Superradiant active optical atomic clocks: motivations and current challenges

TL;DR

This paper reviews the motivations, recent developments, and challenges in creating active optical atomic clocks, which aim to surpass passive clocks by leveraging atomic emission stability.

Contribution

It provides a comprehensive overview of the current state, motivations, and technical challenges in developing superradiant active optical atomic clocks.

Findings

Active optical clocks can potentially achieve higher stability than passive ones.

Superradiant emission enables more stable frequency standards.

Current challenges include technical implementation and maintaining coherence.

Abstract

Current state-of-the-art frequency standards are passive optical atomic clocks where the frequency of an optical resonator is stabilized to a narrow atomic transition. Passive clocks have achieved unprecedented stabilities of 6.6 x 10--19 over one hour of averaging time [1]. However, they face intrinsic limitations, particularly due to thermal and mechanical fluctuations of the local oscillator. To surpass the limitations of the passive clocks and go beyond the state-of-the-art, the idea of building active optical atomic clocks emerges. These clocks would be optical counterparts of hydrogen masers, with the emitted frequency defined by the atomic transition and therefore inherently stable against cavity instabilities. This paper discusses the latest developments and future prospects in the field of active optical atomic clocks.