Superfluorescence in an Ultracold Thermal Vapor FIP Superfluorescence in an Ultracold Thermal Vapor Joel A. Greenberg and Daniel. J. Gauthier Duke University 7/15/2009

Superfluorescence (SF) Pump W N L W2/Ll~1 ‘endfire’ modes Dicke, Phys. Rev. 93, 99 (1954); Bonifacio & Lugiato, Phys. Rev. A 11, 1507 (1975), Polder et al., Phys. Rev. A 19, 1192 (1979), Rehler & Eberly, Phys. Rev A 3, 1735 (1971)

SF Threshold Cooperativity Ppeak tSFtsp/N tsp tD 1 SF Thresh time Spontaneous Emission Amplified Spontaneous Emission (ASE) Superfluorescence (SF) Cooperativity 1 SF Thresh Ppeak Cooperative emission produces short, intense pulse of light PpeakN2 Delay time (tD) before pulse occurs Threshold density/ pump power tSFtsp/N Power tsp tD time Malcuit, M., PhD Dissertation (1987); Svelto, Principles of Lasers, Plenum (1982)

New Regime: Thermal Free-space SF * Counterpropagating, collinear pump beams1 * Large gain path length2 Detector (B) Pump (B) Cold atoms Detector (F) Pump (F) T=20 mK N~109 Rb atoms PF/B~4 mW L=3 cm, R=150 mm  F=R2/lL~1 DF2F’3=-5G NOT BEC! NO CAVITY! ≠ Inouye et al. ≠ Slama et al. 1) Wang et al. PRA 72, 043804; 2) Yoshikawa PRL 94, 083602 Inouye et al. Science 285, 571 (1999); Slama et al. PRL 98, 053603 (2007)

Results - SF Power (mW) t (ms) MOT beams F/B Pumps SF light nearly degenerate with pump frequency Light persists until N falls below threshold F/B temporal correlations ~1 photon/atom  large fraction of atoms participate Forward Backward Power (mW) t (ms) on MOT beams F/B Pumps off

Results - SF Ppeak tD Density/Pump power thresholds PpeakPF/B tD (PF/B)-1/2 Consistent with CARL superradiance* Power tD time tD (ms) Ppeak (mW) PF/B (mW) PF/B (mW) *Piovella et al. Opt. Comm. 187, 165 (2001)

What is the mechanism responsible for SF? Probe Spectroscopy What is the mechanism responsible for SF?

What is the mechanism responsible for SF? Probe Spectroscopy What is the mechanism responsible for SF? Pump (B) Probe Detector (B) (wp =w+d) Cold atoms Detector (F) Pump (F) T=20 mK L=3 cm, R=150 mm PF/B~4 mW N~109 Rb atoms DF2F’3=5G

Recoil-Induced Resonance Atom-photon interaction modifies the energy and momentum of an atom Energy + momentum conservation result in resonance Absorption: atom atom Emission: atom atom

Probe Spectroscopy Forward Detector Backward Detector (FWM) Pout/Pin RIR RIR PCR Raman Raman d (kHz) d (kHz) dSF dSF

Probe Gain Typical SF gain threshold are Pout/Pin~exp(10)=104 PRIR/Pprobe SF Threshold F/B Pump Power (mW)

Self-Organization RIR leads to spatial organization or atoms Backaction between atoms and photons leads to runaway process  Lower SF threshold Scattering enhances grating Grating enhances scattering

Conclusions Applications Observe free-space superfluorescence in a cold, thermal gas Temporal correlation between forward/backward radiation Spectroscopy and beatnote imply RIR scattering as source of SF Applications New insight into free electron laser dynamics Possible source of correlated photon pairs Optical/Quantum memory

Recoil-Induced Resonance (RIR) Resonant Processes Recoil-Induced Resonance (RIR) Vibrational Raman Initial state atom Final state atom

Probe Spectroscopy Probe Power SF signal dSF Probe Power d (kHz) Forward Detector Rayleigh pump beam alignment Probe Power Rayleigh Raman pump beam alignment Raman SF signal dSF Backward Detector (FWM) SF Power Probe Power time (ms) d (kHz)

Beatnote d (kHz) Power (F) Look at beatnote between probe beam and SF light as probe frequency is scanned Power (F) d (kHz)

Beatnote d (kHz) Df~450kHz fSF~-50kHz 1/Df Look at beatnote between probe beam and SF light as probe frequency is scanned Df~450kHz fSF~-50kHz 1/Df time (ms) d (kHz)

Weak probe Pumps (w) Probe (wp=w+d) d (kHz) d (kHz) Backward Forward

Coherence Time 1 Power PR time on toff F/B Pumps off PR toff

Lin || Lin Backward Pumps (w) Forward Power time (ms)

Results - SF Ppeak tD Ppeak (mW) OD  N Power time *Piovella et al. Opt. Comm. 187, 165 (2001)

CARL Regimes Good Cavity: k<wr Bad Cavity: k>wr Quantum: wr>G MIT (1999) Quantum CARL Ultracold Atoms/BEC MIT (2003) Tub (2006) Tub (2006) Semiclassical: wr<G Tub (2003) Thermal In resonator Free space Slama Dissertation (2007)