mean squared error0.05001220554149757
Mitigated root mean squared error0.03205716939118299
Continuous crossover shots338.75338753387524

At 204,800 shots, mitigation has lower modeled MSE. This is an accuracy comparison over repeated hypothetical experiments, not a judgment based on whichever single answer looks closer to an expected result. Biases must be independently characterized before using the model to plan an experiment.

Try the reasoning: At what shot budget does the lower modeled bias repay the extra variance? Explain why a single favorable estimate cannot establish that crossover.

Sources and model boundaries
  • Error mitigation for short-depth quantum circuits ↗

    Error-mitigation methods target expectation-value errors using techniques such as noise extrapolation and quasiprobability sampling. The MSE lab is an independently derived decision model; it does not attribute its assumed residual biases or variance multipliers to this paper.

Error control and measurementCalibrating more often can reduce the measurements you needHow should a refresh interval balance drifting bias against useful acquisition time?

Calibration consumes part of a campaign while attempting to make the remaining measurements more trustworthy. An extremely long interval spends almost all the time acquiring data, but measurements late in the interval may inherit a larger drift. An extremely short interval keeps data young while leaving little useful acquisition time. Neither extreme is automatically the best choice.

The model treats drift after a perfect calibration as a linear bias and assumes measurement ages are uniformly distributed across a repeated acquisition interval. Integrating the squared age-dependent bias gives a mean-squared drift contribution. A separate term reflects the smaller shot count caused by calibration downtime. Adding the two creates a concrete cadence problem whose optimum can be explored without claiming a real laboratory’s drift law is known.

The cases scan integer refresh intervals and compare the best tested choice with a declared reference schedule. They deliberately use a long-run duty-cycle approximation. A short campaign, imperfect calibration, interrupted schedules or random walk drift would need a different calculation. The useful article question is whether a reported improvement includes the time required to establish and maintain the operating point.

Synthetic decision model

Start with the assumptions

  • Each calibration resets bias exactly to zero.
  • Bias then grows linearly at rate r.
  • Campaign boundaries are neglected in the repeated-cycle approximation.

Useful fraction = L/(L+t_cal)

Expected shots = campaign_time × shot_rate × useful_fraction

MSE(L) = r² L²/3 + v/expected_shots

Synthetic calibrating more often can reduce the measurements you need plot: Mean squared error versus Refresh interval.
Synthetic baseline case. Horizontal axis: Refresh interval. Vertical axis: Mean squared error. Curves show Combined model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Campaign time
3600
Calibration time
8
Bias drift per time
0.0001
Shots per useful time
40
Per-shot variance
0.25
Largest refresh interval
180
Reference refresh interval
120
  1. An interval L leaves fraction L/(L + calibration time) for acquisition. At L = 13, that is 0.619048.
  2. Uniform age since a reset gives mean squared drift (r L)^2 / 3 = 5.63333e-07. Shot variance adds 2.80449e-06.
  3. Scan integer intervals 1 through 180; the best is 13. The reference interval 120 gives MSE 4.98519e-05.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested refresh interval13
Useful acquisition fraction0.6190476190476191
Expected acquired shots89142.85714285714
Best modeled MSE0.0000033678205128205124
Reference-interval MSE0.000049851851851851855
Reference / best MSE14.802407569547547

The best tested cadence is 13 time units. It is conditional on deterministic linear drift, a perfect reset and long-campaign duty-cycle accounting. If calibration leaves an offset or the drift is stochastic, both the age term and the optimum change. This model uses fractional expected shots; an actual schedule would need integer acquisitions and explicit start/end effects.

Comparison regime
Complete inputs
Campaign time
3600
Calibration time
18
Bias drift per time
0.0006000000000000001
Shots per useful time
90
Per-shot variance
0.25
Largest refresh interval
180
Reference refresh interval
120
  1. An interval L leaves fraction L/(L + calibration time) for acquisition. At L = 4, that is 0.181818.
  2. Uniform age since a reset gives mean squared drift (r L)^2 / 3 = 1.92e-06. Shot variance adds 4.24383e-06.
  3. Scan integer intervals 1 through 180; the best is 4. The reference interval 120 gives MSE 0.001729.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested refresh interval4
Useful acquisition fraction0.18181818181818182
Expected acquired shots58909.09090909091
Best modeled MSE0.0000061638271604938274
Reference-interval MSE0.0017288873456790127
Reference / best MSE280.4892643259159

The best tested cadence is 4 time units. It is conditional on deterministic linear drift, a perfect reset and long-campaign duty-cycle accounting. If calibration leaves an offset or the drift is stochastic, both the age term and the optimum change. This model uses fractional expected shots; an actual schedule would need integer acquisitions and explicit start/end effects.

Extended regime
Complete inputs
Campaign time
3600
Calibration time
30
Bias drift per time
0.0012000000000000001
Shots per useful time
150
Per-shot variance
0.25
Largest refresh interval
180
Reference refresh interval
120
  1. An interval L leaves fraction L/(L + calibration time) for acquisition. At L = 2, that is 0.0625.
  2. Uniform age since a reset gives mean squared drift (r L)^2 / 3 = 1.92e-06. Shot variance adds 7.40741e-06.
  3. Scan integer intervals 1 through 180; the best is 2. The reference interval 120 gives MSE 0.006913.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested refresh interval2
Useful acquisition fraction0.0625
Expected acquired shots33750
Best modeled MSE0.000009327407407407409
Reference-interval MSE0.0069125787037037055
Reference / best MSE741.1039747458705

The best tested cadence is 2 time units. It is conditional on deterministic linear drift, a perfect reset and long-campaign duty-cycle accounting. If calibration leaves an offset or the drift is stochastic, both the age term and the optimum change. This model uses fractional expected shots; an actual schedule would need integer acquisitions and explicit start/end effects.

Try the reasoning: If calibration no longer resets the bias exactly, which term would you add or replace before using the chosen refresh interval?

Error correction and systems

Error correction and systemsA code distance belongs to a workload, not a headlineHow much protection is needed when every logical operation exposes the machine for several rounds?

A small logical error probability is meaningful only beside the number of opportunities for failure. A memory experiment, a short logical operation and a large algorithm can tolerate very different per-round rates. Choosing a code distance therefore starts with a workload and an explicit accounting convention, rather than a desired number of decimal places.

The model assigns a simple distance-dependent logical error and makes each logical operation consume a number of correction rounds proportional to distance. Increasing distance improves one factor while increasing the exposure count, footprint and serial duration. The calculation then selects the smallest tested odd distance meeting a stated union-bound target. A union bound adds event probabilities and does not require the events to be independent, although the assumed per-location probabilities remain a strong physical modeling choice.

This is an accounting exercise, not a surface-code resource estimate for a named algorithm. A real implementation must also count factories, routing, boundaries, correlated faults, logical gate constructions and recovery behavior. Moving from per-location protection to complete-workload protection requires an explicit exposure count. The footprint must also state which resources it excludes.

Synthetic decision model

Start with the assumptions

  • The error law and coefficients are invented.
  • A serial sequence of logical operations lasts d correction rounds per operation; all stored registers, including idle ones, remain exposed.
  • All counted locations share the stipulated per-location bound.

p_L(d) = A × ratio^((d+1)/2)

Counted locations = logical_registers × base_operations × d

Workload union bound = min(1, counted_locations × p_L)

Toy patch footprint = logical_registers × (2d²-1)

Synthetic a code distance belongs to a workload, not a headline plot: Failure probability bound versus Code distance.
Synthetic baseline case. Horizontal axis: Code distance. Vertical axis: Failure probability bound. Curves show Workload union bound, Target. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Physical error / model threshold
0.12
Scaling prefactor
0.04
Base logical operations
10000
Logical registers
8
Workload failure bound
0.001
Cycle time, microseconds
1
Tested odd distances
3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41
  1. The error model gives p_L(d) = A × ratio^((d + 1)/2). Multiply by logical registers × base operations × distance to count the declared fault opportunities.
  2. At d = 17, the resulting union bound is min(1, 1,360,000 × 2.06391e-10) = 0.000281.
  3. The illustrative rotated-patch allocation is 8 × (2 × 17² - 1) = 4,616 physical qubits. The serial duration is 0.17 seconds. Routing space, factories and extra control patches are excluded.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Smallest passing tested distance17
Chosen-distance logical error per location2.0639121407999993e-10
Counted fault locations1360000
Union-bound workload failure0.0002806920511487999
Illustrative physical-qubit footprint4616
Serial operation time, seconds0.17
Complete tested distance range
DistancePer-location errorCounted locationsWorkload failure boundPhysical qubitsSeconds
30.00057624000011360.03
50.0000691199999999999940000013920.05
70.00000829439999999999856000017760.07
99.95328e-77200000.7166361612880.09
111.1943935999999997e-78800000.1051066367999999719280.11
131.4332723199999996e-810400000.01490603212799999626960.13
151.7199267839999996e-912000000.002063912140799999535920.15
172.0639121407999993e-1013600000.000280692051148799946160.17
192.476694568959999e-1115200000.0000376457574481919957680.19
212.9720334827519992e-1216800000.00000499301625102335970480.21
233.5664401793023986e-1318400006.562249929916414e-784560.23
254.2797282151628786e-1420000008.559456430325757e-899920.25
275.135673858195453e-1521600001.1093055533702179e-8116560.27
296.162808629834545e-1623200001.4297716021216143e-9134480.29
317.395370355801452e-1724800001.8340518482387603e-10153680.31
338.874444426961742e-1826400002.3428533287178998e-11174160.33
351.064933331235409e-1828000002.981813327459145e-12195920.35
371.277919997482491e-1929600003.7826431925481733e-13218960.37
391.533503996978989e-2031200004.784532470574446e-14243280.39
411.8402047963747867e-2132800006.0358717321093e-15268880.41

Distance 17 is the smallest tested odd distance meeting the stated target. The gate count alone is not the exposure count: this model makes each logical operation last d rounds. Its scaling prefactor and threshold ratio are invented. No threshold theorem or device forecast is inferred from the scan.

Comparison regime
Complete inputs
Physical error / model threshold
0.245
Scaling prefactor
0.04
Base logical operations
60000
Logical registers
18
Workload failure bound
0.001
Cycle time, microseconds
1.5
Tested odd distances
3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41
  1. The error model gives p_L(d) = A × ratio^((d + 1)/2). Multiply by logical registers × base operations × distance to count the declared fault opportunities.
  2. At d = 29, the resulting union bound is min(1, 31,320,000 × 2.75138e-11) = 0.000862.
  3. The illustrative rotated-patch allocation is 18 × (2 × 29² - 1) = 30,258 physical qubits. The serial duration is 2.61 seconds. Routing space, factories and extra control patches are excluded.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Smallest passing tested distance29
Chosen-distance logical error per location2.7513843128286442e-11
Counted fault locations31320000
Union-bound workload failure0.0008617335667779314
Illustrative physical-qubit footprint30258
Serial operation time, seconds2.61
Complete tested distance range
DistancePer-location errorCounted locationsWorkload failure boundPhysical qubitsSeconds
30.002401324000013060.27
50.0005882449999999999540000018820.45
70.000144120024999999987560000117460.63
90.0000353094061259720000128980.81
110.00000865080450062511880000143380.99
130.00000211944710265312514040000160661.17
155.192645401500155e-716200000180821.35
171.272198123367538e-7183600001103861.53
193.116885402250468e-8205200000.639584884541796129781.71
217.636369235513648e-9226800000.17319285426144954158581.89
231.8709104627008436e-9248400000.046473415893488954190262.07
254.5837306336170665e-10270000000.01237607271076608224822.25
271.1230140052361812e-10291600000.0032747088392687043262262.43
292.7513843128286442e-11313200000.0008617335667779314302582.61
316.740891566430178e-12334800000.00022568504964408235345782.79
331.6515184337753934e-12356400000.00005886011697975502391862.97
354.046220162749714e-13378000000.000015294712215193918440823.15
379.913239398736799e-14399600000.000003961330463735225492663.33
392.428743652690516e-14421200000.0000010229868265132453547383.51
415.950421949091763e-15442800002.634846839057833e-7604983.69

Distance 29 is the smallest tested odd distance meeting the stated target. The gate count alone is not the exposure count: this model makes each logical operation last d rounds. Its scaling prefactor and threshold ratio are invented. No threshold theorem or device forecast is inferred from the scan.

Extended regime
Complete inputs
Physical error / model threshold
0.395
Scaling prefactor
0.04
Base logical operations
120000
Logical registers
30
Workload failure bound
0.001
Cycle time, microseconds
2.1
Tested odd distances
3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41
  1. The error model gives p_L(d) = A × ratio^((d + 1)/2). Multiply by logical registers × base operations × distance to count the declared fault opportunities.
  2. At d = 41, the resulting union bound is min(1, 147,600,000 × 1.35082e-10) = 0.019938.
  3. The illustrative rotated-patch allocation is 30 × (2 × 41² - 1) = 100,830 physical qubits. The serial duration is 10.332 seconds. Routing space, factories and extra control patches are excluded.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Smallest passing tested distanceNo tested distance passes
Chosen-distance logical error per location1.3508247196523e-10
Counted fault locations147600000
Union-bound workload failure0.01993817286206795
Illustrative physical-qubit footprint100830
Serial operation time, seconds10.332
Complete tested distance range
DistancePer-location errorCounted locationsWorkload failure boundPhysical qubitsSeconds
30.0062410000000000011080000015100.756
50.002465195000000000318000000114701.26
70.000973752025000000325200000129101.764
90.0003846320498750000632400000148302.268
110.0001519296597006250539600000172302.772
130.0000600122155817469468000001101103.276
150.000023704825154790025540000001134703.78
170.00000936340593614206612000001173104.284
190.000003698545344776114684000001216304.788
210.0000014609254111865652756000001264305.292
235.770655374186932e-7828000001317105.796
252.2794088728038384e-7900000001374706.3
279.003665047575162e-8972000001437106.804
293.556447693792189e-81044000001504307.308
311.4047968390479147e-81116000001576307.812
335.548947514239264e-91188000000.6592149646916245653108.316
352.191834268124509e-91260000000.27617111778368814734708.82
378.657745359091812e-101332000000.11532116818310294821109.324
393.419809416841266e-101404000000.048014124212451374912309.828
411.3508247196523e-101476000000.0199381728620679510083010.332

The tested distance range does not meet the target. The gate count alone is not the exposure count: this model makes each logical operation last d rounds. Its scaling prefactor and threshold ratio are invented. No threshold theorem or device forecast is inferred from the scan.

Try the reasoning: Double the number of stored logical registers. Which costs and failure opportunities increase even if the serial operation count stays fixed?

Sources and model boundaries
  • Surface codes: Towards practical large-scale quantum computation ↗

    Surface-code computation requires physical layouts, repeated stabilizer information and logical operation constructions with resource costs. Only architectural context is used. All scaling coefficients and workload values in the lab are invented, and the toy footprint excludes substantial resources.

Error correction and systemsA quiet average can hide a decoder’s busiest minuteWill the decoder respond in time when slow jobs arrive in bursts?

A decoder is a classical computation attached to a quantum experiment. Its response can become part of a time-critical feedback path. Average throughput describes whether work is usually sustainable, while individual response times reveal what happens to the jobs that encounter a backlog. Both are needed to interpret a claim about operating speed.

This laboratory uses a deterministic arrival trace and makes the first two service times in each block longer. A single worker can have an average service time below the arrival spacing and still miss deadlines after those bursts. A second worker changes the schedule, but it does not make either individual service operation faster. The distinction separates hardware acceleration from queue management.

The exact trace is supplied with each worked case, making the result reproducible without a random seed. It is intentionally a classical queue simulation. Real decoders can have batch dependencies, shared memory, communication bottlenecks and different requirements for when an answer becomes necessary. The Model page can use this trace to explain what a latency histogram adds to a mean-speed number, while leaving quantum error-correction performance to its own evidence.

Synthetic decision model

Start with the assumptions

  • Jobs can use any available identical worker.
  • There are no inter-job dependencies or transfer costs.
  • The burst pattern and service times are stipulated.

start_i = max(arrival_i, earliest worker-free time)

finish_i = start_i + service_i

response_i = finish_i - arrival_i; miss if response_i > deadline

Synthetic a quiet average can hide a decoder’s busiest minute plot: Response time versus Job number.
Synthetic baseline case. Horizontal axis: Job number. Vertical axis: Response time. Curves show One worker, Two workers, Deadline. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Arrival spacing
1
Normal service time
0.45
Burst service time
1.6
Burst period
10
Response deadline
2.5
Jobs in trace
60
Burst jobs at start of each period
2
  1. Create 60 arrivals separated by 1 time units. The first two jobs in every 10-job block use burst service 1.6.
  2. For each arrival, select the first available worker; start at max(arrival time, worker-free time). Completion minus arrival is the response time.
  3. The one-worker queue misses 0 deadlines. The two-worker schedule misses 0 under exactly the same arrival and service trace.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Mean service / arrival spacing0.68
One-worker maximum response time2.200000000000003
One-worker missed deadlines0
Two-worker maximum response time1.6000000000000014
Two-worker missed deadlines0
One-worker maximum wait before service1.2000000000000028
First twelve jobs of the 60-job trace; complete trace follows the stated periodic rule
JobService timeOne-worker responseTwo-worker response
11.61.61.6
21.62.21.6
30.451.65000000000000040.4500000000000002
40.451.10000000000000050.4500000000000002
50.450.55000000000000070.4500000000000002
60.450.45000000000000020.4500000000000002
70.450.45000000000000020.4500000000000002
80.450.45000000000000020.4500000000000002
90.450.44999999999999930.4499999999999993
100.450.44999999999999930.4499999999999993
111.61.59999999999999961.5999999999999996
121.62.19999999999999931.5999999999999996

The average utilization proxy is 0.68, while the maximum one-worker response is 2.2. A mean below one does not rule out burst-related deadline failures. The second worker is a scheduling experiment; real decoding may have dependencies, memory contention and communication costs omitted here.

