Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime

TL;DR

This study investigates the spin coherence properties of rare-earth doped crystals at high cooperativity, identifying decoherence mechanisms and demonstrating methods to enhance coherence times, crucial for quantum interface applications.

Contribution

It provides new insights into decoherence mechanisms in high-cooperativity rare-earth systems and demonstrates techniques to extend spin coherence times, including using clock transitions.

Findings

Identified decoherence mechanisms like instantaneous diffusion and spectral diffusion.

Showed magnetic fields and low g-factor transitions can mitigate spectral diffusion.

Achieved spin coherence times up to 6 ms using clock transitions in Yb.

Abstract

Rare-earth doped crystals have long coherence times and the potential to provide quantum interfaces between microwave and optical photons. Such applications benefit from a high cooperativity between the spin ensemble and a microwave cavity -- this motivates an increase in the rare earth ion concentration which in turn impacts the spin coherence lifetime. We measure spin dynamics of two rare-earth spin species, $^{145}$Nd and Yb doped into Y$_{2}$SiO$_{5}$, coupled to a planar microwave resonator in the high cooperativity regime, in the temperature range 1.2 K to 14 mK. We identify relevant decoherence mechanisms including instantaneous diffusion arising from resonant spins and temperature-dependent spectral diffusion from impurity electron and nuclear spins in the environment. We explore two methods to mitigate the effects of spectral diffusion in the Yb system in the low-temperature limit, first, using magnetic fields of up to 1 T to suppress impurity spin dynamics and, second, using transitions with low effective g-factors to reduce sensitivity to such dynamics. Finally, we demonstrate how the `clock transition' present in the $^{171}$Yb system at zero field can be used to increase coherence times up to $T_{2} = 6(1)$ ms.