Experimental Joint Estimation of Phase and Phase Diffusion via Deterministic Bell Measurements

TL;DR

This paper experimentally demonstrates enhanced joint estimation of phase and phase diffusion in quantum systems using deterministic Bell measurements, highlighting the advantages of collective measurements over separable strategies in noisy quantum metrology.

Contribution

It introduces a new framework for joint phase and phase diffusion estimation employing deterministic Bell measurements, surpassing separable measurement limitations.

Findings

Improved estimation precision with collective measurements.

Implementation of deterministic Bell measurements in a linear optical network.

Demonstration of advantages over separable measurement strategies.

Abstract

Accurate phase estimation plays a pivotal role in quantum metrology, yet its precision is significantly affected by noise, particularly phase-diffusive noise caused by phase drift. To address this challenge, the joint estimation of phase and phase diffusion has emerged as an effective approach, transforming the problem into a multi-parameter estimation task. However, the incompatibility between optimal measurements for different parameters prevents single-copy measurements from reaching the fundamental precision limits defined by the quantum Cramer-Rao bound. Meanwhile, collective measurements performed on multiple identical copies can mitigate this incompatibility and thus enhance the precision of joint parameter estimation. This work experimentally demonstrates joint phase and phase-diffusion estimation using deterministic Bell measurements on a two-qubit system. A linear optical network is employed to implement both parameter encoding and deterministic Bell measurements, achieving improved estimation precision compared to any separable measurement strategy. This work proposes a new framework for phase estimation under phase-diffusive noise and underscores the substantial advantages of collective measurements in multi-parameter quantum metrology.