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Light scattering and atom amplification in a Bose-Einstein condensate

Workshop on Chemistry of Cold Molecules. Light scattering and atom amplification in a Bose-Einstein condensate. March 25, 2004 Yoshio Torii Institute of Physics, University of Tokyo, Komaba. The overview. The review of BEC in atomic gases Atom-optics elements for BECs

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Light scattering and atom amplification in a Bose-Einstein condensate

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  1. Workshop on Chemistry of Cold Molecules Light scattering and atom amplification in a Bose-Einstein condensate March 25, 2004 Yoshio Torii Institute of Physics, University of Tokyo, Komaba

  2. The overview • The review of BEC in atomic gases • Atom-optics elements for BECs • Superradiant light scattering in a BEC (Matter wave amplification in a BEC) • Quest for Continuous atom lasers

  3. What is Bose-Einstin condensation? Macroscopic occupation of atoms in the lowest quantum state of motion

  4. The criterion of BEC Predicted by Einstein in 1925 Phase space density (the number of atoms in the lowest quantum state) Thermal de Briglie wave length (the average size of wavepackets) BEC is formed when the wavepackets overlap with each other !

  5. BEC波動論的説明 atoms behave as “billiard balls” T～300K Laser cooling Wave nature begins to manifest T～100μK Evaporative cooling Wavepackets begin to overlap T～1mK Evaporative cooling One giant matter wave Bose-Einstein condensation T～100nK

  6. The history of Bose-Einstein condensation • 1924,25 Bose-Einstein statistics (Bose) • prediction of Bose-Einstein condensation (Einstein) • Superfluidity in liquid helium explained as BEC（London） • BCS theory for Superconductivity （Bardeen, Cooper, Schrieffer ） • 1960 Invention of laser （Maiman） • 1975 The idea of laser cooling （Hänsch ,Schawlow） • 1980～ Deceleration of atomic beam （Phillips）～mK • 1985 Laser cooling of atoms in 3-D （Chu） ～240μK • Polarization Gradient cooling ～3μK • （Phillips, Cohen-Tannoudji） • 1995 Realization of BEC in Rb, Na • （Cornel, Wieman, Ketterle）～100nk Nobel Prize in 1997 Nobel Prize in 2001

  7. The BEC apparatus at Tokyo Univ.

  8. Example 1 : Doppler cooling Example 2: Cavity cooling H. W. Chan, et. al., PRL 90, 063003, 2003 The principle of laser cooling Scattered light: Laser light: →cooling!

  9. Magneto-optical Trap (MOT)

  10. MOT of Rb atoms in a glass cell 4cm

  11. What is evaporative cooling? Nice applet at Colorado University Website http://www.colorado.edu/physics/2000/applets/bec.html

  12. Zeeman shift of Rb87

  13. Cloverleaf coils for magnetic trap

  14. Evaporative cooling an a cigar-shaped magnetic trap 5mm 20 MHz 10 MHz 5 MHz 5 MHz 1MHz

  15. BEC phase transition

  16. The properties of BEC Images of a BEC released from the magnetic trap 1mm • 1. narrow velocity spread • below the recoil velocity （6mm/s for Rb87 ） • 2. Well localized in space • 　 （10μm～100μm） • 3. Spatial density of • ～1014 atoms/cm3 • 4. Coherent 27.5ms 1ms 5.5ms 11ms 16.5ms 22ms 33ms

  17. Acoust-Optics Modulator light wave matter wave (BEC) Modulation of refractive index in the matter Optical standing wave Bragg diffracted light wave Bragg diffracted matter wave Atom-optics elements for BECs The Basic idea: Bragg scattering

  18. Bragg scattering of BEC [M. Kozuma et. al.Phys. Rev. Lett. 82, 871 (1999)]

  19. Absorption Images of Bragg diffracted BEC (20 ms TOF) Half beamsplitter Perfect mirror Y. T, et. al., PRA 61, R041602 (2000)

  20. matter wave (BEC) Mach-Zehnder interferometer for light waves and matter waves Light wave

  21. Mach-Zehnder interferometer for BECs Y. T, et. al., PRA 61, R041602 (2000)

  22. Superradiant Rayleigh scattering in a Bose-Einstein condensate S. Inouye, et. al., Science 285, 571 (1999) Na BEC 100ms 75ms 35ms Off-resonant pump light

  23. Superradiant Rayleigh scattering in a Rb BEC Week pump light Strong pump light RbBEC RbBEC D. Schneble, Y.T., M. Boyd, E. W. Streed, D. E. Pritchard, and W. Ketterle, Science 300, 475 (2003)

  24. Bragg scattering of pump light Recoiling atom Spontaneous emission BEC Pump light Two recoiling atoms Bragg scattering of pump light The origin of superradiance … goes on The rate of light scattering is enhanced by the number of already scattered photons

  25. LaserLight Amplification by Stimulated Emission of Radiation N photons already in the cavity Emission rate from an excited atoms Stimulated emission Spontaneous emission

  26. Matter wave amplification M. Kozuma, et. al., Science 286, 2309 (1999) BEC Pump beam Pump pulse only Nothing happened Bragg pulse only 6.5% of atoms were Bragg diffracted Bragg pulse, then pump pulse 66% of atoms were coupled out (10 fold amplification)

  27. How to check the coherence of the amplified wave

  28. Interferometer for the amplified matter wave seeded Matter wave Bragg pulse pump pulse p Bragg pulse amplified Matter wave reference Matter wave p/2 Bragg pulse M. Kozuma, et. al., Science 286, 2309 (1999)

  29. The gallery of atom lasers NIST ‘99 MIT ‘97 Yale ‘98 Munich ‘99 gravity Bragg pulses Rf sweep Rf knife

  30. 2-D Magnetic guide Rf evaporation E. Mandonnet, et. al., Eur. Phys. J. D 10, 9 (2000) Continuous atom laser A device which converts thermal atoms into a coherent matter wave “continuously” Thermal atoms Coherent matter wave

  31. Goal: MOT loading rate more than 1010atoms/s Our strategy for CW atom laser Zeeman slower

  32. The whole apparatus 2m

  33. Zeeman coils 1m Trimming coils

  34. Velocity distribution of a Zeeman-slowed Rb atomic bean ・Flux of the thermal atoms ～１０１２atoms/s ・Flux of the slowed atoms ～２×１０１１atoms/s （20% of the thermal atoms） ・final velocity ～20 m/s

  35. Loading a MOT from slowed atoms 4cm 2×1010 atoms/s

  36. Chemistry with Molecular BECs The world of Bose-Einstein condensation Condensed-matter physics Quantum Optics 0 1 Superconductor Optical laser Atomic BEC (atom laser) Superfluid

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