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arXiv:cond-mat/0303358 · Europhysics Letters (EPL)

Continuous optical loading of a Bose-Einstein condensate in the Thomas-Fermi regime

F Floegel, L Santos, Maciej Lewenstein

Published Sep 1, 2003• 1 citation
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Abstract

We discuss the optical loading of a Bose-Einstein condensate in the Thomas-Fermi regime. The condensate is loaded via spontaneous emission from a reservoir of excited-state atoms. By means of a master equation formalism, we discuss the modification of the condensate temperature during the loading. We identify the threshold temperature, T th , above (below) which the loading process leads to cooling (heating), respectively. The consequences of our analysis for the continuous loading of an atom laser are discussed.

DOI
10.1209/epl/i2003-00594-y

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We discuss the optical loading of a Bose-Einstein condensate in the Thomas-Fermi regime. The condensate is loaded via spontaneous emission from a reservoir of excited-state atoms. By means of a master equation formalism, we discuss the modification of the condensate temperature during the loading. We identify the threshold temperature, T th , above (below) which the loading process leads to cooling (heating), respectively. The consequences of our analysis for the continuous loading of an atom laser are discussed.
We study the optical loading of a trapped Bose-Einstein condensate by spontaneous emission of atoms in excited electronic state in the boson accumulation regime. We generalize the previous simplified analysis of Cirac and Lewenstein ( Phys. Rev. A , 53 (1996) 2466), to a 3D case in which more than one trap level of the excited-state trap is considered. By solving the corresponding quantum many-body master equation, we demonstrate that also for this general situation the photon reabsorption can help to increase the condensate fraction. Such effect could be employed to realize a continuous atom laser, and to overcome condensate losses.
We analyze the continuous pumping of atoms into a Bose-Einstein condensate via spontaneous emission from a thermal reservoir of atoms. We consider the case of atoms with a three-level $\ensuremath{\Lambda}$ scheme, in which one of the atomic transitions has a very much shorter lifetime than the other one. We found that in such a scenario the photon reabsorption in dense clouds at the frequency of the narrow transition can be considered negligible. If, in addition, inelastic processes can be kept negligible, we find that optical pumping can be used to continuously load and refill Bose-Einstein condensates, i.e., it provides a possible way to achieve a continuous atom laser.
Demonstrating that, despite loss processes, Bose-Einstein condensates can be formed in steady state is a prerequisite for obtaining a coherent beam of atoms in a continuous-wave atom laser. In this paper we propose a method for loading atoms into the thermal component of a Bose condensed cloud confined in a magnetic trap. This method is aimed at allowing steady-state dynamics to be achieved. The proposed scheme involves loading atoms into the conservative magnetic potential using the spontaneous emission of photons. We show that the probability for the reabsorption of these photons may be small.
The dynamics of Bose-condensate generation by a cw atom laser with simultaneous stimulated evaporative cooling in a magnetic trap was analyzed using a quantum-mechanical master equation. The model of the atom laser includes irreversible processes of incoherent trap mode pumping and spontaneous atomic transitions due to the interaction of the atomic ensemble with heat reservoirs. The inelastic atomic collisions in the trap and the continual coherent Bose-condensate output coupling from the trap were considered. At certain values of parameters, the Bose condensate created in this laser scheme occurs in a compressed sub-Poisson state. For large Bose condensates with a mean number of atoms ∼10 6 , the Fano factor may be as high as ≅0.5. The influence of spontaneous transitions from the excited trap modes on the statistics of Bose condensate was analyzed.