Comparison regime
Complete inputs
Arrival spacing
1
Normal service time
0.575
Burst service time
2.5
Burst period
12
Response deadline
2.6
Jobs in trace
60
Burst jobs at start of each period
2
  1. Create 60 arrivals separated by 1 time units. The first two jobs in every 12-job block use burst service 2.5.
  2. For each arrival, select the first available worker; start at max(arrival time, worker-free time). Completion minus arrival is the response time.
  3. The one-worker queue misses 20 deadlines. The two-worker schedule misses 0 under exactly the same arrival and service trace.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Mean service / arrival spacing0.8958333333333333
One-worker maximum response time4
One-worker missed deadlines20
Two-worker maximum response time2.5
Two-worker missed deadlines0
One-worker maximum wait before service3
First twelve jobs of the 60-job trace; complete trace follows the stated periodic rule
JobService timeOne-worker responseTwo-worker response
12.52.52.5
22.542.5
30.5753.5751.0750000000000002
40.5753.15000000000000040.6500000000000004
50.5752.72500000000000050.5750000000000002
60.5752.30000000000000070.5750000000000002
70.5751.87500000000000090.5750000000000002
80.5751.4500000000000010.5750000000000002
90.5751.02500000000000040.5749999999999993
100.5750.59999999999999960.5749999999999993
110.5750.57499999999999930.5749999999999993
120.5750.57499999999999930.5749999999999993

The average utilization proxy is 0.895833, while the maximum one-worker response is 4. A mean below one does not rule out burst-related deadline failures. The second worker is a scheduling experiment; real decoding may have dependencies, memory contention and communication costs omitted here.

Extended regime
Complete inputs
Arrival spacing
1
Normal service time
0.7250000000000001
Burst service time
3.58
Burst period
12
Response deadline
2.8
Jobs in trace
60
Burst jobs at start of each period
2
  1. Create 60 arrivals separated by 1 time units. The first two jobs in every 12-job block use burst service 3.58.
  2. For each arrival, select the first available worker; start at max(arrival time, worker-free time). Completion minus arrival is the response time.
  3. The one-worker queue misses 60 deadlines. The two-worker schedule misses 10 under exactly the same arrival and service trace.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Mean service / arrival spacing1.2008333333333334
One-worker maximum response time15.800000000000026
One-worker missed deadlines60
Two-worker maximum response time3.58
Two-worker missed deadlines10
One-worker maximum wait before service14.800000000000026
First twelve jobs of the 60-job trace; complete trace follows the stated periodic rule
JobService timeOne-worker responseTwo-worker response
13.583.583.58
23.586.163.58
30.72500000000000015.8852.3049999999999997
40.72500000000000015.6099999999999992.0299999999999994
50.72500000000000015.3349999999999991.3049999999999997
60.72500000000000015.0599999999999990.754999999999999
70.72500000000000014.7849999999999980.7249999999999996
80.72500000000000014.5099999999999980.7249999999999996
90.72500000000000014.2349999999999980.7249999999999996
100.72500000000000013.95999999999999730.7249999999999996
110.72500000000000013.6849999999999970.7249999999999996
120.72500000000000013.40999999999999660.7249999999999996

The average utilization proxy is 1.200833, while the maximum one-worker response is 15.8. A mean below one does not rule out burst-related deadline failures. The second worker is a scheduling experiment; real decoding may have dependencies, memory contention and communication costs omitted here.

Try the reasoning: Find a regime with a mean service time below the arrival spacing but a missed deadline. Which burst causes it?

Error correction and systemsEnough resources across the day may still be too lateHow large a reserve keeps a bursty computation supplied?

A quantum computation may need a special resource in bursts while its production machinery works at a steadier pace. Total production can exceed total demand and still fail to serve the schedule, because the resource arrives after the moment it was needed. A supply-rate number by itself cannot settle that timing question.

The constructed schedule treats production and demand as tokens at discrete boundaries. Three slots have no production, and repeated demand bursts create deficits. The smallest initial reserve is determined by the deepest cumulative deficit. After adding that reserve, the highest resulting inventory gives a boundary-capacity requirement. This makes two design questions visible: how much stock must exist before the computation starts, and how much can accumulate later.

If the tokens represent quantum states, the classical balance is only a first layer. States may age, occupy protected qubits, fail a quality test or be consumed by failed operations. The example therefore belongs beside a resource factory explanation with its scope stated clearly. It offers an exact demand-planning calculation without implying that quantum states are interchangeable durable objects in a warehouse.

Synthetic decision model

Start with the assumptions

  • Supply and demand are netted simultaneously at each boundary.
  • Stored tokens neither expire nor lose quality in this calculation.
  • All requested tokens have the same resource meaning.

Cumulative net supply at slot t = sum_{i<=t}(supply_i-demand_i)

Minimum initial reserve = max(0, -minimum cumulative net supply)

Boundary capacity = maximum(initial reserve + cumulative net supply), including time zero

Synthetic enough resources across the day may still be too late plot: Resource tokens versus Schedule slot.
Synthetic baseline case. Horizontal axis: Schedule slot. Vertical axis: Resource tokens. Curves show Inventory with reserve, Zero reserve balance. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Supply per slot
10
Base demand per slot
5
Burst demand
15
Burst period
4
Schedule slots
30
Zero-supply slots, one-based
10, 11, 20
  1. Supply is zero in slots 10, 11 and 20; all other slots produce 10 tokens. Demand includes the declared periodic bursts.
  2. Cumulative net production reaches a minimum of -5. An initial reserve of max(0, -minimum) = 5 prevents a negative end-of-slot balance.
  3. Add that reserve to every cumulative value. The largest start/end boundary inventory is 25; final stock is 20. Supply and demand are netted simultaneously at each boundary.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Total produced tokens270
Total requested tokens255
Minimum initial reserve5
Required capacity at slot boundaries25
Final inventory with that reserve20
Supply-minus-demand over campaign15
Complete 30-slot boundary schedule
SlotSupplyDemandInventory with reserve
110510
210515
310520
4102010
510515
610520
710525
8102015
910520
100515
110510
1210200
131055
1410510
1510515
1610205
1710510
1810515
1910520
200200
211055
2210510
2310515
2410205
2510510
2610515
2710520
28102010
2910515
3010520

The toy schedule needs 5 stored tokens before it begins, even though net production across the campaign is 15. A reserve addresses timing, not state quality. If tokens represent prepared quantum resources, finite storage lifetime and extra storage qubits require a separate physical model.

Comparison regime
Complete inputs
Supply per slot
11
Base demand per slot
7
Burst demand
30
Burst period
6
Schedule slots
30
Zero-supply slots, one-based
10, 11, 20
  1. Supply is zero in slots 10, 11 and 20; all other slots produce 11 tokens. Demand includes the declared periodic bursts.
  2. Cumulative net production reaches a minimum of -63. An initial reserve of max(0, -minimum) = 63 prevents a negative end-of-slot balance.
  3. Add that reserve to every cumulative value. The largest start/end boundary inventory is 83; final stock is 0. Supply and demand are netted simultaneously at each boundary.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Total produced tokens297
Total requested tokens360
Minimum initial reserve63
Required capacity at slot boundaries83
Final inventory with that reserve0
Supply-minus-demand over campaign-63
Complete 30-slot boundary schedule
SlotSupplyDemandInventory with reserve
111767
211771
311775
411779
511783
6113757
711761
811765
911769
100762
110755
12113729
1311733
1411737
1511741
1611745
1711749
18113723
1911727
200720
2111724
2211728
2311732
2411376
2511710
2611714
2711718
2811722
2911726
3011370

The toy schedule needs 63 stored tokens before it begins, even though net production across the campaign is -63. A reserve addresses timing, not state quality. If tokens represent prepared quantum resources, finite storage lifetime and extra storage qubits require a separate physical model.

Extended regime
Complete inputs
Supply per slot
13
Base demand per slot
7
Burst demand
48
Burst period
6
Schedule slots
30
Zero-supply slots, one-based
10, 11, 20
  1. Supply is zero in slots 10, 11 and 20; all other slots produce 13 tokens. Demand includes the declared periodic bursts.
  2. Cumulative net production reaches a minimum of -99. An initial reserve of max(0, -minimum) = 99 prevents a negative end-of-slot balance.
  3. Add that reserve to every cumulative value. The largest start/end boundary inventory is 129; final stock is 0. Supply and demand are netted simultaneously at each boundary.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Total produced tokens351
Total requested tokens450
Minimum initial reserve99
Required capacity at slot boundaries129
Final inventory with that reserve0
Supply-minus-demand over campaign-99
Complete 30-slot boundary schedule
SlotSupplyDemandInventory with reserve
1137105
2137111
3137117
4137123
5137129
6135587
713793
813799
9137105
100798
110791
12135549
1313755
1413761
1513767
1613773
1713779
18135537
1913743
200736
2113742
2213748
2313754
24135512
2513718
2613724
2713730
2813736
2913742
3013550

The toy schedule needs 99 stored tokens before it begins, even though net production across the campaign is -99. A reserve addresses timing, not state quality. If tokens represent prepared quantum resources, finite storage lifetime and extra storage qubits require a separate physical model.

Try the reasoning: Would the same reserve suffice if each slot demanded its tokens before new supply arrived? State the within-slot ordering explicitly.

Error correction and systemsSpare modules cannot repair a shared failureWhere does a redundancy calculation stop improving availability?

A modular system can tolerate some components being unavailable if enough working modules remain to perform the task. That is a capacity requirement, which differs from demanding that every installed component work simultaneously. Adding spares can increase the chance of meeting it under a model of independent failures.

Independence is also the assumption most likely to make a reliability calculation look too optimistic. Modules may share power, timing, network equipment, software updates or operating staff. A common outage can remove the entire service even when each module’s individual availability appears excellent. This lab adds one explicit common event to a binomial module model so the effect can be calculated rather than buried in a footnote.

The resulting ceiling is easy to interpret: no number of otherwise independent spares can exceed the probability that the shared service is available. The cases do not estimate a real vendor’s uptime. They create a disciplined question for a directory or infrastructure article: which failures are independent enough for redundancy to help, and which require diversity or a redesigned shared dependency?

Synthetic decision model

Start with the assumptions

  • The common outage removes all capacity.
  • Outside that event, module availability is independent and identical.
  • Exactly k active modules suffice for the declared workload.

P(enough active modules) = sum_{j=k}^n C(n,j)a^j(1-a)^(n-j)

Usable probability with shared outage q = (1-q) × P(enough active)

Common-mode ceiling = 1-q

Synthetic spare modules cannot repair a shared failure plot: Capacity-qualified availability versus Installed modules.
Synthetic baseline case. Horizontal axis: Installed modules. Vertical axis: Capacity-qualified availability. Curves show Independent model, With common outage. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Installed modules
12
Required active modules
10
Independent module availability
0.82
Common outage probability
0.002
  1. With no common outage, sum the binomial probabilities for 10 through 12 active modules.
  2. The independent capacity probability is 0.629787. Multiply by 0.998, the chance the shared service is available.
  3. Even infinitely many otherwise adequate independent modules cannot exceed the common-mode ceiling 0.998 in this model.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Capacity-qualified independent availability0.6297868795813713
Availability including common outage0.6285273058222085
Common-mode ceiling0.998
Expected active modules without common outage9.84
Expected active modules including common outage9.820319999999999

The installed system has modeled usable capacity probability 0.628527. Extra modules protect against independent outages while the shared failure mode persists. The common outage is an explicit invented mechanism; the independence calculation must not be used as a measured reliability claim for a real modular quantum machine.

Comparison regime
Complete inputs
Installed modules
17
Required active modules
11
Independent module availability
0.8799999999999999
Common outage probability
0.017
  1. With no common outage, sum the binomial probabilities for 11 through 17 active modules.
  2. The independent capacity probability is 0.997678. Multiply by 0.983, the chance the shared service is available.
  3. Even infinitely many otherwise adequate independent modules cannot exceed the common-mode ceiling 0.983 in this model.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Capacity-qualified independent availability0.9976779468023482
Availability including common outage0.9807174217067083
Common-mode ceiling0.983
Expected active modules without common outage14.959999999999997
Expected active modules including common outage14.705679999999997

The installed system has modeled usable capacity probability 0.980717. Extra modules protect against independent outages while the shared failure mode persists. The common outage is an explicit invented mechanism; the independence calculation must not be used as a measured reliability claim for a real modular quantum machine.

Extended regime
Complete inputs
Installed modules
23
Required active modules
13
Independent module availability
0.952
Common outage probability
0.035
  1. With no common outage, sum the binomial probabilities for 13 through 23 active modules.
  2. The independent capacity probability is 1. Multiply by 0.965, the chance the shared service is available.
  3. Even infinitely many otherwise adequate independent modules cannot exceed the common-mode ceiling 0.965 in this model.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Capacity-qualified independent availability0.9999999975419924
Availability including common outage0.9649999976280227
Common-mode ceiling0.965
Expected active modules without common outage21.896
Expected active modules including common outage21.12964

The installed system has modeled usable capacity probability 0.965. Extra modules protect against independent outages while the shared failure mode persists. The common outage is an explicit invented mechanism; the independence calculation must not be used as a measured reliability claim for a real modular quantum machine.

Try the reasoning: Can adding independent modules overcome the common outage ceiling? Which component would need a different reliability model?

Quantum networking

Quantum networkingA finite memory changes whether two quantum links meetHow much does a short storage window improve completion before a deadline?

Two probabilistic links rarely succeed on the same attempt when each has a small heralding probability. Memory can preserve the first success while the second link keeps trying. But an unlimited-memory formula can hide the central engineering constraint: a state may cease to be useful before its partner arrives.

The discrete model tracks whether the request is empty, holds an A herald or holds a B herald, and how many partner-attempt slots remain before expiry. Completion is absorbing. Every time step transfers probability among these states, so the complete deadline probability can be calculated without sampling noise. The accompanying trace checks that completed and unfinished probability still sum to one.

A hard cutoff is deliberately simpler than physical decoherence. The stored state is granted full eligibility until its final valid slot and none afterward. This lets the reader isolate timing and compare no memory, a finite window and memory that lasts to the deadline. A physical networking article would additionally need storage efficiencies, state-quality measurements, swapping success, classical latency and a task-specific definition of usefulness.

Synthetic decision model

Start with the assumptions

  • Link attempts are independent with stationary probabilities.
  • Only the missing link is attempted while one herald is held.
  • A stored herald remains valid for the declared number of additional slots.

Empty-state simultaneous completion probability per slot = p_A p_B

A-held completion probability per partner attempt = p_B

Deadline probability follows exact finite-state probability propagation

Expected capped completion time = sum_{t=0}^{H-1} P(not complete after t slots)

Synthetic a finite memory changes whether two quantum links meet plot: Cumulative completion probability versus Elapsed slots.
Synthetic baseline case. Horizontal axis: Elapsed slots. Vertical axis: Cumulative completion probability. Curves show No memory, Finite memory, Horizon-long memory. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Link A success per slot
0.08
Link B success per slot
0.05
Additional slots a stored herald remains valid
1
Deadline slots
15
  1. Start empty. Each slot gives independent probabilities 0.08 and 0.05 for the two links. Simultaneous success ends the request.
  2. A lone success is held for 1 additional partner-attempt slots. On an unsuccessful final slot it expires; the next slot begins empty. The original link is not re-attempted while its herald is held.
  3. Propagate the exact state probabilities through 15 slots. Completed plus unfinished probability remains one after every update. The completion probability is 0.138833.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Completion by deadline with finite memory0.13883327373410062
Completion by deadline without memory0.0583487736146765
Completion with memory lasting to deadline0.38305044229327084
Expected slots used, capped at deadline14.040693455193052
Extra completion probability from finite memory0.08048450011942412

Finite memory raises deadline completion from 5.834877% to 13.883327%. The hard lifetime cutoff grants perfect usefulness before expiry and none after. It is not a physical fidelity-decay law. Storage write/read loss, swapping, classical latency and quantum-state verification are excluded.

Comparison regime
Complete inputs
Link A success per slot
0.13
Link B success per slot
0.08
Additional slots a stored herald remains valid
6
Deadline slots
30
  1. Start empty. Each slot gives independent probabilities 0.13 and 0.08 for the two links. Simultaneous success ends the request.
  2. A lone success is held for 6 additional partner-attempt slots. On an unsuccessful final slot it expires; the next slot begins empty. The original link is not re-attempted while its herald is held.
  3. Propagate the exact state probabilities through 30 slots. Completed plus unfinished probability remains one after every update. The completion probability is 0.803002.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Completion by deadline with finite memory0.8030018460535358
Completion by deadline without memory0.26921336082933606
Completion with memory lasting to deadline0.9039591903596925
Expected slots used, capped at deadline15.954314385602508
Extra completion probability from finite memory0.5337884852241996

Finite memory raises deadline completion from 26.921336% to 80.300185%. The hard lifetime cutoff grants perfect usefulness before expiry and none after. It is not a physical fidelity-decay law. Storage write/read loss, swapping, classical latency and quantum-state verification are excluded.

Extended regime
Complete inputs
Link A success per slot
0.19
Link B success per slot
0.116
Additional slots a stored herald remains valid
12
Deadline slots
48
  1. Start empty. Each slot gives independent probabilities 0.19 and 0.116 for the two links. Simultaneous success ends the request.
  2. A lone success is held for 12 additional partner-attempt slots. On an unsuccessful final slot it expires; the next slot begins empty. The original link is not re-attempted while its herald is held.
  3. Propagate the exact state probabilities through 48 slots. Completed plus unfinished probability remains one after every update. The completion probability is 0.994875.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Completion by deadline with finite memory0.9948751811056554
Completion by deadline without memory0.6569065636755135
Completion with memory lasting to deadline0.9972698949156154
Expected slots used, capped at deadline10.754122077779469
Extra completion probability from finite memory0.33796861743014195

Finite memory raises deadline completion from 65.690656% to 99.487518%. The hard lifetime cutoff grants perfect usefulness before expiry and none after. It is not a physical fidelity-decay law. Storage write/read loss, swapping, classical latency and quantum-state verification are excluded.

Try the reasoning: Compare a zero-slot memory with a memory lasting to the deadline. Where in the state update does expiry remove a stored herald?

Sources and model boundaries
  • RFC 9340: Architectural Principles for a Quantum Internet ↗

    Quantum network architecture must account for probabilistic entanglement generation, classical coordination, memory lifetime and application requirements. Informational research guidance, not an Internet Standards Track specification or a current performance survey. The synthetic link formulas are not claims made by the RFC.

Quantum networkingA mean link rate does not tell you the age of the older stateWhat does perfect storage save, and how long must the first herald wait?

