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BEC of Rb-87 at Durham University

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Group: Cornish

Authors and contributors: Danny McCarron, Daniel Jenkin, Hung Wen Cho and Simon Cornish.

Figure 1: False-color plots of 87Rb atoms undergoing Bose-Einstein condensation in a combined magnetic and optical potential. The atom number in the BEC is ~2 × 105.

Atom: 87Rb, |F=1, mF = -1>

Trap: Combined magnetic and optical potential. Radial confinement is produced by a single dipole beam with a 65 µm waist. The beam is positioned ~75 µm below the field zero of a quadrupole field such that the quadrupole potential provides axial confinement.

Method:

  • 4 × 108 atoms are loaded into a UHV MOT from a pyramid MOT, 60% are transferred into a magnetic quadrupole trap. At 187 G/cm T = 160 µK and PSD ~ 10-7.
  • After 30 s of RF evaporation in the quadrupole trap N = 2.6 × 107, T = 30 µK and PSD ~ 10-4.
  • 20% of the atoms are transferred into the combined potential by ramping the axial quadrupole gradient down to 29 G/cm. Here T = 6 µK and PSD ~ 10-3.
  • Evaporative cooling, by ramping down the dipole beam power, for 23 s enables us to reach BEC.
  • The onset of BEC is observed with N ~ 106 and the critical temperature ~ 350 nK. The pure condensate atom number ~ 2 x 105.


    Figure 2: The team from L to R: Daniel Jenkin, Simon Cornish, Hung Wen Cho and Danny McCarron.

Posted: 15 Mar 2010     Date: 06 Mar 2010



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