Quantum limits in optical interferometry

TL;DR

This review discusses the fundamental quantum limits of optical interferometry, considering decoherence effects, and evaluates the near-optimality of current quantum-enhanced techniques used in gravitational wave detection.

Contribution

It derives fundamental bounds on quantum-enhanced precision in optical interferometry accounting for decoherence, and assesses the practical attainability of these bounds.

Findings

Quantum bounds are derived considering phase diffusion, losses, and visibility.

Current quantum-enhanced methods in gravitational wave detectors are near optimal.

Decoherence significantly impacts the performance of quantum interferometry.

Abstract

Non-classical states of light find applications in enhancing the performance of optical interferometric experiments, with notable example of gravitational wave-detectors. Still, the presence of decoherence hinders significantly the performance of quantum-enhanced protocols. In this review, we summarize the developments of quantum metrology with particular focus on optical interferometry and derive fundamental bounds on achievable quantum-enhanced precision in optical interferometry taking into account the most relevant decoherence processes including: phase diffusion, losses and imperfect interferometric visibility. We introduce all the necessary tools of quantum optics as well as quantum estimation theory required to derive the bounds. We also discuss the practical attainability of the bounds derived and stress in particular that the techniques of quantum-enhanced interferometry which are being implemented in modern gravitational wave detectors are close to the optimal ones.