### Session X6: Quantum and Nonlinear Optics

Chair: Frank Narducci, Naval Air Systems Command
Room: Arboretum IV-V

 Saturday, May 29, 2010 10:30AM - 10:42AM X6.00001: Lamb-Dicke-enhanced free-space superfluorescence in a cold thermal vapor Joel Greenberg , Daniel Gauthier We observe end-fire mode superfluorescence (SF) from an anisotropic, thermal atomic cloud of rubidium atoms. In contrast to traditional SF experiments that employ a single pump beam, we use a pair of counterpropagating, near-resonant beams to drive the SF process. By loading the atoms into the 1D optical lattice created by the pump beams, we greatly enhance the atomic coherence time by exploiting the Lamb-Dicke effect, thus enabling collective emission to occur without the need for an external cavity or ultracold temperatures. Using this technique, we achieve continuous SF with a coherence time of $\sim$300 $\mu$s and demonstrate all-optical switching with several thousand photons. Saturday, May 29, 2010 10:42AM - 10:54AM X6.00002: Cavity QED with group II atoms Dominic Meiser , Murray J. Holland Group II atoms have inter-combination lines with transition dipole moments many orders of magnitude smaller than normal optically allowed transitions. When put inside a high finesse cavity these atoms give rise to exotic cavity QED systems because of the weakness of the atom-field interaction as well as the extremely long atomic coherence times. We outline some of the general characteristics of such systems. As an application we present results on a light source that promises to have an unprecedentedly narrow linewidth in the millihertz range, surpassing the current state of the art by about two orders of magnitude. This light source could be a valuable tool for precision measurements and atomic clocks. Saturday, May 29, 2010 10:54AM - 11:06AM X6.00003: Substantial interaction between a singe atom and a focused light beam Gleb Maslennikov , Syed Abdullah Aljunid , Jianwei Lee , Brenda Chng , Hoang Lan Dao , Martin Paesold , Valerio Scarani , Christian Kurtsiefer We investigate both theoretically and experimentally the near-resonant interaction between a single atom in an optical dipole trap and a focused coherent light beam. We have demonstrated that even for a moderate focusing strength, a single atom localized at the focus of a simple aspheric lens can scatter a significant fraction of light[1,2], impose a phase shift~[3], and partially reflect a probe beam. With our current experimental system, we observe an extinction of 10\%, a phase shift of about 1$^\circ$ and a reflectivity of 0.17\%. For an optimal focusing geometry, we would expect an extinction up to 92\%, a phase shift of 30$^\circ$. The strength of the observed effect suggests that an efficient interface between atoms and photons for quantum information purposes can be established -- either without cavities, or by enhancing the electrical field in in a low-finesse cavity simply by strong focusing. We report on our experimental progress towards this goal. \\ {[1]} M. K. Tey, et al., Nature Physics {\bf 4} 924 (2008); {[2]} M. K. Tey et. al., New J. Phys. {\bf 11}, 043011 (2009); {[3]} S.A. Aljunid et al., Phys. Rev. Lett. {\bf 103}, 153601 (2009) Saturday, May 29, 2010 11:06AM - 11:18AM X6.00004: Coherent-Light Boosted, Super-Sensitive, Quantum Interferometery William Plick , Jonathan Dowling , Girish Agarwal We present a new scheme for optical interferometry. We utilize coherent-beam stimulated two-mode squeezed light, which interacts with a phase and is then squeezed again before detection. Our protocol has the potential to reach far below the shot noise limit (SNL) in phase sensitivity. This new proposal avoids the pitfalls of other setups, such as difficulty in creating the required resource. Furthermore, our scheme requires no complicated detection protocol, relying instead only on simple intensity measurement. Also, bright, coherent sources boost'' squeezed light, creating a very sensitive device. In the following we present our analysis of this relatively straightforward device, using the operator propagation method. We derive the phase sensitivity and provide a simple numerical example of the power of our new proposal. Sensitivity scales as a shot noise limited Mach-Zehnder Interferometer, multiplied by a sub-Heisenberg contribution from the squeezed light. Saturday, May 29, 2010 11:18AM - 11:30AM X6.00005: Optical Precursor Investigation in an Organic Dye Solution Matthew