Two-photon absorption measurements in the presence of single-photon losses

TL;DR

This paper investigates how two-photon absorption measurements using squeezed and coherent light states can be made robust against linear losses, revealing conditions where TPA detection sensitivity remains unaffected by such losses.

Contribution

It demonstrates that TPA sensitivity with certain quantum states can be loss-independent at high photon numbers, improving measurement accuracy in practical scenarios.

Findings

TPA sensitivity can become loss-independent at high photon numbers.

Large fluctuations in squeezed states counteract linear losses.

Measurement of photon number or anti-squeezed quadrature is particularly robust.

Abstract

We discuss how two-photon absorption (TPA) of squeezed and coherent states of light can be detected in measurements of the transmitted light fields. Such measurements typically suffer from competing loss mechanisms such as experimental imperfections and linear scattering losses inside the sample itself, which can lead to incorrect assessments of the two-photon absorption cross section. We evaluate the sensitivity with which TPA can be detected and find that TPA sensitivity of squeezed vacua or squeezed coherent states can become independent of linear losses at sufficiently large photon numbers. In particular, this happens for measurements of the photon number or of the anti-squeezed field quadrature, where large fluctuations counteract and exactly cancel the degradation caused by single photon losses.