Spontaneous creation and persistence of ground-state coherence in a resonantly driven intra-cavity atomic ensemble

TL;DR

This paper reports the observation of spontaneous ground-state coherence and quantum beats in an intracavity Rb atomic ensemble, demonstrating robustness against perturbations and elucidating interference mechanisms.

Contribution

It provides a comprehensive experimental and theoretical analysis of quantum beats and coherence creation in a cavity QED system, including effects of imperfections and multi-atom interference.

Findings

Quantum beats observed in photon-photon correlations.

Robustness of coherence against spontaneous emission.

Identification of single-atom and multi-atom interference pathways.

Abstract

The spontaneous creation and persistence of ground-state coherence in an ensemble of intracavity Rb atoms has been observed as a quantum beat. Our system realizes a quantum eraser, where the detection of a first photon prepares a superposition of ground-state Zeeman sublevels, while detection of a second erases the stored information. Beats appear in the time-delayed photon-photon coincidence rate (intensity correlation function). We study the beats theoretically and experimentally as a function of system parameters, and find them remarkably robust against perturbations such as spontaneous emission. Although beats arise most simply through single-atom-mediated quantum interference, scattering pathways involving pairs of atoms interfere also in our intracavity experiment. We present a detailed model which identifies all sources of interference and accounts for experimental realities such as imperfect pre-pumping of the atomic beam, cavity birefringence, and the transit of atoms across the cavity mode.