Abstract
We report noninvasive detection of spin coherence in a collection of Raman-driven cold atoms using dispersive Faraday rotation fluctuation measurements, which opens possibilities of probing spin correlations in quantum gases and other similar systems. We demonstrate five orders of magnitude enhancement of the measured signal strength as compared to 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 $\ensuremath{\sim}10{\phantom{\rule{0.16em}{0ex}}}^{9}/{\mathrm{cm}}^{3}$ is of the order of $3\phantom{\rule{0.16em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.16em}{0ex}}10{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at 150 $\ensuremath{\mu}\mathrm{K}$, two orders of magnitude less than $3\phantom{\rule{0.16em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.16em}{0ex}}10{\phantom{\rule{0.16em}{0ex}}}^{5}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ of that of a thermal atomic vapor with atom number density $\ensuremath{\sim}10{\phantom{\rule{0.16em}{0ex}}}^{12}/{\mathrm{cm}}^{3}$ at 373 K.
Highlights
The prospects of noninvasive measurement schemes have found increasing research interest in recent decades to detect equilibrium and nonequilibrium properties of microscopic and mesoscopic quantum system [1,2]
We demonstrate an enhancement of the Faraday rotation fluctuation signal by five orders of magnitude in thermal rubidium atoms driven by coherent Raman radiation fields
We show in detail the dependence of the spin coherence on Raman fields’ polarization state
Summary
The prospects of noninvasive measurement schemes have found increasing research interest in recent decades to detect equilibrium and nonequilibrium properties of microscopic and mesoscopic quantum system [1,2]. In the absence of finite magnetization along the light propagation direction, dynamical magnetic properties of the sample can be found from the temporal fluctuations of dispersive Faraday rotation. Such Faraday rotation noises have been extensively studied within the spin noise spectroscopy (SNS) [14,15,16] technique to detect the intrinsic spin dynamics in atomic vapors [17,18,19,20], semiconductor heterostructures [21], quantum dots [22,23], spin-exchange collisions [24,25], and exciton-polaritons [26,27]. We theoretically develop and experimentally realize this measurement method to demonstrate an enhancement of the signal strength as much as 105 in thermal atoms using coherent Raman drive, which allows us to detect spin coherence in ultracold atoms
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