# Floquet maser

## TL;DR

This paper demonstrates a novel Floquet maser using periodically driven 129Xe gas, revealing multi-mode oscillations at Floquet transition frequencies, and achieving ultra-sensitive magnetic field measurements with potential applications in dark matter detection.

## Contribution

It introduces the first Floquet maser system, extending maser technology to periodically driven quantum systems and enabling new sensing capabilities.

## Key findings

- Observed multi-mode maser oscillations at Floquet transition frequencies
- Achieved femtotesla-level magnetic field sensitivity in the low-frequency range
- Extended maser techniques to Floquet systems, opening new research and application avenues

## Abstract

The invention of the maser stimulated many revolutionary technologies such as lasers and atomic clocks. Despite enormous progress, the realizations of masers are still confined to a limited variety of systems, in particular, the physics of masers remains unexplored in periodically driven (Floquet) systems, which are generally defined by time-periodic Hamiltonians and enable to observe many exotic phenomena such as time crystals. Here we investigate the Floquet system of periodically driven 129Xe gas under damping feedback, and surprisingly observe a multi-mode maser that oscillates at frequencies of transitions between Floquet states. Our findings extend maser techniques to Floquet systems, and open a new avenue to probe Floquet phenomena unaffected by decoherence, enabling a new class of maser sensors. As a first application, our maser offers a unique capability of measuring low-frequency (1-100 mHz) magnetic fields with femtotesla-level sensitivity, which is significantly better than state-of-the-art magnetometers, and can be immediately applied to, for example, ultralight dark matter searches.