Transcript Document

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.
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.
Experimental Sequence
Experimental
sequence:
1. MOT
2. Molasses
3. Quadrupole
magnetic trap
4. Magnetic
transport to chip
5. Load Z-wire
magnetic trap
6. RF evaporation
to quantum
degeneracy
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.
Atom Chip
Technology:
• Electroplated gold wires on a silicon substrate.
• Manufactured by J. Estève (Aspect/Orsay).
Trap Potential: Z-wire trap
Theory
Iz
rf for evaporation
Extra compression at low temperature?
T=19 K
n(r )  13 expU (r ) kT 
T=7 K
faxial boosted by
two (to 26 Hz)
“Dimples”
Take a closer look:
BEC of 87Rb
…Continue evaporation:
@1.740 MHz:
N = 7.3x105, T>Tc
@1.725 MHz:
N = 6.4x105, T~Tc
Surprise! Reach Tc with
only a 30x loss in number.
(trap loaded with 2x107 atoms)
@1.660 MHz:
N=1.4x105, T<Tc
High Evaporation Efficiency
MOT &
Molasses
5-12 s
Magnetic Trap
Transfer to Chip
Chip
Loading
1.10 s
0.26 s
• Log slope efficiency:
 log()

 4.0
 log(N)
• BEC of up to
2x105 atoms.
• Cycle times as
short as 10 seconds.
RF Evaporation
2.50 s
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:
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.
Colors:
Staff/Faculty
Postdoc
Grad Student
Undergraduate
Thywissen Group
S. Aubin
D. McKay
B. Cieslak
S. Myrskog
M. H. T. Extavour
D. Shirokoff
L. J. LeBlanc
A. Stummer
I. Leroux
J. H. Thywissen