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Superradiance and Collective Atomic Recoil Laser: what atoms and fire flies have in common Claus Zimmermann Physikalisches Institut der Universität Tübingen Self-organization A.-L. Barabási, Nature 403, 849 (2000) pace 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) chirping crickets applause synchronization milleniums bridge glow worms Strogatz, et. al, Nature, 438, 43-44 (2005) Kuramoto model • universal coupling (each to all others) • constant amplitude (implies reservoir) • different resonances (within a small range) 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) Elastic scattering from a single localized atom Classical model Cavity Atom Many atoms: instability and self organization reverse field: source term loss bunching parameter: (see also: structure factor, Debey Waller factor) b e 2ikxm m instability: b movie1 First proof of principle: CARL 1. pump cavity from both sides 2. load atoms into the dipole trap 3. atoms are prebunched 4. block the reverse pumping 5. look at the beat signal 6. observe new frequency atoms D.Kruse et al. PRL 91, 183601 (2003) Compare experiment and simulation time domain: frequency domain: approximate analytic experession numerical simulation experiment • Interplay between bunching and scattering similar to free electron laser • Collective atomic recoil laser "CARL" (R.Bonifacio) Include damping: viscous CARL 1. pump cavity from a single side 2. load atoms into the dipole trap 3. activate optical molasses 4. look at the beat signal reverse mode starts spontaneously from noise! D.Kruse et al. PRL 91, 183601 (2003) Simulation add a friction term... ...and do the simulation Threshold behavior observed ! P+(W) threshold due to balance between friction and diffusion. 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) Focker-Planck Simulation BEC in a Ringresonator Ringresonator L = 85 mm (round trip) nfsr= 3.5 GHz w0 = 107 μm finesse: 87000 (p-polarisation), 6400 (s-polarisation) Einblicke ins Labor BEC in a ringcavity Christoph v. Cube and Sebastian Slama Rayleigh scattering in the quantum regime only internal degrees include center of mass motion Scattering requires bunching atom in a momentum eigenstate: homogeneous distribution: destructive interference in backward direction atom in a superposition state: periodic distribution: constructive interference for light with k=Dk/2 Rayleigh scattering is a self organization process momentum optical dipole eigenstates potential momentum eigenstates scattering more reverse light deeper dipole potential stronger mixing stronger bunching enhanced scattering threshold behavior: decay due to decoherence Superradiant Rayleigh scattering exponential gain for matter waves and optical waves Inouye et al. Science 285, 571 (1999) see also Piovella at al. Opt. Comm. 194, 167 (2001) Two regimes Bad cavity: coherence is stored in the density distribution ! Good cavity: coherence is stored in the light ! Simulation of good cavity regime (classical equations) Resonantly enhanced "end fire modes" of thermal atoms BEC atoms (time of flight) light experiment theory forward power • fully classical model • superradiant peak with several revivals • same qualitative behavior for BEC and thermal cloud 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 Future: collective Rabi-oscillations 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 Reflection angle and lattice constant quadratic increase with atom number as expected for coherent scattering Bragg-interferometer Observing the phase of Rayleigh scattering crucial: Lamb Dicke regime Bragg enhancement Sebastian Slama Gordon Krenz Simone Bux Phillipe Courteille CARL team Dietmar Kruse (now Trumpf) Christoph von Cube (now Zeiss) Benjamin Deh (now Rb-Li-mixture in Tübingen) Antje Ludewig (now Amsterdam) Scattering requires bunching 1. Scattering depends on density distribution scattered power depends on N2 for homogeneous r no scattering 2. This also holds for a single atom no scattering if the atom is in a momentum eigenstate: 3. Scattering requires a superposition state Self organization in the quantum picture 1. classical ensemble threshold behavior: diffusion due to heat 2. quantum ensemble (BEC) threshold behavior: decay due to decoherence Results temperatur dependence pump dependence TOF-Aufnahmen Parameter Momentum distribution experiment: bimodal distribution RIR-spectrum of a thermal distribution Christoph von Cube (now Zeiss) Benjamin Deh (different projekt in Tübingen) Antje Ludewig (now Amsterdam) Phillipe Courteille Sebastian Slama Gordon Krenz (not on the picture) Visit us in Tübingen ! Atoms trapped in the modes of a cavity Running wave mode atoms don‘t hit the mirror !