Witnessing Entangled Two-Photon Absorption via Quantum Interferometry

TL;DR

This paper demonstrates that N00N-state quantum interferometers can effectively detect entangled two-photon absorption (eTPA) and distinguish it from single-photon loss effects, advancing quantum spectroscopy methods.

Contribution

It introduces the use of N00N-state interferometry as a loss-insensitive method to verify entangled two-photon absorption in samples.

Findings

N00N states are insensitive to linear single-photon losses.

N00N-state interferometers can certify eTPA independently of loss mechanisms.

Results suggest N00N states are promising for quantum spectroscopy applications.

Abstract

Recent investigations suggest that the use of non-classical states of light, such as entangled photon pairs, may open new and exciting avenues in experimental two-photon absorption spectroscopy. Despite several experimental studies of entangled two-photon absorption (eTPA), there is still a heated debate on whether eTPA has truly been observed. This interesting debate has arisen, mainly because it has been recently argued that single-photon-loss mechanisms, such as scattering or hot-band absorption may mimic the expected entangled-photon linear absorption behavior. In this work, we focus on transmission measurements of eTPA, and explore three different two-photon quantum interferometers in the context of assessing eTPA. We demonstrate that the so-called N00N-state configuration is the only one amongst those considered insensitive to linear (single-photon) losses. Remarkably, our results show that N00N states may become a potentially powerful tool for quantum spectroscopy, and place them as a strong candidate for the certification of eTPA in an arbitrary sample.