Control of conditional quantum beats in cavity QED: amplitude decoherence and phase shifts

TL;DR

This paper presents a feedback protocol in cavity QED to preserve quantum coherence and enhance quantum beat signals by controlling drive and phase evolution, both theoretically and experimentally.

Contribution

It introduces a simple feedback method to reduce decoherence in cavity QED systems, improving quantum beat amplitude and phase stability.

Findings

Quantum beat amplitude more than doubled with feedback

Decoherence caused by Rayleigh scattering mitigated

Phase shifts accurately controlled during dark evolution

Abstract

We implement a simple feedback mechanism on a two-mode cavity QED system to preserve the Zeeman coherence of a ground state superposition that generates quantum beats on the second-order correlation function. Our investigation includes theoretical and experimental studies that show how to prevent a shift away from the Larmor frequency and associated decoherence caused by Rayleigh scattering. The protocol consists of turning off the drive of the system after the detection of a first photon and letting it evolve in the dark. Turning the drive back on after a pre-set time reveals a phase accumulated only from Larmor precession, with the amplitude of the quantum beat more than a factor of two larger than with continuous drive.