Complete physical characterization of QND measurements via tomography

TL;DR

This paper presents a comprehensive tomography method for quantum non-demolition detectors, enabling detailed physical characterization, error diagnosis, and calibration improvements, demonstrated through superconducting qubit readout simulations.

Contribution

It introduces a self-consistent tomography framework for QND detectors that includes measurement processes and fidelity metrics, advancing detector diagnostics and calibration.

Findings

Identifies non-dispersive errors in QND measurements

Quantifies back-action effects in superconducting qubit readout

Calibrates optimal measurement points for improved accuracy

Abstract

We introduce a self-consistent tomography for arbitrary quantum non-demolition (QND) detectors. Based on this, we build a complete physical characterization of the detector, including the measurement processes and a quantification of the fidelity, ideality, and back-action of the measurement. This framework is a diagnostic tool for the dynamics of QND detectors, allowing us to identify errors, and to improve their calibration and design. We illustrate this on a realistic Jaynes-Cummings simulation of superconducting qubit readout. We characterize non-dispersive errors, quantify the back-action introduced by the readout cavity, and calibrate the optimal measurement point.