Duke University, Physics Department and the Fitzpatrick Institute for Photonics · Durham, NC Collective Nonlinear Optical Effects in an Ultracold Thermal Vapor Anisotropic MOT 1 Joel A. Greenberg, Daniel J. Gauthier Introduction Citations 1)J.A. Greenberg, M. Oria, A.M.C. Dawes, D.J. Gauthier, Opt. Express 15, (2007) 2)M. Malcuit, Univ. of Rochester, PhD Dissertation (1987) 3)J.A. Greenberg and D.J. Gauthier, OSA Opt. Photonics Cong. Tech. Digest, ISBN (2009) Length: 3 cm, Radius: 150  m Optical Depth ~55 (I out /I in = e -OD ) Density 7x10 10 atoms/cm 3 Temperature ~30 μK 87 Rb trapped on F=2  F’=3 Applications Funding NSF AMO Grant # PHY ; DARPA Slow Light Contract PO # G-2 Mirror Cooling Trapping Probe z y x MOT Vacuum Cell Magnets 3 cm Our magneto-optical trap (MOT) uses lasers and magnetic fields to trap and cool atoms Collective Effects 2 3 cm cold atoms MOT Characteristics: MOT Setup: Collective optical effects occur when the radiative properties of an atom are effected by the presence of additional atoms Superfluorescence Few-photon NLO elements are critical for quantum information applications, but large atom-photon interaction strengths are needed We obtain large nonlinear couplings in cold atoms by controlling the atoms’ internal and external states Nonlinear Optics (NLO) with Cold Atoms Goal: Single-photon NLO Collective nonlinear effects allow for a drastic enhancement of the atom-photon coupling strength over single-atom effects, and may lower NLO thresholds to the single-photon limit Trapping laser beam configurationPhoto of MOT setup CCD image of trapped atoms 1 Spontaneous Emission (SE) Amplified Spontaneous Emission (ASE) Superfluorescence (SF) SF Thresh Collectivity The influence of the radiators on one another can take on a continuum of values (described by a collectivity parameter). On one end, atoms radiate independently (SE) – on the other, all atoms release their energy at the same time (SF) Power  SF  SE /N  SE DD P peak Cooperative emission produces a short, intense pulse of light P peak  N 2 (N times larger than SE!) Delay time (  D ) before pulse occurs Threshold density/ pump power The degree of atomic organization affects the radiation field, thus producing a nonlocal atom-atom coupling. The net result is a runaway process that gives rise to the collective emission of light Scattering enhances grating Grating enhances scattering P peak (  W) OD  N P F/B (mW)  D (  s) P peak (  W) P F/B (mW) Self-organization Collective Emission Characteristics We observe SF light generated along the trap’s long axis in both the forward and backward directions 3 t (  s) Power (  W) Forward Backward F/B Pump beams MOT beams on off SF light is nearly degenerate with pump frequency Light persists until atomic density falls below threshold F/B SF temporal correlations ~1 photon emitted/atom SF Characteristics Experimental Setup Pump (F) Pump (B) Cold atoms Detector (B) Detector (F) SF light Counter-propagating pump beams Detect emitted light in forward (F) and backward (B) directions The forces exerted on atoms by multiple light beams give rise to a global spatial organization of the atoms Atomic density grating SF light An atom recoils when it absorbs or a emits a photon atom Example: Absorption SF Light Observed on Detectors SF Light Trends beforeafter Laser timing scheme We find good agreement with the predictions of superfluorescent collective atomic recoil lasing (CARL) theory New insight into free electron laser dynamics Possible source of correlated photon pairs Optical/Quantum memory We may be seeing a nonlinear (N 2 ) scaling of the peak SF power with atom number SF Power vs N time