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AIP conference proceedings

Experimental nonlinear dynamical studies in cesium magneto-optical trap using time-series analysis

M. Anwar, Rameez‐ul Islam, Muhammad Hamza Faisal, M. Sikandar, Mushtaq Ahmed

Published Jan 1, 2015• 0 citations
Publisher

Abstract

A magneto-optical trap of neutral atoms is essentially a dissipative quantum system. The fast thermal atoms continuously dissipate their energy to the environment via spontaneous emissions during the cooling. The atoms are, therefore, strongly coupled with the vacuum reservoir and the laser field. The vacuum fluctuations as well as the field fluctuations are imparted to the atoms as random photon recoils. Consequently, the external and internal dynamics of atoms becomes stochastic. In this paper, we have investigated the stochastic dynamics of the atoms in a magneto-optical trap during the loading process. The time series analysis of the fluorescence signal shows that the dynamics of the atoms evolves, like all dissipative systems, from deterministic to the chaotic regime. The subsequent disappearance and revival of chaos was attributed to chaos synchronization between spatially different atoms in the magneto-optical trap.

DOI
10.1063/1.4914204

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A magneto-optical trap of neutral atoms is essentially a dissipative quantum system. The fast thermal atoms continuously dissipate their energy to the environment via spontaneous emissions during the cooling. The atoms are, therefore, strongly coupled with the vacuum reservoir and the laser field. The vacuum fluctuations as well as the field fluctuations are imparted to the atoms as random photon recoils. Consequently, the external and internal dynamics of atoms becomes stochastic. In this paper, we have investigated the stochastic dynamics of the atoms in a magneto-optical trap during the loading process. The time series analysis of the fluorescence signal shows that the dynamics of the atoms evolves, like all dissipative systems, from deterministic to the chaotic regime. The subsequent disappearance and revival of chaos was attributed to chaos synchronization between spatially different atoms in the magneto-optical trap.
The dynamics of magneto-optical trap loading by light-induced atom desorption (LIAD) are investigated theoretically and experimentally. The loading of the MOT has been described by a theoretical model. We have paid close attention to the background gases which are essentially important for the ultimate vacuum pressure. The experiment is done based on a glass cell and all the results are well in agreement with the theory. The decay process of the background vacuum pressure caused by the untrapped cesium atoms after shutting off the desorption light is explained quantitatively. The LIAD effect is proved to be an effective tool to control the loading of the MOT and the neutral single atoms in experiment.
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Investigations of optical processes for laser cooled and trapped atoms are described. Fluorescence from Cs atoms in a magneto-optical trap is detected under conditions of very low atomic density. Discrete steps are observed in the fluorescent signal versus time and are associated with the arrival and departure of individual trapped atoms. Histograms of the frequency of occurrence of a given level of fluorescence exhibit a series of uniformly spaced peaks that are attributed to the presence of N = 0, 1, 2 atoms in the trap. In addition, numerical absorption and emission spectra for three-level [...], [...], and V systems under intense radiations are calculated. Absorption spectra for a [...] system is used to explain the probe-wave amplification and absorption spectra recorded for Cs atoms cooled and confined in a magneto-optical trap, in which novel spectral features of narrow frequency widths with single-pass gain exceeding 20% are observed. The consequence of the optical gain is demonstrated to lead to negative radiation pressure, which is investigated together with other mechanical forces in the trap. Various alternative trapping schemes in three-level and two-level atoms are proposed as possible means to compress an atomic sample and demonstrated for a two-level magneto-optical trap.
Expansion of a cold cloud of cesium atoms trapped in a magneto-optical trap is studied by switching off a pair of counter propagating trapping beams. This corresponds to 1-D expansion of the cold cloud in presence of near resonant laser beams that are orthogonal to the expansion direction. Fluorescence imaging of the expanding cloud shows that the dynamics of expansion is complex and includes three distinctive temporal features- initial contraction followed by ballistic expansion and eventually sputtering of the cloud to leave a core that exhibits damped expansion. These are respectively related to the reduction in the repulsive radiation trapping force, initial temperature of the cold cloud and the stochastic heating arising from the random nature of the photon absorption and emission processes.
The use of a cryogenic apparatus has several advantages for the magneto-optical and magnetostatic trapping of atoms. We have measured the lifetimes of magneto-optical and magnetostatic traps for cesium to be greatly increased in a cryogenic vacuum environment relative to a room-temperature vacuum environment, due to reduced background pressure and reduced mass and kinetic energy of background gas atoms. Another advantage of a cryogenic apparatus is that superconducting magnetic field coils can easily be used to generate very high magnetic field gradients for stronger confinement of the trapped atoms. We report the first measurements of the stability of MOT's at high magnetic field gradients and laser intensities, and compare the results to a model based on evaporation of atoms from the MOT using a Fokker-Planck equation approach. This model is more consistent with the data than an alternative model based on ejection of atoms by magnetic dipole forces. We also measure the dynamical parameters for magneto-optically trapped atoms at both high and low magnetic field gradients and with trapping laser intensities above saturation and compare the data to a simple physical model based on polarization gradient cooling. Consistent with measurements by other groups, the measured friction is consistent with the polarization gradient model, but the measured spring constant is drastically reduced and more consistent with the predictions of the Doppler theory.
Summary form only given.To go beyond the first generation of quantum-chaos experiments, we set up an experiment with cesium. The small recoil velocity of cesium relative to sodium ensures that the 6-kicked approximation is valid over a much larger range of momenta. The resulting momentum boundary in phase space is then pushed out much further, opening the door for experimental studies of noise-induced delocalization as well as other directions of fundamental interest. Cesium atoms are first trapped and cooled in a magneto-optical trap (MOT) via diode lasers.