Robust readout of bosonic qubits in the dispersive coupling regime

TL;DR

This paper introduces a robust readout scheme for bosonic qubits in dispersive coupling regimes, combining repeated QND measurements and higher-level encodings to significantly improve measurement fidelity in quantum systems.

Contribution

It proposes a new measurement protocol that overcomes fundamental fidelity limits by utilizing higher-level encodings and repeated measurements in bosonic systems.

Findings

Asymptotic suppression of relaxation and measurement errors.

Calculation of measurement fidelity based on experimental parameters.

Application to cat and binomial codes demonstrating improved robustness.

Abstract

High-fidelity qubit measurements play a crucial role in quantum computation, communication, and metrology. In recent experiments, it has been shown that readout fidelity may be improved by performing repeated quantum non-demolition (QND) readouts of a qubit's state through an ancilla. For a qubit encoded in a two-level system, the fidelity of such schemes is limited by the fact that a single error can destroy the information in the qubit. On the other hand, if a bosonic system is used, this fundamental limit could be overcome by utilizing higher levels such that a single error still leaves states distinguishable. In this work, we present a robust readout scheme, applicable to bosonic systems dispersively coupled to an ancilla, which leverages both repeated QND readouts and higher-level encodings to asymptotically suppress the effects of qubit/cavity relaxation and individual measurement infidelity. We calculate the measurement fidelity in terms of general experimental parameters, provide an information-theoretic description of the scheme, and describe its application to several encodings, including cat and binomial codes.