Quantum enhanced metrology in the presence of arbitrary loss

TL;DR

This paper explores how entanglement can enhance measurement precision in quantum interferometry even with arbitrary loss, proposing methods for detecting and utilizing pre-measurement photon correlations.

Contribution

It introduces a new perspective on entanglement-enhanced interferometry by focusing on detected photon correlations and demonstrates feasible experimental implementations.

Findings

Entanglement can surpass the standard quantum limit despite loss.

Detection of pre-measurement photon correlations enables enhanced measurement.

A proof of principle experiment using linear optics is proposed.

Abstract

We introduce the concept of entanglement enhanced interferometry from the viewpoint of the detected photons. The standard quantum limit is achieved when sequentially detected photons are assumed to be in an uncorrelated product state. However when we access the correlations between the detected photons that existed before the interferometer it becomes clear that entanglement enhanced measurement beyond the quantum limit could be achieved independent of loss. We describe possible realisations of this post-measurement entanglement detection using a small array of spin photon entangling gates. We then describe a proof of principle experiment using only linear optics resources.