Quantum sensing of displacements with stabilized GKP states

TL;DR

This paper introduces a method using stabilized GKP states for high-precision, continuous two-quadrature displacement sensing that surpasses classical limits and approaches the quantum Cramer-Rao bound, with practical advantages like backaction evasion.

Contribution

It demonstrates how GKP state stabilization protocols can be applied for advanced displacement sensing, enabling continuous, backaction-evading measurements that outperform Gaussian limits.

Findings

Achieves displacement sensitivities near the quantum Cramer-Rao bound.

Demonstrates unconditional surpassing of Gaussian sensing limits.

Provides numerical evidence of robustness in realistic noisy environments.

Abstract

We demonstrate how recent protocols developed for the stabilization of Gottesman-Kitaev-Preskill (GKP) states can be used for the estimation of two-quadrature displacement sensing, with sensitivities approaching the multivariate quantum Cramer-Rao bound. Thanks to the stabilization, this sensor is backaction evading and can function continuously without reset, making it well suited for the detection of itinerant signals. Additionally, we provide numerical simulations showing that the protocol can unconditionally surpass the Gaussian limit of displacement sensing with prior information, even in the presence of realistic noise. Our work shows how reservoir engineering in bosonic systems can be leveraged for quantum metrology, with potential applications in force sensing, waveform estimation and quantum channel learning.