Quantum limited amplification with a nonlinear cavity detector

TL;DR

This paper analyzes a nonlinear cavity amplifier near a bifurcation point, demonstrating quantum-limited amplification and detection by exploiting correlations, with implications for signal amplification and mechanical cooling.

Contribution

It provides asymptotic expressions for noise and response in a nonlinear cavity amplifier and identifies conditions for quantum-limited performance.

Findings

Quantum-limited linear amplification is achievable with correlated noise.

Amplification of non-resonant signals enables quantum-limited detection.

Backaction can be utilized for cooling mechanical modes.

Abstract

We consider the quantum measurement properties of a driven cavity with a Kerr-type nonlinearity which is used to amplify a dispersively coupled input signal. Focusing on an operating regime which is near a bifurcation point, we derive simple asymptotic expressions describing the cavity's noise and response. We show that the cavity's backaction and imprecision noise allow for quantum limited linear amplification and position detection only if one is able to utilize the sizeable correlations between these quantities. This is possible when one amplifies a non-resonant signal, but is not possible in QND qubit detection. We also consider the possibility of using the nonlinear cavity's backaction for cooling a mechanical mode.