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arXiv:1811.10535 · Physical review. B./Physical review. B

Enhanced spin coherence of rubidium atoms in solid parahydrogen

Sunil Kumar Upadhyay, Ugne Dargyte, Robert Prater, Vsevolod D. Dergachev, Sergey A. Varganov, Timur V. Tscherbul, David Patterson, Jonathan D. Weinstein

Published Jul 15, 2019• 12 citations

Abstract

We measure the transverse relaxation of the spin state of an ensemble of ground-state rubidium atoms trapped in solid parahydrogen at cryogenic temperatures. We find the spin dephasing time of the ensemble (${T}_{2}^{*}$) is limited by inhomogeneous broadening. We determine that this broadening is dominated by electrostaticlike interactions with the host matrix, and can be reduced by preparing nonclassical spin superposition states. Driving these superposition states gives significantly narrower electron paramagnetic resonance lines and the longest reported electron spin ${T}_{2}^{*}$ in any solid-phase system other than solid helium.

DOI: 10.1103/physrevb.100.024106

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We measure the transverse relaxation of the spin state of an ensemble of ground-state rubidium atoms trapped in solid parahydrogen at cryogenic temperatures. We find the spin dephasing time of the ensemble (

{T}_{2}^{*}

) is limited by inhomogeneous broadening. We determine that this broadening is dominated by electrostaticlike interactions with the host matrix, and can be reduced by preparing nonclassical spin superposition states. Driving these superposition states gives significantly narrower electron paramagnetic resonance lines and the longest reported electron spin

{T}_{2}^{*}

in any solid-phase system other than solid helium.

Coherence time is an essential parameter for quantum sensing, quantum information, and quantum computation. In this work, we demonstrate electron spin coherence times as long as 0.1 s for an ensemble of rubidium atoms trapped in a solid parahydrogen matrix. We explore the underlying physics limiting the coherence time. The properties of these matrix isolated atoms are very promising for future applications, including quantum sensing of nuclear spins. If combined with efficient single-atom readout, this would enable NMR and magnetic resonance imaging of single molecules cotrapped with alkali-metal atom quantum sensors within a parahydrogen matrix.

We have grown crystals of solid parahydrogen using a single closed-cycle cryostat. We have doped the crystals with rubidium atoms at densities on the order of 10^{17} cm^{-3} and used optical pumping to polarize the spin state of the implanted atoms. The optical spectrum of the rubidium atoms shows larger broadening than previous work in which the rubidium was implanted in solid argon or neon. However, the optical pumping behavior is significantly improved, with both a larger optical pumping signal and a longer longitudinal relaxation time. The spin relaxation time shows a strong dependence on orthohydrogen impurity levels in the crystal, as well as the applied magnetic field. Current performance is comparable to state-of-the-art solid state systems at comparable spin densities, with potential for improvement at higher parahydrogen purities.

It is known from ensemble measurements that rubidium atoms trapped in solid parahydrogen have favorable properties for quantum sensing of magnetic fields. To use a single rubidium atom as a quantum sensor requires a technique capable of efficiently measuring the internal state of a single atom, such as laser-induced fluorescence. In this work we search for laser-induced fluorescence from ensembles of rubidium atoms trapped in solid parahydrogen and, separately, in solid neon. In parahydrogen we find no evidence of fluorescence over the range explored, and we place upper limits on the radiative branching ratio. In neon, we observe laser-induced fluorescence, measure the spectrum of the emitted light, and measure the excited-state lifetime in the matrix. Bleaching of atoms from the excitation light is also reported.