Light scattering and atom amplification in a Bose-Einstein condensate

1
Light scattering and atom amplification in a
Bose-Einstein condensate
Workshop on Chemistry of Cold Molecules

• March 25, 2004
• Yoshio Torii
• Institute of Physics, University of Tokyo, Komaba

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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

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What is Bose-Einstin condensation?
Macroscopic occupation of atoms in the lowest
quantum state of motion
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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 !
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BEC??????
atoms behave as billiard balls
T300K
Laser cooling
Wave nature begins to manifest
T100µK
Evaporative cooling
Wavepackets begin to overlap
T1mK
Evaporative cooling
One giant matter wave Bose-Einstein condensation
T100nK
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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
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The BEC apparatus at Tokyo Univ.
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The principle of laser cooling
Scattered light
Laser light
?cooling!
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Magneto-optical Trap (MOT)
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MOT of Rb atoms in a glass cell
4cm
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What is evaporative cooling?
Nice applet at Colorado University Website
http//www.colorado.edu/physics/2000/applets/bec.h
tml
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Zeeman shift of Rb87
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Cloverleaf coils for magnetic trap
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Evaporative cooling an a cigar-shaped magnetic
trap
5mm
20 MHz
10 MHz
5 MHz
5 MHz
1MHz
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BEC phase transition
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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
• (10µm100µm)
• 3. Spatial density of
• 1014 atoms/cm3
• 4. Coherent

1ms
16.5ms
11ms
5.5ms
22ms
27.5ms
33ms
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Atom-optics elements for BECs
The Basic idea Bragg scattering
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Bragg scattering of BEC
M. Kozuma et. al.Phys. Rev. Lett. 82, 871
(1999)
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Absorption Images of Bragg diffracted BEC (20 ms
TOF)
Half beamsplitter
Perfect mirror
Y. T, et. al., PRA 61, R041602 (2000)
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Mach-Zehnder interferometer for light waves and
matter waves
Light wave
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Mach-Zehnder interferometer for BECs
Y. T, et. al., PRA 61, R041602 (2000)
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Superradiant Rayleigh scattering in a
Bose-Einstein condensate
S. Inouye, et. al., Science 285, 571 (1999)
Na BEC
75ms
100ms
35ms
Off-resonant pump light
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Superradiant Rayleigh scattering in a Rb BEC
Week pump light
Strong pump light
Rb BEC
Rb BEC
D. Schneble, Y.T., M. Boyd, E. W. Streed, D. E.
Pritchard, and W. Ketterle, Science 300, 475
(2003)
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The origin of superradiance
goes on
The rate of light scattering is enhanced by the
number of already scattered photons
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LaserLight Amplification by Stimulated Emission
of Radiation
N photons already in the cavity
Emission rate from an excited atoms
Stimulated emission
Spontaneous emission
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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)
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How to check the coherence of the amplified wave
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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)
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The gallery of atom lasers
NIST 99
MIT 97
Munich 99
Yale 98
gravity
Bragg pulses
Rf sweep
Rf knife
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Continuous atom laser
A device which converts thermal atoms into a
coherent matter wave continuously
Thermal atoms
Coherent matter wave
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Our strategy for CW atom laser
Zeeman slower
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The whole apparatus
2m
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Zeeman coils
1m
Trimming coils
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Velocity distribution of a Zeeman-slowed Rb
atomic bean
Flux of the thermal atoms
1012atoms/s Flux of the slowed atoms
21011atoms/s (20 of the thermal
atoms) final velocity 20 m/s
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Loading a MOT from slowed atoms
4cm
21010 atoms/s
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The world of Bose-Einstein condensation
Condensed-matter physics
Quantum Optics
0
1
Superconductor
Optical laser
Atomic BEC (atom laser)
Superfluid