Spin coherence and optical properties of alkali-metal atoms in solid parahydrogen

TL;DR

This study investigates the spin coherence and optical properties of alkali-metal atoms in solid parahydrogen, revealing species-dependent coherence times and developing a theory to explain inhomogeneous broadening effects.

Contribution

The paper provides the first comprehensive experimental and theoretical analysis of spin coherence in alkali-metal atoms within solid parahydrogen, highlighting species-specific coherence times and modeling inhomogeneous broadening.

Findings

Longest ensemble T2* times reported for high-density electron spins

Significant variation in T2* times among different alkali species

Theoretical model accurately predicts observed coherence times

Abstract

We present a joint experimental and theoretical study of spin coherence properties of 39K, 85Rb, 87Rb, and 133Cs atoms trapped in a solid parahydrogen matrix. We use optical pumping to prepare the spin states of the implanted atoms and circular dichroism to measure their spin states. Optical pumping signals show order-of-magnitude differences depending on both matrix growth conditions and atomic species. We measure the ensemble transverse relaxation times (T2*) of the spin states of the alkali-metal atoms. Different alkali species exhibit dramatically different T2* times, ranging from sub-microsecond coherence times for high mF states of 87Rb, to ~100 microseconds for 39K. These are the longest ensemble T2* times reported for an electron spin system at high densities (n > 10^16 cm^-3). To interpret these observations, we develop a theory of inhomogenous broadening of hyperfine transitions of ^2S atoms in weakly-interacting solid matrices. Our calculated ensemble transverse relaxation times agree well with experiment, and suggest ways to longer coherence times in future work.