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Institut für Laserphysik. Universität Hamburg. Krynica, June 2005 Quantum Optics VI . „Fermi-Bose mixtures of 40 K and 87 Rb atoms: Does a Bose Einstein condensate float in a Fermi sea?". Klaus Sengstock. Mixtures of ultracold Bose- and Fermi-gases

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slide1

Institut für Laserphysik

Universität Hamburg

Krynica, June 2005 Quantum Optics VI

„Fermi-Bose mixtures of 40K and 87Rb atoms:Does a Bose Einstein condensate float in a Fermi sea?"

Klaus Sengstock

Mixtures of ultracold Bose- and Fermi-gases

Bright Fermi-Bose solitons

Dynamics of the system: e.g.: mean field driven collapse

slide2

Spinor-BEC

Fermi-Bose-Mixture

Atom-Guiding in PBF

BEC ‘in Space‘

Cold Quantum Gas Group

Hamburg

slide3

Spinor-BEC

Fermi-Bose-Mixture

Poster by Silke Ospelkauson Tuesday

Poster by Jochen Kronjägeron Monday

Cold Quantum Gas Group

Hamburg

slide4

Bose-Einstein Condensation

Bose-Einstein distribution

critical temperature for BEC

S. N. Bose

A. Einstein

T>Tc

T<Tc

N0/N

1-(T/Tc)3

1

Tc

T

slide5

Bose-Einstein Condensation

Bose-Einstein distribution

High-temperature effect !!!

critical temperature for BEC

T>Tc

T<Tc

N0/N

1-(T/Tc)3

1

Tc

T

fermions in a harmonic trap
Fermions in a Harmonic Trap

Fermi-Dirac distribution

Fermi temperature

E. Fermi

P.A.M. Dirac

T>TF

T=0

f(e)

T=0

T~TF

1

eF

T>TF

eF

e

slide7

Fermions in a Harmonic Trap

Fermi-Dirac distribution

Quantum statistical effects also forT~TF, but more difficult to see...

Fermi temperature

T>TF

T<TF

f(e)

T=0

T~TF

1

T>TF

eF

e

slide8

Fermionic Quantum Gases

difficulty to reach low temperatures for Fermi gases:

no s-wave scattering of identical fermions! no thermalization in evaporative cooling

a)  use different spin components (D. Jin et al. 98)

b)  use e.g. a BEC to cool a Fermi sea

(and look to the details...)

thermal

Bosons

condensate

fraction

Fermions

e g momentum distributions of fermions and bosons
e.g.: Momentum Distributions of Fermions and Bosons

P(p)

P(p)

T>>Tc,TF

-pF

pF

0

0

p

p

P(p)

P(p)

T<Tc,TF

p

p

-pF

pF

0

0

P(p)

P(p)

T<<Tc,TF

p

p

-pF

pF

0

0

slide10

e.g.: Momentum Distributions of Fermions and Bosons

P(p)

P(p)

T>>Tc,TF

-pF

pF

0

0

p

p

P(p)

P(p)

T<Tc,TF

p

p

-pF

pF

0

0

e g superfluidity in quantum gases a bosons
e.g.: Superfluidity in Quantum Gases: a) Bosons
  • drag free motion

MIT

C. Raman et al., PRL. 83, 2502-2505 (1999).

  • scissors modes

Oxford

O.M. Maragò et al., PRL 84, 2056 (2000)

  • vortices, vortex lattice

JILA, ENS, MIT

Image from: P. Engels and E. A. Cornell

superfluidity in quantum gases b fermions
Superfluidity in Quantum Gases: b) Fermions

Cooper pairs - BCS superfluidity

T0

exponentially difficult to reach

(valid for kF|a|<<1)

e.g.: kFa=-0.2 -> TBCS~ 10-4TF (very very small)

(very) low-temperature effect

slide13

Superfluidity in Quantum Gases: b) Fermions

ways out of it:

manipulate TBCS using a Feshbach resonance

BEC of molecules

BEC/BCS crossover

  • Duke
  • ENS
  • Innsbruck
  • JILA
  • MIT
  • Rice

use additional particles to mediate interactions - Bosons

  • ? ...
slide14

  Fermi-Bose Mixtures

  • boson mediated superfluidity

L. Viverit, Phys. Rev. A 66, 023605 (2002)

F. Matera, Phys. Rev. A 68, 043624 (2003)

T. Swislocki, T. Karpiuk, M. Brewsczyk, Poster 1, Monday

...

