We explore the applications of spin noise spectroscopy (SNS) for detection of the spin properties of atomic ensembles in and out of equilibrium. In SNS, a linearly polarized far-detuned probe beam on passing through an ensemble of atomic spins acquires the information of the spin correlations of the system which is extracted using its time-resolved Faraday-rotation noise. We measure various atomic, magnetic and sub-atomic properties as well as perform precision magnetometry using SNS in rubidium atomic vapor in thermal equilibrium. Thereafter, we manipulate the relative spin populations between different ground state hyperfine levels of rubidium by controlled optical pumping which drives the system out of equilibrium. We then apply SNS to probe such spin imbalance nonperturbatively. We further use this driven atomic vapor to demonstrate that SNS can have better resolution than typical absorption spectroscopy in detecting spectral lines in the presence of various spectral broadening mechanisms. I. INTRODUCTIONControl of spin population and its simultaneous nondestructive detection play a crucial role in diverse scientific fields such as atom interferometry [1], precision mag- netometry [2], atomic clocks [3], quantum simulation [4]and quantum information processing [5]. While external magnetic fields and optical pumping can be used to manipulate the spin polarization and population in an atomic system, spin noise spectroscopy (SNS) [6-8] provides a means of the detection of such spin coherences * mswar@rri.res.in † srishic@rri.res.in ‡ sanjukta@rri.res.in mal agitation of the electrons in an electrical conductor [9], the intensity fluctuations in the emission of random lasers [10,11] and the stochastic fluctuations in clonal cellular constituents [12,13].The optical SNS technique has been developed by Aleksandrov and Zapasskii [14] to passively probe intrinsic spin fluctuations or magnetization noise in a thermal ensemble of spins. These spin ensembles can be made of electron spins in atomic systems and spins of electrons or holes in semiconductors and other solid-state materials.A study of SNS in alkali atomic vapor of Rb and potassium (K) in thermodynamic equilibrium was carried out by [15], which indicated that the electronic and nuclear gfactors, isotope abundance ratios, nuclear moments and hyperfine splittings could be measured. The first successful application of SNS to a solid-state system was performed by [16], for measuring the electron's Lande gfactor and spin relaxation time in a n-doped GaAs semiconductor. There has been significant progress in the recent years to extend the applicability of SNS [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32].First, we perform the SNS of Rb atoms in thermal equilibrium. We demonstrate accurate measurements of several physical quantities such as electron's g-factor, nuclear g-factor, isotope abundance ratios, and develop precision magnetometry with our thermal Rb vapor in the presence of a static magnetic field perpendicular to probe laser. While prio...

No 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.

No abstract

We report our experimental measurements and theoretical analysis of the position response function of cold atoms in a magneto-optical trap (MOT) by applying a transient homogeneous magnetic field as a perturbing force. We observe a transition from a damped oscillatory motion to an over-damped relaxation, stemming from a competition between the viscous drag provided by the optical molasses and the restoring force of the MOT. Our observations are in agreement with the predictions of our model based on the Langevin equation. We also study the diffusion of the atomic cloud in the optical molasses and find the measured value of diffusion coefficient matching with the prediction of our theoretical model.