Cross-Platform Verification of Intermediate Scale Quantum Devices with Randomized Measurements
summary
Protocol uses randomized local unitaries on a single copy plus projective measurements to estimate second-order statistics that equal the trace overlap and Rényi-2 purity, implemented with local single-qubit random rotations and repeated shots (hundreds of unitaries × O(100) repeats typical). Applied to a 10-ion trapped-ion experiment to extract subsystem purities and cross-platform fidelities; experiment matches itself better than theory, showing the method works for ~10–20 qubits despite exponential scaling in subsystem size.
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