„Fermi-Bose mixtures of 40 K and 87 Rb atoms: Does a Bose Einstein condensate float in a Fermi sea?" Klaus Sengstock Krynica, June 2005 Quantum Optics VI Institut für Laserphysik Universität Hamburg Mixtures of ultracold Bose- and Fermi-gases Bright Fermi-Bose solitons Dynamics of the system: e.g.: mean field driven collapse

Cold Quantum Gas Group Hamburg Fermi-Bose-Mixture Spinor-BEC BEC ‘in Space‘ Atom-Guiding in PBF

Cold Quantum Gas Group Hamburg Fermi-Bose-Mixture Spinor-BEC Poster by Silke Ospelkaus on Tuesday Poster by Jochen Kronjäger on Monday

Bose-Einstein Condensation TTcTc 1 N 0 /N 1-(T/T c ) 3 T>T c T<T c Bose-Einstein distribution S. N. BoseA. Einstein critical temperature for BEC

Bose-Einstein Condensation TTcTc 1 N 0 /N 1-(T/T c ) 3 T>T c T<T c Bose-Einstein distribution critical temperature for BEC High-temperature effect !!!

Fermions in a Harmonic Trap FF 1 f()f() T>T F T=0 Fermi-Dirac distribution E. FermiP.A.M. Dirac T=0 T~T F T>T F Fermi temperature FF

Quantum statistical effects also for T~T F, but more difficult to see... Fermions in a Harmonic Trap FF 1 f()f() T>T F T<T F Fermi-Dirac distribution T=0 T~T F T>T F Fermi temperature

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 Fermions condensate fraction

e.g.: Momentum Distributions of Fermions and Bosons 0 p P(p) 0 p pFpF -p F T<<T c,T F 0 0 p p P(p) 0 0 p p pFpF -p F pFpF T>>T c,T F T<T c,T F

e.g.: Momentum Distributions of Fermions and Bosons 0 0 p p P(p) 0 0 p p pFpF -p F pFpF T>>T c,T F T<T c,T F

e.g.: Superfluidity in Quantum Gases: a) Bosons C. Raman et al., PRL. 83, (1999). Image from: P. Engels and E. A. Cornell O.M. Maragò et al., PRL 84, 2056 (2000) drag free motion scissors modes vortices, vortex lattice MIT Oxford JILA, ENS, MIT

Superfluidity in Quantum Gases: b) Fermions Cooper pairs - BCS superfluidity T0T0exponentially difficult to reach (valid for k F |a|<<1 ) e.g.: k F a=-0.2 -> T BCS ~ T F (very very small) (very) low-temperature effect

Superfluidity in Quantum Gases: b) Fermions ways out of it: manipulate T BCS using a Feshbach resonance BEC of molecules BEC/BCS crossover Duke ENS Innsbruck JILA MIT Rice use additional particles to mediate interactions - Bosons ?...

  Fermi-Bose Mixtures boson mediated superfluidity boson mediated superfluidity in a lattice F. Illuminati and A. Albus, Phys. Rev. Lett. 93, (2004)... L. Viverit, Phys. Rev. A 66, (2002) F. Matera, Phys. Rev. A 68, (2003) T. Swislocki, T. Karpiuk, M. Brewsczyk, Poster 1, Monday...  interplay between tunneling and various on-site-interactions

Fermi-Bose Mixtures special interest: mixtures in optical lattices  new phases, composite particles,... composite fermions M. Cramer et al., Phys. Rev. Lett. 93, (2004) there is even more: U bf U bb II FD II SF II FL I FL I DM II SF II FL II DM II FL 01  b  U bb.... II DM M. Lewenstein et al., Phys. Rev. Lett. 92, (2004)

effective interactions: bosons fermions Bose-Bose int.Bose-Fermi int. see also: G. Modugno et al., Science 297, 2240 (2002) S. Inouye et al., PRL 93, (2004) e.g.: 40 K - 87 Rb mixture: g B > 0 (a BB ~ 100 a 0 ) g BF < 0 (a BF ~ -280 a 0 ) Fermi-Bose Mixtures new degrees of freedom due to additional interactions tunable by Feshbach resonances!

