Towards ultra-cold Bose-Fermi mixtures

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Towards ultra-cold Bose-Fermi mixtures in a
micro-magnetic trap
Seth Aubin University of Toronto / Thywissen
Group
Work supported by NSERC, CFI, OIT, and Research
Corporation.
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Why ultra-cold bosons and fermions?
Why on a chip?
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Experimental Sequence

• Experimental sequence
• MOT
• Molasses
• Quadrupole magnetic trap
• Magnetic transport to chip
• Load Z-wire magnetic trap
• RF evaporation to quantum degeneracy

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Light-Induced Atom Desorption (LIAD)

• Conflicting pressure requirements
• Large Alkali partial pressure ? large MOT.
• UHV vacuum ? long magnetic trap lifetime.

Solution Use LIAD to control pressure
dynamically !

• 405nm LEDs (power170 mW) in a pyrex cell.

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Atom Chip

• Technology
• Electroplated gold wires on a silicon
  substrate.
• Manufactured by J. Estève (Aspect/Orsay).

Trap Potential Z-wire trap
Theory
rf for evaporation
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Extra compression at low temperature?
T19 ?K
T7 ?K
faxial boosted by two (to 26 Hz)
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Dimples
Take a closer look
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BEC of 87Rb
Continue evaporation
_at_1.725 MHz N 6.4x105, TTc
_at_1.660 MHz N1.4x105, TltTc
_at_1.740 MHz N 7.3x105, TgtTc
Surprise! Reach Tc with only a 30x loss in number.
(trap loaded with 2x107 atoms)
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High Evaporation Efficiency
MOT Molasses
Chip Loading
Magnetic Trap Transfer to Chip
RF Evaporation
0.26 s
5-12 s
1.10 s
2.50 s

• Log slope efficiency

• BEC of up to 2x105 atoms.
• Cycle times as short as 10 seconds.

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87Rb - 40K Bose-Fermi Mixture on a Chip
Simultaneously, we have loaded up to 1.5x107
87Rb atoms.
4x104 40K atoms
How to see dilute fermions? 1D chip MOT
fluorescence detection
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Outlook

• Summary
• 2 elements trapped simultaneously on a chip.
• Cold boson-fermion mixture in a micro-magnetic
  trap.
• Very efficient evaporation.
• 2x105 87Rb BEC.
• 10-20 s production duty cycle.

• Future
• Fermi-degeneracy of 40K.
• Fabrication of next-generation chip
• Experiments.

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Thywissen Group