# Lasing by driven atoms-cavity system in collective strong coupling regime

## TL;DR

This paper demonstrates that driven cold atoms in a strongly coupled cavity can produce lasing without a seed laser, with potential applications in precision measurement and quantum optics.

## Contribution

It provides the first experimental observation of lasing in a driven atoms-cavity system under collective strong coupling, supported by theoretical modeling.

## Key findings

- Lasing observed with vacuum Rabi splitting in the system
- Lasing threshold, polarization purity, and line narrowing demonstrated
- Continuous operation without seed laser achieved

## Abstract

The interaction of laser cooled and trapped atoms with resonant light is limited by the linewidth of the excited state of the atom. Another precise optical oscillator is an optical Fabry-P\'erot cavity. The combining of cold atoms with optical oscillators is emerging as an area with great potential for precision measurements and the creation of versatile quantum optics systems. Here we show that when driven atoms are in the collectively strongly coupled regime with the cavity, exhibiting vacuum Rabi splitting (VRS), lasing is observed for the emitted light, red detuned from atomic transition. This is demonstrated experimentally by the observation of a lasing threshold, polarisation purity, mode purity, and line narrowing. The laser is created spontaneously by the atomic emission into the cavity mode, which stimulates cavity emission, and is capable of operating continuously without a seed laser. The gain mechanism is understood by theoretical modelling and illustrates why the observed lasing is generic to the coupled system. This opens up a range of possibilities of using the phenomenon for a variety of new measurements.