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 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 6 Li/ 7 Liat Duke U., ENS Paris, Innsbruck U., Rice U. 6 Li/ 23 Na at MIT 40 K/ 87 Rbat LENS Florence, Jila Boulder, Hamburg U., ETH Zürich

Hamburg Setup two-species 2D-MOT flux: 87 Rb ~ 5 · 10 9 s K ~ 5·10 6 s -1 two-species 3D-MOT Rb ~ K ~ 3·10 7 within s magnetic trap ax ~ 11 Hz (Rb) rad ~ 260 Hz (Rb) in addition: dipole trap soon: optical lattice

Hamburg Setup experimental setup laser systems Mai 2003 first BEC 7/2004 first degenerate Fermi gas 8/2004

Sympathetic Cooling state of the art (temperature): 5x Li at T~0.05 T F 1x K at T~0.15 T F (for K-Rb cooling) number of K-atoms number of Rb-atoms ax =11Hz, r =330Hz ax =11Hz, r =267Hz only BEC: >5*10 6 only Fermions: >1*10 6 state of the art (particle numbers):

Attractive Boson-Fermion Interaction experimental signatures: Fermion cloud without BEC a K-Rb ~ -279 a 0 + BEC =  effective potential for fermions: Fermion cloud with BEC

Mean Field Instability of the System BEC Fermi-Sea BEC attraction of fermions BEC density increase runaway collapse

Collapse Experiments 7 Li collapse Sackett et al., PRL 82, 876 (1999) J.M. Gerton et al., Nature 8, 692 (2000) 85 Rb "Bosenova" Donley et al., Nature 412, 295 (2001) G. Modugno et al., Science 297, 2240 (2002) Images from: 40 K / 87 Rb Fermi-Bose collapse

Fermi-Bose Mixtures in the Large Particle Limit: Local Collapse Dynamics

Fermi-Bose Mixtures in the Large Particle Limit: Collapse but...: is it just losses??  locally high density: enhanced two- and three-body losses??

Lifetime Regimes  = 21ms  = 197ms time/frequency scales: - r (K) = 394 Hz - ax (K) = 17 Hz - thermalization ms - collapse: ~ 20 ms - loss processes ms 3-body-loss -> collapse-time due to trap dynamics loss and collapse dynamics can be distinguished!

3-Body Losses 0 T dt d 3 rn B 2 r,tn F r,t N K t m 6 s lnN K T N K 0 T Measurement does not depend on K atom Rb |2,2> decay, we reproduce the Result: number calibration For 87 value from Söding et al. [Appl. Phys. B69, 257 (1999)] K KRb cm 6 s ( +/- 0.2)

Fermi-Bose Mixtures in the Large Particle Limit: Stability Diagram stable mixture non stable mixture a KRb =-281 a 0 (S. Inouye et al., PRL 93, (2004)) N Boson N Fermion

Does a Bose Einstein condensate float in a Fermi sea?... it depends...

Solitons in Matter Waves S. Burger et al., PRL 83, 5198 (1999) J. Denschlag et al., Science 287, 97 (2000) g>0 B. P. Anderson et al., PRL 86, 2926 (2001) filled solitons B. Eiermann et al. PRL 92, (2004) gap solitons "negative mass" dark solitons quantum pressure interactions L. Khaykovich et al., Science 296, 1290 (2002) g<0 bright solitons quasi-1D regime collapse for E int >E radial N Soliton < 10 4 K.S. Strecker et al., Nature 417, 150 (2002)

1D: Bright Mixed ‘‘Solitons‘‘ Bose-Bose repulsion versus Fermi-Bose attraction T. Karpiuk, M. Brewczyk, S. Ospelkaus-Schwarzer, K. Bongs, M. Gajda, and K. Rzążewski, PRL 93, (2004) behaviour in the trap: after switching off the trap: dynamics: constant envelope simulation from M. Brewczyk et al. theory our data theory by T. Karpiuk, M. Brewczyk, M. Gaida, K. Rzazewski

Collision simulation shows complex dynamics: - repulsive - shape oscillations - particle exchange fermionic character due to the Pauli-principle ? Simulation from M. Brewczyk et al.

Bose-Fermi Mixtures with Attractive Interactions Physics in the High Density Limit trap aspect ratio effective interaction ("density") collapse bright mixed soliton attractive repulsive boson-induced BCS ? Influence of loss processes ?

Hamburg Team Kai Bongs - Atom optics V. M. Baev - Fibre lasers Spinor BEC: Jochen Kronjäger Christoph Becker Thomas Garl Martin Brinkmann Fermi-Bose mixtures K-Rb: Silke Ospelkaus-Schwarzer Christian Ospelkaus Philipp Ernst Oliver Wille Manuel Succo Stefan Salewski Ortwin Hellmig Arnold Stark Sergej Wexler Oliver Back Gerald Rapior Victoria Romano Dieter Barloesius Reinhard Mielck K. Se Staff Q. Gu - Theory BEC in Space: Anika Vogel Malte Schmidt Atom guiding in PCF: Stefan Vorath Peter Moraczewski

Cold Quantum Gas Group Hamburg Hamburg is a nice city... (for physics ) (and for visits!)