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Self-consistent quantum process tomography

Seth Merkel, IBM Watson Research Center

(Session 7a : Friday from 3:30 - 4:00)

Abstract. Quantum process tomography is a necessary tool for verifying quantum gates and diagnosing faults in architectures and gate design. We will show that the standard approach of process tomography fails in the case where the states and measurement operators used to interrogate the system are generated by gates that have some systematic error, a situation all but unavoidable in any practical setting. These errors cannot be compensated for by statistical oversampling or through increasing the number of measurement settings. We present an alternative method for tomography to reconstruct an entire library of gates in a self-consistent manner where the essential new ingredient is to define a likelihood function that treats the gates used for preparation and measurement on equal footing with the gate being reconstructed. We compare this new method of tomography to standard process tomography in both simulation and experiments on superconducting circuits.