Parallel tomography of quantum non-demolition measurements in multi-qubit devices

Abstract

An efficient characterization of QND measurements is an important ingredient toward certifying and improving the performance and scalability of quantum processors. In this work, we introduce a parallel tomography of QND measurements that addresses single- and two-qubit readout on a multi-qubit quantum processor. We provide an experimental demonstration of the tomographic protocol on a 7-qubit IBM-Q device, characterizing the quality of conventional qubit readout as well as generalized measurements such as parity or measurement-and-reset schemes. Our protocol reconstructs the Choi matrices of the measurement processes, extracts relevant quantifiers—fidelity, QNDness, destructiveness—and identifies sources of errors that limit the performance of the device for repeated QND measurements. We also show how to quantify measurement crosstalk and use it to certify the quality of simultaneous readout on multiple qubits.

A randomized benchmarking suite for mid-circuit measurements

“…However, for the characterization of mid-circuit measurements a POVM description is insufficient. In this case full characterization of the measurement action leading to each outcome is described by a quantum channel, and hence process tomography is required [18][19][20]. While one can imagine extensions of these protocols to small stabilizer check circuits, the exponential resource scaling of process tomography make such characterization approaches impractical to deploy for larger quantum codes.…”