Nonlinear Interferometry for Quantum-Enhanced Measurements of Multiphoton Absorption

TL;DR

This paper demonstrates that nonlinear interferometry with squeezed light significantly enhances the sensitivity of multiphoton absorption measurements, reducing required intensities and maintaining robustness against losses.

Contribution

It introduces a nonlinear SU(1,1)-interferometer setup that improves multiphoton absorption detection sensitivity beyond traditional methods.

Findings

Sensitivity scales better with photon flux compared to classical methods.

Enhanced robustness against photon losses.

Optimal squeezing improves measurement precision.

Abstract

Multiphoton absorption is of vital importance in many spectroscopic, microscopic or lithographic applications. However, given that it is an inherently weak process, the detection of multiphoton absorption signals typically requires large field intensities, hindering its applicability in many practical situations. In this work, we show that placing a multiphoton absorbent inside an imbalanced nonlinear interferometer can enhance the precision of multiphoton cross-section estimation with respect to strategies based on direct transmission measurements by coherent or even squeezed light. In particular, the power scaling of the sensitivity with photon flux can be increased by an order of magnitude compared to transmission measurements of the sample with coherent light, meaning that a signal could be observed at substantially reduced excitation intensities. Furthermore, we show that this enhanced measurement precision is robust against experimental imperfections leading to photon losses, which usually tend to degrade the detection sensitivity. We trace the origin of this enhancement to an optimal degree of squeezing which has to be generated in a nonlinear SU(1,1)-interferometer.