Detection of Spin Coherence in Cold Atoms via Faraday Rotation Fluctuations

Abstract

We report non-invasive detection of spin coherence in a collection of Raman-driven cold atoms using dispersive Faraday rotation fluctuation measurements, which opens up new possibilities of probing spin correlations in quantum gases and other similar systems. We demonstrate five orders of magnitude enhancement of the measured signal strength than the traditional spin noise spectroscopy with thermal atoms in equilibrium. Our observations are in good agreement with the comprehensive theoretical modeling of the driven atoms at various temperatures. The extracted spin relaxation rate of cold rubidium atoms with atom number density ∼10 9 /cm 3 is of the order of 2π×0.5 kHz at 150 µK, two orders of magnitude less than ∼ 2π×50 kHz of a thermal atomic vapor with atom number density ∼10 12 /cm 3 at 373 K.

Collision-induced spin noise

“…Therefore, our technique is well suited to studying collisions at microscopic scales, which are now the focus of many studies in nanoscale sciences [49], such as local atom-surface collisions [48,55]. Moreover, spin-noise techniques have been recently demonstrated in cold atoms with the capability of avoiding unwanted perturbations [56], such as extra heating effects and atom loss caused by laser pumping [57]. Thus, our technique provides a possible way for studying non-perturbative cold atom-molecule collisions [58].…”