Tomography of a High-Purity Narrowband Photon From a Transient Atomic Collective Excitation

TL;DR

This paper reports the generation and full quantum state characterization of high-purity, narrow-bandwidth single photons from a transient atomic collective excitation, suitable for quantum memory and light-atom interfaces.

Contribution

It introduces a method for efficiently producing and fully reconstructing the quantum state of narrowband single photons from atomic vapors, advancing quantum light sources.

Findings

Wigner function reaches zero without correction

High spectral brightness of the photon source

Compatibility with atomic quantum memories

Abstract

We demonstrate the efficient heralded generation of high purity narrow-bandwidth single photons from a transient collective spin excitation in a hot atomic vapour cell. Employing optical homodyne tomography, we fully reconstruct the density matrix of the generated photon and observe a Wigner function reaching the zero value without correcting for any inefficiencies. The narrow bandwidth of the photon produced is accompanied by a high generation rate yielding a high spectral brightness. The source is therefore compatible with atomic-based quantum memories as well as other applications in light-atom interfacing. This work paves the way to preparing and measuring arbitrary superposition states of collective atomic excitations.