IBM tests four quantum links between two Nighthawk chips
An October 21 preprint separates state-transfer fidelity from the harder task of operating across processors.
IBM researchers report four superconducting interconnects between two 120- Nighthawk R1 processors. Only a development subset of the chips was wired and measured. Each connection includes an 80-centimeter cable installed after the modules were mounted in the refrigerator.[1]
The team reports 99% mean state-transfer fidelity under network benchmarking. Remote , which entangle qubits on separate chips, achieved a different figure: 94.75% mean fidelity. Two neighboring links also generated Bell pairs simultaneously.[1]
The unreviewed study demonstrates interconnects and cross-chip operations rather than a complete 240-qubit workload. Its assembly method addresses a practical obstacle to modular machines, while reproducibility, additional links and lower operating errors still need testing. Connecting chips becomes useful computing capacity only when the whole workload tolerates the connections it relies on.[1]
QubitWire analysis
Our assessment is that modularity moves the engineering question from the size of one chip to the reliability of the connections between chips. A useful follow-up would run a specified workload across modules and compare its result with an appropriate single-module implementation. That comparison should expose how much time is spent moving states, how failures are detected and whether the connections remain stable through repeated operation.
A reader should keep three quantities separate: the capacity printed on each processor, the qubits actually involved in the experiment and the operations completed across the link. Adding the first quantity across modules does not establish the third. Evidence about assembly and repeatability would also help explain whether the approach simplifies a larger machine or transfers complexity into its wiring, calibration and maintenance.