Cold Quantum Gas Group Hamburg

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

2 Fermi Bose Mixture Project Quantum Degenerate Fermi-Bose Mixtures of 40K/87Rb at Hamburg: since 5/03 Special interest: Fermi-Bose Mixtures in optical lattices:

3 Latest Results degenerate Fermi gas with 40 K in combination with Rb BEC Fermion cloud TOF: 5ms BEC TOF: 30ms T/T F ~ 0.75 N F ~ TOF: 15ms TOF: 15ms preliminary T/T F ~ 0.3 +/- 0.1 N F ~ N B ~ see Poster Nr. 10 by Silke Ospelkaus-Schwarzer

4 Dresden, October 2004 Multi-Component Quantum Gases Magnetism and a New Realisation of BEC Spinor quantum gas systems -> Magnetism in quantum gases Klaus Sengstock Multi-component thermodynamics -> New path to BEC Universität Hamburg Institut für Laserphysik

5 The System Bose-Einstein condensates in weakly interacting gases: (experiments since 1995) usually (due to magnetic trapping): single component BEC F= condensate fraction N 0 /N 1 1-(T/T c ) 3 normal component T c T simultaneous trapping of more components, e.g. trapping of all m F -levels in optical dipole traps: -> multi-component spinor quantum gases

6 The System Multi-component spinor-quantum-gases very rich sytem due to: - several different interactions (within condensate fraction, within normal cloud and in between) - exchange of population possible (within condensate fractions and between condensate fraction and normal cloud) F=1 F=

7 Relevant Interactions Small difference in weak interactions of quantum gases i.e. different s-wave scattering lengths for different total spin e.g a 0 a 2 total-spin conservation!

8 Relevant Interactions Small difference in weak interactions of quantum gases i.e. different s-wave scattering lengths for different total spin e.g.: > a 0 a

9 Relevant Interactions Small difference in weak interactions of quantum gases i.e. different s-wave scattering lengths for different total spin e.g a 0 a 2 total spin of collision process determines s-wave scattering length 87 Rb: 23 Na: F=1 F=2 a 0, a 2 a 0, a 2, a 4 110,0±4a B, 107,0±4a B 89,4±3a B, 94,5±3a B, 106,0±4a B, T.-L. Ho, PRL, 81, 742 (1998); C.V. Ciobanu et al., PRA 61, (2000) J. Stenger, et al.,nature 396, 345 (1998)..

10 Relevant Interactions Small difference in weak interactions of quantum gases i.e. different s-wave scattering lengths for different total spin e.g a 0 a 2 note: total dipole-dipole spin of collision interactions process present determines but negligible s-wave scattering length 87 Rb: F=1 F=2 a 0, a 2 a 0, a 2, a 4 110,0±4a B, 107,0±4a B 89,4±3a B, 94,5±3a B, 106,0±4a B, E dd ~10-33 J T.-L. Ho, PRL, 81, 742 (1998); C.V. Ciobanu et al., PRA 61, (2000) J. Stenger, et al.,nature 396, 345 (1998).. studies on dipole-dipole interactions, e.g. in Stuttgart (Cr-atoms) E mf ~10-32 J

11 Magnetism in Solid State Sytems spin (½) in periodic lattice + exchange interaction r r H = J S S ferromagnet spin 1 2 < i, j> interaction energy ~ 100 k B K i j anti-ferromagnet domain structures

12 Magnetism in a Gas free spins + collisions + external magnetic field interaction energies ~ k B nk "ferromagnetism" "anti-ferromagnetism" domain structures

13 single comp. mean field n 0 n -1 System Interactions mean field exchange interaction linear Zeeman F= quadratic Zeeman F=2 n +1 n -2 n +2 chemical potential ~ 120nK 1 1 F r r F=1 F=1: 1 F 2 ~35 µk/g but: g 1 ~10nK, g 2 ~0.2nK cancels due to spin conservation ~14nK/G 2 Spin-depended energy functional: F=1 E s pin = ( - p <F z > + q <F Z 2 > + g 1 <F> 2 n + g 2 <P 0 > 2 n ) n lin. Zeeman energy quadratic Zeeman energy Spin dependend mean field [1] additional mean field for F=2 [2] [1] T.-L. Ho, PRL, 81, p.742 (1998) [2] M. Koashi, M. Ueda, PRL, 84, p.1066 (2000)

