High cooperativity coupling of electron-spin ensembles to superconducting cavities

TL;DR

This paper demonstrates strong coupling between electron spin ensembles and superconducting cavities, enabling broadband spectroscopy and detailed spin structure analysis at millikelvin temperatures, advancing quantum memory technologies.

Contribution

It reports the first demonstration of electron spin ensemble coupling to superconducting resonators with coupling strengths exceeding cavity decay rates.

Findings

Achieved coupling strengths comparable to spin linewidths

Performed broadband spectroscopy of ruby at millikelvin temperatures

Observed hyperfine structure and spin relaxation in diamond P1 centers

Abstract

Electron spins in solids are promising candidates for quantum memories for superconducting qubits because they can have long coherence times, large collective couplings, and many quantum bits can be encoded into the spin-waves of a single ensemble. We demonstrate the coupling of electron spin ensembles to a superconducting transmission-line resonator at coupling strengths greatly exceeding the cavity decay rate and comparable to spin linewidth. We also use the enhanced coupling afforded by the small cross-section of the transmission line to perform broadband spectroscopy of ruby at millikelvin temperatures at low powers. In addition, we observe hyperfine structure in diamond P1 centers and time domain saturation-relaxation of the spins.