Institut für Laserphysik 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 Institut für Laserphysik Universität Hamburg

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

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

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

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 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

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

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 P(p) P(p) T>>Tc,TF p -pF pF p P(p) P(p) T<Tc,TF p p -pF pF P(p) P(p) T<<Tc,TF p p -pF pF

e.g.: Momentum Distributions of Fermions and Bosons P(p) P(p) T>>Tc,TF p -pF pF p P(p) P(p) T<Tc,TF p p -pF pF

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 Cooper pairs - BCS superfluidity T0 exponentially difficult to reach (valid for kF|a|<<1) e.g.: kFa=-0.2 -> TBCS ~ 10-4 TF (very very small) (very) low-temperature effect

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 ? ...

  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

Fermi-Bose Mixtures there is even more: special interest: mixtures in optical lattices  new phases, composite particles, ... Ubf Ubb 1 2 -1 -2 IIFD IISF IIFL IFL IDM IIDM mb/Ubb . composite fermions M. Lewenstein et al., Phys. Rev. Lett. 92, 050401 (2004) M. Cramer et al., Phys. Rev. Lett. 93, 190405 (2004)

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)

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

Sympathetic Cooling 5x107 6Li at T~0.05 TF state of the art (temperature): 5x107 6Li at T~0.05 TF 1x106 40K at T~0.15 TF (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

Attractive Boson-Fermion Interaction aK-Rb ~ -279 a0 + BEC = effective potential for fermions: Fermion cloud with BEC experimental signatures: Fermion cloud without BEC

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

Collapse Experiments 7Li collapse 85Rb "Bosenova" 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)

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 t = 197ms t = 21ms time/frequency scales: 3-body-loss -> collapse-time due to trap dynamics time/frequency scales: - nr(K) = 394 Hz - nax(K) = 17 Hz - thermalization 10..50 ms - collapse: ~ 20 ms - loss processes 100..200 ms loss and collapse dynamics can be distinguished!

3-Body Losses measurement of the 3-body KRb decay rate N 1 d r n , t 2 , t F model for 3-body inelastic decay in thermal mixture: integration over time: ln T dt -2.5 -2 -1.5 -1 -0.5 20 40 60 80 100 120 140 160 180 T ln N T ln N Result: K K cm 6 K ( +/- 0.2) 3.5 10 28 K Rb Rb s Measurement does not depend on K atom number calibration For 87 Rb |2,2> decay, we reproduce the value from Söding et al. [Appl. Phys. B69, 257 (1999)] T d 3 r n 2 r , t n r , t dt B F 10 38 m 6 s N t K

Fermi-Bose Mixtures in the Large Particle Limit: Stability Diagram NBoson stable mixture non stable mixture aKRb=-281 a0 (S. Inouye et al., PRL 93, 183201 (2004)) NFermion

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

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)

1D: Bright Mixed ‘‘Solitons‘‘ Bose-Bose repulsion versus Fermi-Bose attraction our data after switching off the trap: 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)

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

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

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 Vorath Peter Moraczewski

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