Complete temporal characterization of a single photon

TL;DR

This paper introduces a method to fully characterize the temporal mode of a single photon by measuring its autocorrelation function at multiple frequencies, enabling better quantum communication device optimization.

Contribution

The authors propose and experimentally validate a technique to determine both real and imaginary parts of a single photon's temporal density matrix, advancing quantum state characterization.

Findings

Accurately measured the temporal density matrix of single photons.

Achieved excellent agreement with theoretical models.

Demonstrated the method on photons from atomic vapor sources.

Abstract

Precise information about the temporal mode of optical states is crucial for optimizing their interaction efficiency between themselves and/or with matter in various quantum communication devices. Here we propose and experimentally demonstrate a method of determining both the real and imaginary components of a single photon's temporal density matrix by measuring the autocorrelation function of the photocurrent from a balanced homodyne detector at multiple local oscillator frequencies. We test our method on single photons heralded from biphotons generated via four-wave mixing in an atomic vapor and obtain excellent agreement with theoretical predictions for several settings.