# Self-induced superradiant masing

## TL;DR

This paper shows that direct spin interactions in diamond can drive superradiant masing, leading to pulsed and continuous microwave emissions.

## Contribution

The study demonstrates that dipole–dipole interactions, not light-mediated ones, can drive superradiance in a spin-cavity system.

## Key findings

- A train of emission pulses followed by quasi-continuous masing was observed after an initial superradiant burst.
- Spectral hole refilling redistributes spin inversion into the cavity-resonant superradiant window.
- Microscopic simulations confirm that dipole–dipole interactions drive the observed superradiant behavior.

## Abstract

In cavity quantum electrodynamics and particularly superradiance, emitters are typically assumed to be independent, interacting only through light shared via a common mode. Although such photon-mediated interactions lead to a wide range of collective optical effects, direct dipole–dipole interactions within the emitter ensemble are generally viewed as a source of decoherence. Here we report the role of direct spin–spin interactions as a drive for the superradiant dynamics of a hybrid system of nitrogen-vacancy centre spins in a diamond coupled to a superconducting microwave cavity. After an initial fast superradiant burst, we observe a train of subsequent emission pulses followed by quasi-continuous masing for up to one millisecond. We show that this behaviour arises from spectral hole refilling, where spin inversion is redistributed into the superradiant window of spins resonant with the cavity. We report measurements that exclude other cavity-related effects and perform microscopic simulations that confirm that the observed behaviour is driven by dipole–dipole interactions between the spins. These findings open pathways for exploring complex spin–spin interactions in dense disordered systems and offer possibilities for ultranarrow-linewidth solid-state superradiant masers powered purely by microwave-driven spin control.

Superradiance is usually driven by light-mediated couplings, leaving the role of direct emitter interactions unclear. Now, it is shown that dipole–dipole interactions in diamond spins drive self-induced pulsed and continuous superradiant masing.