Cavity QED with magnetically coupled collective spin states

TL;DR

This paper demonstrates strong coupling between nitrogen-vacancy center spins in diamond and a superconducting microwave resonator, revealing collective effects, hyperfine interactions, and non-destructive spin relaxation measurements at millikelvin temperatures.

Contribution

It provides the first direct observation of the collective coupling scaling and measures hyperfine interactions, advancing quantum memory research with NV centers.

Findings

Collective coupling strength scales with the square root of the number of spins.

Hyperfine coupling to 13C nuclear spins is observed.

Relaxation time T1 is measured non-destructively at millikelvin temperatures.

Abstract

We report strong coupling between an ensemble of nitrogen-vacancy center electron spins in diamond and a superconducting microwave coplanar waveguide resonator. The characteristic scaling of the collective coupling strength with the square root of the number of emitters is observed directly. Additionally, we measure hyperfine coupling to 13C nuclear spins, which is a first step towards a nuclear ensemble quantum memory. Using the dispersive shift of the cavity resonance frequency, we measure the relaxation time T1 of the NV center at millikelvin temperatures in a non-destructive way.