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Quantum Electronics and Laser Science Conference

Beyond the usual approximations: time-dependent magnetic traps revisited

Jörg Helge Müller, O. Morsch, D. Ciampini, Marco Anderlini, R. Mannella, E. Arimondo

Published Nov 13, 2002• 0 citations
Publisher

Abstract

Summary form only given. In the present work, we report experimental results that clearly demonstrate dynamical phenomena beyond the usual approximations applied to time-orbiting-potential (TOP) traps. The paper is organized as follows: After a brief review of the theory of TOP-traps we describe our experimental apparatus and procedure. In the following sections, experimental results and theoretical considerations concerning the breakdown of the time-averaging and the adiabatic approximations are presented. Finally, we summarize our results and discuss the importance of our findings for atom-trapping and BEC experiments.

DOI
10.1109/qels.2001.962061

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Summary form only given. In the present work, we report experimental results that clearly demonstrate dynamical phenomena beyond the usual approximations applied to time-orbiting-potential (TOP) traps. The paper is organized as follows: After a brief review of the theory of TOP-traps we describe our experimental apparatus and procedure. In the following sections, experimental results and theoretical considerations concerning the breakdown of the time-averaging and the adiabatic approximations are presented. Finally, we summarize our results and discuss the importance of our findings for atom-trapping and BEC experiments.
The classical model that describes the motion of an atom in a magnetic trap is solved in order to investigate the relationship between the failure of the usual adiabatic approximation assumption and the physical parameters of the trap. This allows to evaluate the effect that reversing of the bias field rotation produces on the vertical position of the atomic orbit, a displacement that is closely related to the adiabatic character of the trap motion. The present investigation has been motivated by a similar experimental test previously carried out in the actual magnetic time orbiting potential trap. We find that the non-adiabatic effects provided by the classical model are extremely small. Thus, we conclude that the theoretical explanation of the experimental measures, requires a quantum description of the dynamics in magnetic traps.
We have observed Bose-Einstein condensation of large numbers of 87Rb{}^{87}\mathrm{Rb}87Rb atoms in a magnetic time-averaged orbiting potential (TOP) trap. Over $1.5\ifmmode\times\else\texttimes\fi{}{10}^{9}$ atoms are captured in the trap and evaporatively cooled to produce condensates containing up to $2\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms. We discuss special considerations relating to the production of large Bose-Einstein condensates in a TOP trap, and present measurements of the condensate fraction for this case.
In this paper, for the first time in the context of time orbiting potential (TOP) trap, the necessary and sufficient conditions for the adiabatic evolution of weak field seeking states have been quantitatively examined. It has been well accepted since decades that adiabaticity has to be obeyed by the atoms for successful magnetic trapping. However, we show, on the contrary, that atoms can also be confined beyond the adiabatic limit. For the demonstration, we have considered a toy model of a single weak field seeking atom in its ground state and have calculated its survival probability inside a TOP trap. Our findings open new possibilities to relax the restrictions of atom trapping in laboratories.
Summary form only given. We report the observation of Bose-Einstein condensation of a very large number of /sup 87/Rb atoms in a time orbiting potential (TOP) trap. We found that for such large samples, efficient cooling in the TOP trap is complicated to some extent by undesired losses of atoms at the orbiting magnetic field zero point, but that these difficulties can be overcome. In our experiments, we first load /sup 87/Rb atoms from a slow beam into a magneto-optic atom trap (MOT). Second, we then compress the atoms with a forced dark MOT, further cool them with optical molasses, and optically pump them into the desired state.