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Nonlinear Spectroscopy of Cold Atoms, Preparations for the BEC Experiments

Nonlinear Spectroscopy of Cold Atoms, Preparations for the BEC Experiments. Jerzy Zachorowski M. Smoluchowski Institute of Physics, Jagiellonian University. Tomasz Brzozowski Maria Mączyńska Jerzy Zachorowski Michał Zawada Wojciech Gawlik . IF UJ. The Group. I. I. Magneto-Optical Trap.

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Nonlinear Spectroscopy of Cold Atoms, Preparations for the BEC Experiments

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  1. Nonlinear Spectroscopy of Cold Atoms, Preparations for the BECExperiments Jerzy Zachorowski M. Smoluchowski Institute of Physics, Jagiellonian University

  2. Tomasz Brzozowski Maria Mączyńska Jerzy Zachorowski Michał Zawada Wojciech Gawlik IF UJ The Group

  3. I I Magneto-Optical Trap 85Rb N  108 T  100 K

  4. = 22.4 · I I 0 - 50 - 40 - 30 - 20 - 10 0 10 20 Detuning from the 3 - 4 resonance [MHz] -2 -1 0 2 1 -2 -1 0 1 2 -40 -20 0 20 trap-probe[MHz] Spectroscopy of Cold Atoms

  5. Laser system

  6. Central Structure • Raman transitions between light-shifted Zeeman sublevels • Raman transitions between vibrational levels in the optical lattice

  7. Zeeman sublevels

  8. Vibrational levels • Electric field in the trap: 6 beams of different polarizations. • Relative phases not fixed, but relatively stable. • Interference: intensity and/or polarization modulation. • Additional optical forces (dipole forces). • Atoms cooled and localized in the lattice nodes. • Atomic movement quantized: vibrational energy levels.

  9. Difference absorption-wave mixing Ultra-narrow central resonance Remarks New experiments: trap modulation

  10. Ketterle, PRL 77, 416 (1996) Bose-Einstein Condensation de Broglie wavelength: density n, distance n1/3, condensation when:

  11. 100 K 100 nK 300 K MOT MT Lower temperatures • Spontaneous emission: temperatures limited to 10 – 1mK • „Dark traps”: optical dipole or magnetic forces • Cooling by evaporation

  12. Three steps to BEC 1. Magneto-Optical Trap:temperature 10 mK, density 1010 cm-3limit – interaction with light. 2. Magnetic Trap:trap in field minimum - only „low-field-seeking” stateslosses at B = 0. 3. Evaporation cooling:forced evaporation of hot atoms,thermalisationby collisions.

  13. 1995 - E. Cornell & C. Wieman Rb87 50 nK 200 nK 400 nK • Evidence: • narrow peak in velocity distribution • peak’s amplitude  when T • cloud shape same as that of the potential well

  14. Now Over 30 laboratories produce BEC 87Rb, 23Na, 7Li, ↑H , He*, ... Experiments with BEC • Matter-wave optics: condensate interference, atom laser • Nonlinear atom optics • Superfluidity, vortices • Ultra-low density condensed-matter: Mott insulator • Cold fermions

  15. NIST MPQ MIT Matter-wave Optics– Atom Optics coherent waves  interference ”atom laser”

  16. light waves • (material mediumnonlinearity)  kin = kout  in = out b)   matter waves (always nonlinear) BEC Nonlinear atom-optics 1999 NIST (W. Phillips) & Marek Trippenbach (UW)

  17. MIT LENS, Florence Superfluidity, Vortices

  18. Ultra-low density condensed-matter Mott transition MPQ – Garching

  19. Micro-BEC 6000 87Rb atoms loading time 8 s cooling time 2,1 s current 2A Garching

  20. Micro-BEC 2 Tubingen 87Rb Number of atoms in BEC: 106 Condensation at T=1mK Cooling time 27s

  21. Li7 Li6 Cold fermions Do not thermalize (Pauli exclusion) Sympathetic coolinge.g. fermion 40K & boson 87Rb,fermion 6Li & boson 7Li 1999 D. Jin (JILA) 40K 2001 R. Hulet (Rice)

  22. Magneto-optical trapping T 30 K, N 108 MOT Transfer to magnetic trap by radiation pressure, recapture in a MOTseparated vacuum regions differential pumping(10-8mbar 10-11mbar) Magnetic trapping:forced evaporation of hottest atoms, thermalization by collisionsT 100 nK, N 105- 106 MT Our way towards BEC Element 87Rb

  23. Transfer of atoms • repetitive pushing by resonant light beam, recapture in lower MOTcollection speed: 108–1010 s-1loading of lower MOT: 107–109 s-1 • constant pushing by narrow light beam (Dalibard) flux: ~108 s-1 • magnetic transfer directly into magnetic trap (Hänsch)30% efficiency, complicated.

  24. Magnetic traps QUIC = Quadrupole + Joffe configuration: B ≠ 0 at trap center Dalibard Hänsch

  25. September 2002 • Laser system prepared • Upper MOT ready & operating • Next steps: transfer & recapture magnetic trapping

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