Stimulated resonant spin amplification reveals millisecond electron spin coherence time of rare-earth ions in solids

TL;DR

This paper demonstrates a method to measure millisecond electron spin coherence times in rare-earth ions within solids by using stimulated resonant spin amplification, overcoming inhomogeneity effects.

Contribution

It introduces a combined rf and optical pulse technique to decouple spin coherence from inhomogeneous broadening, enabling precise measurement of long $T_2$ times.

Findings

Measured 50 Hz electron spin resonance in Ce$^{3+}$ ions in YAG.

Achieved millisecond-long $T_2$ coherence times.

Inhomogeneous dephasing time $T_2^*$ is only 25 ns.

Abstract

The inhomogeneity of an electron spin ensemble as well as fluctuating environment acting upon individual spins drastically shorten the spin coherence time $T_2$ and hinder coherent spin manipulation. We show that this problem can be solved by the simultaneous application of a radiofrequency (rf) field, which stimulates coherent spin precession decoupled from an inhomogeneous environment, and periodic optical pulses, which amplify this precession. The resulting resonance, taking place when the rf field frequency approaches the laser pulse repetition frequency, has a width determined by the spin coherence time $T_2$ that is free from the inhomogeneity effects. We measure a 50-Hz-narrow electron spin resonance and milliseconds-long $T_2$ for electrons in the ground state of Ce$^{3+}$ ions in the YAG lattice at low temperatures, while the inhomogeneous spin dephasing time $T_2^*$ is only 25 ns. This study paves the way to coherent optical manipulation in spin systems decoupled from their inhomogeneous environment.