Tomography of the temporal-spectral state of subnatural-linewidth single photons from atomic ensembles

TL;DR

This paper demonstrates the complete characterization of the temporal mode of subnatural-linewidth single photons from atomic ensembles using heterodyne and homodyne detection, revealing their pure temporal-spectral state.

Contribution

It is the first to fully reconstruct the temporal mode function of such photons, advancing quantum photonics characterization techniques.

Findings

Recovered the temporal density matrix of single photons.

Verified the pure temporal-spectral state through autocorrelation measurements.

Demonstrated heterodyne detection as a tool for full temporal mode reconstruction.

Abstract

Subnatural-linewidth single-photon source is a potential candidate for exploring the time degree of freedom in photonic quantum information science. This type of single-photon source has been demonstrated to be generated and reshaped in atomic ensembles without any external cavity or filter, and is typically characterized through photon-counting technology. However, the full complex temporal mode function(TMF) of the photon source is not able to be revealed from direct photon counting measurement. Here, for the first time, we demonstrate the complete temporal mode of the subnatural-linewidth single photons generated from a cold atomic cloud. Through heterodyne detection between the single photon and a local oscillator with various central frequencies, we recover the temporal density matrix of the single photons at resolvable time bins. Further we demonstrate that the reduced autocorrelation function measured through homodyne detection perfectly reveals the pure temporal-spectral state of the subnatural-linewidth single photons.