Synchronization of Active Atomic Clocks via Quantum and Classical Channels

TL;DR

This paper investigates the synchronization behavior of two active atomic clocks coupled via quantum and classical channels, revealing distinct phase diagrams and comparing different coupling mechanisms to enhance atomic clock coherence.

Contribution

It demonstrates that synchronization persists in cascaded setups with unique phase diagrams and compares quantum versus classical coupling methods for atomic clock synchronization.

Findings

Synchronization occurs in cascaded atomic clocks with distinct phase diagrams.

Quantum and classical channels produce different synchronization characteristics.

Classical feedback can effectively synchronize atomic clocks via phase-sensitive measurements.

Abstract

Superradiant lasers based on atomic ensembles exhibiting ultra-narrow optical transitions can emit light of unprecedented spectral purity and may serve as active atomic clocks. We consider two frequency-detuned active atomic clocks, which are coupled in a cascaded setup, i.e. as master & slave lasers, and study the synchronization of the slave to the master clock. In a setup where both atomic ensembles are coupled to a common cavity mode such synchronization phenomena have been predicted by Xu et al. [Phys. Rev. Lett. 113, 154101 (2014)] and experimentally observed by Weiner et al. [arXiv:1503.06464 (2015)]. Here we demonstrate that synchronization still occurs in cascaded setups but exhibits distinctly different phase diagrams. We study the characteristics of synchronization in comparison to the case of coupling through a common cavity. We also consider synchronization through a classical channel where light of the master laser is measured phase sensitively and the slave laser is injection locked by feedback and compare to the results achievable by coupling through quantum channels.