When two independent links are attempted together, the first successful herald arrives before the pair is ready. Perfect storage can convert that early success into useful progress instead of requiring a fresh simultaneous success. The resulting waiting time is governed by the maximum of two geometric random variables, not by their product alone.

A simple identity makes the calculation approachable: the larger wait equals the sum of the two waits minus the smaller. The first-herald time has a geometric distribution because each slot can succeed on A, B or both. Combining these expectations gives the mean time to have both heralds. A second identity gives the average age of the earlier herald at pairing.

That age is a separate result from the completion rate. A faster mean completion can still require memory to preserve information for a demanding interval. The cases vary the balance between the links and compare perfect memory with simultaneous-only operation. The finite-memory lab then answers the different question of how often the request finishes before an expiry or external deadline.

Synthetic decision model

Start with the assumptions

  • Waiting times count positive integer attempt slots.
  • Both links begin at the same time.
  • Perfect memory has no loss, expiry or readout penalty.

E[min(X,Y)] = 1/(p_A+p_B-p_A p_B)

E[max(X,Y)] = 1/p_A+1/p_B-E[min(X,Y)]

E[|X-Y|] = 2E[max(X,Y)]-1/p_A-1/p_B

Simultaneous-only mean wait = 1/(p_A p_B)

Synthetic a mean link rate does not tell you the age of the older state plot: Mean slots until both heralds versus Link B success per slot.
Synthetic baseline case. Horizontal axis: Link B success per slot. Vertical axis: Mean slots until both heralds. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Link A success per slot
0.08
Link B success per slot
0.015
Slot duration, milliseconds
0.25
  1. The first successful link arrives with per-slot probability a + b - a b = 0.0938. Its mean wait is 10.660981 slots.
  2. For positive-integer geometric waits X and Y, max(X,Y) = X + Y - min(X,Y). The expected synchronized wait is 68.505686 slots.
  3. The earlier herald waits |X - Y| slots. Using |X-Y| = 2 max(X,Y) - X - Y gives 57.844705. Simultaneous-only operation instead waits 833.333333 slots on average.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Expected first herald, slots10.660980810234543
Expected both heralds with perfect memory, slots68.50568585643212
Expected age of older herald at pairing, slots57.844705046197575
Expected simultaneous-only wait, slots833.3333333333334
Perfect-memory mean completion, milliseconds17.12642146410803
Simultaneous-only / memory wait12.164440409804177

Perfect storage shortens the modeled mean wait by a factor of 12.16444, but the older state waits an average of 14.461176 milliseconds. A mean age does not specify a tail probability or surviving fidelity; use the finite-memory lab when a deadline or cutoff defines usefulness.

Comparison regime
Complete inputs
Link A success per slot
0.14
Link B success per slot
0.055
Slot duration, milliseconds
0.5
  1. The first successful link arrives with per-slot probability a + b - a b = 0.1873. Its mean wait is 5.339028 slots.
  2. For positive-integer geometric waits X and Y, max(X,Y) = X + Y - min(X,Y). The expected synchronized wait is 19.985647 slots.
  3. The earlier herald waits |X - Y| slots. Using |X-Y| = 2 max(X,Y) - X - Y gives 14.646619. Simultaneous-only operation instead waits 129.87013 slots on average.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Expected first herald, slots5.339028296849974
Expected both heralds with perfect memory, slots19.98564702782535
Expected age of older herald at pairing, slots14.64661873097538
Expected simultaneous-only wait, slots129.87012987012986
Perfect-memory mean completion, milliseconds9.992823513912676
Simultaneous-only / memory wait6.4981698960917305

Perfect storage shortens the modeled mean wait by a factor of 6.49817, but the older state waits an average of 7.323309 milliseconds. A mean age does not specify a tail probability or surviving fidelity; use the finite-memory lab when a deadline or cutoff defines usefulness.

Extended regime
Complete inputs
Link A success per slot
0.21200000000000002
Link B success per slot
0.103
Slot duration, milliseconds
0.8
  1. The first successful link arrives with per-slot probability a + b - a b = 0.293164. Its mean wait is 3.41106 slots.
  2. For positive-integer geometric waits X and Y, max(X,Y) = X + Y - min(X,Y). The expected synchronized wait is 11.014659 slots.
  3. The earlier herald waits |X - Y| slots. Using |X-Y| = 2 max(X,Y) - X - Y gives 7.603599. Simultaneous-only operation instead waits 45.795933 slots on average.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Expected first herald, slots3.41106002101213
Expected both heralds with perfect memory, slots11.014658975141012
Expected age of older herald at pairing, slots7.603598954128882
Expected simultaneous-only wait, slots45.79593332112108
Perfect-memory mean completion, milliseconds8.81172718011281
Simultaneous-only / memory wait4.157725938177291

Perfect storage shortens the modeled mean wait by a factor of 4.157726, but the older state waits an average of 6.082879 milliseconds. A mean age does not specify a tail probability or surviving fidelity; use the finite-memory lab when a deadline or cutoff defines usefulness.

Try the reasoning: Why is the average age of the older herald insufficient to infer the average surviving state fidelity?

Sources and model boundaries
  • RFC 9340: Architectural Principles for a Quantum Internet ↗

    Quantum network architecture must account for probabilistic entanglement generation, classical coordination, memory lifetime and application requirements. Informational research guidance, not an Internet Standards Track specification or a current performance survey. The synthetic link formulas are not claims made by the RFC.

Quantum networkingThe highest delivery chance may consume too much route capacityWhich path maximizes eligible output under one shared attempt budget?

A route can be attractive for one attempt while being unattractive for the service as a whole. Additional stages may improve some component properties but consume more of a shared resource. Waiting also changes whether a delivered result remains eligible for the intended task. A useful comparison therefore names both the quality rule and the capacity denominator.

This lab uses an intentionally generic probabilistic workflow. Each candidate has a product of stage yields, a delay-dependent eligibility factor and an attempt cost proportional to its number of stages. The result with the largest per-attempt probability need not have the largest eligible output rate. All three routes are evaluated against the same total attempt-resource budget.

The abstraction is suitable for introducing a routing question, but it is not a formula for quantum entanglement quality. State fidelity does not generally multiply as these independent survival flags do. An actual quantum-network comparison must specify entanglement generation, swapping, memory, purification and scheduling. The lesson is to keep the optimization objective visible before translating a better link component into a faster useful network.

Synthetic decision model

Start with the assumptions

  • Stages have independent survival flags.
  • The exponential term is an invented eligibility model, not fidelity.
  • Every stage consumes one unit of the same attempt resource.

Eligibility probability = product(stage yields) × exp(-delay/tau)

Attempts per second = shared resource budget / stages consumed per attempt

Eligible rate = attempts per second × eligibility probability

Synthetic the highest delivery chance may consume too much route capacity plot: Eligible requests per second versus Candidate route.
Synthetic baseline case. Horizontal axis: Candidate route. Vertical axis: Eligible requests per second. Curves show Eligible rate. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Eligibility decay time, milliseconds
5
Attempt-resource budget per second
6000
Long-route efficiency factor
0.8
Direct delay, milliseconds
8
Two-stage delay, milliseconds
3
Three-stage delay, milliseconds
1.5
Direct stage yield
0.4
Two-stage yield per stage
0.78
Three-stage yield per stage before efficiency factor
0.91
  1. For each candidate, multiply independent stage yields, then the declared age eligibility exp(-delay/5). This is a generic survival flag, not an entangled-state fidelity.
  2. Divide the shared attempt-resource budget 6,000 by the number of stages consumed per attempt. Multiplying by eligibility gives a resource-normalized rate.
  3. The highest rate is 1,001.690998 per second through Two stages; the highest individual-attempt eligibility belongs to Three stages.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Best rate routeTwo stages
Best eligible rate per second1001.6909981988172
Highest per-attempt eligibility routeThree stages
Direct eligible rate484.55164318717294
Two-stage eligible rate1001.6909981988172
Three-stage eligible rate893.2146038037487
Candidate route accounting
RouteStagesYield before waitingAge eligibility factorEligible probabilityEligible outputs / second
Direct10.40.201896517994655380.08075860719786215484.55164318717294
Two stages20.60840.54881163609402640.33389699939960571001.6909981988172
Three stages30.60285680000000010.74081822068171790.4466073019018743893.2146038037487

A longer route can improve per-attempt delivery while consuming enough shared capacity to lose on rate. The route comparison is an original stochastic workflow abstraction. Real entanglement routing needs link scheduling, state-quality composition and correlated-resource constraints that this multiplication does not describe.

Comparison regime
Complete inputs
Eligibility decay time, milliseconds
15
Attempt-resource budget per second
6000
Long-route efficiency factor
0.875
Direct delay, milliseconds
13
Two-stage delay, milliseconds
5
Three-stage delay, milliseconds
2.5
Direct stage yield
0.4
Two-stage yield per stage
0.78
Three-stage yield per stage before efficiency factor
0.91
  1. For each candidate, multiply independent stage yields, then the declared age eligibility exp(-delay/15). This is a generic survival flag, not an entangled-state fidelity.
  2. Divide the shared attempt-resource budget 6,000 by the number of stages consumed per attempt. Multiplying by eligibility gives a resource-normalized rate.
  3. The highest rate is 1,307.812948 per second through Two stages; the highest individual-attempt eligibility belongs to Three stages.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Best rate routeTwo stages
Best eligible rate per second1307.8129480592802
Highest per-attempt eligibility routeThree stages
Direct eligible rate1008.8409228208367
Two-stage eligible rate1307.8129480592802
Three-stage eligible rate1116.2971398382037
Candidate route accounting
RouteStagesYield before waitingAge eligibility factorEligible probabilityEligible outputs / second
Direct10.40.42035038450868190.168140153803472771008.8409228208367
Two stages20.60840.71653131057378930.43593764935309341307.8129480592802
Three stages30.65937462500000010.84648172489061410.55814856991910191116.2971398382037

A longer route can improve per-attempt delivery while consuming enough shared capacity to lose on rate. The route comparison is an original stochastic workflow abstraction. Real entanglement routing needs link scheduling, state-quality composition and correlated-resource constraints that this multiplication does not describe.

Extended regime
Complete inputs
Eligibility decay time, milliseconds
27
Attempt-resource budget per second
6000
Long-route efficiency factor
0.9650000000000001
Direct delay, milliseconds
19
Two-stage delay, milliseconds
7.4
Three-stage delay, milliseconds
3.7
Direct stage yield
0.4
Two-stage yield per stage
0.78
Three-stage yield per stage before efficiency factor
0.91
  1. For each candidate, multiply independent stage yields, then the declared age eligibility exp(-delay/27). This is a generic survival flag, not an entangled-state fidelity.
  2. Divide the shared attempt-resource budget 6,000 by the number of stages consumed per attempt. Multiplying by eligibility gives a resource-normalized rate.
  3. The highest rate is 1,387.655311 per second through Two stages; the highest individual-attempt eligibility belongs to Three stages.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Best rate routeTwo stages
Best eligible rate per second1387.6553106767851
Highest per-attempt eligibility routeThree stages
Direct eligible rate1187.398801671488
Two-stage eligible rate1387.6553106767851
Three-stage eligible rate1268.1395782815182
Candidate route accounting
RouteStagesYield before waitingAge eligibility factorEligible probabilityEligible outputs / second
Direct10.40.494749500696453350.197899800278581341187.398801671488
Two stages20.60840.76027575645232580.462551770225595071387.6553106767851
Three stages30.72719601500000020.87193793153660070.63406978914075911268.1395782815182

A longer route can improve per-attempt delivery while consuming enough shared capacity to lose on rate. The route comparison is an original stochastic workflow abstraction. Real entanglement routing needs link scheduling, state-quality composition and correlated-resource constraints that this multiplication does not describe.

Try the reasoning: Which route maximizes eligibility per attempt, and which maximizes eligible output per second? Identify the shared-resource cost behind any difference.

Sources and model boundaries
  • RFC 9340: Architectural Principles for a Quantum Internet ↗

    Quantum network architecture must account for probabilistic entanglement generation, classical coordination, memory lifetime and application requirements. Informational research guidance, not an Internet Standards Track specification or a current performance survey. The synthetic link formulas are not claims made by the RFC.

Photonics and sensing

Photonics and sensingMore detector clicks can mean fewer clean single eventsHow many parallel channels help when the target is exactly one real signal?

Multiplexing creates more opportunities for a useful event, but it also creates more opportunities for extra signals and background clicks. Whether that is a benefit depends on the accepted event class. An experiment that needs one clean signal asks a different probability question from an experiment that counts any detector activity.

The model assigns every channel independent signal and background probabilities. It calculates exactly one signal with no backgrounds, any click of any origin, and background-only click frames. These quantities can move in different directions as more channels are added. A scan selects the largest clean-event probability within a declared range while keeping the much broader click probability visible.

The distinction is especially useful in an article about photon sources, heralded operations or detector arrays. A model can know the latent origin of every event while a real detector cannot. The clean-event calculation therefore does not assert that all clean events can be selected perfectly, or that false backgrounds can be identified in the data. That gap requires an explicit detection and validation model.

Synthetic decision model

Start with the assumptions

  • Signals and backgrounds are independent across and within channels.
  • A frame contains one binary opportunity of each type per channel.
  • Exactly one signal and no background defines the target class.

P(exactly one signal, no background) = m s (1-s)^(m-1)(1-b)^m

P(any click) = 1-(1-s)^m(1-b)^m

P(background only) = (1-s)^m[1-(1-b)^m]

Synthetic more detector clicks can mean fewer clean single events plot: Frame probability versus Independent channels.
Synthetic baseline case. Horizontal axis: Independent channels. Vertical axis: Frame probability. Curves show One clean signal, Any click. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Signal probability per channel
0.015
Background probability per channel
0.0005
Maximum channels
80
Frames per second
1000
  1. Exactly one signal among m independent channels has probability m s (1-s)^(m-1). Require zero independent backgrounds by multiplying by (1-b)^m.
  2. The scan over 1 to 80 channels peaks at m = 64, with clean-event probability 0.3588.
  3. Any click has probability 0.631856, which also includes unwanted multiplets and backgrounds. Background-only frames account for 1.895079% of click frames.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested channel count for one clean signal64
One-signal, no-background probability0.35880034788423176
Any-click probability at that channel count0.631855893056283
Background-only probability0.011974169898660951
Background-only share of all click frames0.018950792467475403
Clean single-signal frames per second358.80034788423177

The useful model rate is 358.800348 frames per second at 64 channels. More clicks do not necessarily mean more single-signal events. This calculation assumes the desired event class is physically meaningful; it does not assert that an ordinary detector can identify and reject every background-only frame.

Comparison regime
Complete inputs
Signal probability per channel
0.045
Background probability per channel
0.0025
Maximum channels
80
Frames per second
3500
  1. Exactly one signal among m independent channels has probability m s (1-s)^(m-1). Require zero independent backgrounds by multiplying by (1-b)^m.
  2. The scan over 1 to 80 channels peaks at m = 21, with clean-event probability 0.357002.
  3. Any click has probability 0.639221, which also includes unwanted multiplets and backgrounds. Background-only frames account for 3.046199% of click frames.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested channel count for one clean signal21
One-signal, no-background probability0.3570016568785008
Any-click probability at that channel count0.6392205478106157
Background-only probability0.01947193166197464
Background-only share of all click frames0.030461992701373022
Clean single-signal frames per second1249.5057990747528

The useful model rate is 1,249.505799 frames per second at 21 channels. More clicks do not necessarily mean more single-signal events. This calculation assumes the desired event class is physically meaningful; it does not assert that an ordinary detector can identify and reject every background-only frame.

Extended regime
Complete inputs
Signal probability per channel
0.081
Background probability per channel
0.0049
Maximum channels
80
Frames per second
6500
  1. Exactly one signal among m independent channels has probability m s (1-s)^(m-1). Require zero independent backgrounds by multiplying by (1-b)^m.
  2. The scan over 1 to 80 channels peaks at m = 11, with clean-event probability 0.362716.
  3. Any click has probability 0.625885, which also includes unwanted multiplets and backgrounds. Background-only frames account for 3.318567% of click frames.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested channel count for one clean signal11
One-signal, no-background probability0.3627160777397321
Any-click probability at that channel count0.6258854372134526
Background-only probability0.02077042648041057
Background-only share of all click frames0.03318566824766527
Clean single-signal frames per second2357.6545053082586

The useful model rate is 2,357.654505 frames per second at 11 channels. More clicks do not necessarily mean more single-signal events. This calculation assumes the desired event class is physically meaningful; it does not assert that an ordinary detector can identify and reject every background-only frame.

Try the reasoning: Why can the any-click probability keep rising after the probability of exactly one clean signal has peaked?

Neutral-atom hardware

Neutral-atom hardwareExtra loading sites help until movement becomes the limitHow many spare sites improve a complete register rather than only its initial loading?

A neutral-atom array can contain more loading sites than the final computation requires. Spares give the system a chance to select enough atoms even when individual loading is probabilistic. The relevant loading event is then at least the required number of occupied sites, rather than every site being occupied.

That change introduces a second stage. Selected atoms may need to survive movement into the target arrangement. The constructed model treats enough initial loading and survival of a fixed number of required moves as independent conditions. Increasing the number of loading sites raises the first probability while leaving the second unchanged. The result has a clear ceiling that extra empty traps cannot repair.

This simplified sequence gives readers a way to separate trap capacity, loading yield and assembled-register yield. It does not model a real rearrangement algorithm, where the number and length of moves depend on the initial pattern and many atoms may already be in useful positions. A strong follow-up article would report the distribution of loading patterns and movement costs, keeping a reliable final arrangement distinct from a large photograph of illuminated sites.

Synthetic decision model

Start with the assumptions

  • Sites load independently with the same probability.
  • Exactly k required moves occur after successful loading.
  • Movement survival is independent of loading and the other moves.

