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Ultracold Quantum Gases: An Experimental Review

Ultracold Quantum Gases: An Experimental Review. Herwig Ott University of Kaiserslautern OPTIMAS Research Center. Outline. Laser cooling , magnetic trapping and BEC Optical dipole traps, fermions Optical lattices : Superfluid to Mott insulator transition

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Ultracold Quantum Gases: An Experimental Review

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  1. Ultracold Quantum Gases:An Experimental Review Herwig Ott University of Kaiserslautern OPTIMAS Research Center

  2. Outline • Laser cooling, magnetictrappingand BEC • Optical dipole traps, fermions • Optical lattices:Superfluid to Mott insulatortransition • Magneticmicrotraps: Atom chipsand 1D physics

  3. Outline • Feshbachresonances: tamingtheinteraction • The BEC-BCS transition • Single atomdetection

  4. Lab impressionsfrom all overtheworld Munich Tübingen Osaka Austin

  5. Magneto-optical trap (MOT) MOT: 3s, 1 x 109 atoms

  6. MOT: Limits andextensions Temperature: 50 – 150 µK foralkalis Atom number: 1 … 109 Hugeloading rate (Zeeman slower, 2D-MOT) Single atom MOT (strong quadrupolefield) Narrow transitions: below 1µK (e.g. Strontium)

  7. The beauty of magneto-optical traps sodium strontium lithium ytterbium dysprosium erbium

  8. Magnetictrapping Working principle:Magneticfieldminimumprovidestrapping potential Evaporativecoolingwithradiofrequencyinducedspinflips Technical issues: heatproduction in thecoils, control of fieldminimum Pros: robust, large atomnumber Cons: longcoolingcycle (20 s – 60 s), limited opticalaccess

  9. Magnetic traps for neutral atoms Ioffe- Pritchardtrap Cloverleaftrap 4 cm

  10. Imaging an ultracoldquantum gas „Time offlight“ technique Credits: Immanuel Bloch

  11. coherent matter wave „Standard“ Bose-Einstein condensation classical gas Tc ~ 1µK Bose-Einstein condensation

  12. The first BEC 1995: Cornell andWieman, Boulder

  13. The earlyphase: 1995 - 1999 expansion: condensatefraction Duke speed of sound Boulder MIT

  14. The earlyphase: 1995 - 1999 Interferencebetweentwocondensates (MIT) MIT

  15. The earlyphase: 1995 - 1999 Vortices Boulder

  16. Optical dipole traps Working principle: exploit AC Stark shift single beam dipoletrap crosseddipoletrap 1 mm

  17. Optical dipole traps Arbitrarytrappingpotentialspossible Requirementsfor a gooddipoletrap: a lot of laserpower: 100 W @ 1064 nmavailable Pro: independent of magnetic sub-level, magneticfieldbecomesfreeparameter Con: high power laser, stabilization, limited trapdepth -> smalleratomnumber

  18. Ultracold Fermi gases The challenge: • Identicalfermions do not collideatultralowtemperatures • Fermions aremoresubtlethanbosons -> everythingismoredifficult The solution: Take tow different spin-statesoradmixbosons Duke university

  19. After release from the trap Bosons (rubidium) Fermions (potassium) Ultracold Fermi gases Bose-Fermi mixtures Florence

  20. Optical lattices Laser configuration 2D lattice (makes 1D tubes) 3D lattice Band structure

  21. Optical lattices Expansion of a superfluid: interferencepatternvisible Expansion withoutcoherence Munich

  22. Optical lattices Superfluidity: tunnelingdominates Mott insulator: Interaction energy Dominates (nointerference)

  23. Atoms meetsolids: atomchips Working principle: makeminiaturizedmagnetic traps withminaturizedelectricwires: HomogeneousOffest-field Magneticfield of a wire Trapping potential fortheatomsalongthewire => one-dimensional geometry

  24. Atom chips Todays‘ssetup: Basel

  25. Atom chips: 1D physics Radial confinementleadstostrongerinteraction Lieb-Linigerinteractionparameter: Inducedantibunching: Tonks-Girardeau gas Penn state

  26. Newton‘scradlewithatoms Penn State

  27. Feshbachresonances Microscopicinnteractionmechanismsbetweentheultacoldatoms: s-wavescattering, and (moreandmoreoften) dipole-dipole interaction Change the s-wavescatteringlength via magneticfield: Working principle:

  28. Genericproperties of a Feshbachresonance The situationforfermionic6Li: Unitaryregime Repulsive interaction Attractiveinteraction

  29. Making ultracoldmolecules Evaporativecooling in a dipoletrap Maximum possiblenumber of trapped non-interactingfermions a = + 3500 a0 a = - 3500 a0 Innsbruck

  30. Molecules form Bose-Einstein condensates Twofermionicatoms form a bosonicmolecule Result:bimodaldistribution of moleculardensitydistribution Condensatefraction Boulder

  31. Controlling theinteractionbetweenfermions a>0: weak repulsive interaction, BEC of molecules a<0: weakattractiveinteraction, BCS type of pairing Whathappens in between?

  32. Test superfluiditywithcreation of vortices Set atoms in rotationandtestsuperfluiditybytheformationof vortices MIT

  33. Unitaryregime Result: fermionare superfluid acrossthecrossover MIT

  34. Dynamic of inelasticprocesses Lifetime of thevortices MIT

  35. Single atomdetection Fluorescenceimaging: • shine resonant light on atomsandkeepthemtrappedatthe same time • collectenoughphotonstodetecttheatoms Single atoms in a 1D opticallattice Bonn

  36. Single atomdetection in a 2D system The Mott insulatorstate Munich

  37. Single atomdetectionwithelectronmicroscopy Comeandseetomorrow!

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