  • boson mediated superfluidity in a lattice

F. Illuminati and A. Albus, Phys. Rev. Lett. 93, 090406 (2004)

...

 interplay between tunneling and various on-site-interactions

slide15

Fermi-Bose Mixtures

IIFD

IISF

IIFL

2

1

IDM

Ubf

Ubb

IFL

0

IIDM

IIFL

IDM

-1

IISF

IIFL

.

.

IIDM

-2

0

1

mb/Ubb

there is even more:

  • special interest: mixtures in optical lattices

 new phases, composite particles, ...

  • composite fermions

M. Lewenstein et al.,

Phys. Rev. Lett. 92, 050401 (2004)

M. Cramer et al.,

Phys. Rev. Lett. 93, 190405 (2004)

slide16

Fermi-Bose Mixtures

effective interactions:

Bose-Bose int.

Bose-Fermi int.

bosons

fermions

new degrees of freedom due to additional interactions

e.g.: 40K - 87Rb mixture:

gB > 0 (aBB ~ 100 a0)

gBF < 0 (aBF ~ -280 a0)

tunable by Feshbach resonances!

S. Inouye et al., PRL 93, 183201 (2004)

see also:

G. Modugno et al., Science 297, 2240 (2002)

slide17

Fermi-Bose Mixtures

  •  detailed understanding of interactions

and also of loss processes is necessary

Bose-Fermi interaction physics

- system boundary conditions

- coupled excitations

(e.g. exp. in Jin group, JILA and Inguscio group, LENS)- Bose-Fermi interactions

- interspecies correlations

- novel phases

- heteronuclear molecules

6Li/7Li at Duke U., ENS Paris, Innsbruck U., Rice U.

6Li/23Na at MIT

40K/87Rb at LENS Florence, Jila Boulder, Hamburg U.,ETH Zürich

hamburg setup
Hamburg Setup

two-species 2D-MOT

flux:87Rb ~ 5 · 109 s-1

40K ~ 5·106 s-1

two-species 3D-MOT

Rb ~ 1010

K ~ 3·107

within 10..20 s

in addition: dipole trap

magnetic trap

nax ~ 11 Hz (Rb)

nrad ~ 260 Hz (Rb)

soon: optical lattice

hamburg setup1
Hamburg Setup

Mai 2003

laser systems

experimental setup

first BEC 7/2004

first degenerate

Fermi gas 8/2004

slide20

Sympathetic Cooling

state of the art(temperature):

5x1076Li at T~0.05TF

1x10640K at T~0.15TF (for K-Rb cooling)

nax=11Hz, nr=330Hz

state of the art(particle

numbers):

nax=11Hz, nr=267Hz

number of K-atoms

only BEC: >5*106

only Fermions: >1*106

number of Rb-atoms

slide21

Attractive Boson-Fermion Interaction

aK-Rb ~ -279 a0

effective potential for fermions:

=

+

BEC

Fermion cloud with BEC

experimental signatures:

Fermion cloud without BEC

mean field instability of the system
Mean Field Instability of the System

BEC

BEC attraction

of fermions

Fermi-Sea

collapse

BEC density

increase

runaway

slide23

Collapse Experiments

7Li collapse

Sackett et al., PRL 82, 876 (1999)

J.M. Gerton et al., Nature 8, 692 (2000)

85Rb "Bosenova"

Donley et al., Nature 412, 295 (2001)

Images from: http://spot.colorado.edu/~cwieman/Bosenova.html

40K / 87Rb Fermi-Bose collapse

G. Modugno et al., Science 297, 2240 (2002)

slide25

Fermi-Bose Mixtures in the Large Particle Limit: Collapse

but...: is it just losses?? locally high density: enhanced two- and three-body losses??

slide26

Lifetime Regimes

-> collapse-time

due to trap dynamics

3-body-loss

loss and collapse dynamics can be distinguished!

