Complete chip QND measurement tomography and applications to IBM-Q

Characterizing and improving quantum non-demolition measurements are fundamental tasks to achieve fault-tolerant quantum computing. In this work, we present an efficient scaling strategy to characterize all the single-qubit QND measurements of a device by quantum tomography. The protocol reconstructs the Choi matrices that describe the measurements of every single qubit and all the pairs of physically connected qubits. The protocol requires a number of measurements that scale with the maximum number of connections that qubits have, and not with the number of qubits. Using these operators, we study the readout fidelity, QND-ness, destructiveness, and measurement crosstalk. We perform an experimental implementation of the protocol to fully characterize all the detectors of a 7-qubits IBM-Q quantum device.