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ABSTRACT: We have observed time-varying spin relaxation of trapped cold atoms due to photon scattering in blue-detuned, crossed, hollow Laguerre-Gaussian beams. These beams are formed by imparting an azimuthal phase of ℓφ to a Gaussian beam, where ℓ is an integer, and have an intensity distribution that scales with r2ℓ to the lowest order. For all degrees of anharmonicity, we observe a time-varying spin-relaxation rate due to energy-dependent photon scattering. For ℓ=8, we directly measure temperature-dependent scattering rates and show that by removing the most energetic atoms from the trap, a more purely spin-polarized sample remains. The results agree well with Monte Carlo simulations, and we present a simple functional form for the spin-relaxation curves.
Phys. Rev. A. 08/2011; 84(2).
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Computer Physics Communications. 01/2010; 181:2063-2071.
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ABSTRACT: We demonstrate confinement of $^{85}$Rb atoms in a dark, toroidal optical trap. We use a spatial light modulator to convert a single blue-detuned Gaussian laser beam to a superposition of Laguerre-Gaussian modes that forms a ring-shaped intensity null bounded harmonically in all directions. We measure a 1/e spin-relaxation lifetime of ~1.5 seconds for a trap detuning of 4.0 nm. For smaller detunings, a time-dependent relaxation rate is observed. We use these relaxation rate measurements and imaging diagnostics to optimize trap alignment in a programmable manner with the modulator. The results are compared with numerical simulations.
03/2008;
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ABSTRACT: We observe velocity-selective two-photon resonances in a cold atom cloud in the presence of a magnetic field. We use these resonances to demonstrate a simple magnetometer with sub-mG resolution. The technique is particularly useful for zeroing the magnetic field and does not require any additional laser frequencies than are already used for standard magneto-optical traps. We verify the effects using Faraday rotation spectroscopy.
02/2008;
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ABSTRACT: This work concerns the development of a gridless method for modeling the inter-particle collisions of a gas. Conventional fixed-grid algorithms are susceptible to grid-mismatch to the physical system, resulting in erroneous solutions. On the contrary, a gridless algorithm can be used to simulate various physical systems without the need to perform grid-mesh optimization. An octree algorithm provides the gridless character to a direct simulation Monte Carlo (DSMC) code by automatically sorting nearest-neighbor gas particles into local clusters. Automatic clustering allows abstraction of the DSMC algorithm from the physical system of the problem in question. This abstraction provides flexibility for domains with complex geometries as well as a decreased code development time for a given physical problem. To evaluate the practicality of this code, the time required to perform the gridless overhead from the octree sort is investigated. This investigation shows that the gridless method can indeed be practical and compete with other DSMC codes. To validate gridless DSMC, results of several benchmark simulations are compared to results from a fixed-grid code. The benchmark simulations include several Couette flows of differing Knudsen number, low-velocity flow past a thin plate, and two hypersonic flows past embedded objects at a Mach number of 10. The results of this comparison to traditional DSMC are favorable. This work is intended to become part of a larger gridless simulation tool for collisional plasmas. Corresponding work includes a gridless field solver using an octree for the evaluation of long range electrostatic forces. We plan to merge the two methods creating a gridless framework for simulating collisional-plasmas.
Journal of Computational Physics.