P(enough loaded) = sum_{j=k}^n C(n,j)p^j(1-p)^(n-j)

P(all required moves survive) = movement_survival^k

Assembly probability = P(enough loaded) × P(all moves survive)

Synthetic extra loading sites help until movement becomes the limit plot: Complete-register probability versus Loading sites.
Synthetic baseline case. Horizontal axis: Loading sites. Vertical axis: Complete-register probability. Curves show Assembly probability, Target. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Required atoms
12
Available loading sites
20
Independent loading probability
0.6
Survival per required move
0.99
Desired assembled-register probability
0.75
Additional sites included in search
80
  1. Sum the binomial loading distribution from 12 successes through 20. The chance of enough atoms is 0.595599.
  2. Assume exactly 12 independent required moves, each surviving with probability 0.99. Their joint survival is 0.886385.
  3. Multiply the independent loading and movement stages to obtain 0.52793. Search 12 through 92 sites for the declared target 0.75.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Probability enough atoms load0.5955987253122249
All required moves survive0.8863848717161292
Combined assembly probability0.5279296997301666
No-spares complete-and-moved probability0.0019294669316492952
Minimum sites meeting target in tested range24
Movement-only ceiling as sites increase0.8863848717161292

The tested minimum is 24 loading sites. Extra sites fix loading shortages but cannot remove the movement ceiling 0.886385. Real rearrangement may require a variable number of moves; then its movement survival must be conditioned on the actual loading pattern.

Comparison regime
Complete inputs
Required atoms
22
Available loading sites
35
Independent loading probability
0.725
Survival per required move
0.9885
Desired assembled-register probability
0.75
Additional sites included in search
80
  1. Sum the binomial loading distribution from 22 successes through 35. The chance of enough atoms is 0.92533.
  2. Assume exactly 22 independent required moves, each surviving with probability 0.9885. Their joint survival is 0.77533.
  3. Multiply the independent loading and movement stages to obtain 0.717437. Search 22 through 102 sites for the declared target 0.75.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Probability enough atoms load0.925330389694105
All required moves survive0.7753304137431637
Combined assembly probability0.7174367938906533
No-spares complete-and-moved probability0.0006560288895928319
Minimum sites meeting target in tested range37
Movement-only ceiling as sites increase0.7753304137431637

The tested minimum is 37 loading sites. Extra sites fix loading shortages but cannot remove the movement ceiling 0.77533. Real rearrangement may require a variable number of moves; then its movement survival must be conditioned on the actual loading pattern.

Extended regime
Complete inputs
Required atoms
34
Available loading sites
53
Independent loading probability
0.875
Survival per required move
0.9867
Desired assembled-register probability
0.75
Additional sites included in search
80
  1. Sum the binomial loading distribution from 34 successes through 53. The chance of enough atoms is 0.999997.
  2. Assume exactly 34 independent required moves, each surviving with probability 0.9867. Their joint survival is 0.634299.
  3. Multiply the independent loading and movement stages to obtain 0.634298. Search 34 through 114 sites for the declared target 0.75.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Probability enough atoms load0.999997255392694
All required moves survive0.6342994851361967
Combined assembly probability0.6342977442331956
No-spares complete-and-moved probability0.00676968033341188
Minimum sites meeting target in tested rangeTarget unavailable in tested range
Movement-only ceiling as sites increase0.6342994851361967

No tested loading-site count reaches the target. Extra sites fix loading shortages but cannot remove the movement ceiling 0.634299. Real rearrangement may require a variable number of moves; then its movement survival must be conditioned on the actual loading pattern.

Try the reasoning: Compare the desired assembly probability with the movement-only ceiling before adding more loading sites.

Hardware control and infrastructure

Hardware control and infrastructureAn idle cable can consume the margin needed to read a qubitHow does installed idle heat change the number of channels that can operate together?

More control channels appear to promise more simultaneous operations. But installed infrastructure can add a heat load even when only a subset is active. The capacity question is therefore not just the heat of the channels currently being used. It also includes the background cost of supporting every installed channel.

The lab separates fixed system heat, idle heat per installed channel and the additional heat caused by activation. The remaining budget determines how many channels can be active together. If that number is smaller than the total channel count, the readout must be scheduled in groups. A heat constraint has then become a cycle-time constraint, even though the individual readout operation is unchanged.

This is a deliberately steady-state teaching model. Real cryogenic systems have thermal time constants, frequency-dependent dissipation, unequal cable routes and temperature limits that cannot be summarized by one instantaneous wattage ceiling. The useful Model interaction is nevertheless clear: adding channels changes both available parallelism and background heat. Readers can see why a larger connector count does not, by itself, establish a proportionate increase in useful throughput.

Synthetic decision model

Start with the assumptions

  • Loads are modeled as steady and additive.
  • Every installed channel contributes idle heat.
  • Readout groups run sequentially under one heat ceiling.

Installed idle load = fixed heat + channels × idle heat

Active increment per channel = active heat - idle heat

Simultaneous capacity = floor((cooling - idle load)/active increment), capped at installed channels

Cycle time = ceil(channels/capacity) × group time + other operations

Synthetic an idle cable can consume the margin needed to read a qubit plot: Total heat, microwatts versus Simultaneously active channels.
Synthetic baseline case. Horizontal axis: Simultaneously active channels. Vertical axis: Total heat, microwatts. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Installed channels
24
Cooling power, microwatts
80
Fixed heat, microwatts
20
Idle heat per channel, microwatts
0.6
Active heat per channel, microwatts
3
Readout group time, microseconds
4
Other cycle time, microseconds
12
  1. The installed idle load is fixed heat + channels × idle heat = 34.4 microwatts. All installed channels contribute even while their group waits.
  2. Each active channel adds 2.4 microwatts above that idle load. Floor the remaining margin divided by the increment, then cap at 24 installed channels.
  3. Read 2 groups in sequence and add other operations: 20 microseconds.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Idle installed heat, microwatts34.4
Margin above installed idle heat45.6
Maximum simultaneous active channels19
Required readout groups2
Complete cycle time, microseconds20
All-at-once heat, microwatts92

This is a steady-load scheduling abstraction. It illustrates why additional wires can add idle heat while providing little extra simultaneous capacity. Pulsed thermal transients, unequal channels, heat sinking and maximum permissible temperatures require a real thermal analysis before applying the result to a device.

Comparison regime
Complete inputs
Installed channels
44
Cooling power, microwatts
100
Fixed heat, microwatts
20
Idle heat per channel, microwatts
0.75
Active heat per channel, microwatts
3.6
Readout group time, microseconds
4
Other cycle time, microseconds
12
  1. The installed idle load is fixed heat + channels × idle heat = 53 microwatts. All installed channels contribute even while their group waits.
  2. Each active channel adds 2.85 microwatts above that idle load. Floor the remaining margin divided by the increment, then cap at 44 installed channels.
  3. Read 3 groups in sequence and add other operations: 24 microseconds.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Idle installed heat, microwatts53
Margin above installed idle heat47
Maximum simultaneous active channels16
Required readout groups3
Complete cycle time, microseconds24
All-at-once heat, microwatts178.4

This is a steady-load scheduling abstraction. It illustrates why additional wires can add idle heat while providing little extra simultaneous capacity. Pulsed thermal transients, unequal channels, heat sinking and maximum permissible temperatures require a real thermal analysis before applying the result to a device.

Extended regime
Complete inputs
Installed channels
68
Cooling power, microwatts
124
Fixed heat, microwatts
20
Idle heat per channel, microwatts
0.9299999999999999
Active heat per channel, microwatts
4.32
Readout group time, microseconds
4
Other cycle time, microseconds
12
  1. The installed idle load is fixed heat + channels × idle heat = 83.24 microwatts. All installed channels contribute even while their group waits.
  2. Each active channel adds 3.39 microwatts above that idle load. Floor the remaining margin divided by the increment, then cap at 68 installed channels.
  3. Read 6 groups in sequence and add other operations: 36 microseconds.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Idle installed heat, microwatts83.24
Margin above installed idle heat40.760000000000005
Maximum simultaneous active channels12
Required readout groups6
Complete cycle time, microseconds36
All-at-once heat, microwatts313.76

This is a steady-load scheduling abstraction. It illustrates why additional wires can add idle heat while providing little extra simultaneous capacity. Pulsed thermal transients, unequal channels, heat sinking and maximum permissible temperatures require a real thermal analysis before applying the result to a device.

Try the reasoning: What happens to idle heat and simultaneous capacity when more channels are installed? Check both before using the cycle-time estimate.

Sources and model boundaries
  • A Quantum Engineer's Guide to Superconducting Qubits ↗

    Superconducting qubit engineering links device physics, noise, control and measurement infrastructure. No contemporary device specification, operating temperature, pulse duration or thermal budget is inferred from this historical review.

Hardware control and infrastructureReadout can move its bottleneck without changing the detectorWhat is gained when acquisition, transfer and processing overlap?

A measurement can produce far more data than the final bit returned to an application. Raw waveforms may support discrimination, calibration and diagnostics, while the later result contains only a compact decision. The complete readout workflow therefore includes acquisition, transport and processing resources with different timing and storage needs.

A sequential schedule pays all three stage times for every shot. A perfectly overlapped pipeline pays the fill cost once and then completes shots at the pace of the slowest stage. Improving a stage that is already faster than the bottleneck may have little effect on sustained throughput. Reducing raw data near the detector can alter the transfer requirement, but it may also discard information useful for auditing a classifier.

The cases calculate byte counts and batch durations under explicit decimal bandwidth units. The pipeline is idealized: stages have separate resources and there is no feedback dependence between consecutive shots. Those assumptions are often the first thing to examine in a mid-circuit-control claim. A result that depends on the previous measurement cannot automatically receive the same overlap as an independent batch of final readouts.

Synthetic decision model

Start with the assumptions

  • Stages have dedicated resources and sufficient buffers.
  • All shots have identical stage durations.
  • Consecutive shots are independent for scheduling purposes.

Raw bytes = channels × samples per channel × bytes per complex sample

Transfer time = raw bytes / transfer bandwidth

Serial batch = N × sum(stage times)

Ideal pipeline batch = sum(stage times) + (N-1) × max(stage times)

Synthetic readout can move its bottleneck without changing the detector plot: Milliseconds per shot versus Stage.
Synthetic baseline case. Horizontal axis: Stage. Vertical axis: Milliseconds per shot. Curves show Stage time. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Readout channels
8
Samples per channel
512
Bytes per complex sample
4
Transfer bandwidth, MB per second
200
Feature extraction, milliseconds
0.4
Acquisition, milliseconds
0.2
Shots in batch
1000
  1. Multiply channels × samples × bytes per complex sample to obtain 16,384 raw bytes. MB uses 1,000,000 bytes in this case.
  2. Divide by link bandwidth: transfer requires 0.08192 milliseconds per shot. The other stage times are 0.2 and 0.4 milliseconds.
  3. A perfectly overlapped three-stage pipeline fills once, then completes one shot per slowest-stage interval. Total = sum(stage times) + (shots - 1) × max(stage times) = 0.400282 seconds.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Raw bytes per shot16384
Transfer time per shot, milliseconds0.08192
Serial batch duration, seconds0.6819200000000001
Ideal pipeline batch duration, seconds0.40028192
Raw bytes / one-bit-per-channel result bytes16384
Pipeline limiting stage, milliseconds0.4

The pipeline model shortens this batch from 0.68192 to 0.400282 seconds. It assumes distinct resources, sufficient buffers and no next-shot dependence on the previous result. Mid-circuit feedback can impose dependencies that prevent this overlap. A compressed result may omit waveform information needed for later calibration checks.

Comparison regime
Complete inputs
Readout channels
28
Samples per channel
640
Bytes per complex sample
4
Transfer bandwidth, MB per second
250
Feature extraction, milliseconds
0.65
Acquisition, milliseconds
0.25
Shots in batch
1000
  1. Multiply channels × samples × bytes per complex sample to obtain 71,680 raw bytes. MB uses 1,000,000 bytes in this case.
  2. Divide by link bandwidth: transfer requires 0.28672 milliseconds per shot. The other stage times are 0.25 and 0.65 milliseconds.
  3. A perfectly overlapped three-stage pipeline fills once, then completes one shot per slowest-stage interval. Total = sum(stage times) + (shots - 1) × max(stage times) = 0.650537 seconds.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Raw bytes per shot71680
Transfer time per shot, milliseconds0.28672000000000003
Serial batch duration, seconds1.18672
Ideal pipeline batch duration, seconds0.6505367200000001
Raw bytes / one-bit-per-channel result bytes20480
Pipeline limiting stage, milliseconds0.65

The pipeline model shortens this batch from 1.18672 to 0.650537 seconds. It assumes distinct resources, sufficient buffers and no next-shot dependence on the previous result. Mid-circuit feedback can impose dependencies that prevent this overlap. A compressed result may omit waveform information needed for later calibration checks.

Extended regime
Complete inputs
Readout channels
52
Samples per channel
896
Bytes per complex sample
4
Transfer bandwidth, MB per second
250
Feature extraction, milliseconds
0.9500000000000001
Acquisition, milliseconds
0.31
Shots in batch
1000
  1. Multiply channels × samples × bytes per complex sample to obtain 186,368 raw bytes. MB uses 1,000,000 bytes in this case.
  2. Divide by link bandwidth: transfer requires 0.745472 milliseconds per shot. The other stage times are 0.31 and 0.95 milliseconds.
  3. A perfectly overlapped three-stage pipeline fills once, then completes one shot per slowest-stage interval. Total = sum(stage times) + (shots - 1) × max(stage times) = 0.951055 seconds.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Raw bytes per shot186368
Transfer time per shot, milliseconds0.7454719999999999
Serial batch duration, seconds2.005472
Ideal pipeline batch duration, seconds0.9510554720000001
Raw bytes / one-bit-per-channel result bytes28672
Pipeline limiting stage, milliseconds0.9500000000000001

The pipeline model shortens this batch from 2.005472 to 0.951055 seconds. It assumes distinct resources, sufficient buffers and no next-shot dependence on the previous result. Mid-circuit feedback can impose dependencies that prevent this overlap. A compressed result may omit waveform information needed for later calibration checks.

Try the reasoning: Which stage would need to be faster to improve steady pipeline throughput? Would a next-shot feedback dependency allow the same overlap?

Sources and model boundaries
  • A Quantum Engineer's Guide to Superconducting Qubits ↗

    Superconducting qubit engineering links device physics, noise, control and measurement infrastructure. No contemporary device specification, operating temperature, pulse duration or thermal budget is inferred from this historical review.

Hardware control and infrastructureQuieting a microwave line also decides where heat appearsHow does distributing attenuation change thermal occupation and signal dissipation?

An attenuator reduces a traveling signal but also couples the line to its own environment. At microwave frequencies, a temperature is most useful when compared with the mode’s quantum energy scale. The mean thermal occupation expresses that relationship and lets a simple matched-loss model track noise through successive stages.

Each ideal stage transmits a fraction of the incoming occupation and replaces the lost fraction with its own thermal contribution. Moving attenuation between warmer and colder stages therefore changes which environment dominates the output. The same distribution also determines where incident classical signal power is dissipated. A quiet output and a manageable cold-stage heat load are related but distinct objectives.

The lab tracks two stages using invented attenuation values and temperatures. It explicitly balances only the declared incident signal power, not every thermal pathway in a refrigerator. Broadband radiation, cable conduction, reflections, filters and nonlinearity are omitted. The result is appropriate as a Model explanation of why control wiring is engineered in stages, while remaining far narrower than a design for an operating quantum processor.

Synthetic decision model

Start with the assumptions

  • One bosonic mode and ideal matched linear attenuation are modeled.
  • Each attenuator has a fixed temperature.
  • The stated power balance concerns only incident classical signal power.

Thermal occupation n(T) = 1/[exp(h f/(k_B T))-1]

Power transmission eta = 10^(-attenuation_dB/10)

Matched-stage occupation n_out = eta n_in + (1-eta)n_stage

Signal dissipation = incident signal power × (1-eta)

Synthetic quieting a microwave line also decides where heat appears plot: Mean occupation versus Cold-stage attenuation, dB.
Synthetic baseline case. Horizontal axis: Cold-stage attenuation, dB. Vertical axis: Mean occupation. Curves show Output thermal occupation. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Mode frequency, GHz
4
Input temperature, K
300
Warm-stage attenuation, dB
10
Cold-stage attenuation, dB
30
Warm-stage temperature, K
4
Cold-stage temperature, K
0.02
Incident signal power, microwatts
10
Planck constant / Boltzmann constant, K seconds
4.799243073e-11
  1. For one bosonic mode, n(T) = 1/(exp(h f / kT) - 1). The stipulated input temperature gives occupation 1,562.246488.
  2. Each ideal matched attenuator mixes transmitted input noise with its own thermal noise: n_out = eta n_in + (1 - eta)n_stage. The two stages give 174.531205 and 0.174599.
  3. Classical incident signal power dissipates as P_in(1 - eta) at each stage, after accounting for preceding attenuation. The signal-power balance sums to 10 microwatts.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Incoming mean thermal occupation1562.2464876937408
After warm stage occupation174.53120527593762
After cold stage occupation0.1745989733869517
Warm-stage signal dissipation, microwatts9
Cold-stage signal dissipation, microwatts0.999
Remaining signal power, microwatts0.001

Moving attenuation changes both the final noise occupation and where the signal power is dissipated. This calculation accounts only for the declared traveling mode and incident signal. It omits reflections, broadband thermal transport, cable conduction and nonlinear components, so it is an explanatory balance rather than a refrigerator wiring design.

Comparison regime
Complete inputs
Mode frequency, GHz
5
Input temperature, K
300
Warm-stage attenuation, dB
20
Cold-stage attenuation, dB
20
Warm-stage temperature, K
4
Cold-stage temperature, K
0.025
Incident signal power, microwatts
15
Planck constant / Boltzmann constant, K seconds
4.799243073e-11
  1. For one bosonic mode, n(T) = 1/(exp(h f / kT) - 1). The stipulated input temperature gives occupation 1,249.697214.
  2. Each ideal matched attenuator mixes transmitted input noise with its own thermal noise: n_out = eta n_in + (1 - eta)n_stage. The two stages give 28.509523 and 0.285162.
  3. Classical incident signal power dissipates as P_in(1 - eta) at each stage, after accounting for preceding attenuation. The signal-power balance sums to 15 microwatts.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Incoming mean thermal occupation1249.6972141512078
After warm stage occupation28.509523411031747
After cold stage occupation0.2851623916978089
Warm-stage signal dissipation, microwatts14.85
Cold-stage signal dissipation, microwatts0.1485
Remaining signal power, microwatts0.0015

Moving attenuation changes both the final noise occupation and where the signal power is dissipated. This calculation accounts only for the declared traveling mode and incident signal. It omits reflections, broadband thermal transport, cable conduction and nonlinear components, so it is an explanatory balance rather than a refrigerator wiring design.

