Superradiance and Collective Atomic Recoil Laser: what atoms and fire flies have in common
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Transcript of Superradiance and Collective Atomic Recoil Laser: what atoms and fire flies have in common
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Claus ZimmermannPhysikalisches Institut der Universität
Tübingen
Superradiance and Collective Atomic Recoil Laser: what atoms and fire flies have in common
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Self-organizationpace maker cells, chirping crickets, fire flies,..Bènard convection, laser arrays, Josephson junctions, CARL...economy ...see for instance S. H. Strogatz, Physica D 143, 1 (2000)
applause synchronization
A.-L. Barabási, Nature 403, 849 (2000)
milleniums bridge
Strogatz, et. al, Nature, 438, 43-44 (2005)
glow worms
chirping crickets
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Kuramoto model
• universal coupling (each to all others)• constant amplitude (implies reservoir)• different resonances (within a small range)
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Experiment: atoms in a resonator-dipole-trap
B. Nagorny et.al., Phys, Rev. A 67, 031401 (R) (2003); D. Kruse et al., Phys. Rev. A 67, 051802 (R) (2003)
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Elastic scattering from a single localized atom
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Classical model
Atom
Cavity
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Many atoms: instability and self organization
reverse field:
loss source term
m
ikxmeb 2
bunching parameter:(see also: structure factor, Debey Waller factor)
instability:
b
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movie1
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First proof of principle: CARL
atoms
D.Kruse et al. PRL 91, 183601 (2003)
1. pump cavity from both sides2. load atoms into the dipole trap3. atoms are prebunched4. block the reverse pumping5. look at the beat signal6. observe new frequency
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Compare experiment and simulation
time domain:
frequencydomain:
numerical simulation
approximate analytic experession
experiment
• Interplay between bunching and scattering similar to free electron laser• Collective atomic recoil laser "CARL" (R.Bonifacio)
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Include damping: viscous CARL
1. pump cavity from a single side2. load atoms into the dipole trap3. activate optical molasses4. look at the beat signal
reverse mode starts spontaneously from noise!
D.Kruse et al. PRL 91, 183601 (2003)
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Simulation
...and do the simulationadd a friction term...
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Threshold behavior observed !
Theory: G.R.M. Robb, et al. Phys. Rev. A 69,041403 (R) (2004) Experiment: Ch. von Cube et al. Phys. Rev. Lett. 93, 083601 (2004)
threshold due to balance between friction and diffusion.
P+(W)
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Focker-Planck Simulation
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BEC in a Ringresonator
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Ringresonator
L = 85 mm (round trip)fsr= 3.5 GHz
w0 = 107 μm
finesse: 87000 (p-polarisation), 6400 (s-polarisation)
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Einblicke ins Labor
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BEC in a ringcavity
Christoph v. Cube and Sebastian Slama
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Rayleigh scattering in the quantum regime
only internal degrees include center of mass motion
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Scattering requires bunching
atom in a momentum eigenstate:
homogeneous distribution: destructive interference in backward direction
periodic distribution: constructive interference for light with k=k/2
atom in a superposition state:
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Rayleigh scattering is a self organization process
scattering
more reverse light
deeper dipole potential
stronger mixing
stronger bunching
enhanced scattering
momentumeigenstates
optical dipolepotential
momentumeigenstates
threshold behavior: decay due to decoherence
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Superradiant Rayleigh scattering
Inouye et al. Science 285, 571 (1999)
exponential gain for matter waves and optical waves
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Two regimes
Good cavity:coherence is stored in the light !
Bad cavity:coherence is stored in the density distribution !
see also Piovella at al. Opt. Comm. 194, 167 (2001)
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Simulation of good cavity regime(classical equations)
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Resonantly enhanced "end fire modes" ofthermal atoms
• fully classical model
• superradiant peak with several revivals
• same qualitative behavior for BEC and thermal cloud
experiment
theory forward power
light BEC atoms (time of flight)
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Varying the atom number
good cavity limit (high finesse)
- - -: N 4/3
..... : N 2
superradiant limit (low finesse)
- - -: N 4/3
..... : N 2
includes mirror scattering
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Future: collective Rabi-oscillations
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Excursion: Bragg reflection
setup for Bragg reflection observed Bragg reflection
Bragg beam resonant with 5p-6p transition (421.7nm)waist: 0.25 mm, power: 3µW
3000 Bragg planes with 106 atoms total
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Reflection angle and lattice constant
quadratic increase with atom numberas expected for coherent scattering
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Bragg-interferometer
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Observing the phase of Rayleigh scattering
crucial:Lamb Dicke regimeBragg enhancement
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CARL team
Sebastian Slama
Gordon Krenz
Simone Bux
Phillipe Courteille
Dietmar Kruse(now Trumpf)
Christoph von Cube (now Zeiss)
Benjamin Deh (now Rb-Li-mixture in Tübingen)
Antje Ludewig (now Amsterdam)
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Scattering requires bunching
1. Scattering depends on density distribution
for homogeneous no scattering
scattered power depends on N2
2. This also holds for a single atom
no scattering if the atom is in a momentum eigenstate:
3. Scattering requires a superposition state
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Self organization in the quantum picture
2. quantum ensemble(BEC)
1. classical ensemble
threshold behavior:
threshold behavior:
decay due to decoherence
diffusion due to heat
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Results
temperatur dependence pump dependence
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TOF-Aufnahmen
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Parameter
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Momentum distribution
RIR-spectrum ofa thermal distribution
experiment:bimodal distribution
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Visit us in Tübingen !
Phillipe Courteille
Sebastian Slama
Gordon Krenz (not on the picture)
Christoph von Cube (now Zeiss)
Benjamin Deh (different projekt in Tübingen)
Antje Ludewig (now Amsterdam)
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Atoms trapped in the modes of a cavity
Running wave mode
atoms don‘t hit the mirror !
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