Cavity Sub- and Superradiance Enhanced Ramsey Spectroscopy

TL;DR

This paper introduces a cavity-based Ramsey spectroscopy method that reduces interaction-induced shifts and superradiance in dense ultra-cold atom ensembles, enhancing measurement precision through a novel geometry and collective excitation control.

Contribution

It proposes a new cavity geometry with controlled collective excitation to suppress superradiance and improve Ramsey spectroscopy accuracy in dense atomic ensembles.

Findings

Suppression of superradiance via controlled collective spin states.

Observation of regular self-pulsing in cavity output under continuous illumination.

Qualitative agreement between cumulant expansion and quantum simulations.

Abstract

Ramsey spectroscopy in large, dense ensembles of ultra-cold atoms trapped in optical lattices suffers from dipole-dipole interaction induced shifts and collective superradiance limiting its precision and accuracy. We propose a novel geometry implementing fast signal readout with minimal heating for large atom numbers at lower densities via an optical cavity operated in the weak single atom but strong collective coupling regime. The key idea is controlled collective transverse $\pi/2$-excitation of the atoms to prepare a macroscopic collective spin protected from cavity superradiance. This requires that the two halves of the atomic ensemble are coupled to the cavity mode with opposite phase, which is naturally realized for a homogeneously filled volume covering odd and even sites of the cavity mode along the cavity axis. The origin of the superior precision can be traced back to destructive interference among sub-ensembles in the complex nonlinear collective atom field dynamics. In the same configuration we find surprising regular self-pulsing of the cavity output for suitable continuous illumination. Our simulations for large atom numbers employing a cumulant expansion are qualitatively confirmed by a full quantum treatment of smaller ensembles.