Claus ZimmermannPhysikalisches Institut der Universität

Tübingen

Superradiance and Collective Atomic Recoil Laser: what atoms and fire flies have in common

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

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

Atom

Cavity

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

movie1

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

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)

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)

Simulation

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

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)

Focker-Planck Simulation

BEC in a Ringresonator

Ringresonator

L = 85 mm (round trip)fsr= 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

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

momentumeigenstates

optical dipolepotential

momentumeigenstates

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" 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)

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 numberas expected for coherent scattering

Bragg-interferometer

Observing the phase of Rayleigh scattering

crucial:Lamb Dicke regimeBragg 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 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

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

Results

temperatur dependence pump dependence

TOF-Aufnahmen

Parameter

Momentum distribution

RIR-spectrum ofa 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 !