Technology
IBM links two 120-qubit processors with four metre-scale cables
IBM researchers joined two 120-qubit Nighthawk R1 processors with four 80-centimetre superconducting aluminium cables fixed after both chips were already mounted in one dilution refrigerator. State transfer averaged 99% fidelity, with a best link at 99.29%, and two-qubit gates across the chips averaged 94.75%. The arXiv preprint argues the couplers make modular multi-chip machines practical, though fidelity is not yet high enough to run two processors as one.