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Physical Review A

Atom reflection in a tapered magnetic guide

Boon-Keng Kevin Teo, Georg A. Raithel

Published May 2, 2002• 13 citations
Publisher

Abstract

We have constructed a two-wire magnetic atom guide incorporating a tapered section, in which the transverse guiding potential steepens as a function of the position along the guide axis. Atoms are slowed as they move into the tapered section and can become reflected. A classical adiabatic model is used to explain the behavior. The model shows and we experimentally observe that the action of the transverse motion, which is an adiabatic invariant, can be used as a control parameter for the atom reflectivity, allowing us to selectively reflect and trap atoms with large transverse action.

DOI
10.1103/physreva.65.051401

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We have constructed a two-wire magnetic atom guide incorporating a tapered section, in which the transverse guiding potential steepens as a function of the position along the guide axis. Atoms are slowed as they move into the tapered section and can become reflected. A classical adiabatic model is used to explain the behavior. The model shows and we experimentally observe that the action of the transverse motion, which is an adiabatic invariant, can be used as a control parameter for the atom reflectivity, allowing us to selectively reflect and trap atoms with large transverse action.
We have constructed a tapered magnetic atom guide that is integrated with a magneto-optical trap. We have observed atom guiding over distances of up to 20 cm. This integrated strategy is useful for loading atoms into wire guides. We have shown that tapered sections in atom guides. i.e. sections with a variable steepness of the transverse guiding potential, can reflect atoms propagating in the guide. The reflection arises from the adiabatic conservation of the action of the transverse motion; the latter can be used as a control parameter for the atom reflectivity. A method of producing a slow, dark atomic beam of atoms is demonstrated. Atoms that are extracted from a magneto-optical trap using a push beam are quickly pumped into a dark state, which does not interact with the push laser beam. This method is capable of producing atoms with a velocity of order 1 m/s. The slow atoms can be coupled into atom guides. In related research, we observe tunneling resonances of atoms in a 1D optical lattice through the measurement of the magnetization. These resonances manifest themselves as modulations in the magnetization curves. The resonances are shown to be related to the coherence properties of the atoms, and exist only under conditions where the coherence time exceeds the tunneling period of the atoms.
We present a method of coupling laser-cooled atoms from a vapor-cell magneto-optic trap (MOT) into a magnetic atom guide. The axis of the four-wire quadrupole guide passes directly through the center of the MOT. The guide is tilted at a small angle with respect to the horizontal plane to facilitate the propagation of the atoms released from the MOT into the guide. We demonstrate the loading of 10587Rb{10}^{5}{ }^{87}\mathrm{Rb}10587Rb atoms into the guide and measure their propagation up to distances of 17 cm (limited by the guide length). The guide incorporates a tapered section in which the guide diameter reduces by a factor of about 3.
We study modal propagation of cold atomic gases in a straight magnetic waveguide consisting of a current wire and a uniform magnetic field. This configuration is known to generate a transverse confining potential for atoms with magnetic dipole moment oriented anti-parallel to the magnetic field. The potential has azimuthal symmetry to first order in powers of the atomic distance to the waveguide axis. We obtain the modal dispersion curves by means of the WKB quantization method, and introduce a parameter Q that characterizes symmetric atomic waveguides as the parameter V does in optical fibers. We simulate propagation of cold atomic beams by means of the BPM (Beam Propagation Method) and show the spatial evolution of transverse monomode and multimode profiles obtained for different values of Q and arbitrary input beam profiles. We demonstrate, analytically and numerically, the existence of a threshold Q-value for guidance of matter waves analogous to the V-threshold for propagation in a TE00 mode in optical fibers and obtain that, under the experimental conditions reported in the literature, the already observed Gaussian profile of guided atomic beams corresponds to multimode propagation. RIAO/OPTILAS'04.
We present an intense source of 87 Rb atoms that has been set up to produce a continuous, slow and cold beam in a magnetic guide. It consists of a two-dimensional magneto-optical trap whose cooling laser power is provided by a master-oscillator tapered-amplifier system. This trap produces an atomic beam with a flux of over 10 10 atoms/s and a mean velocity of 40 m/s. The beam is recaptured by a second trap whose purpose consists in reducing the beam's velocity, in further cooling the atoms and injecting them into the magnetic guide. The article focusses on the first stage of the process described above.