Extended regime
Complete inputs
Mode frequency, GHz
6.2
Input temperature, K
300
Warm-stage attenuation, dB
32
Cold-stage attenuation, dB
8
Warm-stage temperature, K
4
Cold-stage temperature, K
0.031
Incident signal power, microwatts
21
Planck constant / Boltzmann constant, K seconds
4.799243073e-11
  1. For one bosonic mode, n(T) = 1/(exp(h f / kT) - 1). The stipulated input temperature gives occupation 1,007.723589.
  2. Each ideal matched attenuator mixes transmitted input noise with its own thermal noise: n_out = eta n_in + (1 - eta)n_stage. The two stages give 13.576839 and 2.151841.
  3. Classical incident signal power dissipates as P_in(1 - eta) at each stage, after accounting for preceding attenuation. The signal-power balance sums to 21 microwatts.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Incoming mean thermal occupation1007.7235886980283
After warm stage occupation13.576838751448957
After cold stage occupation2.1518410159052763
Warm-stage signal dissipation, microwatts20.986749895765918
Cold-stage signal dissipation, microwatts0.011150104234084053
Remaining signal power, microwatts0.002099999999999999

Moving attenuation changes both the final noise occupation and where the signal power is dissipated. This calculation accounts only for the declared traveling mode and incident signal. It omits reflections, broadband thermal transport, cable conduction and nonlinear components, so it is an explanatory balance rather than a refrigerator wiring design.

Try the reasoning: Move attenuation between the warm and cold stages while keeping total decibels fixed. Track both output occupation and the location of signal dissipation.

Sources and model boundaries
  • A Quantum Engineer's Guide to Superconducting Qubits ↗

    Superconducting qubit engineering links device physics, noise, control and measurement infrastructure. No contemporary device specification, operating temperature, pulse duration or thermal budget is inferred from this historical review.

Simulation and scientific validity

Simulation and scientific validityA neat finite-size fit can point to the wrong limitWhat does a held-out size reveal that an in-sample residual cannot?

A finite quantum simulator answers a finite question. Researchers may then ask how the observable changes as the represented system becomes larger. Extrapolation can be informative, but the inferred limit depends on a functional form and a range of sizes. A narrow fitted residual is evidence about the observed window, not automatic evidence about an unobserved limit.

This lab creates an exact curve with both inverse-size and inverse-size-squared terms. It deliberately fits only the first term. Because the generating limit is known, the error in the extrapolated intercept is visible. Comparing all sizes with the largest two, and testing a new holdout size, reveals sensitivity that the fitted line alone could conceal.

The example avoids simulated measurement noise so the source of error stays clear: the model is misspecified. In a real study, sampling noise, control error and different finite-size corrections can coexist. Comparing fit windows alongside explicit extrapolation assumptions exposes this sensitivity. Readers should be able to distinguish a directly measured finite-size observable from an inferred large-system value.

Synthetic decision model

Start with the assumptions

  • The generating curve is known only because this is synthetic.
  • Fits use exact values without measurement noise.
  • Ordinary least squares weights all supplied sizes equally.

Synthetic observable y(L) = y_infinity + a/L + b/L²

Deliberately restricted fit y_fit(L) = intercept + slope/L

Holdout error = fitted prediction at unused size - generating value

Synthetic a neat finite-size fit can point to the wrong limit plot: Illustrative observable versus Inverse system size, 1/L.
Synthetic baseline case. Horizontal axis: Inverse system size, 1/L. Vertical axis: Illustrative observable. Curves show Generating curve, Linear fit. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Infinite-size reference
0.6
Inverse-size coefficient
1.5
Curvature coefficient
2
System sizes
6, 10, 16, 24
Unfitted holdout size
40
  1. Generate y(L) = reference + a/L + b/L² at L = 6, 10, 16, 24. These are exact synthetic function values, not noisy observations.
  2. Fit a straight line in 1/L while omitting curvature. Using all sizes gives intercept 0.582319; the largest two give 0.594792.
  3. At the held-out size 40, the all-size fit predicts 0.630441 and the generating curve gives 0.63875. Their difference is -0.008309.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
All-size linear extrapolated intercept0.5823186709873579
Largest-two extrapolated intercept0.5947916666666666
Known synthetic infinite-size reference0.6
All-size intercept bias-0.017681329012642077
In-sample residual RMS0.003240669796073463
Unfitted holdout prediction minus truth-0.008308929428708534
Exact generating values used in the fit
System sizeObservable
60.9055555555555556
100.77
160.7015625
240.6659722222222222

The known intercept is 0.6, so the fitted intercept error can be measured directly here. A small residual over the observed window does not guarantee an accurate extrapolation outside it. On a real experiment the infinite-size answer is unknown; varying the fit window and testing held-out sizes becomes evidence about model sensitivity, not proof of the limit.

Comparison regime
Complete inputs
Infinite-size reference
0.65
Inverse-size coefficient
1.1
Curvature coefficient
8
System sizes
11, 15, 21, 29
Unfitted holdout size
50
  1. Generate y(L) = reference + a/L + b/L² at L = 11, 15, 21, 29. These are exact synthetic function values, not noisy observations.
  2. Fit a straight line in 1/L while omitting curvature. Using all sizes gives intercept 0.621764; the largest two give 0.636864.
  3. At the held-out size 50, the all-size fit predicts 0.66398 and the generating curve gives 0.6752. Their difference is -0.01122.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
All-size linear extrapolated intercept0.6217640825006453
Largest-two extrapolated intercept0.6368637110016419
Known synthetic infinite-size reference0.65
All-size intercept bias-0.028235917499354724
In-sample residual RMS0.0027585201551087405
Unfitted holdout prediction minus truth-0.01121975718117707
Exact generating values used in the fit
System sizeObservable
110.8161157024793388
150.758888888888889
210.7205215419501134
290.6974435196195006

The known intercept is 0.65, so the fitted intercept error can be measured directly here. A small residual over the observed window does not guarantee an accurate extrapolation outside it. On a real experiment the infinite-size answer is unknown; varying the fit window and testing held-out sizes becomes evidence about model sensitivity, not proof of the limit.

Extended regime
Complete inputs
Infinite-size reference
0.71
Inverse-size coefficient
0.62
Curvature coefficient
15.2
System sizes
17, 21, 27, 35
Unfitted holdout size
62
  1. Generate y(L) = reference + a/L + b/L² at L = 17, 21, 27, 35. These are exact synthetic function values, not noisy observations.
  2. Fit a straight line in 1/L while omitting curvature. Using all sizes gives intercept 0.682791; the largest two give 0.693915.
  3. At the held-out size 62, the all-size fit predicts 0.714273 and the generating curve gives 0.723954. Their difference is -0.009681.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
All-size linear extrapolated intercept0.6827909087164262
Largest-two extrapolated intercept0.6939153439153434
Known synthetic infinite-size reference0.71
All-size intercept bias-0.02720909128357374
In-sample residual RMS0.0015193266736859916
Unfitted holdout prediction minus truth-0.009680813148590484
Exact generating values used in the fit
System sizeObservable
170.7990657439446367
210.7739909297052153
270.7538134430727023
350.7401224489795918

The known intercept is 0.71, so the fitted intercept error can be measured directly here. A small residual over the observed window does not guarantee an accurate extrapolation outside it. On a real experiment the infinite-size answer is unknown; varying the fit window and testing held-out sizes becomes evidence about model sensitivity, not proof of the limit.

Try the reasoning: Can a two-point fit with zero residual certify the infinite-size limit? Compare the fit-window change and the held-out-size error.

Simulation and scientific validityMore simulation steps can improve the formula and worsen the experimentWhere is the optimum when approximation error falls while implementation error grows?

Splitting an evolution into more steps can make a product-formula approximation more faithful to the target mathematical evolution. The implementation then performs more operations, each of which may introduce error or consume resources. A step count therefore sits between two models: the mathematical approximation and the physical realization.

The deliberately simple objective in this lab contains one term that falls as an inverse power of the step count and one that grows linearly. Its continuous minimum can be derived by differentiation, then compared with the allowed integers. Both contributions remain visible. This prevents a decreasing approximation bound from being mistaken for a decreasing total experimental error.

The cited product-formula work supplies the context that approximation error depends on mathematical structure. It does not supply this toy model’s coefficients or certify that a linear implementation term is appropriate. Before applying the sum to a real experiment, the two contributions would need compatible units and an error measure for which the combination is justified. Changing the step count is meaningful only while those model assumptions remain appropriate.

Synthetic decision model

Start with the assumptions

  • The two contributions share a compatible illustrative error measure.
  • Coefficients are positive and fixed.
  • The implementation term is assumed linear for teaching purposes.

Illustrative error objective E(r) = a/r^q + b r

Continuous stationary point r* = (q a/b)^(1/(q+1))

Integer optimum is selected from the stated finite step range

Synthetic more simulation steps can improve the formula and worsen the experiment plot: Illustrative error objective versus Step count.
Synthetic baseline case. Horizontal axis: Step count. Vertical axis: Illustrative error objective. Curves show Approximation, Implementation, Sum. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Approximation coefficient
0.4
Error added per step
0.0002
Inverse-step power
1
Maximum steps
120
  1. The deliberately assumed objective is a/r^q + b r. Differentiate: -q a/r^(q+1) + b = 0, giving r* = 44.72136.
  2. Scan positive integers up to 120. The minimum occurs at r = 45, where the terms are 0.008889 and 0.009.
  3. The summed quantity is an illustrative error objective. Its coefficients must refer to a compatible error measure before terms can be physically added. It is not a general Trotter bound for an arbitrary Hamiltonian.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Continuous unconstrained optimum44.721359549995796
Best tested integer step count45
Approximation contribution at optimum0.008888888888888889
Implementation contribution at optimum0.009000000000000001
Combined illustrative error objective0.01788888888888889
One-step objective / best objective22.371428571428567

The numerical optimum is 45 steps. Increasing steps beyond it reduces one term while increasing the other. The cited product-formula literature motivates the existence of approximation error, but the additive linear implementation term and all coefficients are assumptions created for this decision exercise.

Comparison regime
Complete inputs
Approximation coefficient
0.9
Error added per step
0.0007
Inverse-step power
2
Maximum steps
120
  1. The deliberately assumed objective is a/r^q + b r. Differentiate: -q a/r^(q+1) + b = 0, giving r* = 13.700134.
  2. Scan positive integers up to 120. The minimum occurs at r = 14, where the terms are 0.004592 and 0.0098.
  3. The summed quantity is an illustrative error objective. Its coefficients must refer to a compatible error measure before terms can be physically added. It is not a general Trotter bound for an arbitrary Hamiltonian.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Continuous unconstrained optimum13.700134211888825
Best tested integer step count14
Approximation contribution at optimum0.004591836734693878
Implementation contribution at optimum0.0098
Combined illustrative error objective0.014391836734693877
One-step objective / best objective62.58408961996597

The numerical optimum is 14 steps. Increasing steps beyond it reduces one term while increasing the other. The cited product-formula literature motivates the existence of approximation error, but the additive linear implementation term and all coefficients are assumptions created for this decision exercise.

Extended regime
Complete inputs
Approximation coefficient
1.5
Error added per step
0.0013000000000000002
Inverse-step power
2
Maximum steps
120
  1. The deliberately assumed objective is a/r^q + b r. Differentiate: -q a/r^(q+1) + b = 0, giving r* = 13.214761.
  2. Scan positive integers up to 120. The minimum occurs at r = 13, where the terms are 0.008876 and 0.0169.
  3. The summed quantity is an illustrative error objective. Its coefficients must refer to a compatible error measure before terms can be physically added. It is not a general Trotter bound for an arbitrary Hamiltonian.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Continuous unconstrained optimum13.214760630124598
Best tested integer step count13
Approximation contribution at optimum0.008875739644970414
Implementation contribution at optimum0.016900000000000002
Combined illustrative error objective0.025775739644970416
One-step objective / best objective58.24469135235646

The numerical optimum is 13 steps. Increasing steps beyond it reduces one term while increasing the other. The cited product-formula literature motivates the existence of approximation error, but the additive linear implementation term and all coefficients are assumptions created for this decision exercise.

Try the reasoning: At the continuous stationary point, what relation holds between the approximation and implementation terms for inverse-step power q?

Sources and model boundaries
  • A Theory of Trotter Error ↗

    Product-formula approximation error depends on the mathematical structure of Hamiltonian terms. The lab does not reproduce a paper benchmark or a Hamiltonian-specific bound. Its additive implementation-error term is a teaching assumption.

Simulation and scientific validityA perfect sampled fit can describe the wrong oscillationCan two different continuous frequencies produce the same recorded values?

An oscilloscope or software logger records samples, not an unbroken view of a waveform. Different continuous signals can agree at those sample times. If an analysis chooses between them only by how well it fits the recorded values, it can have no basis for preferring the physically correct one.

The constructed experiment samples a zero-phase cosine at a fixed rate. Folding its frequency into the base interval gives an alias with the same ideal sample sequence. The numerical comparison makes the ambiguity concrete: two plotted continuous explanations can diverge between sample times while their recorded points coincide. More elaborate fitting does not recover information that the measurement procedure never distinguished.

This lesson applies to control waveforms, spectroscopy traces and simulated dynamics. A justified bandwidth limit, anti-alias filtering or a changed sampling schedule can supply the missing constraint. The example also distinguishes Fourier-bin spacing from a universal resolution claim. A longer record changes the analysis grid, but identifiability still depends on the signal model, window and measurement process.

Synthetic decision model

Start with the assumptions

  • The signal is a zero-phase cosine with a known fixed amplitude.
  • Sampling is exact and uniformly spaced.
  • Floating-point discrepancies are numerical error, not physical noise.

Samples occur at t_k = k/f_s

Cosine alias = |((f+f_s/2) modulo f_s)-f_s/2|

DFT-bin spacing = f_s/N

Synthetic a perfect sampled fit can describe the wrong oscillation plot: Sampled amplitude versus Sample number.
Synthetic baseline case. Horizontal axis: Sample number. Vertical axis: Sampled amplitude. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Sampling rate, Hz
80
Actual sinusoid frequency, Hz
91
Sample count
32
Signal amplitude
1
  1. Fold the actual frequency into the interval from zero to fs/2: |((f + fs/2) mod fs) - fs/2| = 11 Hz.
  2. Evaluate zero-phase cosines at t_k = k/fs for k = 0,...,31. The largest difference between actual and aliased sample values is 2.29816e-14, arising from floating-point arithmetic.
  3. The spacing of the discrete Fourier transform bins is fs/N = 2.5 Hz. This is a grid spacing, not a universal resolution limit or a proof that adjacent lines are separable.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Folded alias frequency, Hz11
Sampling Nyquist boundary, Hz40
Observation duration N/fs, seconds0.4
DFT-bin spacing fs/N, Hz2.5
Maximum numerical sample discrepancy2.298161660974074e-14
First twelve of the uniformly spaced samples; full sequence follows the displayed cosine formula
IndexTime, secondsActual-frequency sampleAlias-frequency sample
0011
10.01250.64944804833018350.6494480483301837
20.025-0.1564344650402312-0.1564344650402308
30.0375-0.8526401643540921-0.852640164354092
40.05-0.9510565162951534-0.9510565162951536
50.0625-0.38268343236509145-0.38268343236509034
60.0750.45399049973954610.4539904997395458
70.08750.9723699203976750.9723699203976762
80.10.80901699437494670.8090169943749476
90.11250.078459095727849660.07845909572784569
100.125-0.7071067811865449-0.7071067811865467
110.1375-0.9969173337331282-0.996917333733128

The 91 Hz and 11 Hz zero-phase cosines give the same ideal sample sequence. A better-fitting sampled curve cannot identify which continuous signal was present. Filtering, an independently justified bandwidth limit or a changed sampling rate supplies information absent from the original samples.

Comparison regime
Complete inputs
Sampling rate, Hz
130
Actual sinusoid frequency, Hz
281
Sample count
40
Signal amplitude
1.5
  1. Fold the actual frequency into the interval from zero to fs/2: |((f + fs/2) mod fs) - fs/2| = 21 Hz.
  2. Evaluate zero-phase cosines at t_k = k/fs for k = 0,...,39. The largest difference between actual and aliased sample values is 1.00031e-13, arising from floating-point arithmetic.
  3. The spacing of the discrete Fourier transform bins is fs/N = 3.25 Hz. This is a grid spacing, not a universal resolution limit or a proof that adjacent lines are separable.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Folded alias frequency, Hz21
Sampling Nyquist boundary, Hz65
Observation duration N/fs, seconds0.3076923076923077
DFT-bin spacing fs/N, Hz3.25
Maximum numerical sample discrepancy1.000310945187266e-13
First twelve of the uniformly spaced samples; full sequence follows the displayed cosine formula
IndexTime, secondsActual-frequency sampleAlias-frequency sample
001.51.5
10.0076923076923076930.79146036615920060.791460366159199
20.015384615384615385-0.6647873183988586-0.6647873183988624
30.023076923076923078-1.4929974520764726-1.492997452076473
40.03076923076923077-0.9107437617280726-0.910743761728066
50.0384615384615384640.53190733056379250.5319073305638033
60.0461538461538461561.47205518920911921.47205518920912
70.053846153846153851.02152378818019531.0215237881801955
80.06153846153846154-0.3940610672978664-0.39406106729788226
90.06923076923076923-1.4373687436637468-1.4373687436637494
100.07692307692307693-1.1227661222566674-1.1227661222566518
110.084615384615384620.25253556202054070.2525355620205592

The 281 Hz and 21 Hz zero-phase cosines give the same ideal sample sequence. A better-fitting sampled curve cannot identify which continuous signal was present. Filtering, an independently justified bandwidth limit or a changed sampling rate supplies information absent from the original samples.

