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.
@article{arxiv.1910.05430,
title = {Spin coherence and optical properties of alkali-metal atoms in solid parahydrogen},
author = {Sunil Upadhyay and Ugne Dargyte and Vsevolod D. Dergachev and Robert P. Prater and Sergey A. Varganov and Timur V. Tscherbul and David Patterson and Jonathan D. Weinstein},
journal= {arXiv preprint arXiv:1910.05430},
year = {2019}
}