Simultaneous amplitude and phase spectroscopy using two-photon interference

TL;DR

This paper introduces a quantum spectroscopy method using entangled photon pairs to simultaneously measure absorption and phase shifts in samples with low light intensities, enabling detailed characterization of chemical and biological specimens.

Contribution

The work demonstrates a novel quantum interferometry scheme that combines intensity correlations with two-photon interference for comprehensive sample analysis.

Findings

Simultaneous measurement of absorption and phase shift achieved.

Low-intensity probing with rapid acquisition times.

Applicable to chemical and biological sample characterization.

Abstract

Quantum spectroscopy seeks to probe chemical systems using nonclassical light, which has properties that are qualitatively and quantitatively different than conventional light sources. One promising technique uses intensity-correlated twin beams of light to reduce the noise sources inherent to absorption spectroscopy. However, measurements of the phase shift imparted by the chemical sample, which provides complementary information to the absorption, continue to be a challenge. Here, we propose and demonstrate a scheme using entangled photon pairs that can simultaneously measure both the absorption and phase shift of a sample with extremely low optical intensities and with relatively fast few-minute acquisition times. This method combines the previous use of intensity correlations with a broadband quantum interferometer utilizing two-photon interference to measure the complete linear optical response of the sample. Our work shows that precise measurements of absorption can also be made phase-sensitive using suitable choices of probe beam and detection scheme. This enables a new class of quantum spectroscopy schemes which measure absorption and phase with a single probe. Our technique is relevant to the characterization of a wide array of chemical and biological samples, such as quantum dots and organic fluorophores, and may be useful for spectroscopic measurements that are otherwise constrained in intensity.