[show abstract][hide abstract] ABSTRACT: We demonstrate a 1-D velocity selection technique which relies on combining magnetic and optical potentials. We have selected atom clouds with temperatures as low as 2.9% of the initial temperature, with an efficiency of 1%. The efficiency (percentage of atoms selected) of the technique can vary as slowly as the square root of the final temperature. In addition to selecting the coldest atoms from a cloud, this technique imparts a sharp cut-off in the velocity distribution. The cold selected atoms are confined in a small well, spatially separated from higher energy atoms. Such a non-thermal distribution may be useful for atom optics experiments, such as studies of atom tunneling.
[show abstract][hide abstract] ABSTRACT: We discuss a velocity selection technique for obtaining cold atoms, in which all atoms below a certain energy are spatially selected from the surrounding atom cloud. Velocity selection can in some cases be more efficient than other cooling techniques for the preparation of ultracold atom clouds in one dimension. With quantum mechanical and classical simulations and theory we present a scheme using a dipole force barrier to select the coldest atoms from a magnetically trapped atom cloud. The dipole and magnetic potentials create a local minimum which traps the coldest atoms. A unique advantage of this technique is the sharp cut-off in the velocity distribution of the sample of selected atoms. Such a non-thermal distribution should prove useful for a variety of experiments, including proposed studies of atomic tunneling and scattering from quantum potentials. We show that when the rms size of the atom cloud is smaller than the local minimum in which the selected atoms are trapped, the velocity selection technique can be more efficient in 1-D than some common techniques such as evaporative cooling. For example, one simulation shows nearly 6% of the atoms retained at a temperature 100 times lower than the starting condition. Comment: 13 pages, 7 figures
Journal of Optics B Quantum and Semiclassical Optics 03/2005; · 1.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the current status of an experiment to resolve spatial tunneling of atomic Rubidium through an optical potential barrier. To obtain the long de Broglie wavelength necessary for atoms to tunnel through our optical barrier, we velocity-select the lowest-energy atoms from our sample. In one dimension, velocity selection can be more efficient than evaporative cooling, as well as providing the sharp energy cutoff required for a clear signature of tunneling. We use a 1D optical lattice to select the coldest atoms and translate them into contact with a repulsive sheet of light. Atoms are trapped in a local potential well formed by the combination of gravity and the blue-detuned light sheet. By varying the intensity and width of the beam, the tunneling rate of atoms from this quasi-bound state can be modified. The ultimate goal is to probe the atoms during the process of escape through the barrier.