Extended regime
Complete inputs
Sampling rate, Hz
190
Actual sinusoid frequency, Hz
413
Sample count
40
Signal amplitude
2.1
  1. Fold the actual frequency into the interval from zero to fs/2: |((f + fs/2) mod fs) - fs/2| = 33 Hz.
  2. Evaluate zero-phase cosines at t_k = k/fs for k = 0,...,39. The largest difference between actual and aliased sample values is 9.54792e-14, arising from floating-point arithmetic.
  3. The spacing of the discrete Fourier transform bins is fs/N = 4.75 Hz. This is a grid spacing, not a universal resolution limit or a proof that adjacent lines are separable.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Folded alias frequency, Hz33
Sampling Nyquist boundary, Hz95
Observation duration N/fs, seconds0.21052631578947367
DFT-bin spacing fs/N, Hz4.75
Maximum numerical sample discrepancy9.547918011776346e-14
First twelve of the uniformly spaced samples; full sequence follows the displayed cosine formula
IndexTime, secondsActual-frequency sampleAlias-frequency sample
002.12.1
10.0052631578947368420.96881644225524620.9688164422552444
20.010526315789473684-1.2060901916341784-1.2060901916341815
30.015789473684210527-2.0816545455866473-2.081654545586648
40.021052631578947368-0.7146156663274583-0.714615666327451
50.026315789473684211.42229130041405121.4222913004140565
60.0315789473684210542.02693871158242982.026938711582432
70.036842105263157890.447929224561900930.44792922456187023
80.042105263157894736-1.6136423327993934-1.6136423327994034
90.04736842105263158-1.936808485452508-1.9368084854525074
100.05263157894736842-0.1734166254919114-0.17341662549189743
110.057894736842105261.77680003008396611.7768000300839641

The 413 Hz and 33 Hz zero-phase cosines give the same ideal sample sequence. A better-fitting sampled curve cannot identify which continuous signal was present. Filtering, an independently justified bandwidth limit or a changed sampling rate supplies information absent from the original samples.

Try the reasoning: How would a second sampling rate or a verified analog bandwidth limit distinguish the continuous frequencies that share these samples?

Simulation and scientific validityOne more checkpoint can remove a whole parallel jobHow do memory boundaries change a simulator batch schedule?

Classical simulation resources grow rapidly with the number of represented qubits, but a state-vector size is only the start of memory accounting. Workspaces, snapshots and concurrent jobs compete for the same allocation. A modest extra resident buffer can push a job across a discrete concurrency boundary.

The lab budgets a dense complex128 state, a workspace factor and a declared number of resident checkpoint copies. It then floors available RAM divided by the complete per-job footprint. The number of waves needed to complete a batch can jump even when the footprint changes smoothly. A save-time cost adds a second effect that is kept separate from the lost parallel capacity.

Checkpointing can still be valuable because it protects work against failures. The no-failure schedule here deliberately does not assign that benefit a made-up value. A complete decision would model checkpoint location, restart frequency, save duration and recovery time. The existing state-vector calculator can use this example as an extension from abstract storage growth to a realistic question about which resources must coexist.

Synthetic decision model

Start with the assumptions

  • Checkpoints are additional resident full-state copies.
  • All jobs take the same time and can run independently.
  • No failures occur during this schedule comparison.

Dense complex128 state bytes = 16 × 2^qubits

Resident job GiB = state_GiB × (workspace factor + checkpoint copies)

Concurrency = floor(available_GiB / job_GiB)

Batch time = ceil(jobs/concurrency) × (base runtime + checkpoint-save time)

Synthetic one more checkpoint can remove a whole parallel job plot: Resident GiB per job versus Simulated qubits.
Synthetic baseline case. Horizontal axis: Simulated qubits. Vertical axis: Resident GiB per job. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Simulated qubits
24
Available RAM, GiB
64
Workspace factor
1.5
Checkpoint copies per job
1
Independent jobs
24
Base runtime per job, seconds
20
Save time per checkpoint, seconds
2
  1. Complex128 amplitudes use 16 × 2^24 bytes = 0.25 GiB. A GiB is 2^30 bytes.
  2. Workspace plus resident checkpoint copies multiply that state footprint by 2.5, giving 0.625 GiB per job. Floor available RAM divided by that footprint.
  3. The 24 jobs require 1 waves, each taking 22 seconds.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Dense state-vector memory, GiB0.25
Memory per checkpointed job, GiB0.625
Checkpointed concurrent jobs102
Checkpointed batch duration, seconds22
No-checkpoint concurrent jobs170
No-checkpoint duration, seconds20

Resident checkpoints can reduce concurrency at a discrete memory boundary, making the batch slower even before save time is counted. They may still be valuable for recovering failed work, but this no-failure schedule does not credit that benefit. Disk checkpoints, shared buffers, distributed simulation and restart probabilities need different accounting.

Comparison regime
Complete inputs
Simulated qubits
26
Available RAM, GiB
128
Workspace factor
1.5
Checkpoint copies per job
3
Independent jobs
24
Base runtime per job, seconds
45
Save time per checkpoint, seconds
4
  1. Complex128 amplitudes use 16 × 2^26 bytes = 1 GiB. A GiB is 2^30 bytes.
  2. Workspace plus resident checkpoint copies multiply that state footprint by 4.5, giving 4.5 GiB per job. Floor available RAM divided by that footprint.
  3. The 24 jobs require 1 waves, each taking 57 seconds.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Dense state-vector memory, GiB1
Memory per checkpointed job, GiB4.5
Checkpointed concurrent jobs28
Checkpointed batch duration, seconds57
No-checkpoint concurrent jobs85
No-checkpoint duration, seconds45

Resident checkpoints can reduce concurrency at a discrete memory boundary, making the batch slower even before save time is counted. They may still be valuable for recovering failed work, but this no-failure schedule does not credit that benefit. Disk checkpoints, shared buffers, distributed simulation and restart probabilities need different accounting.

Extended regime
Complete inputs
Simulated qubits
29
Available RAM, GiB
128
Workspace factor
1.5
Checkpoint copies per job
3
Independent jobs
24
Base runtime per job, seconds
75
Save time per checkpoint, seconds
6.4
  1. Complex128 amplitudes use 16 × 2^29 bytes = 8 GiB. A GiB is 2^30 bytes.
  2. Workspace plus resident checkpoint copies multiply that state footprint by 4.5, giving 36 GiB per job. Floor available RAM divided by that footprint.
  3. The 24 jobs require 8 waves, each taking 94.2 seconds.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Dense state-vector memory, GiB8
Memory per checkpointed job, GiB36
Checkpointed concurrent jobs3
Checkpointed batch duration, seconds753.6
No-checkpoint concurrent jobs10
No-checkpoint duration, seconds225

Resident checkpoints can reduce concurrency at a discrete memory boundary, making the batch slower even before save time is counted. They may still be valuable for recovering failed work, but this no-failure schedule does not credit that benefit. Disk checkpoints, shared buffers, distributed simulation and restart probabilities need different accounting.

Try the reasoning: At which memory boundary does an additional resident checkpoint remove a concurrent job? What benefit is missing from this no-failure comparison?

Algorithms and useful work

Algorithms and useful workThe best answer depends on how many complete attempts fitWhich solver gives the best result before one fixed deadline?

A fast solver can make many modest attempts while a slower solver spends more effort on each attempt. Comparing only their best single-run success probabilities ignores that operational difference. Comparing only runtime ignores the quality distribution. A fixed wall-clock deadline gives the two quantities a common setting.

The constructed strategies return one of three quality levels with known probabilities. The distribution of the best answer after repeated independent runs follows from the probability that every answer stays below a threshold. That gives both the chance of reaching top quality and the expected best score. These are related but distinct summaries of the same campaign.

The lab includes a one-time setup cost before counting complete runs. It does not grant either strategy free tuning or changing instances. The cases can enrich an optimization guide by showing how a quality-versus-time claim should be framed. A real benchmark would need actual distributions from matched instances, confidence intervals and a clear policy for incomplete runs. The synthetic result supplies a comparison design, not evidence for a quantum solver advantage.

Synthetic decision model

Start with the assumptions

  • Runs are independent and their distributions do not change.
  • Both strategies use the same quality scale and fixed problem.
  • Incomplete runs return no usable answer.

Completed runs = floor((deadline-setup)/time per run), with minimum zero

P(best answer below threshold) = P(one answer below threshold)^runs

Expected best quality is a sum of quality increments times exceedance probabilities

Synthetic the best answer depends on how many complete attempts fit plot: Quality / probability versus Strategy.
Synthetic baseline case. Horizontal axis: Strategy. Vertical axis: Quality / probability. Curves show Expected best quality, Top-quality probability. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Time budget, seconds
80
Setup per strategy, seconds
10
A seconds per run
4
B seconds per run
15
A high-quality probability
0.04
B high-quality probability
0.3
Quality levels
0.4, 0.7, 1
A fraction of non-top outcomes at lowest quality
0.55
B fraction of non-top outcomes at lowest quality
0.3
  1. Subtract setup before counting complete runs: A fits 17; B fits 4. An unfinished run contributes no result.
  2. For independent repeats, the probability all answers lie below a quality level is the single-run cumulative probability raised to the number of runs. This gives the distribution of the best answer.
  3. The top-quality probabilities are 0.500413 and 0.7599. Summing the quality-level increments times their exceedance probabilities gives expected best values 0.850118 and 0.927387.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Completed A runs17
Completed B runs4
A probability of top-quality answer0.5004131923201862
B probability of top-quality answer0.7599
A expected best quality0.8501181780939879
B expected best quality0.927386557
Complete single-run quality distributions
QualityA probabilityB probability
0.40.5280.21
0.70.4320.48999999999999994
10.040.3

B has the higher expected best quality under the declared deadline. The quality scale, distributions and runtimes are invented. This comparison is meaningful only if both methods solve the same fixed instance and use the same scoring rule; repeated attempts must not silently receive new tuning information.

Comparison regime
Complete inputs
Time budget, seconds
180
Setup per strategy, seconds
20
A seconds per run
6
B seconds per run
20
A high-quality probability
0.07
B high-quality probability
0.4
Quality levels
0.4, 0.7, 1
A fraction of non-top outcomes at lowest quality
0.55
B fraction of non-top outcomes at lowest quality
0.3
  1. Subtract setup before counting complete runs: A fits 26; B fits 8. An unfinished run contributes no result.
  2. For independent repeats, the probability all answers lie below a quality level is the single-run cumulative probability raised to the number of runs. This gives the distribution of the best answer.
  3. The top-quality probabilities are 0.84845 and 0.983204. Summing the quality-level increments times their exceedance probabilities gives expected best values 0.954535 and 0.994961.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Completed A runs26
Completed B runs8
A probability of top-quality answer0.8484497481581527
B probability of top-quality answer0.98320384
A expected best quality0.9545349163730907
B expected best quality0.9949608214011828
Complete single-run quality distributions
QualityA probabilityB probability
0.40.51150.18
0.70.41850.42
10.070.4

B has the higher expected best quality under the declared deadline. The quality scale, distributions and runtimes are invented. This comparison is meaningful only if both methods solve the same fixed instance and use the same scoring rule; repeated attempts must not silently receive new tuning information.

Extended regime
Complete inputs
Time budget, seconds
300
Setup per strategy, seconds
32
A seconds per run
6
B seconds per run
26
A high-quality probability
0.10600000000000001
B high-quality probability
0.52
Quality levels
0.4, 0.7, 1
A fraction of non-top outcomes at lowest quality
0.55
B fraction of non-top outcomes at lowest quality
0.3
  1. Subtract setup before counting complete runs: A fits 44; B fits 10. An unfinished run contributes no result.
  2. For independent repeats, the probability all answers lie below a quality level is the single-run cumulative probability raised to the number of runs. This gives the distribution of the best answer.
  3. The top-quality probabilities are 0.992775 and 0.999351. Summing the quality-level increments times their exceedance probabilities gives expected best values 0.997832 and 0.999805.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Completed A runs44
Completed B runs10
A probability of top-quality answer0.9927747841325296
B probability of top-quality answer0.9993507493789145
A expected best quality0.9978324352397507
B expected best quality0.9998052236635464
Complete single-run quality distributions
QualityA probabilityB probability
0.40.49170.144
0.70.40230.33599999999999997
10.106000000000000010.52

B has the higher expected best quality under the declared deadline. The quality scale, distributions and runtimes are invented. This comparison is meaningful only if both methods solve the same fixed instance and use the same scoring rule; repeated attempts must not silently receive new tuning information.

Try the reasoning: Which strategy maximizes the expected best score, and which maximizes top-quality probability? Would a different deadline change the choice?

Algorithms and useful workThe most likely single quantum search is not always the best campaignHow should an ideal search trade amplification depth for additional attempts?

Amplitude amplification rotates an ideal state toward a marked subspace, but continuing the rotation can move it away again. A familiar teaching problem asks how many iterations maximize the success of one attempt. A complete workflow can ask a different question: how many iterations leave the best overall chance of success within one time budget?

The lab uses the ideal two-dimensional rotation formula and adds an explicit preparation cost and oracle-equivalent timing convention. Each candidate depth allows a different number of complete restarts. The campaign success is then calculated from those independent attempts. The best single attempt and best whole campaign are reported separately rather than forcing them into one headline ratio.

This is an extension of an algorithm lesson, not a practical speedup estimate. A real oracle must be constructed and uncomputed, data preparation must be counted, and marked outputs need verification. Those costs can dominate an application. The useful interaction lets the reader increase preparation cost while leaving the ideal quantum rotation unchanged, making clear that algorithmic probability and complete workload time are separate layers of evidence.

Synthetic decision model

Start with the assumptions

  • The ideal amplitude-amplification model is exact in the synthetic calculation.
  • The timing convention is chosen for this exercise.
  • Restarts are independent and verification is included only through the declared budget convention.

theta = asin(sqrt(marked fraction))

Ideal per-attempt success = sin²((2k+1)theta)

Declared attempt time = preparation + (2k+1) × oracle-equivalent time

Campaign success = 1-(1-per-attempt success)^complete_attempts

Synthetic the most likely single quantum search is not always the best campaign plot: Success probability versus Amplification iterations per attempt.
Synthetic baseline case. Horizontal axis: Amplification iterations per attempt. Vertical axis: Success probability. Curves show Per attempt, Whole campaign. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Marked fraction
0.015625
Oracle-equivalent time
1
Preparation time
2
Total time budget
80
Maximum iterations per attempt
24
  1. The ideal success after k iterations is sin²((2k+1)theta), where theta = asin(sqrt(0.015625)).
  2. The declared attempt time is preparation + (2k+1) × oracle-equivalent time. The factor 2k+1 is this exercise’s accounting convention, not a universal decomposition of a Grover circuit.
  3. At k = 6, 5 complete independent attempts fit. Their combined success is 1-(1-p)^attempts = 1.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested iterations per attempt6
Attempts fitting the budget5
Success per chosen attempt0.9965856807867991
Campaign success probability0.999999999999536
Best single-attempt iteration count6
Unamplified campaign success0.3359894766227789
Unamplified attempt and the two distinct optimization objectives
IterationsSingle-attempt successDurationComplete attemptsCampaign success
00.0156253260.3359894766227789
60.99658568078679911550.999999999999536

The best tested campaign choice is k = 6; the best single-attempt probability occurs at k = 6. They optimize different quantities. A real advantage claim must also establish the oracle construction, state preparation, verification and fair classical search cost; this ideal rotation model supplies none of those performance facts.

Comparison regime
Complete inputs
Marked fraction
0.004464285714285714
Oracle-equivalent time
1.5
Preparation time
27
Total time budget
180
Maximum iterations per attempt
24
  1. The ideal success after k iterations is sin²((2k+1)theta), where theta = asin(sqrt(0.004464)).
  2. The declared attempt time is preparation + (2k+1) × oracle-equivalent time. The factor 2k+1 is this exercise’s accounting convention, not a universal decomposition of a Grover circuit.
  3. At k = 11, 2 complete independent attempts fit. Their combined success is 1-(1-p)^attempts = 0.999999.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested iterations per attempt11
Attempts fitting the budget2
Success per chosen attempt0.9989180813519019
Campaign success probability0.9999988294520389
Best single-attempt iteration count11
Unamplified campaign success0.026488540084901542
Unamplified attempt and the two distinct optimization objectives
IterationsSingle-attempt successDurationComplete attemptsCampaign success
00.00446428571428571528.560.026488540084901542
110.998918081351901961.520.9999988294520389

The best tested campaign choice is k = 11; the best single-attempt probability occurs at k = 11. They optimize different quantities. A real advantage claim must also establish the oracle construction, state preparation, verification and fair classical search cost; this ideal rotation model supplies none of those performance facts.

Extended regime
Complete inputs
Marked fraction
0.002403846153846154
Oracle-equivalent time
2.1
Preparation time
57
Total time budget
300
Maximum iterations per attempt
24
  1. The ideal success after k iterations is sin²((2k+1)theta), where theta = asin(sqrt(0.002404)).
  2. The declared attempt time is preparation + (2k+1) × oracle-equivalent time. The factor 2k+1 is this exercise’s accounting convention, not a universal decomposition of a Grover circuit.
  3. At k = 16, 2 complete independent attempts fit. Their combined success is 1-(1-p)^attempts = 0.999995.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested iterations per attempt16
Attempts fitting the budget2
Success per chosen attempt0.9977158771365623
Campaign success probability0.9999947827827447
Best single-attempt iteration count16
Unamplified campaign success0.011961584744724526
Unamplified attempt and the two distinct optimization objectives
IterationsSingle-attempt successDurationComplete attemptsCampaign success
00.00240384615384615459.150.011961584744724526
160.9977158771365623126.320.9999947827827447

The best tested campaign choice is k = 16; the best single-attempt probability occurs at k = 16. They optimize different quantities. A real advantage claim must also establish the oracle construction, state preparation, verification and fair classical search cost; this ideal rotation model supplies none of those performance facts.

Try the reasoning: Compare the campaign optimum with the single-attempt optimum. Which preparation and restart costs make their objectives differ?

Sources and model boundaries
  • Grover's algorithm ↗

    Ideal amplitude amplification rotates a state in a two-dimensional subspace and can overshoot the desired marked population. The lab's timing convention and campaign budget are independently chosen; no hardware runtime, API version or practical advantage is claimed.

Algorithms and useful workA small experiment schedule should expose what it valuesWhich subset of experiments fits the available time under a declared additive objective?

A laboratory may have more worthwhile experiments than available time. The choice is rarely settled by selecting the fastest experiment or the one with the largest individual expected value. Some combinations fit the schedule better than others. The objective also deserves scrutiny: a numerical value assigned to a task is a planning preference until it has a defensible information model behind it.

This example enumerates every subset of eight tasks, keeping only schedules under a fixed time budget. It compares the exact best subset with input-order packing and a value-per-time greedy rule. Because the example is small, exhaustive classical search is transparent and cheap. It demonstrates the optimization problem without creating a claim that quantum computation is required to solve it.

