Towards ultra-cold Bose-Fermi mixturesTowards ultra-cold Bose-Fermi mixturesin a micro-magnetic trapin 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?

Advantages:

• Short experimental cycle.

• Single UHV chamber.

• Complex multi-trap geometries.

Why on a chip?

Objectives:

• Condensed matter simulations.

• Boson-fermion mixtures.

• Atom interferometry.

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

T=19 K

T=7 K

faxial boosted by two (to 26 Hz)

kTrUrn )(exp)( 31

Extra compression at low temperature?

“Dimples”

Take a closer look:

BEC of 87Rb

@1.725 MHz:N = 6.4x105, T~Tc

@1.660 MHz:N=1.4x105, T<Tc

@1.740 MHz:N = 7.3x105, T>Tc

Surprise! Reach Tc with only a 30x loss in number.

…Continue evaporation:

(trap loaded with 2x107 atoms)

High Evaporation EfficiencyMOT &Molasses

Magnetic TrapTransfer to Chip

ChipLoading RF Evaporation

5-12 s 1.10 s 0.26 s 2.50 s

• BEC of up to 2x105 atoms.

• Cycle times as short as 10 seconds.

• Log slope efficiency:

log()

log(N)4.0

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:

OutlookSummary:

• 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.

Thywissen GroupThywissen Group

J. H. Thywissen

S. Aubin M. H. T. Extavour

A. StummerS. Myrskog

L. J. LeBlanc

D. McKay

B. Cieslak

D. Shirokoff

Staff/FacultyPostdocGrad StudentUndergraduate

Colors:

I. Leroux