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

Abstract

We present a joint experimental and theoretical study of spin coherence properties of 39 K, 85 Rb, 87 Rb, and 133 Cs 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 (T * 2 ) of the spin states of the alkali-metal atoms. Different alkali species exhibit dramatically different T * 2 times, ranging from sub-microsecond coherence times for high mF states of 87 Rb, to ∼ 10 2 microseconds for 39 K. These are the longest ensemble T * 2 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 2 S 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. arXiv:1910.05430v1 [physics.atom-ph]

Ultralong Spin-Coherence Times for Rubidium Atoms in Solid Parahydrogen via Dynamical Decoupling

“…The longest measured Hahn-echo T 2 times of 2 ms are significantly shorter than the longitudinal relaxation time T 1 . Under typical probe beam conditions used in this paper we observe a T 1 of ∼ 0.2 s, reduced from the 1 s T 1 's observed with the probe beam at a lower duty cycle [1,3]. The probe's intensity and duty cycle are varied to verify that it has a negligible effect on T 2 .…”

“…The dependence of T 2 on species and superposition is very different than what was previously observed for the ensemble dephasing time T * 2 . First, 133 Cs has a T * 2 roughly one order of magnitude shorter than 85 Rb [3]. Second, for 85 Rb, the (+1, −1) superposition had a significantly longer T * 2 than the (0, −1) superposition [2].…”

“…Optical pumping and detection of the spin states of ensembles of alkali atoms trapped in solid parahydrogen has been previously demonstrated [1]. The atoms exhibit excellent ensemble transverse spin relaxation properties, with a long spin dephasing time T * 2 [2,3]. In this work, we use Hahn spin echo [4,5] and alternating-phase Carr-Purcell pulse sequences [6] to measure the spin decoherence time T 2 .…”

“…We trap alkali-metal atoms in a solid parahydrogen matrix at a temperature of ∼ 3 K, as described in references [1,3]. The samples are grown by vacuum deposition onto a cryogenic sapphire window.…”

“…The vast majority of data we present is for rubidum atoms, due to their favorable properties as detailed in Ref. [3]. We can vary the alkali-metal atom and orthohydrogen density in the matrix.…”