Active optical frequency standards using cold atoms: perspectives and challenges

TL;DR

This paper explores active optical frequency standards using cold atoms, focusing on superradiant lasers and their potential for higher stability than traditional cavity-stabilized lasers, discussing approaches, challenges, and key parameters.

Contribution

It reviews existing approaches and discusses the parameters and challenges for realizing high-stability active optical frequency standards with cold atoms.

Findings

Superradiant lasers can surpass traditional laser stability.

Optical lattice and atomic beam lasers are promising approaches.

Key challenges include atomic ensemble parameters and practical implementation issues.

Abstract

We consider various approaches to the creation of a high-stability active optical frequency standard, where the atomic ensemble itself produces a highly stable and accurate frequency signal. The short-time frequency stability of such standards may overcome the stability of lasers stabilized to macroscopic cavities which are used as local oscillators in the modern optical frequency standard systems. The main idea is to create a "superradiant" laser operating deep in the bad cavity regime, where the decay rate of the cavity field significantly exceeds the decoherence rate of the lasing transition. Two main approaches towards the realization of an active optical frequency standard have been proposed already: the optical lattice laser, and the atomic beam laser. We consider these and some alternative approaches, and discuss the parameters for atomic ensembles necessary to attain the metrology relevant level of short-time frequency stability, and various effects and main challenges critical for practical implementations.