Nonlinear optical signals and spectroscopy with quantum light

TL;DR

This paper introduces a diagrammatic approach to nonlinear spectroscopy using quantum light, especially entangled photons, enabling enhanced resolution and control in spectroscopic measurements beyond classical limits.

Contribution

It presents a novel diagrammatic method for calculating quantum light-induced signals, focusing on entangled photons with nonclassical bandwidths, expanding the toolkit for quantum-enhanced spectroscopy.

Findings

Entangled photon pairs bypass classical Fourier limitations.

The approach effectively models ultrafast signals with quantum light.

Applications demonstrated on simple multi-level systems.

Abstract

Conventional nonlinear spectroscopy uses classical light to detect matter properties through the variation of its response with frequencies or time delays. Quantum light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. We present an intuitive diagrammatic approach for calculating ultrafast spectroscopy signals induced by quantum light, focusing on applications involving entangled photons with nonclassical bandwidth properties - known as "time-energy entanglement". Nonlinear optical signals induced by quantized light fields are expressed using time ordered multipoint correlation functions of superoperators. These are different from Glauber's g- functions for photon counting which use normally ordered products of ordinary operators. Entangled photon pairs are not subjected to the classical Fourier limitations on the joint temporal and spectral resolution. After a brief survey of properties of entangled photon pairs relevant to their spectroscopic applications, different optical signals, and photon counting setups are discussed and illustrated for simple multi-level model systems.