Efficient direct evaporative cooling in an atom-chip magnetic trap

Daniel M. Farkas, Kai M. Hudek, Shengwang Du, and Dana Z. Anderson
Phys. Rev. A 87, 053417 – Published 31 May 2013

Abstract

We demonstrate direct evaporative cooling of 87Rb atoms confined in a dimple trap produced by an atom chip. By changing the two chip currents and two external bias fields, we show theoretically that the trap depth can be lowered in a controlled way with no change in the trap frequencies or the value of the field at the trap center. Experimentally, we maximized the decrease in trap depth by allowing some loosening of the trap. In total, we reduced the trap depth by a factor of 20. The geometric mean of the trap frequencies was reduced by less than a factor of 6. The measured phase-space density in the final two stages increased by more than two orders of magnitude, and we estimate an increase of four orders of magnitude over the entire sequence. A subsequent rf evaporative sweep of only a few megahertz produced Bose-Einstein condensates. We also produce condensates in which raising the trap bottom pushes hotter atoms into an rf “knife” operating at a fixed frequency of 5 MHz.

  • Received 12 March 2013

DOI:https://doi.org/10.1103/PhysRevA.87.053417

©2013 American Physical Society

Authors & Affiliations

Daniel M. Farkas1, Kai M. Hudek1, Shengwang Du2, and Dana Z. Anderson1,*

  • 1JILA, University of Colorado, and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA
  • 2Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China

  • *dana@jila.colorado.edu

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Vol. 87, Iss. 5 — May 2013

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