Quantum computing,
made visible.

Planck connects the size of an energy step to frequency

Why does a hot object emit more light at some frequencies than at others? Max Planck calculated its spectrum by counting energy in steps. The higher the frequency of an oscillator, the larger each energy step.

Still to solvePlanck was explaining heat radiation. His original proposal was not yet the modern picture of light particles or quantum computers.

In plain EnglishQuantum A discrete amount; “quanta” is the plural. Planck connected its energy to frequency.

The next questionDiscrete energy exchange was one clue. The next challenge was finding rules that could predict the results of experiments.

Born connects the wave equation to a detector reading

In a collision experiment, an electron can scatter in several directions. Max Born interpreted the wave calculation as a prediction of how likely each direction was. Repeating the experiment could test that prediction.

Still to solveProbabilistic results do not let us read every possible answer at once. Measurement returns an outcome, not the whole mathematical description.

In plain EnglishMeasurement An interaction that produces a recorded outcome, such as reading a qubit as 0 or 1.

The next questionA rule for measurement also raises a question: what happens when two systems must be described together?

Bell gives experimenters a way to test entanglement

Could two distant particles simply carry a shared set of instructions for how to respond? John Bell showed that such local explanations obey a limit on how often the answers can agree across different measurement settings. For certain entangled states, quantum theory predicts correlations beyond that limit.

Still to solveBell supplied the theoretical test; experiments followed. Violating a Bell inequality does not create a faster-than-light communication method.

In plain EnglishEntanglement A shared quantum state that cannot be described as independent states of its parts, even allowing ordinary randomness.

The next questionThe rules were becoming testable. A different question would follow: could people use those rules to process information?

Feynman proposes using one quantum system to study another

Richard Feynman argued that simulating quantum systems can be difficult for ordinary computers, and that controlled quantum systems offer a natural alternative. His influential paper followed a talk given in 1981.

Still to solveThis was a proposal about simulation, not proof that a quantum computer would accelerate every kind of calculation.

In plain EnglishSimulation Using one system or a mathematical model to study how another system behaves.

The next questionA machine that imitates nature is one possibility. Could a quantum machine also follow different programs?

Deutsch describes a programmable quantum computer

David Deutsch developed a model of a universal quantum computer: a machine that could perform different quantum computations through suitable instructions. The aim expanded from specialized simulations to a general framework for quantum information processing.

Still to solve“Universal” describes what the model can represent. It does not mean that every problem becomes easy or faster to solve.

In plain EnglishQubit A quantum unit of information. Reading it in the usual computational basis gives 0 or 1.

The next questionA programmable model gives researchers a place to begin. Next comes the search for a calculation worth building it for.

Shor shows how a quantum computer could factor large numbers

Multiplying 7 by 11 gives 77. Factoring asks the reverse question. For the huge numbers used by RSA, that reversal is difficult with known classical methods. Peter Shor showed how a quantum computer could factor efficiently and solve a related problem called the discrete logarithm.

Still to solveAttacking real cryptographic keys requires a sufficiently large, reliable quantum computer. The algorithm’s discovery did not immediately break deployed encryption.

In plain EnglishPublic-key cryptography Methods using related public and private keys to protect information or verify signatures.

The next questionA powerful algorithm is only useful if its delicate quantum information survives long enough to run.

Shor shows how nine qubits can protect one

Shor’s code spreads the state of one logical qubit across nine physical qubits. If one of the nine suffers an error, checks on the group reveal enough to correct it while keeping the stored quantum information hidden from those checks.

Still to solveThis was a theoretical code, not a finished reliable computer. Protection needs extra physical resources and sufficiently accurate operations.

In plain EnglishLogical qubit A unit of quantum information encoded with redundancy so that errors can be detected or corrected.

The next questionA protective method is a plan. Carrying it out still requires physical operations that researchers can control.

