Bose-Fermi DegeneracyBose-Fermi Degeneracyin ain a

Micro-Magnetic TrapMicro-Magnetic Trap

Seth A. M. Aubin

University of Toronto / Thywissen Group

February 25, 2006

CIAR Ultra-cold Matter Workshop, Banff.

Work supported by NSERC, CFI, OIT, PRO and Research Corporation.

OutlineOutline

Motivation

Micro-magnetic traps and apparatus

Boson and Fermion degeneracyBoson and Fermion degeneracy

Surprises in Rb-K scattering

Future experiments

Why ultra-cold bosons and fermions?Why ultra-cold bosons and fermions?

Advantages:

Short experimental cycle.

Single UHV chamber.

Complex multi-trap geometries.

Advantages:

Short experimental cycle.

Single UHV chamber.

Complex multi-trap geometries.

Why on a chip?Why on a chip?

Objectives:

Condensed matter physics.

Boson-fermion mixtures.

Atom interferometry.

Objectives:

Condensed matter physics.

Boson-fermion mixtures.

Atom interferometry.

Micro-Magnetic TrapMicro-Magnetic TrapTechnology: Electroplated gold wires on a silicon substrate.

Manufactured by J. Estève (Aspect/Orsay).

Technology: Electroplated gold wires on a silicon substrate.

Manufactured by J. Estève (Aspect/Orsay).

Trap Potential: Z-wire trap Iz

RF for evaporation

Z-trap current

defects

Evaporated Ag and Au (B. Cieslak and S. Myrskog)

Light-Induced Atom Desorption (LIAD)Light-Induced Atom Desorption (LIAD)Conflicting pressure requirements:• Large Alkali partial pressure large MOT.

• UHV vacuum long magnetic trap lifetime.

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=600 mW) in a pyrex cell.

RapidRapid

High EfficiencyHigh Efficiency

Bose-Fermi DegeneracyBose-Fermi Degeneracy

High Efficiency Evaporation of High Efficiency Evaporation of 8787RbRb

1.095.3ln(N)

ln(PSD)

d

d

Evaporation Efficiency

BECthermalatoms

magnetictrapping

evap.coolingMOT

10-13 110-6 105

PSD

8787Rb BECRb BEC

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

(trap loaded with 2x107 atoms)

Experimental cycle = 5 - 15 seconds

RF@1.740 MHz:

N = 7.3x105, T>Tc

RF@1.725 MHz:

N = 6.4x105, T~Tc

RF@1.660 MHz:

N=1.4x105, T<Tc

Sympathetic CoolingSympathetic Cooling

of fermionic of fermionic 4040K with bosonic K with bosonic 8787RbRb

8ln(N)

ln(PSD)

Cooling EfficiencyCooling Efficiency

10-8

10-6

10-4

10-2

100

102

104

105 106 107

Atom Number

Pha

se S

pac

e D

ensi

ty

Non-Gaussian DistributionNon-Gaussian Distribution11stst signature of Fermi Degeneracy signature of Fermi Degeneracy

Opt

ical

Den

sity

0 200 400Radial distance (m)

Fit

Res

idua

ls

0 200 400Radial distance (m)

Fit:Fit:

Residuals:Residuals:

N = 4104

TF = 960 nK

T/TF = 0.14(2)

z = 1.4103

N = 4104

TF = 960 nK

T/TF = 0.14(2)

z = 1.4103

2.2|2 Gaussian

9.0|2 Fermi

Non-Thermal Non-Thermal DistributionDistribution

EF

EF

kTRb/EF

EK

,rel

ease

/EF

Pauli Pressure -- Pauli Pressure -- 22ndnd signature of Fermi Degeneracy signature of Fermi Degeneracy

Fermi

Boltzmann

Gaussian Fit

SurprisesSurprises

with Rb-Kwith Rb-K

cold collisionscold collisions

Naïve Scattering TheoryNaïve Scattering Theory

Sympathetic cooling 1Sympathetic cooling 1stst try: try: “Should just work !” -- Anonymous

Add 40K to 87Rb BEC No sympathetic cooling observed !

Sympathetic cooling 1Sympathetic cooling 1stst try: try: “Should just work !” -- Anonymous

Add 40K to 87Rb BEC No sympathetic cooling observed !

RbRbRbRbRbRbRb vn

Rb-RbRb-Rb

Collision RatesCollision Rates

28 RbRba

nm 238.5RbRba

RbKRbKRbRbK vn

Rb-KRb-K

24 RbKa

nm 8.10RbKa

7.2RbRb

RbK

Sympathetic cooling Sympathetic cooling should work really well !!!should work really well !!!

Experiment: Experiment:

Sympathetic cooling only worksSympathetic cooling only works

for for slowslow evaporation evaporation

10-8

10-6

10-4

10-2

100

102

104

105 106 107

Atom Number

Pha

se S

pace

Den

sity

10-8

10-6

10-4

10-2

100

102

104

105 106 107

10-8

10-6

10-4

10-2

100

102

104

10-8

10-6

10-4

10-2

100

102

104

10-8

10-6

10-4

10-2

100

102

104

105 106 107105 106 107

Atom Number

Pha

se S

pace

Den

sity

Evaporation 33 times slower than for BEC

Evaporation 33 times slower than for BEC

Cross-Section MeasurementCross-Section Measurement

TK

40 (K

)

Thermalization of 40K with 87Rb

What’s happening?What’s happening?

Rb

-K c

ross

-sec

tio

n (

nm

2 )

Future Experiments Future Experiments … come see the poster… come see the poster

Pauli Blocking of light scattering: Fermi sea reduces number of states an excited atom can recoil into.

Atomic lifetime increases, linewidth decreases.B. DeMarco and D. Jin, Phys. Rev. A 58, R4267 (1998).

Pauli Blocking of light scattering: Fermi sea reduces number of states an excited atom can recoil into.

Atomic lifetime increases, linewidth decreases.B. DeMarco and D. Jin, Phys. Rev. A 58, R4267 (1998).

Species-specific trapping potentials ? Bosons and fermions in different trapping potentials.

Isothermal “cooling” of fermions with bosons.

Boson-mediated interaction of fermions in an optical lattice.

Species-specific trapping potentials ? Bosons and fermions in different trapping potentials.

Isothermal “cooling” of fermions with bosons.

Boson-mediated interaction of fermions in an optical lattice.

… or use a “magic” wavelength for Rb and K.C. Precilla and R. Onofrio, Phys. Rev. Lett.90, 030404 (2003).

SummarySummary

87Rb BEC with up to 2105 atoms. cycle time as short as 5 s.

40K Fermi degeneracy: T/TF~0.1with 4104 atoms.

Sympathetic cooling to 0.1TF in 6 s. cycle time of 30 s.

Observation of severe reduction of Rb-K scattering cross-section at high T.

Bose-Fermi degeneracy in a chip trap.

EF

First time on a chip !arXiv: cond-mat/0512518

Thywissen GroupThywissen Group

J. H. Thywissen

S. Aubin M. H. T. Extavour

A. StummerS. Myrskog

L. J. LeBlanc

D. McKay

B. Cieslak

Staff/FacultyPostdocGrad StudentUndergraduate

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