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Modern Physics Letters A

Survival of weak-field seekers inside a TOP trap even beyond the adiabatic condition

Nirupam Dutta, Anirban Dey, Prasanta Kumar Panigrahi

Published Sep 27, 2019• 0 citations
Publisher

Abstract

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.

DOI
10.1142/s0217732319503474

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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.
In this article, for the first time in the context of 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. Hence, our findings open new possibilities to relax the restrictions of atom trapping in laboratories.
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.
In a time-orbiting-potential magnetic trap the neutral atoms are confined by means of an inhomogeneous magnetic field superimposed onto an uniform rotating one. We perform an analytic study of the atomic motion by taking into account the nonadiabatic effects arising from the spin dynamics about the local magnetic field. Geometric like magnetic fields determined by Berry's phase appear within the quantum description. Application of the time-dependent variational principle on the original quantum equation leads to a set of dynamical evolution equations for the quantum average value of the position operator and spin variables. Within this approximation we derive the quantum-mechanical ground-state configuration matching the classical adiabatic solution and perform some numerical simulations.
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.
We describe a new type of magnetic trap whose time-averaged, orbiting potential (TOP) supplies tight and harmonic confinement of atoms. The TOP trap allows for long storage times even for cold atom samples by suppressing the loss due to nonadiabatic spin flips which limits the storage time in an ordinary magnetic quadrupole trap. In preliminary experiments on evaporative cooling of 87Rb{}^{87}\mathrm{Rb}87Rb atoms in the TOP trap, we obtain a phase-space density enhancement of up to 3 orders of magnitude and temperatures as low as 200 nK.