1. 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.

2. Why ultra-cold bosons and fermions?
Objectives:
Condensed matter simulations.
Boson-fermion mixtures.
Atom interferometry.
Why on a chip?
Advantages:
Short experimental cycle.
Single UHV chamber.
Complex multi-trap geometries.

3. Experimental Sequence
MOT
Molasses
Quadrupole magnetic trap
Magnetic transport to chip
Load Z-wire magnetic trap
RF evaporation to quantum degeneracy

4. 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 (power=170 mW) in a pyrex cell.

5. Atom Chip Technology: Electroplated gold wires on a silicon substrate.
Manufactured by J. Estève (Aspect/Orsay).
Trap Potential: Z-wire trap Iz
Theory
rf for evaporation

6. Extra compression at low temperature?
T=19 K
T=7 K
faxial boosted by two (to 26 Hz)

7. “Dimples”
Take a closer look:

8. BEC of 87Rb Surprise! Reach Tc with only a 30x loss in number.
…Continue evaporation:
@1.740 MHz:
N = 7.3x105, T>Tc
@1.725 MHz:
N = 6.4x105, T~Tc
@1.660 MHz:
N=1.4x105, T<Tc
Surprise! Reach Tc with only a 30x loss in number.
(trap loaded with 2x107 atoms)

9. High Evaporation Efficiency
MOT &
Molasses
Magnetic Trap
Transfer to Chip
Chip
Loading
RF Evaporation
5-12 s
1.10 s
0.26 s
2.50 s
Log slope efficiency:
BEC of up to 2x105 atoms.
Cycle times as short as 10 seconds.

10. 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:

11. 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.

12. Thywissen Group Staff/Faculty Postdoc Grad Student Undergraduate
Colors:
Thywissen Group
S. Aubin
B. Cieslak
L. J. LeBlanc
I. Leroux
M. H. T. Extavour
J. H. Thywissen
D. McKay
S. Myrskog
D. Shirokoff
A. Stummer