Coupling light to a nuclear spin gas with a two-photon linewidth of five millihertz

Abstract

Nuclear spins of noble gases feature extremely long coherence times but are inaccessible to optical photons. Here, we realize a coherent interface between light and noble-gas spins that is mediated by alkali atoms. We demonstrate the optical excitation of the noble-gas spins and observe the coherent back action on the light in the form of high-contrast two-photon spectra. We report on a record two-photon linewidth of 5 ± 0.7 mHz above room temperature, corresponding to a 1-min coherence time. This experiment provides a demonstration of coherent bidirectional coupling between light and noble-gas spins, rendering their long-lived spin coherence accessible for manipulations in the optical domain.

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“…Using a linearly polarized optical probe beam, we measure the collective spin of the rubidium along the truex̂ axis via its imprint on the polarization of the probe beam, which rotates after traversing the alkali medium. The polarization rotation is subsequently measured with a set of differential photodiodes in a homodyne configuration ( 44 – 46 ). While the polarized rubidium spins are initially oriented along the trueẑ axis, they are tilted by an angleθRbfalse(f=fDMfalse)=γRbbXeθXefalse∣iΓRb+fRb−fDMfalse∣Here, b Xe θ Xe is the transverse spin-exchange field.…”

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