Large gain quantum-limited qubit measurement using a two-mode nonlinear cavity

TL;DR

This paper theoretically demonstrates that a driven, parametrically-coupled cavity system with a weak Kerr nonlinearity can achieve near quantum-limited, high-gain qubit measurement in circuit QED without external non-reciprocal components.

Contribution

It introduces a novel on-chip measurement scheme using a two-mode nonlinear cavity system capable of high gain and near quantum-limited performance.

Findings

Achieves high measurement gain with minimal backaction.

Operates effectively in the standard linear-response regime.

Eliminates need for circulators or non-reciprocal amplifiers.

Abstract

We provide a thorough theoretical analysis of qubit state measurement in a setup where a driven, parametrically-coupled cavity system is directly coupled to the qubit, with one of the cavities having a weak Kerr nonlinearity. Such a system could be readily realized using circuit QED architectures. We demonstrate that this setup is capable in the standard linear-response regime of both producing a highly amplified output signal while at the same time achieving near quantum-limited performance: the measurement backaction on the qubit is near the minimal amount required by the uncertainty principle. This setup thus represents a promising route for performing efficient large-gain qubit measurement that is completely on-chip, and that does not rely on the use of circulators or complex non-reciprocal amplifiers.