t= 197ms

t= 21ms

time/frequency scales:

- nr(K) = 394 Hz

- nax(K) = 17 Hz

- thermalization 10..50 ms

- collapse: ~ 20 ms

- loss processes 100..200 ms

slide27

3-Body Losses

measurement of the 3-body KRb decay rate

N

K

1

model for 3-body

inelastic

K

K

Rb

Rb

3

2

d

r

n

r

,

t

n

r

,

t

decay in thermal mixture:

B

F

N

N

K

K

3

2

d

r

n

r

,

t

n

r

,

t

T

T

B

F

integration over time:

ln

N

T

ln

N

0

K

dt

K

K

K

Rb

Rb

N

t

0

K

0

-0.5

-1

-1.5

-2

-2.5

0

20

40

60

80

100

120

140

160

180

T

Result:

ln

N

T

ln

N

0

K

K

6

cm

( +/- 0.2)

28

K

3.5

10

K

Rb

Rb

s

Measurement does not depend on K atom

number calibration

For

Rb |2,2> decay, we reproduce the

87

value from Söding et al.

[Appl. Phys. B69, 257 (1999)]

3

2

d

r

n

r

,

t

n

r

,

t

T

B

F

38

6

dt

10

m

s

N

t

0

K

slide28

Fermi-Bose Mixtures in the Large Particle Limit:

Stability Diagram

stable mixture

non stable mixture

NBoson

aKRb=-281 a0

(S. Inouye et al.,

PRL 93, 183201 (2004))

NFermion

solitons in matter waves
Solitons in Matter Waves

g>0

g<0

dark solitons

filled solitons

bright solitons

quantum pressure

interactions

K.S. Strecker et al., Nature 417, 150 (2002)

B. P. Anderson et al., PRL 86, 2926 (2001)

gap solitons

"negative mass"

L. Khaykovich et al., Science 296, 1290 (2002)

NSoliton< 104

S. Burger et al., PRL 83, 5198 (1999)

quasi-1D regime

collapse for Eint>Eradial

J. Denschlag et al., Science 287, 97 (2000)

B. Eiermann et al. PRL 92, 230401(2004)

slide31

1D: Bright Mixed ‘‘Solitons‘‘

after switching

off the trap:

our data

Bose-Bose repulsion versus Fermi-Bose attraction

behaviour in

the trap:

theory

theory by T. Karpiuk, M. Brewczyk, M. Gaida, K. Rzazewski

dynamics:

constant

envelope

simulation from M. Brewczyk et al.

T. Karpiuk, M. Brewczyk, S. Ospelkaus-Schwarzer, K. Bongs, M. Gajda, and K. Rzążewski, PRL 93, 100401 (2004)

slide32

Collision

fermionic character due to the Pauli-principle ?

simulation shows complex dynamics:

- repulsive

- shape oscillations

- particle exchange

Simulation from

M. Brewczyk et al.

slide33

Bose-Fermi Mixtures with Attractive InteractionsPhysics in the High Density Limit

Influence of loss processes ?

effective interaction

("density")

bright

mixed

soliton

collapse

attractive

boson-induced BCS ?

repulsive

trap aspect ratio

hamburg team
Hamburg Team

K. Se

Kai Bongs - Atom optics

V. M. Baev - Fibre lasers

Spinor BEC:

Jochen Kronjäger

Christoph Becker

Thomas Garl

Martin Brinkmann

Stefan Salewski

Ortwin Hellmig Arnold Stark

Sergej Wexler

Oliver Back

Gerald Rapior

Fermi-Bose mixtures K-Rb:

Silke Ospelkaus-Schwarzer

Christian Ospelkaus

Philipp Ernst

Oliver Wille

Manuel Succo

Q. Gu - Theory

BEC in Space:

Anika Vogel

Malte Schmidt

Staff

Victoria Romano

Dieter Barloesius

Reinhard Mielck

Atom guiding in PCF:

Stefan VorathPeter Moraczewski

slide35

Cold Quantum Gas Group

Hamburg

Hamburg is a nice city...

(for physics ) (and for visits!)