Claus Zimmermann Physikalisches Institut der Universität Tübingen Superradiance and Collective Atomic Recoil Laser: what atoms and fire flies have in common

Self-organization 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) applause synchronization A.-L. Barabási, Nature 403, 849 (2000) milleniums bridge Strogatz, et. al, Nature, 438, (2005) glow worms chirping crickets

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, (R) (2003); D. Kruse et al., Phys. Rev. A 67, (R) (2003)

Elastic scattering from a single localized atom

Classical model Atom Cavity

Many atoms: instability and self organization reverse field: loss source term bunching parameter: (see also: structure factor, Debey Waller factor) instability:

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First proof of principle: CARL atoms D.Kruse et al. PRL 91, (2003) 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

Compare experiment and simulation time domain: frequency domain: numerical simulation approximate analytic experession 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, (2003)

Simulation...and do the simulationadd a friction term...

Threshold behavior observed ! Theory: G.R.M. Robb, et al. Phys. Rev. A 69, (R) (2004) Experiment: Ch. von Cube et al. Phys. Rev. Lett. 93, (2004) threshold due to balance between friction and diffusion. P + (W)

Focker-Planck Simulation

BEC in a Ringresonator

Ringresonator L = 85 mm (round trip) fsr = 3.5 GHz w 0 = 107 μm finesse: (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 periodic distribution: constructive interference for light with k=  k/2 atom in a superposition state:

Rayleigh scattering is a self organization process scattering more reverse light deeper dipole potential stronger mixing stronger bunching enhanced scattering momentum eigenstates optical dipole potential momentum eigenstates threshold behavior: decay due to decoherence

Superradiant Rayleigh scattering Inouye et al. Science 285, 571 (1999) exponential gain for matter waves and optical waves

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)

Simulation of good cavity regime (classical equations)

Resonantly enhanced "end fire modes" of thermal 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)

Varying the atom number good cavity limit (high finesse) - - -: N 4/ : N 2 superradiant limit (low finesse) - - -: N 4/ : N 2 includes mirror scattering

Future: collective Rabi-oscillations

Excursion: Bragg reflection setup for Bragg reflectionobserved Bragg reflection Bragg beam resonant with 5p-6p transition (421.7nm) waist: 0.25 mm, power: 3µW 3000 Bragg planes with 10 6 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

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)

Scattering requires bunching 1. Scattering depends on density distribution for homogeneous  no scattering scattered power depends on N 2 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 2. quantum ensemble (BEC) 1. classical ensemble threshold behavior: decay due to decoherence diffusion due to heat

Results temperatur dependencepump dependence

TOF-Aufnahmen

Parameter

Momentum distribution RIR-spectrum of a thermal distribution experiment: bimodal distribution

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)

Atoms trapped in the modes of a cavity Running wave mode atoms don‘t hit the mirror !