Active optical clock based on four-level quantum system

TL;DR

This paper proposes a four-level quantum system scheme for active optical clocks, aiming to improve accuracy and stability by overcoming limitations of two- and three-level systems, and discusses a rubidium-based implementation capable of producing ultra-narrow linewidth laser output.

Contribution

The paper introduces a novel four-level quantum system scheme for active optical clocks, reducing limitations faced by previous systems and providing a practical rubidium-based implementation.

Findings

Population inversion achieved in 1 microsecond

Laser with linewidth narrower than 1 Hz theoretically possible

Experimental setup designed for realization

Abstract

Active optical clock, a new conception of atomic clock, has been proposed recently. In this report, we propose a scheme of active optical clock based on four-level quantum system. The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam. To three-level quantum system, they are mainly limited by light shift of pumping laser field. These limitations can be avoided effectively by applying the scheme proposed here. Rubidium atom four-level quantum system, as a typical example, is discussed in this paper. The population inversion between $6S_{1/2}$ and $5P_{3/2}$ states can be built up at a time scale of $10^{-6}$s. With the mechanism of active optical clock, in which the cavity mode linewidth is much wider than that of the laser gain profile, it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory. An experimental configuration is designed to realize this active optical clock.