Two properties of one ion carry out a logic gate

A NIST team used two properties of a single trapped ion as qubits. One described its vibration and the other an internal state. Laser pulses made a flip of the internal state depend on the vibrational state. The operation is called a controlled-NOT gate.

Still to solveThe two information carriers were properties of one ion, not two separate ions. One operation does not make a complete computer.

In plain EnglishQuantum gate An instruction that transforms the state of one or more qubits. Some gates make one qubit’s operation depend on another’s state.

The next questionWhile experiments tested the building blocks, algorithms continued to reveal different kinds of possible advantage.

Grover shows how to search with fewer checks

Suppose one item among a million passes a yes-or-no test, and there is no shortcut for finding it. Ordinary search can take hundreds of thousands of checks. In Grover’s ideal quantum algorithm, the number of checks is on the order of a thousand.

Still to solveThe comparison counts calls to a test that can run inside a quantum circuit. Preparing the data, implementing that test and reading the answer all take work.

In plain EnglishAlgorithm A step-by-step method for solving a specified problem, including how to recognize a useful result.

The next questionAn algorithm describes operations. The hardware question remains: what physical object should carry each qubit?

Researchers control a qubit on a tiny electrical circuit

Yasunobu Nakamura, Yuri Pashkin and Jaw-Shen Tsai used short voltage pulses to control quantum behavior in a tiny superconducting circuit. Its two charge states formed a qubit: an engineered object whose quantum state could be deliberately changed.

Still to solveThis controlled one qubit. It did not yet demonstrate a large processor, reliable computation or a practical speed advantage.

In plain EnglishSuperconducting qubit A quantum bit made from an electrical circuit operated at very low temperature.

The next questionBuilding a controllable qubit is a start. Keeping unwanted disturbances from spoiling it becomes the next engineering problem.

The transmon design makes charge fluctuations less disruptive

Jens Koch and collaborators proposed the transmon, a redesigned superconducting qubit. Their analysis showed how changing the circuit could sharply reduce its sensitivity to fluctuating electric charge while retaining the ability to control its quantum states.

Still to solveThis paper proposed and analyzed a design. Reducing sensitivity to charge noise does not remove every source of error.

In plain EnglishNoise Unwanted disturbances that change a quantum system or interfere with its control and measurement.

The next questionImproved components are one part of the story. Wider access would let more people learn to program real hardware.

IBM opens a five-qubit processor to the public

IBM made a five-qubit quantum processor accessible through the internet. People outside the laboratory could submit quantum circuits, run experiments on real hardware and inspect the results through a cloud service.

Still to solveAccess to real quantum hardware does not guarantee a useful speedup. Small processors remain limited by size, errors and available operations.

In plain EnglishQuantum circuit An ordered set of operations and measurements that describes a quantum computation.

The next questionAccess brings more people into the field. Research also needs institutions that can support years of development.

A U.S. law coordinates quantum research across agencies

The United States enacted the National Quantum Initiative Act. It established a coordinated federal program for quantum research and development, bringing multiple agencies into a shared effort. A laboratory field was also becoming a long-term institutional priority.

Still to solveA law organizes an effort. Authorized funding and actual spending are different, and neither demonstrates a computer’s performance.

In plain EnglishQuantum industry The researchers, companies, suppliers, software tools and institutions working to develop and use quantum technologies.

The next questionA wider effort needs a way to judge results. What does it mean when a quantum machine claims to beat a classical one?

Google’s Sycamore tests the limits of classical simulation

Google’s Sycamore processor used 53 qubits to sample results from specially constructed random circuits. The team reported a large speed advantage over its estimate of the classical computing effort needed to reproduce the task.

Still to solveThis was not a useful general application. The classical runtime estimate was contested, and classical simulation methods subsequently improved.

In plain EnglishBenchmark A specified test task used to compare performance under stated conditions.

The next questionA difficult benchmark is one test. Another is whether the machine can keep information reliable as its protective encoding grows.

