Mode engineering for realistic quantum-enhanced interferometry

TL;DR

This paper presents a method to improve quantum-enhanced interferometry by designing the modal structure of input photons, which mitigates imperfections like photon distinguishability, demonstrated experimentally with a two-photon Mach-Zehnder interferometer.

Contribution

It introduces a novel approach of mode engineering to counteract photon distinguishability issues in quantum interferometry, validated through laboratory experiments.

Findings

Restores entanglement-enhanced precision in realistic interferometers

Mitigates effects of spectral distinguishability using spatial mode design

Enhances robustness of quantum metrology against practical imperfections

Abstract

Quantum metrology overcomes standard precision limits by exploiting collective quantum superpositions of physical systems used for sensing, with the prominent example of non-classical multiphoton states improving interferometric techniques. Practical quantum-enhanced interferometry is, however, vulnerable to imperfections such as partial distinguishability of interfering photons. Here we introduce a method where appropriate design of the modal structure of input photons can alleviate deleterious effects caused by another, experimentally inaccessible degree of freedom. This result is accompanied by a laboratory demonstration that a suitable choice of spatial modes combined with position-resolved coincidence detection restores entanglement-enhanced precision in the full operating range of a realistic two-photon Mach-Zehnder interferometer, specifically around a point which otherwise does not even attain the shot-noise limit due to the presence of residual distinguishing information in the spectral degree of freedom. Our method highlights the potential of engineering multimode physical systems in metrologic applications.