14 Magnetism in Quantum Gases System allows studies of spinor condensate dynamics and ground state properties e.g. F=1 F=2 Ho et al. 98 Ketterle et al s 3 s 0 ms 10 ms 300 ms Cornell et al. 98 Bigelow et al. 98 Ueda et al. 99 Cirac, Zoller 01 You et al. 02, 04 Lewenstein et al m F m F Hamburg group 03 Chapman et al.03 1,2 s coupled Gross Pitaevskii equations vs. physics beyond GPE (entanglement, damping,...) spinor BEC in optical lattices quantum information applications

15 Experimental scheme creation of Rb-BEC in a far detuned optical dipole trap m F = +2 preparation of initial spin distribution by RAP and LZ sweeps e.g. m F = 0 time evolution of spinor condensate for a variable hold time in the optical dipole trap at low bias field m F =? detection after Stern-Gerlach and time-of-flight m F

16 Experimental Scheme initial spin preparation m F m F

17 Experimental scheme creation of Rb-BEC in a far detuned optical dipole trap m F = +2 preparation of initial spin distribution by RAP and LZ sweeps e.g. m F = 0 time evolution of spinor condensate for a variable hold time in the optical dipole trap at low bias field m F =? detection after Stern-Gerlach and time-of-flight m F important to remember for interpretation of dynamics:!!! pictures taken after Stern Gerlach separation!!!

18 F=1 Magnetic Ground States (quadr.zeeman: ) representation as function of total spin (s) and offset-magnetic field (q). Schmaljohann et al. Laser Phys. 14, 1252 (2004). J. Stenger, et al., Nature 396, 345 (1998). ferromagnetic anti-ferromagnetic

19 Magnetic Ground States Rb F = 1 is ferromagnetic! 0 s 5 s 10 s 0 s 5 s 5 s 10 s m F m F H. Schmaljohann et al. Phys. Rev. Lett. 92, (2004). see also: work by Georgia-Tech group M.-S. Chang et al., Phys. Rev. Lett. 93, (2004).

20 Magnetic Ground States F=2 our calculations: (quadr.zeeman: ) ferromagnetic anti-ferromagnetic cyclic Schmaljohann et al. J. Mod. Opt. 51,1829 (2004) 87 Rb F = 2 is antiferromagnetic H. Schmaljohann et al. Phys. Rev. Lett. 92, (2004). 0 ms 200 ms m F =

21 Spin Dynamics for 87 Rb, F=2 Example: Preparation in m F = 0 0 ms 10 ms 300 ms m F fast (~10 ms) spin dynamics initial delay oscillations coherent dynamics vs. damping H. Schmaljohann et al., Phys. Rev. Lett. 92, (2004).

22 Spin Dynamics - Simulation based on coupled GPE ( T = 0 ), homogenous case: delayed build up, oscillations,... strongly depend on phases and initial conditions F=2: Simulations for finite temperature M. Guilleumas, M. Lewenstein et al. Poster 13, Tuesday small seed in +/-1 and +/-2 comp.: 10-4

23 Spin Dynamics for 87 Rb, F=1 very slow ( sec) spin dynamics in F = 1! 0 s 5 s 10 s m F

24 87 Rb Spinor-Ground States F = 2 : Antiferromagnetic fast 0 ms 87 Rb 200 ms m F = F = 1 : Ferromagnetic slow 0 s ferromagnet coherent coupling antiferrom. 5 s 10 s m F

25 Quantum Gas Four-wave-mixing quantum optics viewpoint four-wave-mixing optics: ω 1 ω 3 for BEC (Phillips et al.): ω 2 ω 4 spinor condensates (J. P. Burke et al., cond-mat/ ) F=2: even more complex four wave mixing fully equivalent description to populate empty modes: - seed - quantum fluctuations DGLs: multi mode coupling competing four wave mixing channels

26 Quantum Gas Four-wave-mixing adding kinetic energy plus magnetic fields: additional processes possible e.g.: F= ( p r = 0) quadratic Zeeman energy proposed experiment: FWM into zero momentum states F=1, m F =0 Raman excitation offset field ~ 3G 2hk = ˆ 2 h k 2m r r h k, + hk 1, p r = 0 r 0, hk + 1, p r = 0 r + 0, + hk phonon driven spin dynamics??! for very small offset B-field k r T e.g. quadrupole mode phonon 0 coupling to spin conversion coupling of spinor components and finite T excitations?