A larger quantum memory makes slightly fewer errors

Google stored one logical qubit in two sizes of error-correcting code. The larger code averaged about 2.91% logical errors per correction cycle, compared with about 3.03% for the smaller codes. Adding more hardware had produced a small but measurable improvement.

Still to solveThe improvement was modest and concerned memory. It did not establish reliable, arbitrary computations or practical advantage.

In plain EnglishError correction Encoding information and checking for faults so mistakes can be detected and, when possible, corrected.

The next questionProtecting memory is only part of the job. Researchers also need operations on the information they have encoded.

Trapped atoms run sampling circuits with up to 48 logical qubits

Researchers held atoms in laser light, then grouped them to encode quantum information. Some circuits used up to 48 logical qubits to generate samples. The team could detect certain errors and exclude the affected runs when analyzing the results.

Still to solveDetecting errors and rejecting affected runs helped the results. This was not 48 fully error-corrected qubits running arbitrary long calculations.

The next questionHardware experiments continue. Meanwhile, the possibility of stronger machines already calls for changes to ordinary security systems.

NIST publishes standards for shared keys and digital signatures

Two computers may need a shared secret to protect a connection. They may also need to verify who signed a message or software update. NIST finalized one post-quantum standard for establishing a shared key and two for digital signatures.

Still to solveThese methods run on ordinary computers. Publishing the standards did not mean that quantum computers could already break deployed encryption.

In plain EnglishPost-quantum cryptography Mathematical security methods designed to resist classical and quantum attacks, without requiring quantum hardware.

The next questionSecurity can prepare before a large quantum computer arrives. Back in the lab, reliability still has to be demonstrated.

On Willow, larger codes roughly halve memory errors at each step

Google tested three sizes of surface code, a layout that uses neighboring qubits to check for errors. Each step up in size reduced the logical error rate per correction cycle by about a factor of two. All three sizes stored a single logical qubit.

Still to solveThe result protected quantum memory. It did not demonstrate a large computer performing arbitrary useful calculations with full error correction.

In plain EnglishBelow threshold Errors are low enough that increasing the error-correcting code’s size improves protection.

The next questionA stronger memory result raises the next challenge: can storage, operations and error correction work together?

An atom processor combines correction, logic and qubit reuse

A neutral-atom processor demonstrated several ingredients needed for reliable quantum computation, including repeated error correction, logical operations and reusing atoms during a computation. The work connected capabilities that must eventually function together in a larger machine.

Still to solveThese were demonstrations of building blocks and architecture. They did not establish a fully scaled machine solving practical problems beyond classical reach.

In plain EnglishFault tolerance Designing operations so that faults remain manageable by error correction, rather than spreading uncontrollably.

The next questionDifferent hardware approaches tackle these problems differently. One newer approach protects memory with fewer active control steps.

A trapped ion protects a memory without a measurement loop

Researchers stored one logical qubit in several internal states of a trapped ion. Engineered interactions and cooling with a second ion removed errors without repeated measurement and feedback, extending memory lifetime beyond the unprotected comparison.

Still to solveThis protected quantum memory under specified noise conditions. It did not demonstrate universal computation or remove the need for further engineering.

In plain EnglishBreak-even A memory benchmark. The protected and comparison memories are equally long-lived at break-even. Beyond it, the protected memory lasts longer.

The next questionProgress in memory remains distinct from a complete machine. Organizations can still prepare for the possibilities ahead.

NIST maps how to replace vulnerable cryptography

In 2024, NIST published standards for new cryptographic tools. Its 2026 transition report connects the old tools to their replacements. An organization can use the report to identify which of its key-establishment and signature methods need to change.

Still to solvePost-quantum cryptography runs on ordinary computers. A migration roadmap does not predict when a quantum computer will break deployed encryption.

In plain EnglishPost-quantum cryptography Security methods designed to resist attacks from both classical and future quantum computers.

The next questionThe story has no finish line yet. Read each new claim by asking what was tested, against which comparison and with what limits.