Extreme non-linear response of ultra-narrow optical transitions in cavity QED for laser stabilization

TL;DR

This paper investigates the use of ultra-narrow atomic transitions in cavity QED for laser stabilization, highlighting the potential for achieving extremely narrow linewidths beyond traditional methods by leveraging non-linear effects and atomic references.

Contribution

It derives fundamental limits for laser stabilization using ultra-narrow atomic lines in cavity QED, revealing potential for unprecedented laser linewidths at the microhertz level.

Findings

Laser linewidths of about 1 mHz are achievable with current lattice clock setups.

Ultimate stabilization limits could reach 1 μHz.

Non-linear effects like bistability are crucial in the high saturation regime.

Abstract

We explore the potential of direct spectroscopy of ultra-narrow optical transitions of atoms localized in an optical cavity. In contrast to stabilization against a reference cavity, which is the approach currently used for the most highly stabilized lasers, stabilization against an atomic transition does not suffer from Brownian thermal noise. Spectroscopy of ultra-narrow optical transitions in a cavity operates in a very highly saturated regime in which non-linear effects such as bistability play an important role. From the universal behavior of the Jaynes-Cummings model with dissipation, we derive the fundamental limits for laser stabilization using direct spectroscopy of ultra-narrow atomic lines. We find that with current lattice clock experiments, laser linewidths of about 1 mHz can be achieved in principle, and the ultimate limitations of this technique are at the 1 $\mu$ Hz level.