Ultra Narrow Linewidth Frequency Reference via Measurement and Feedback

TL;DR

This paper explores a novel method for generating ultra-narrow linewidth light by coherently driving atoms in a cavity, analyzing fundamental limits for frequency stabilization, and comparing results to superradiant lasers.

Contribution

It introduces a new approach to produce spectrally pure light using coherent driving in cavity QED systems and evaluates the fundamental frequency stabilization limits.

Findings

Linewidths comparable to superradiant lasers are achievable.

Fundamental limits depend on input intensity and atom-light interaction.

Optimal conditions identified for state-of-the-art alkaline-earth atom experiments.

Abstract

The generation of very narrow linewidth light sources is of great importance in modern science. One such source is the superradiant laser, which relies on collectively interacting ultra long lived dipoles driven by incoherent light. Here we discuss a different way of generating spectrally pure light by coherently driving such dipoles inside an optical QED cavity. The light exiting the cavity carries information about the detuning between the driving light and the atomic transition, but is also affected by the noise originating from all the decoherence processes that act on the combined atom-cavity system. We calculate these effects to obtain fundamental limits for frequency estimation and stabilization across a range of values of input light intensities and atom-light interaction strengths, estimate these limits in state-of-the-art cavity experiments with alkaline-earth atoms and identify favorable operating conditions. We find that the achievable linewidths are comparable to those of the superradiant laser.