IQM Reports Entanglement Across Its 54 Qubit Processor

IQM Quantum Computers (IQM) said on October 29 that it prepared a collective entangled state across all 54 qubits of its Emerald processor. The Greenberger–Horne–Zeilinger (GHZ) state is a standard test of correlations shared across many qubits. IQM reports fidelity of 0.516 after readout error mitigation, compared with the 0.5 boundary used to witness this form of genuine multipartite entanglement. 1

Fidelity measures agreement with the intended state. Readout mitigation statistically adjusts measurement results for characterized detection errors; it does not make the underlying processor error-free. The threshold is meaningful for this particular state test, rather than a general pass mark for useful computing. Earlier research describes the same GHZ verification approach and the need to account for measurement uncertainty. 2 3

IQM attributes the result partly to an automated preparation routine that balances gate quality against time spent idle, and says cloud users can access the improved system performance. Repeated measurements, uncertainty around the threshold and performance on longer circuits will help establish its practical reach. Preparing this state across the chip is a hardware-control benchmark; it establishes neither error-corrected computation nor an advantage over classical computers on a useful task. 1

Sources

• IQM October 29 announcement and readout-mitigated result

• Mooney and colleagues on GHZ verification and uncertainty

• Wei and colleagues on scalable GHZ entanglement measurement