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Physical Review A

Coherence-induced population redistribution in optical pumping

Yehuda Nafcha, M. Rosenbluh, Pierre‐Luc Tremblay, Claude Jacques

Published Oct 1, 1995• 5 citations
Publisher

Abstract

We present experimental and theoretical investigations of the ground-state levels of the Cs cycling transition. We show that in such multilevel nondegenerate systems, the populations of the extreme Zeeman sublevels, under optical pumping, can have asymmetric (``dispersive'') line shapes as a function of laser frequency. A density-matrix model which takes into account optical, Zeeman, and hyperfine coherences, and allows for a fluctuating laser field, correctly predicts the experimental observations. A comparison of the density-matrix model with a rate-equation model demonstrates the role of coherences in the population distribution. Investigation of the effect theoretically and experimentally for \ensuremath{\sigma} and \ensuremath{\pi} laser polarizations is presented in the paper.

DOI
10.1103/physreva.52.3216

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Physical Review A•Jul 1, 1993•97 citations
We present experimental and theoretical investigations of the ground-state levels of the Cs cycling transition. We show that in such multilevel nondegenerate systems, the populations of the extreme Zeeman sublevels, under optical pumping, can have asymmetric (``dispersive'') line shapes as a function of laser frequency. A density-matrix model which takes into account optical, Zeeman, and hyperfine coherences, and allows for a fluctuating laser field, correctly predicts the experimental observations. A comparison of the density-matrix model with a rate-equation model demonstrates the role of coherences in the population distribution. Investigation of the effect theoretically and experimentally for \ensuremath{\sigma} and \ensuremath{\pi} laser polarizations is presented in the paper.
We have observed a sudden reversal in the direction of population transfer between nearly degenerate Zeeman sublevels during optical pumping of the cesium 6S1/2{\mathit{S}}_{1/2}S1/2​(F=4)\ensuremath{\rightarrow}6P3/2{\mathit{P}}_{3/2}P3/2​(F'=5) cycling transition. As a result of the reversal, the number of atoms in an atomic beam, with quantum numbers 6S1/2{\mathit{S}}_{1/2}S1/2​ (F=4; mF{\mathrm{m}}_{\mathit{F}}mF​=-4), is a function of laser frequency and has a sharp dispersive shape. A rate-equation model indicates that similar dispersive shapes for the population can be expected in the optical pumping of any nondegenerate system with more than two levels, if the level spacing is much smaller than the laser linewidth.
We have investigated atomic coherence changes caused by optical pumping applied to electromagnetically induced absorption (EIA) occurring at the open system, which consists of the transition between the F g = 2 ground state and the F e = 3 excited state in the 85 Rb D1-line. For optical pumping, another laser resonantly tuned to the transition between the F g = 3 ground state and the F e = 2 excited state was used. We found that the atomic coherence for EIA can be changed not by increasing the pumping rate but by pumping differently populations into the Zeeman sublevels in the F g = 2 ground state, which is realized by changing the polarization of the pumping laser. The experimental results were able to be analysed by density matrix equations in the simple model system.
The evolution of the hyperfine structure magnetic sublevel populations of 87 Rb and 133 Cs atoms in resonant linearly polarized laser fields is theoretically analyzed. Analytical expressions are obtained for stationary populations of the magnetic sublevels of the ground state 5 2 S 1/2 F g = 1, F f = 2 in 87 Rb and 6 2 S 1/2 F g = 3, F f = 4 in 133 Cs under optical pumping at the F g ↔ F e = F g and F f ↔ F e = F f transitions of the D 2 lines ( n 2 S 1/2 n 2 P 3/2 ) versus the initial populations. The characteristic population stabilization time are obtained by numerical solution for the density matrix equations, depending on the intensity of the laser fields and the detuning of the optical resonance. It is shown that the alternation of the polarization direction of the laser field at the transition F f ↔ F e = F f almost completely transfers atoms to the lower sublevel of the "clock" M1 transition F g M = 0 ↔ F f M = 0 in rubidium and cesium frequency standards, which proportionally increases the signal of the recording system.
Abstract This work investigates laser control of populations of magnetic sublevels of the ground hyperfine level of the cesium atom on the D2 line (6S1/2 → 6P3/2). A theoretical model is developed within the full density-matrix formalism based on the Lindblad equation, which accounts for coherent interaction with the laser field, spontaneous decay, and decoherence processes. The dynamics of the system is described by a set of coupled ordinary differential equations that reflect the complete Zeeman level structure and the competing relaxation channels characteristic of a realistic multilevel atomic medium. The aim of this work is the controlled redistribution and transfer of population between selected magnetic sublevels while minimizing the population of excited states. To this end, an optimization problem for the laser field parameters is formulated, including pulse amplitudes, frequency detunings, phases, and temporal profiles. Numerical calculations are performed by integrating the high-dimensional system of density-matrix evolution equations. The proposed approach constitutes a scalable computation platform for modeling and controlling Zeeman population dynamics in complex quantum systems and can be applied to problems of quantum state control and preparation.
The optical-pumping cycle in the three-level system e,g,f (J e =1=J f , J g =0), irradiated by two monochromatic sigma -polarized laser light waves is analysed theoretically by the successive approximation (iteration) method up to fourth order. The solutions of the density-matrix evolution equations describe (i) in second order, the influence of the Zeeman structure of the e and f states on the saturation resonances in the intermediate level g (second-order population effect) and (ii) in fourth order, the influence of the Hanle effects and the saturation phenomena on the shape of the double-quantum Hanle resonances and on the two-photon transition probabilities.
We report an experimental observation of coherent population transfer in a multilevel system by adiabatic following through a trapped state. Raman transitions between ground-state sublevels are induced by two partially overlapping ${\mathrm{\ensuremath{\sigma}}}^{\ifmmode\pm\else\textpm\fi{}}$ polarized laser beams, tuned to the hyperfine transition F=4\ensuremath{\rightarrow}F'=4 of the cesium D2{\mathit{D}}_{2}D2​ line. An efficiency of more than 50% is observed for the mF{\mathit{m}}_{\mathit{F}}mF​=+4\ensuremath{\rightarrow}mF{\mathit{m}}_{\mathit{F}}mF​=-4 population transfer. The influence of other excited hyperfine levels on the transfer efficiency is pointed out. The feasibility of the technique with counterpropagating laser beams is also demonstrated.