Enhanced nonlinear interferometry via seeding

TL;DR

Seeding a nonlinear interferometer with a small number of photons significantly enhances its phase sensitivity and signal quality, even with losses and detector inefficiencies, broadening its practical applications.

Contribution

This work analytically demonstrates how seeding improves nonlinear interferometry performance under realistic conditions, including losses and detector inefficiencies.

Findings

Seeding enhances interference visibility, contrast, and phase sensitivity.

A few tens of seeded photons can match unseeded quantum-limited sensitivity.

No difference between number and coherent seeding in low-gain regime.

Abstract

We analyse a nonlinear interferometer, also known as an SU(1,1) interferometer, in the presence of internal losses and inefficient detectors. To overcome these limitations, we consider the effect of seeding one of the interferometer input modes with either a number state or a coherent state. We derive analytical expressions for the interference visibility, contrast, phase sensitivity, and signal-to-noise ratio, and show a significant enhancement in all these quantities as a function of the seeding photon number. For example, we predict that, even in the presence of substantial losses and highly inefficient detectors, we can achieve the same quantum-limited phase sensitivity of an unseeded nonlinear interferometer by seeding with a few tens of photons. Furthermore, we observe no difference between a number or a coherent seeding state when the interferometer operates in the low-gain regime, which enables seeding with an attenuated laser. Our results expand the nonlinear interferometry capabilities in the field of quantum imaging, metrology, and spectroscopy under realistic experimental conditions.