Superradiance on the milliHertz linewidth strontium clock transition

TL;DR

This paper demonstrates superradiant emission from a strontium atomic ensemble on a millihertz linewidth clock transition, showing potential for highly stable, cavity-immune atomic clocks.

Contribution

It presents the first experimental realization of superradiant lasing on a millihertz linewidth optical clock transition in strontium atoms, including seeding and interference techniques.

Findings

Achieved over 10,000-fold collective emission enhancement

Demonstrated seeding of superradiant emission

Observed interference between two lasing transitions

Abstract

Today's best atomic clocks are limited by frequency noise on the lasers used to interrogate the atoms. A proposed solution to this problem is to create a superradiant laser using an optical clock transition as its gain medium. This laser would act as an active atomic clock, and would be highly immune to the fluctuations in reference cavity length that limit today's best lasers. Here, we demonstrate and characterize superradiant emission from the mHz linewidth clock transition in an ensemble of laser-cooled $^{87}$Sr atoms trapped within a high-finesse optical cavity. We measure a collective enhancement of the emission rate into the cavity mode by a factor of more than 10,000 compared to independently radiating atoms. We also demonstrate a method for seeding superradiant emission and observe interference between two independent transitions lasing simultaneously. We use this interference to characterize the relative spectral properties of the two lasing sub-ensembles.