# Off resonance coupling between a cavity mode and an ensemble of driven spins

## TL;DR

This paper investigates how a driven spin ensemble influences the damping of a superconducting cavity mode, revealing off-resonance coupling effects and comparing experimental results with theoretical models.

## Contribution

It demonstrates the off-resonance coupling between a cavity and driven spins, showing how the driven spins modify the cavity's effective damping rate.

## Key findings

- The cavity's damping rate is shifted by driven spins.
- The shift is due to the retarded response of the cavity to the spins.
- Experimental results agree with theoretical predictions.

## Abstract

We study the interaction between a superconducting cavity and a spin ensemble. The response of a cavity mode is monitored while simultaneously the spins are driven at a frequency close to their Larmor frequency, which is tuned to a value much higher than the cavity resonance. We experimentally find that the effective damping rate of the cavity mode is shifted by the driven spins. The measured shift in the damping rate is attributed to the retarded response of the cavity mode to the driven spins. The experimental results are compared with theoretical predictions and fair agreement is found.