27 Quantum Gas Four-wave-mixing F=2: the other way round Zeeman energy kinetic energy 0 +1 four wave mixing for k 1 =k 2 =0! no grating!? Bragg diffraction condition not necessary for FWM? -> spin grating present! entanglement source

28 II. Multi Component Quantum Gas Thermodynamics How do different quantum gas components at different T do interact with each other and how do they exchange population? T 1 T 2 T special here: temperature reservoir and particle reservoir - different time scales for spin dynamics within condensate and thermalization τ ~ 5 s (F=1) or: τ ~ 5 ms (F=2) -allows, e.g.: new path to BEC condensate melting temperature driven magnetization! τ ~ 100 ms

29 BEC new aspects 3 T db c n Λ ( ) = N 0 /N 1 const. T approach T c T BEC

30 BEC new aspects A. Einstein, Sitzungsber. Preuss. Akad. Wiss., 3, 1925

31 Realisation for F=1 normal components +/-1: temperature reservoir condensate fractions +/-1:particle reservoir m F =-1 m F =0 m F =+1 T start: m F = 0 empty slow spin dynamics populates m F =0 -> fast thermalisation if critical density for component reached: BEC transition only population of m F =0 condensate component T no relevant spin dynamics in thermal cloud

32 Experimental Realisation start: m F = 0 empty t=0s filling up m F =0 normal component t=3s critical density reached t=8s population of m F =0 condensate t=10s

33 Multi Component Thermodynamics description by a rate equation model based on 7 variables N 0,N 0 0,N 0,N t,n t 0,N t,t thermalisation X N 0, th X N t,th N X th 0 N t N X N th 0 t T th th TN 0 1-body losses X N 0,1b X N t,1b N X 1 0 N X 1 t spin dynamics N 0, sp sp1 N 0 0 N N 0, sp 2 sp1 N 0 0 N body losses N N sp2 0 0 N 0,3b 2 sp2 N 0 N 0 X N 0 X Lc 3 N evaporation X N t,ev N X e t T ev e T T e phase space redistribution If N t X N c T : N 0 X t t N 0 X t N t X t N c N t X t t N c T t t T t 1 N t N t 0 0 N t t t

34 Constant Temperature BEC time m F = M. Erhard et al. cond-mat/ related work: Ketterle et al.: dimple trap Cornell et al.: decoherence driven cooling

35 "Free" Condensate Fraction Important aspect: Condensate fraction is independend of normal component saturated normal component ( Einstein ) condensate fraction Possibility to add more and more particles to the condensate fraction without changing N thermal

36 Multi Component BEC at Finite T Another example: Magnetisation of a BEC preparation of mixture 0,+1: Spin Average Spin per atom 1 normal 0.8 components equalise, (via spin dynamics) -> total spin = 0 exp., BEC 0.6 exp., thermal exp., all sim, BEC sim, thermal 0.4 sim, all condensate 0.2 spin increases! 0 temperature driven Hold Time [s] magnetisation of BEC! Spin

37 Realization of Condensate Melting 87 Rb offers both regimes, condensate melting in F=2: Fast spin dynamics, slow thermalisation 0 ms 0 -component 40 ms "pure" condensates 125 ms condensate melting

38 Mixed Hyperfine State Feshbach Resonance in 87 Rb ) experiment, this work M. Erhard et al., PRA in press ( / G ) 4.) theoretical calculation Tiemann, priv. com. offers further opportunities for manipulation of 87Rb spin mixtures and entanglement 1.) theoretical prediction ( E. van Kempen et al. PRL 88, (2002)) 3.) experiment, München A. Widera et al., cond-mat/ ( / G )

39 Multi-Component BEC Magnetic properties of spinor condensates H. Schmaljohann et al. Phys. Rev. Lett. 92, (2004), J. Mod. Opt. 51,1829 (2004), Laser Phys. 14, 1252 (2004). Text book quantum gas thermodynamics M. Erhard et al. Phys. Rev. A. 70, (2004), H. Schmaljohann et al. Apl. Phys. B, in press (2004). Advanced studies on spin-dynamics - coupling ferro- and antiferromagnetic states - investigation of coherence and entanglement - physics beyond Gross-Pitaevskii equation Playing text-book thermodynamics - exploration of new regimes Filled Spinor Solitons Spinor BEC in optical lattices ferromagnet coherent coupling antiferromagnet

40 The Hamburg team K. Se Kai Bongs - Atom optics Spinor BEC: (Holger Schmaljohann) (Michael Erhard) Jochen Kronjäger Christoph Becker Thomas Garl Martin Brinkmann Fermi-Bose mixtures K-Rb: Christian Ospelkaus Silke Ospelkaus-Schwarzer Oliver Wille Marlon Nakat BEC in Space: Anika Vogel Malte Schmidt Atom guiding in PCF: Stefan Vorath Q. Gu -Theory V. M. Baev - Fibre lasers Stefan Salewski Arnold Stark Sergej Wexler Oliver Back Gerald Rapior Ortwin Hellmig Staff Victoria Romano Dieter Barloesius Reinhard Mielck

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