Observation of Purcell Effect in Electrically Coupled Cavity-Magnet System

TL;DR

This paper demonstrates the observation of the Purcell effect in a cavity-magnet hybrid system using electric-field-mediated coupling, revealing strong coupling rates and cavity modifications at very small magnetic volumes.

Contribution

It introduces a novel electric-field-mediated coupling method to observe the Purcell effect in a cavity-magnet system, with high coupling rates at small magnetic volumes.

Findings

Coupling rates up to 56 MHz observed.

Cavity photon lifetime modified by magnetic field.

Strong Purcell regime achieved despite small magnetic volume.

Abstract

We report the observation of the Purcell effect in a cavity-metallic magnet hybrid system using electric-field-mediated coupling. In this configuration, microwave-induced axial currents in the microwire induce circular magnetic fields that drive the ferromagnetic resonance (FMR) of the magnetized microwire. Field-dependent transmission and reflection spectroscopies reveal a clear cavity perturbation consistent with the Purcell regime, in which the magnetic loss rate exceeds the light-matter coupling strength. Despite the small magnetic volume ($\sim 10^{-13}\,\text{m}^3$), measurements performed at both room temperature and $T = 7$ mK show coupling rates as high as $g/2pi = 56$ MHz, one order of magnitude stronger than the one expected from conventional coupling at the magnetic antinode. Time-domain ringdown measurements directly show the magnetic-field-dependent modification of the cavity photon lifetime, in agreement with theoretical predictions. These results establish a versatile approach for coupling microwave fields to metallic magnets via geometric and electric-field-mediated interactions, opening new opportunities for hybrid cavity-magnet systems.