Phase-Modulated Interferometry, Spectroscopy, and Refractometry using Entangled Photon Pairs

TL;DR

This paper demonstrates phase-modulated interferometry and spectroscopy using entangled photon pairs, enhancing measurement sensitivity and enabling detailed analysis of samples' linear response with reduced sampling requirements.

Contribution

It introduces a novel phase modulation and lock-in detection technique for entangled photon interferometry, improving signal-to-noise ratio and enabling individual quantum pathway analysis.

Findings

Enhanced detection sensitivity through phase modulation.

Reduced sampling requirements for interference pattern reconstruction.

Ability to analyze quantum pathways in molecular spectroscopy.

Abstract

The authors demonstrate a form of two-photon-counting interferometry by measuring the coincidence counts between single-photon-counting detectors at an output port of a Mach-Zehnder Interferometer (MZI) following injection of broad-band time-frequency-entangled photon pairs (EPP) generated from collinear spontaneous parametric down conversion into a single input port. Spectroscopy and refractometry are performed on a sample inserted in one internal path of the MZI by scanning the other path in length, which acquires phase and amplitude information about the samples linear response. Phase modulation and lock-in detection are introduced to increase detection signal-to-noise ratio and implement a down-sampling technique for scanning the interferometer delay, which reduces the sampling requirements needed to reproduce fully the temporal interference pattern. The phase-modulation technique also allows the contributions of various quantum-state pathways leading to the final detection outcomes to be extracted individually. Feynman diagrams frequently used in the context of molecular spectroscopy are used to describe the interferences resulting from the coherence properties of time-frequency EPPs passing through the MZI. These results are an important step toward implementation of a proposed method for molecular spectroscopy, i.e. quantum-light-enhanced two-dimensional spectroscopy.