The cases give all task durations and values, along with the exact selected subset. The most useful follow-up is to challenge the assumptions: two experiments may answer the same question, one may enable another, or learning from an early result may change the remaining choices. Those effects require dependencies or adaptive information value. Stating the simple objective makes those omissions easier to discuss than hiding the choice behind a generic intelligent scheduler label.

Synthetic decision model

Start with the assumptions

  • Task values are additive, known and invented.
  • Task durations are fixed.
  • There are no dependencies or benefits from partial completion.

Choose a subset S with sum_{i in S} time_i <= available time

Maximize sum_{i in S} declared learning_value_i

Eight tasks have 2^8 = 256 subsets

Synthetic a small experiment schedule should expose what it values plot: Learning-value units versus Task number.
Synthetic baseline case. Horizontal axis: Task number. Vertical axis: Learning-value units. Curves show Declared learning value. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Task durations
9, 14, 7, 20, 11, 17, 8, 13
Declared learning values
12, 20, 9, 31, 14, 24, 10, 18
Available time
35
  1. Enumerate every subset of 8 tasks: 2^8 = 256 candidates. Keep only those whose total time does not exceed 35.
  2. Maximize the declared value sum, breaking ties by less time. The selected tasks are 2, 4, taking 34 time units.
  3. Input-order packing gives value 41; greedy value-per-time packing gives 51. The exact search gives 51.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Exact best selected task numbers2, 4
Exact best total learning value51
Exact best used time34
Input-order schedule value41
Value-per-time greedy schedule value51
Total subsets checked256
Complete task menu
TaskDurationDeclared learning valueSelected by exact search
1912No
21420Yes
379No
42031Yes
51114No
61724No
7810No
81318No

This small classical calculation makes an experimental planning objective explicit. The learning values are invented preferences, not measured information gain or a ranking of scientific importance. Dependencies between experiments, uncertain duration and complementary results violate the additive model. No quantum optimization advantage is claimed.

Comparison regime
Complete inputs
Task durations
9, 14, 7, 20, 11, 17, 8, 13
Declared learning values
17, 20, 19, 31, 19, 24, 15, 18
Available time
50
  1. Enumerate every subset of 8 tasks: 2^8 = 256 candidates. Keep only those whose total time does not exceed 50.
  2. Maximize the declared value sum, breaking ties by less time. The selected tasks are 1, 2, 3, 5, 7, taking 49 time units.
  3. Input-order packing gives value 87; greedy value-per-time packing gives 90. The exact search gives 90.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Exact best selected task numbers1, 2, 3, 5, 7
Exact best total learning value90
Exact best used time49
Input-order schedule value87
Value-per-time greedy schedule value90
Total subsets checked256
Complete task menu
TaskDurationDeclared learning valueSelected by exact search
1917Yes
21420Yes
3719Yes
42031No
51119Yes
61724No
7815Yes
81318No

This small classical calculation makes an experimental planning objective explicit. The learning values are invented preferences, not measured information gain or a ranking of scientific importance. Dependencies between experiments, uncertain duration and complementary results violate the additive model. No quantum optimization advantage is claimed.

Extended regime
Complete inputs
Task durations
9, 14, 7, 20, 11, 17, 8, 13
Declared learning values
23, 20, 31, 31, 25, 24, 21, 18
Available time
68
  1. Enumerate every subset of 8 tasks: 2^8 = 256 candidates. Keep only those whose total time does not exceed 68.
  2. Maximize the declared value sum, breaking ties by less time. The selected tasks are 1, 3, 4, 5, 7, 8, taking 68 time units.
  3. Input-order packing gives value 130; greedy value-per-time packing gives 149. The exact search gives 149.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Exact best selected task numbers1, 3, 4, 5, 7, 8
Exact best total learning value149
Exact best used time68
Input-order schedule value130
Value-per-time greedy schedule value149
Total subsets checked256
Complete task menu
TaskDurationDeclared learning valueSelected by exact search
1923Yes
21420No
3731Yes
42031Yes
51125Yes
61724No
7821Yes
81318Yes

This small classical calculation makes an experimental planning objective explicit. The learning values are invented preferences, not measured information gain or a ranking of scientific importance. Dependencies between experiments, uncertain duration and complementary results violate the additive model. No quantum optimization advantage is claimed.

Try the reasoning: Why can sorting by learning value per time miss the exact subset optimum? Which dependency between experiments would break the additive model?

Algorithms and useful workA cheaper gradient can spend its savings on an omitted directionHow does ignoring coordinates change the error budget for a variational update?

A variational routine may require many expectation-value measurements to estimate a gradient. Measuring only a subset of parameters appears to reduce the work, but the omitted directions can contribute a systematic error to the update. The fair comparison asks how both choices meet the same gradient-error target.

The model uses a standard two-shift estimator where each derivative is half the difference of two independent sample means. Summing the coordinate variances gives an expected squared Euclidean sampling error. A subset estimator receives an additional squared-error contribution from the known synthetic gradient components it omits. If that contribution already exceeds the target, no number of extra shots on the retained coordinates can repair the estimate.

The omitted norm is supplied by construction, which is a major advantage unavailable in most real optimization runs. The lab should therefore accompany a discussion of screening, pilot estimates or structural assumptions used to select parameters. It explains what a claimed measurement saving must preserve, while avoiding the claim that an actual algorithm can discover harmless omissions without paying for information.

Synthetic decision model

Start with the assumptions

  • The gate supports the stated parameter-shift rule.
  • Shifted measurements and coordinates are independently estimated.
  • Omitted-gradient norm is known only in this synthetic example.

Derivative estimate = (mean_plus - mean_minus)/2

Per-coordinate variance with n shots per shift = v/(2n)

Full expected squared gradient error = parameters × v/(2n)

Subset total = omitted squared norm + active_parameters × v/(2n)

Synthetic a cheaper gradient can spend its savings on an omitted direction plot: Acquired shots versus Estimator.
Synthetic baseline case. Horizontal axis: Estimator. Vertical axis: Acquired shots. Curves show Total shots. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Total parameters
12
Active subset parameters
4
Per-shift shot variance
0.4
Squared gradient-error target
0.01
Squared norm of omitted gradient
0.001
Shot time, milliseconds
0.1
  1. For one parameter, the estimator is (mean_plus - mean_minus)/2. Independent equal-variance shifted samples give variance v/(2n).
  2. The expected squared Euclidean sampling error sums over 12 coordinates. Set parameters × v/(2n) <= target, giving 240 shots at each of the two shifts.
  3. The active-subset estimate leaves known synthetic omitted squared norm 0.001. Only 0.009 remains for sampling error; if this is nonpositive, no shot count repairs the omission.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Shots per shift, full gradient240
Total full-gradient shots5760
Full-gradient acquisition, seconds0.576
Subset remaining squared-error budget0.009
Total subset-gradient shots712
Subset acquisition, seconds0.0712

Measuring fewer coordinates can reduce work or consume the error budget through omitted directions. The omitted-gradient norm is provided by construction here; an actual optimizer normally does not know it for free. Parameter-shift identities require an appropriate gate generator and shift rule. Correlations within or between the two shifted sample means can change each coordinate variance; cross-coordinate covariance alone does not change the trace-based squared-error sum.

Comparison regime
Complete inputs
Total parameters
22
Active subset parameters
9
Per-shift shot variance
0.4
Squared gradient-error target
0.01
Squared norm of omitted gradient
0.0055
Shot time, milliseconds
0.2
  1. For one parameter, the estimator is (mean_plus - mean_minus)/2. Independent equal-variance shifted samples give variance v/(2n).
  2. The expected squared Euclidean sampling error sums over 22 coordinates. Set parameters × v/(2n) <= target, giving 440 shots at each of the two shifts.
  3. The active-subset estimate leaves known synthetic omitted squared norm 0.0055. Only 0.0045 remains for sampling error; if this is nonpositive, no shot count repairs the omission.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Shots per shift, full gradient440
Total full-gradient shots19360
Full-gradient acquisition, seconds3.872
Subset remaining squared-error budget0.0045
Total subset-gradient shots7200
Subset acquisition, seconds1.44

Measuring fewer coordinates can reduce work or consume the error budget through omitted directions. The omitted-gradient norm is provided by construction here; an actual optimizer normally does not know it for free. Parameter-shift identities require an appropriate gate generator and shift rule. Correlations within or between the two shifted sample means can change each coordinate variance; cross-coordinate covariance alone does not change the trace-based squared-error sum.

Extended regime
Complete inputs
Total parameters
34
Active subset parameters
15
Per-shift shot variance
0.4
Squared gradient-error target
0.01
Squared norm of omitted gradient
0.0109
Shot time, milliseconds
0.32
  1. For one parameter, the estimator is (mean_plus - mean_minus)/2. Independent equal-variance shifted samples give variance v/(2n).
  2. The expected squared Euclidean sampling error sums over 34 coordinates. Set parameters × v/(2n) <= target, giving 680 shots at each of the two shifts.
  3. The active-subset estimate leaves known synthetic omitted squared norm 0.0109. Only -0.0009 remains for sampling error; if this is nonpositive, no shot count repairs the omission.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Shots per shift, full gradient680
Total full-gradient shots46240
Full-gradient acquisition, seconds14.796800000000001
Subset remaining squared-error budget-0.0009
Total subset-gradient shotsOmitted gradient alone exhausts target
Subset acquisition, secondsInfeasible

Measuring fewer coordinates can reduce work or consume the error budget through omitted directions. The omitted-gradient norm is provided by construction here; an actual optimizer normally does not know it for free. Parameter-shift identities require an appropriate gate generator and shift rule. Correlations within or between the two shifted sample means can change each coordinate variance; cross-coordinate covariance alone does not change the trace-based squared-error sum.

Try the reasoning: When the omitted squared gradient norm meets or exceeds the target, can more shots make the subset estimator feasible?

Sources and model boundaries
  • Evaluating analytic gradients on quantum hardware ↗

    Parameter-shift identities can estimate exact expectation derivatives for specified gate generators. Finite-sample uncertainty and covariance are independently derived; the two-shift identity is not claimed for every parameterization.

  • Combining uncertainty components ↗

    Uncertainty propagation includes sensitivities and covariance; independent terms simplify the variance sum. Covariance, bias and distribution assumptions in the teaching models are declared separately; no NIST endorsement is implied.

Sensing and timekeeping

Sensing and timekeepingA longer interrogation can stop being the more informative oneWhat interrogation time best balances phase accumulation, contrast and repeated measurements?

A Ramsey experiment turns a frequency difference into a phase accumulated during a controlled interval. A longer interval makes the phase more sensitive to frequency, but the signal can lose contrast and fewer complete cycles fit into the same campaign. Preparation and readout dead time further change that tradeoff.

This lab uses a local projection-noise expression with independent atoms and a stipulated exponential visibility loss. It counts whole cycles before evaluating the uncertainty. The best point is selected on a declared finite grid, so the answer is a tested numerical minimum rather than an unsupported analytic optimum. Increasing the dead time can change the preferred interrogation even if the atom and contrast law remain identical.

The model does not describe all clock noise. Local oscillator fluctuations, phase wrapping, correlations and systematic shifts can dominate a real experiment. It also predicts a local frequency-estimation uncertainty, not accuracy against a reference. The useful article extension is to place the complete cycle beside the free-evolution interval and show which assumptions allow the stated square-root averaging benefit.

Synthetic decision model

Start with the assumptions

  • The experiment operates near the most sensitive fringe point.
  • Atoms and complete cycles are independent.
  • The exponential contrast law and all time values are invented.

Cycles = floor(campaign/(interrogation + dead time))

C(t) = initial contrast × exp(-t/T2)

Local frequency uncertainty = 1/[2 pi C(t) t sqrt(cycles × atoms)]

Synthetic a longer interrogation can stop being the more informative one plot: Standard uncertainty, Hz versus Interrogation time, seconds.
Synthetic baseline case. Horizontal axis: Interrogation time, seconds. Vertical axis: Standard uncertainty, Hz. Curves show Frequency uncertainty. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Campaign duration, seconds
1200
Dead time per cycle, seconds
0.05
Visibility decay time, seconds
0.6
Independent atoms per shot
100
Initial contrast
0.9
Interrogation grid points
300
Minimum interrogation / decay time
0.02
Maximum interrogation / decay time
4
  1. Test 300 interrogation times from T2/50 to 4 T2. At each time, floor campaign/(interrogation + dead time) to count complete cycles.
  2. Use contrast C(t) = initial contrast × exp(-t/T2). At the selected time 0.339452, C = 0.511139 and 3081 cycles fit.
  3. Near the most sensitive Ramsey fringe point, the stipulated independent projection-noise model gives frequency uncertainty 1/(2 pi C t sqrt(cycles × atoms)) = 0.001653 Hz.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested interrogation, seconds0.3394515050167224
Completed cycles3081
Visibility at chosen interrogation0.5111393506892022
Linearized frequency standard uncertainty, Hz0.0016525599638816018
At-T2 reference uncertainty, Hz0.0018646829739183317
Best / at-T2 standard uncertainty0.8862417831858102

Long interrogation increases phase accumulation while reducing visibility and the number of cycles. Dead time changes the balance. The grid optimum is a result of the declared local linear-response model; oscillator noise, phase wrapping, correlations and systematic shifts are excluded. It is not a measured clock accuracy or a universal optimum.

Comparison regime
Complete inputs
Campaign duration, seconds
1200
Dead time per cycle, seconds
0.55
Visibility decay time, seconds
1.2
Independent atoms per shot
350
Initial contrast
0.85
Interrogation grid points
300
Minimum interrogation / decay time
0.02
Maximum interrogation / decay time
4
  1. Test 300 interrogation times from T2/50 to 4 T2. At each time, floor campaign/(interrogation + dead time) to count complete cycles.
  2. Use contrast C(t) = initial contrast × exp(-t/T2). At the selected time 0.838635, C = 0.422578 and 864 cycles fit.
  3. Near the most sensitive Ramsey fringe point, the stipulated independent projection-noise model gives frequency uncertainty 1/(2 pi C t sqrt(cycles × atoms)) = 0.000817 Hz.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested interrogation, seconds0.8386354515050167
Completed cycles864
Visibility at chosen interrogation0.42257775832249656
Linearized frequency standard uncertainty, Hz0.0008166752346075334
At-T2 reference uncertainty, Hz0.0008662338163331558
Best / at-T2 standard uncertainty0.9427884471938439

Long interrogation increases phase accumulation while reducing visibility and the number of cycles. Dead time changes the balance. The grid optimum is a result of the declared local linear-response model; oscillator noise, phase wrapping, correlations and systematic shifts are excluded. It is not a measured clock accuracy or a universal optimum.

Extended regime
Complete inputs
Campaign duration, seconds
1200
Dead time per cycle, seconds
1.1500000000000001
Visibility decay time, seconds
1.92
Independent atoms per shot
650
Initial contrast
0.79
Interrogation grid points
300
Minimum interrogation / decay time
0.02
Maximum interrogation / decay time
4
  1. Test 300 interrogation times from T2/50 to 4 T2. At each time, floor campaign/(interrogation + dead time) to count complete cycles.
  2. Use contrast C(t) = initial contrast × exp(-t/T2). At the selected time 1.418488, C = 0.377374 and 467 cycles fit.
  3. Near the most sensitive Ramsey fringe point, the stipulated independent projection-noise model gives frequency uncertainty 1/(2 pi C t sqrt(cycles × atoms)) = 0.00054 Hz.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Best tested interrogation, seconds1.4184882943143813
Completed cycles467
Visibility at chosen interrogation0.37737408328628846
Linearized frequency standard uncertainty, Hz0.0005396437924807968
At-T2 reference uncertainty, Hz0.0005664966052937949
Best / at-T2 standard uncertainty0.952598457674655

Long interrogation increases phase accumulation while reducing visibility and the number of cycles. Dead time changes the balance. The grid optimum is a result of the declared local linear-response model; oscillator noise, phase wrapping, correlations and systematic shifts are excluded. It is not a measured clock accuracy or a universal optimum.

Try the reasoning: Why can a longer interrogation lower local phase noise yet worsen the frequency estimate once visibility and completed cycles are counted?

Sources and model boundaries
  • Quantum Limits to Spectroscopy ↗

    Independent-atom Ramsey spectroscopy has a projection-noise sensitivity that depends on interrogation time and the number of atoms and measurements. The checked primary excerpt supports the projection-noise relation. The added exponential contrast model, dead time and integer schedule are original synthetic assumptions. Uncertainty is not accuracy.

Sensing and timekeepingCommon noise cancels only when the channels agree on gainHow can a quiet differential measurement still report a false spatial gradient?

Differential sensing compares nearby measurements to reject a disturbance shared by both. That rejection depends on the two channels responding consistently. If one channel amplifies the common signal slightly more than the other, subtracting them can leave a residual that looks like the spatial difference the instrument was meant to measure.

The constructed model places two sensors symmetrically across a constant gradient and assigns one a gain error. The mean inferred gradient can then be expanded into the true gradient, a common-field leakage term and a smaller gradient-proportional gain term. Correlated random noise is propagated separately. The final root mean squared error combines the random spread with the systematic offset instead of treating a quiet trace as an accurate result.

Increasing the separation reduces the conversion of some noise and leakage terms into gradient units. It also changes the region being sampled, so a real field may no longer have a constant gradient across that baseline. A gain comparison therefore needs explicit field and geometry assumptions. This keeps a cancellation mechanism understandable without suggesting that correlation alone eliminates every practical disturbance.

Synthetic decision model

Start with the assumptions

  • The true gradient is constant across the separation.
  • Only sensor A has the declared gain error.
  • Readout noise covariance is known and independent of the mean-field model.

