Theory of quantum comb enhanced interferometry

TL;DR

This paper develops a comprehensive theory for quantum combs in interferometry, demonstrating quantum advantages in sensing that are robust to loss, surpassing traditional quantum sensing limits.

Contribution

It introduces a theoretical framework for designing and analyzing quantum combs, including protocols with quantum advantages scalable with squeezing and entanglement.

Findings

Quantum comb protocols outperform classical limits in interferometry.

Certain protocols show robustness to loss in spectroscopy.

Quantum advantages scale with squeezing and entanglement strength.

Abstract

Optical frequency combs, named for their comb-like peaks in the spectrum, are essential for various sensing applications. As the technology develops, its performance has reached the standard quantum limit dictated by the quantum fluctuations of coherent light field. Quantum combs, with their quantum fluctuation engineered via squeezing and entanglement, are the necessary ingredient for overcoming such limits. We develop the theory for designing and analyzing quantum combs, focusing on dual-comb interferometric measurement. Our analyses cover both squeezed and entangled quantum combs with division receivers and heterodyne receivers, leading to four protocols with quantum advantages scalable with squeezing/entanglement strength. In the spectroscopy of a single absorption line, whereas the division receiver with the squeezed comb suffers from amplified thermal noise, the other three protocols demonstrate a surprising robustness to loss at a few comb lines. Such a unique loss-robustness of a scalable quantum advantage has not been found in any traditional quantum sensing protocols.