Performing quantum entangled biphoton spectroscopy using classical light pulses

TL;DR

This paper demonstrates that for certain quantum light spectroscopy experiments, classical light pulses can replicate the signals obtained with entangled photon pairs, offering a pathway to quantum-inspired classical spectroscopy.

Contribution

The authors prove the equivalence between biphoton-based quantum spectroscopy and classical-like coherent state probes using an input-output formulation, enabling classical simulation of quantum experiments.

Findings

Classical-like coherent states can replicate biphoton signals in certain QLS experiments.

Numerical comparison confirms the equivalence between quantum and classical probe setups.

Insights for designing future quantum spectroscopy experiments with potential quantum advantage.

Abstract

We show that for a class of quantum light spectroscopy (QLS) experiments using n = 0,1,2,$\cdots$ classical light pulses and an entangled photon pair (a biphoton state) where one photon acts as a reference without interacting with the matter sample, identical signals can be obtained by replacing the biphotons with classical-like coherent states of light, where these are defined explicitly in terms of the parameters of the biphoton states. An input-output formulation of quantum nonlinear spectroscopy is used to prove this equivalence. We demonstrate the equivalence numerically by comparing a classical pump - quantum probe experiment with the corresponding classical pump - classical probe experiment. This analysis shows that understanding the equivalence between entangled biphoton probes and carefully designed classical-like coherent state probes leads to quantum-inspired classical experiments and provides insights for future design of QLS experiments that could provide a true quantum advantage.