True local fields = B ± G L/2

Estimated gradient = [(1+g)(B+G L/2)-(B-G L/2)]/L

Bias = gB/L + gG/2

Random gradient variance = (s_A²+s_B²-2rho s_A s_B)/L²

Synthetic common noise cancels only when the channels agree on gain plot: Gradient root mean squared error versus Sensor separation, meters.
Synthetic baseline case. Horizontal axis: Sensor separation, meters. Vertical axis: Gradient root mean squared error. Curves show Model. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Sensor separation, meters
0.15
True gradient, field units per meter
0.6
Common field, field units
40
A relative gain error
0.0002
A noise standard deviation
0.08
B noise standard deviation
0.1
Noise correlation
0.2
  1. The true sensor fields are B ± G L/2. Multiply A by (1 + gain error), subtract B’s reading, then divide by separation.
  2. The resulting bias is gB/L + gG/2 = 0.053393. The common field cancels only when the gains match.
  3. Random variance of the difference is s_A² + s_B² - 2 rho s_A s_B. Dividing its square root by L gives 0.765942, and combining variance with squared bias gives RMSE 0.7678.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Mean inferred gradient0.6533933333333646
Gradient bias from gain mismatch0.0533933333333646
Gradient random standard uncertainty0.7659416862050705
Gradient root mean squared error0.7678004393793445
Shared-field leakage term gB/L0.05333333333333334
Gradient-proportional gain term gG/20.00006

The common-field leakage contributes 0.053333 gradient units. A quiet difference can still be biased if gain mismatch converts a large shared field into an apparent gradient. Increasing separation changes both noise conversion and spatial interpretation; the model assumes a constant gradient across every tested baseline.

Comparison regime
Complete inputs
Sensor separation, meters
0.35
True gradient, field units per meter
0.6
Common field, field units
65
A relative gain error
0.0012000000000000001
A noise standard deviation
0.08
B noise standard deviation
0.1
Noise correlation
0.45
  1. The true sensor fields are B ± G L/2. Multiply A by (1 + gain error), subtract B’s reading, then divide by separation.
  2. The resulting bias is gB/L + gG/2 = 0.223217. The common field cancels only when the gains match.
  3. Random variance of the difference is s_A² + s_B² - 2 rho s_A s_B. Dividing its square root by L gives 0.274048, and combining variance with squared bias gives RMSE 0.353451.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Mean inferred gradient0.823217142857199
Gradient bias from gain mismatch0.22321714285719907
Gradient random standard uncertainty0.27404751561786966
Gradient root mean squared error0.3534514587346581
Shared-field leakage term gB/L0.22285714285714292
Gradient-proportional gain term gG/20.00036

The common-field leakage contributes 0.222857 gradient units. A quiet difference can still be biased if gain mismatch converts a large shared field into an apparent gradient. Increasing separation changes both noise conversion and spatial interpretation; the model assumes a constant gradient across every tested baseline.

Extended regime
Complete inputs
Sensor separation, meters
0.59
True gradient, field units per meter
0.6
Common field, field units
95
A relative gain error
0.0024000000000000002
A noise standard deviation
0.08
B noise standard deviation
0.1
Noise correlation
0.75
  1. The true sensor fields are B ± G L/2. Multiply A by (1 + gain error), subtract B’s reading, then divide by separation.
  2. The resulting bias is gB/L + gG/2 = 0.387161. The common field cancels only when the gains match.
  3. Random variance of the difference is s_A² + s_B² - 2 rho s_A s_B. Dividing its square root by L gives 0.112428, and combining variance with squared bias gives RMSE 0.403154.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Mean inferred gradient0.987160677966123
Gradient bias from gain mismatch0.38716067796612297
Gradient random standard uncertainty0.11242795899509833
Gradient root mean squared error0.4031543581892567
Shared-field leakage term gB/L0.3864406779661017
Gradient-proportional gain term gG/20.00072

The common-field leakage contributes 0.386441 gradient units. A quiet difference can still be biased if gain mismatch converts a large shared field into an apparent gradient. Increasing separation changes both noise conversion and spatial interpretation; the model assumes a constant gradient across every tested baseline.

Try the reasoning: Compare the common-field leakage gB/L with the true gradient. Can a small random standard uncertainty certify the measurement as accurate?

Sources and model boundaries
  • Combining uncertainty components ↗

    Uncertainty propagation includes sensitivities and covariance; independent terms simplify the variance sum. Covariance, bias and distribution assumptions in the teaching models are declared separately; no NIST endorsement is implied.

Sensing and timekeepingThree clock comparisons can reveal an inconsistent linkWhat can a closed comparison loop establish without an absolute time reference?

A pairwise clock comparison reports a relative offset. With three clocks and three pairwise measurements, the numbers should close around the loop if they represent consistent offsets at the same time. Adding B minus A to C minus B should reproduce C minus A. A nonzero closure signals inconsistency in the comparison set.

The lab first calculates that closure and its uncertainty under independent edge errors. It then fixes clock A as an arbitrary zero and fits the two remaining offsets by weighted least squares. The fitted comparisons close exactly, while residuals show how the original observations depart from one consistent set of clock values. The weights express the relative uncertainties assigned to the links.

A failed closure cannot, by itself, identify which clock or transfer path is responsible. A common offset shared by every clock can also escape the loop entirely. These limits make the example useful for an article about networked clocks or time transfer: internal consistency and accuracy against an external reference are different achievements. The coordinate choice A equals zero is bookkeeping, not a claim that A is the truth.

Synthetic decision model

Start with the assumptions

  • Comparisons refer to one common epoch.
  • Edge errors are independent with known standard uncertainties.
  • Clock A is fixed to zero only to choose a reference coordinate.

Loop closure = measured(B-A) + measured(C-B) - measured(C-A)

Independent closure uncertainty = sqrt(s_AB²+s_BC²+s_AC²)

Weighted least-squares offsets solve (X^T W X) beta = X^T W y

Synthetic three clock comparisons can reveal an inconsistent link plot: Relative offset, nanoseconds versus Clock comparison.
Synthetic baseline case. Horizontal axis: Clock comparison. Vertical axis: Relative offset, nanoseconds. Curves show Observed, Consistent fit. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Measured B minus A, nanoseconds
4
Measured C minus B, nanoseconds
3
Measured C minus A, nanoseconds
7
Edge standard uncertainties, nanoseconds
0.4, 0.7, 0.5
  1. If all comparisons reflected consistent offsets, (B-A) + (C-B) - (C-A) would equal zero. The observed closure is 0 nanoseconds.
  2. With independent edge errors, closure uncertainty is sqrt(s_AB²+s_BC²+s_AC²) = 0.948683. The standardized closure is 0.
  3. Fix clock A as the arbitrary zero and solve weighted least squares for B and C. The fitted offsets are 4 and 7; residuals are 0, -8.88178e-16, -8.88178e-16.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Observed loop closure, nanoseconds0
Loop standard uncertainty, nanoseconds0.9486832980505138
Closure / standard uncertainty0
Fitted B offset relative to A, nanoseconds4
Fitted C offset relative to A, nanoseconds7.000000000000001
Weighted residual sum of squares4.765363835620806e-30
Weighted fit residuals
ComparisonObserved, nsStandard uncertainty, nsResidual, ns
B − A40.40
C − B30.7-8.881784197001252e-16
C − A70.5-8.881784197001252e-16

The loop detects inconsistent comparisons but cannot identify the responsible clock or link by itself. A shared calibration offset can evade the loop entirely, and correlated transfer errors change its uncertainty. Fixing A to zero is a coordinate choice, not evidence that clock A is accurate against an external time standard.

Comparison regime
Complete inputs
Measured B minus A, nanoseconds
5
Measured C minus B, nanoseconds
2.5
Measured C minus A, nanoseconds
9
Edge standard uncertainties, nanoseconds
0.5, 0.7, 0.5
  1. If all comparisons reflected consistent offsets, (B-A) + (C-B) - (C-A) would equal zero. The observed closure is -1.5 nanoseconds.
  2. With independent edge errors, closure uncertainty is sqrt(s_AB²+s_BC²+s_AC²) = 0.994987. The standardized closure is -1.507557.
  3. Fix clock A as the arbitrary zero and solve weighted least squares for B and C. The fitted offsets are 5.378788 and 8.621212; residuals are -0.378788, -0.742424, 0.378788.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Observed loop closure, nanoseconds-1.5
Loop standard uncertainty, nanoseconds0.99498743710662
Closure / standard uncertainty-1.507556722888818
Fitted B offset relative to A, nanoseconds5.378787878787879
Fitted C offset relative to A, nanoseconds8.621212121212123
Weighted residual sum of squares2.272727272727273
Weighted fit residuals
ComparisonObserved, nsStandard uncertainty, nsResidual, ns
B − A50.5-0.3787878787878789
C − B2.50.7-0.742424242424244
C − A90.50.3787878787878771

The loop detects inconsistent comparisons but cannot identify the responsible clock or link by itself. A shared calibration offset can evade the loop entirely, and correlated transfer errors change its uncertainty. Fixing A to zero is a coordinate choice, not evidence that clock A is accurate against an external time standard.

Extended regime
Complete inputs
Measured B minus A, nanoseconds
6.2
Measured C minus B, nanoseconds
1.9
Measured C minus A, nanoseconds
11.4
Edge standard uncertainties, nanoseconds
0.62, 0.7, 0.5
  1. If all comparisons reflected consistent offsets, (B-A) + (C-B) - (C-A) would equal zero. The observed closure is -3.3 nanoseconds.
  2. With independent edge errors, closure uncertainty is sqrt(s_AB²+s_BC²+s_AC²) = 1.060377. The standardized closure is -3.1121.
  3. Fix clock A as the arbitrary zero and solve weighted least squares for B and C. The fitted offsets are 7.328175 and 10.666275; residuals are -1.128175, -1.4381, 0.733725.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Observed loop closure, nanoseconds-3.3000000000000007
Loop standard uncertainty, nanoseconds1.060377291344925
Closure / standard uncertainty-3.112099841193751
Fitted B offset relative to A, nanoseconds7.3281750266808965
Fitted C offset relative to A, nanoseconds10.666275346851654
Weighted residual sum of squares9.685165421558166
Weighted fit residuals
ComparisonObserved, nsStandard uncertainty, nsResidual, ns
B − A6.20.62-1.1281750266808963
C − B1.90.7-1.4381003201707574
C − A11.40.50.7337246531483466

The loop detects inconsistent comparisons but cannot identify the responsible clock or link by itself. A shared calibration offset can evade the loop entirely, and correlated transfer errors change its uncertainty. Fixing A to zero is a coordinate choice, not evidence that clock A is accurate against an external time standard.

Try the reasoning: Would a shared offset in all clocks be visible in the loop closure? Explain what setting clock A to zero actually fixes.

Sources and model boundaries
  • Combining uncertainty components ↗

    Uncertainty propagation includes sensitivities and covariance; independent terms simplify the variance sum. Covariance, bias and distribution assumptions in the teaching models are declared separately; no NIST endorsement is implied.

Sensing and timekeepingA stability curve remembers how the data were madeHow does a known drift appear when adjacent averages are compared?

A time series can look quieter after averaging while still changing systematically from one interval to the next. Frequency-stability analysis therefore often compares adjacent averages rather than treating all observations as unrelated draws around a fixed mean. The chosen averaging time becomes part of the question.

This lab constructs a finite record from a repeated bounded pattern plus a linear drift. For several averaging factors, it forms non-overlapping block means and calculates half the mean squared difference between adjacent blocks. The square root is the displayed Allan deviation. The corresponding drift-only curve can be derived exactly, making the growth with averaging time easy to interpret.

The periodic pattern is disclosed because it creates its own apparent sweet spots. The minimum of this finite synthetic curve is not a statistically validated optimum for a random clock. A real analysis needs a noise model, data-quality checks, uncertainty estimates and a reason to choose overlapping or non-overlapping estimators. Inspecting the supplied record construction alongside the stability curve reveals where its apparent improvements come from.

Synthetic decision model

Start with the assumptions

  • The finite 240-point record is deterministic and fully specified by the supplied pattern, repeat count and drift.
  • Non-overlapping adjacent block means are used.
  • No white-noise or population confidence claim is attached to the repeated pattern.

Block mean at factor m = mean of m consecutive frequency samples

Non-overlapping Allan variance = one half × mean of adjacent block-mean differences squared

For pure linear drift per sample r, Allan deviation = |r|m/sqrt(2)

Synthetic a stability curve remembers how the data were made plot: Allan deviation versus Averaging time, seconds.
Synthetic baseline case. Horizontal axis: Averaging time, seconds. Vertical axis: Allan deviation. Curves show Constructed record, Linear drift alone. These are computed teaching examples, not measured hardware results.

Compare the input regimes

Each case uses invented inputs. The results follow from this model and do not describe measured hardware.

Baseline regime
Complete inputs
Sampling interval, seconds
1
Drift per sample
5e-15
Bounded fluctuation scale
1e-12
Repeated bounded pattern
-0.8, 0.5, -0.3, 1, -0.6, 0.2, -1, 0.7, 0.1, -0.2, 0.6, -0.4
Pattern repeats
20
Tested averaging factors
1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30
  1. Generate 240 samples from a declared 12-point bounded pattern repeated twenty times, plus linear drift 5e-15 per sample. This is deterministic, not simulated white noise.
  2. For each averaging factor m, form non-overlapping adjacent block means. Allan variance is one half of the mean squared difference between successive block means.
  3. The smallest tested deviation is 3.13036e-14 at m = 6, or 6 seconds. Pure linear drift would contribute deviation |slope|m/sqrt(2) = 2.12132e-14.
Baseline regime · synthetic calculated results
Calculated quantitySynthetic result
Smallest deviation among tested averaging factors3.130358653436584e-14
Averaging factor at that minimum6
Corresponding averaging time, seconds6
One-sample Allan deviation7.596657145797418e-13
Drift-only deviation at selected factor2.1213203435596423e-14
Original frequency samples240
Every tested averaging factor
Averaging factorAveraging time, secondsNon-overlapping Allan deviation
117.596657145797418e-13
222.3330291918628097e-13
331.8648796260591664e-13
441.437976155479921e-13
551.16954937676049e-13
663.130358653436584e-14
887.713833856042058e-14
10105.970944139166223e-14
12124.2426406871192846e-14
15156.654920207107143e-14
20207.573128331625758e-14
24248.485281374238569e-14
30301.054958059799776e-13

The minimum depends on the synthetic periodic pattern as well as drift. It is not a confidence-calibrated estimate of an optimal averaging time for a random clock. The exercise teaches the adjacent-average calculation and shows why a finite stability curve needs a documented data-generating process and sufficient independent information.

Comparison regime
Complete inputs
Sampling interval, seconds
3
Drift per sample
1.5e-14
Bounded fluctuation scale
1.75e-12
Repeated bounded pattern
-0.8, 0.5, -0.3, 1, -0.6, 0.2, -1, 0.7, 0.1, -0.2, 0.6, -0.4
Pattern repeats
20
Tested averaging factors
1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30
  1. Generate 240 samples from a declared 12-point bounded pattern repeated twenty times, plus linear drift 1.5e-14 per sample. This is deterministic, not simulated white noise.
  2. For each averaging factor m, form non-overlapping adjacent block means. Allan variance is one half of the mean squared difference between successive block means.
  3. The smallest tested deviation is 7.49451e-14 at m = 6, or 18 seconds. Pure linear drift would contribute deviation |slope|m/sqrt(2) = 6.36396e-14.
Comparison regime · synthetic calculated results
Calculated quantitySynthetic result
Smallest deviation among tested averaging factors7.494513662855988e-14
Averaging factor at that minimum6
Corresponding averaging time, seconds18
One-sample Allan deviation1.3294497988951771e-12
Drift-only deviation at selected factor6.363961030678927e-14
Original frequency samples240
Every tested averaging factor
Averaging factorAveraging time, secondsNon-overlapping Allan deviation
131.3294497988951771e-12
264.086997405690106e-13
393.2750256330794895e-13
4122.538848320497214e-13
5152.0971041330083852e-13
6187.494513662855988e-14
8241.511943070376773e-13
10301.363015957353398e-13
12361.2727922061357854e-13
15451.7521389045223385e-13
20602.1668718944178915e-13
24722.5455844122715713e-13
30903.171246687906123e-13

The minimum depends on the synthetic periodic pattern as well as drift. It is not a confidence-calibrated estimate of an optimal averaging time for a random clock. The exercise teaches the adjacent-average calculation and shows why a finite stability curve needs a documented data-generating process and sufficient independent information.

Extended regime
Complete inputs
Sampling interval, seconds
3
Drift per sample
2.7e-14
Bounded fluctuation scale
2.65e-12
Repeated bounded pattern
-0.8, 0.5, -0.3, 1, -0.6, 0.2, -1, 0.7, 0.1, -0.2, 0.6, -0.4
Pattern repeats
20
Tested averaging factors
1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30
  1. Generate 240 samples from a declared 12-point bounded pattern repeated twenty times, plus linear drift 2.7e-14 per sample. This is deterministic, not simulated white noise.
  2. For each averaging factor m, form non-overlapping adjacent block means. Allan variance is one half of the mean squared difference between successive block means.
  3. The smallest tested deviation is 1.2906e-13 at m = 6, or 18 seconds. Pure linear drift would contribute deviation |slope|m/sqrt(2) = 1.14551e-13.
Extended regime · synthetic calculated results
Calculated quantitySynthetic result
Smallest deviation among tested averaging factors1.290599310861656e-13
Averaging factor at that minimum6
Corresponding averaging time, seconds18
One-sample Allan deviation2.0131980174146246e-12
Drift-only deviation at selected factor1.145512985522207e-13
Original frequency samples240
Every tested averaging factor
Averaging factorAveraging time, secondsNon-overlapping Allan deviation
132.0131980174146246e-12
266.192708770139663e-13
394.969849396501868e-13
4123.865899037838768e-13
5153.221027819309538e-13
6181.290599310861656e-13
8242.4314441295158097e-13
10302.313022561404279e-13
12362.2910259710444143e-13
15453.079292787974874e-13
20603.8725880690144055e-13
24724.582051942088829e-13
30905.711057431345528e-13

The minimum depends on the synthetic periodic pattern as well as drift. It is not a confidence-calibrated estimate of an optimal averaging time for a random clock. The exercise teaches the adjacent-average calculation and shows why a finite stability curve needs a documented data-generating process and sufficient independent information.

Try the reasoning: Which averaging factors align with the constructed twelve-sample pattern? Why does the resulting minimum not estimate a random-clock confidence bound?

Sources and model boundaries
  • Handbook of Frequency Stability Analysis, NIST SP 1065 ↗

    Frequency stability can be characterized through differences between averages at stated averaging times; estimator choice and noise processes matter. The supplied sequence is deterministic and periodic with an added drift. Its calculated minimum is not a population confidence result.

Explore the underlying physical mechanisms →