Transverse optical pumping of spin states

Abstract

Optical pumping is an efficient method for initializing and maintaining atomic spin ensembles in a well-defined quantum spin state. Standard optical-pumping methods orient the spins by transferring photonic angular momentum to spin polarization. Generally the spins are oriented along the propagation direction of the light due to selection rules of the dipole interaction. Here we present and experimentally demonstrate that by modulating the light polarization, angular momentum perpendicular to the optical axis can be transferred efficiently to cesium vapor. The transverse pumping scheme employs transversely oriented dark states, allowing for control of the trajectory of the spins on the Bloch sphere. This new mechanism is suitable and potentially beneficial for diverse applications, particularly in quantum metrology.Optical pumping is the prevailing technique for orienting atomic spins, conveying order from polarized light onto the state of spins [1][2][3]. Many applications in precision metrology [4][5][6][7], quantum information [8][9][10], noble gas hyper-polarization [11][12][13], and searches for new physics beyond the standard model [14,15] employ optical pumping for initializing the orientation moment of the spins, that is, for pointing the spins towards a preferred direction. The required degree of polarization depends on the specific application, where optimized performance in quantum metrology is often practically achieved around 50% polarization [16][17][18]. Standard optical pumping schemes generate polarization along the propagation direction of the laser beam. These schemes include depopulation pumping [1], synchronous pumping [19][20][21], spin-exchange indirect pumping [22,23], alignment-toorientation conversion [24], and hybrid spin-exchange pumping [16]. However in various applications, it is often desired to polarize the spins along an applied magnetic field, perpendicular to the optical axis [18,[25][26][27][28]. While at extreme magnetic fields, it is possible to polarize the spins transversely [29], at moderate magnetic fields, typical to alkali-metal spins experiments for example, the pumping efficiency is rather low.Here we propose and demonstrate an optical pumping scheme for efficient spin polarization transversely to the propagation direction of the laser beam. The scheme incorporates a polarization-modulated light beam, which steers the spins in helical-like trajectories on the Bloch sphere around and along a transverse magnetic field, while gradually increasing their polarization. The scheme exhibits sharp resonances, reaching maximum efficiency when the optical modulation is resonant with the Larmor precession of the spins. We develop a simple analytical model for analyzing the experimental results and discuss the applicability of the scheme for various applications.In standard optical pumping schemes, the atomic ground state is polarized via repeated cycles of absorption and spontaneous emission. Ideally, the atoms cease to absorb the pump photons when they reach a 'dark state', whic...

Spin noise correlations in multispecies hot atomic vapors

“…The analytical calculation for the 133 Cs atom in a magnetic field of B = 0.5 G yields In Fig. 2.3 we plot the time evolution of the normalized transverse spin component of a 87 Rb atom in a magnetic field of B = 0.5 G. The mixing of the various frequencies, as indicated above, result in the quantum revival and quantum super-revival beatings.…”

“…Deeper understanding of spin noise and its relation to the collisional relaxation processes [85][86][87] paves the way towards improving quantum enhanced metrology in hot vapor systems [88][89][90][91]. Some of the modern applications of spin noise spectroscopy in hot vapors are: measurement of zero-field spin noise using magnetic pulses [92], measurement of higher order spin noise like alignment noise [93,94], spin noise measurements with time-dependent magnetic fields [95,96], demonstration of quantum random number generator using spin noise [97], effects of atomic diffusion on the spin noise spectrum [98,99] and dual-species spin noise measurements [100][101][102][103][104].…”

“…Chapter 4 is devoted to the experimental measurement of spin-noise correlations in dual species alkali vapors of 87 Rb and 133 Cs. At the beginning of the chapter we introduce the balanced polarimeter scheme and we explore the practical limitations set to it, for example by photon shot noise.…”

“…Given the size of alkali atoms and the near infra-red wavelengths of D 1 and D 2 transitions in 133 Cs and 87 Rb we can apply the dipole approximation…”

“…We have performed a precision experiment regarding spin-noise correlations in multispecies hot alkali vapors. In particular, we observe non-zero spin-noise correlations and coherence transfer effects in equilibrium between overlapping 133 Cs and 87 Rb spin ensembles, having different gyromagnetic ratios. Both observations stem from the spontaneous and incessant spin-exchange collisions that tend to couple the two atomic species through the coherent exchange of spin-polarization.…”