Remnants of semiclassical bistability in the few-photon regime of cavity QED

TL;DR

This study demonstrates that even in the quantum regime of cavity QED with about 10 photons, remnants of semiclassical bistability persist, showing metastable states and hysteresis despite quantum fluctuations destabilizing true bistability.

Contribution

The paper provides experimental evidence of residual semiclassical bistability features in the few-photon regime of cavity QED, bridging classical and quantum optical behaviors.

Findings

Metastable states with finite lifetimes observed

Hysteretic response detected under modulated drive

Quantum fluctuations destabilize true bistability

Abstract

Broadband homodyne detection of the light transmitted by a Fabry-Perot cavity containing a strongly-coupled $^{133}$Cs atom is used to probe the dynamic optical response in a regime where semiclassical theory predicts bistability but strong quantum corrections should apply. While quantum fluctuations destabilize true equilibrium bistability, our observations confirm the existence of metastable states with finite lifetimes and a hysteretic response is apparent when the optical drive is modulated on comparable timescales. Our experiment elucidates remnant semiclassical behavior in the attojoule ($\sim10$ photon) regime of single-atom cavity QED, of potential significance for ultra-low power photonic signal processing.