Springer , Wenlong Yang , Alexei Sokolov , George Kattawar , Alexandre Kolomenski Recent interest in Sommerfeld-Brillouin optical precursors has brought attention to the possibility of optical precursor observation in bulk matter. We investigate the possible development of optical precursors in an organic dye solution with a sharp absorption resonance and anomalous dispersion at a wavelength of approximately 800nm. We explore this regime experimentally with femtosecond laser pulses of sub-10fs duration, measured by an autocorrelation technique after transmission through the dye. The observed experimental autocorrelation results are compared with computational simulations which indicate important dispersion effects in the shape of the propagated pulse, including precursor-like behavior in its time evolution. Saturday, May 29, 2010 11:30AM - 11:42AM X6.00006: Low-loss nonlinear polaritonics Barry Sanders , Sergey Moiseev , Ali Kamli We propose large low-loss cross-phase modulation between two coupled surface polaritons propagating through a double electromagnetically-induced transparency medium situated close to a negative-index metamaterial. A mutual pi phase shift is attainable between the two pulses at the single photon level. Saturday, May 29, 2010 11:42AM - 11:54AM X6.00007: Single-photon light shifts of ground-state quantum beats D.G. Norris , L.A. Orozco , P. Barberis , H.J. Carmichael We present measurements of optical correlations from a high-finesse cavity in the intermediate coupling regime, which supports two modes of orthogonal linear polarization. The combination of the two modes with the magnetic structure of 85 Rb atoms allows us to separate photons originating from spontaneous emission from those that come from the driving laser. The second-order intensity correlation function reveals quantum beats at twice the ground-state Larmor frequency for a small applied magnetic field. The beats arise from a coherent ground-state superposition that evolves in time between photon emissions. The frequency of oscillation is sensitive to different parameters of the system; in this talk we show evidence of power-dependent shifts in the oscillation frequencies, visible even at driving intensities of less than one photon on average in the cavity. We discuss a theoretical model that quantitatively includes many of the characteristics of the experiment and shows the frequency shifts. Saturday, May 29, 2010 11:54AM - 12:06PM X6.00008: ABSTRACT WITHDRAWN Saturday, May 29, 2010 12:06PM - 12:18PM X6.00009: Controlled, $i.e.$ negative, peak velocity of light in ordinary dispersive media Alexei Sokolov , Xi Wang , Gombojav Ariunbold , Marlan Scully We introduce a concept of controlling the propagation velocity of a laser pulse's intensity peak. This is achieved by preparing, at the input of an ordinary dispersive medium, a special pulse shape. For example, a sequence of pulses with a varying amount of negative pre-chirp can be used, such that each pulse compresses to a transform-limited shape at a certain distance into the dispersive medium. Then, when the pulse delays are properly adjusted, one will be able to achieve a situation when these pulses produce an overall intensity peak, and therefore (possibly) a nonlinear excitation, which propagate at an arbitrary controlled speed, forward or backward, $i.e.$ at -$c$. We implement this idea to show that the directionality of lasing can be controlled through pump pulse shaping and timing. In our proof-of-principle experiments, we use a laser dye solution pumped through a nonlinear (two-photon) excitation, and demonstrate that mirror-less lasing in this system can be forced to preferentially occur in the backward direction. In general one can consider setting the velocity of the pulse peak anywhere from plus infinity to minus infinity, and matching the excitation speed to for example speed of sound, or making this speed variable and allowing acceleration. Saturday, May 29, 2010 12:18PM - 12:30PM X6.00010: Generation of twin beams using four-wave mixing: theory and experiments Quentin Glorieux , Romain Dubessy , Samuel Guibal , Luca Guidoni , Jean Pierre Likforman , Thomas Coudreau , Ennio Arimondo Recently, four-wave mixing has drawn a large interest as a simple and efficient source of non classical light [1]. Using a strong pump (400 mW) propagating in a heated rubidium cell, it is possible to generate quantum correlated beams. The set-up has the advantage of both simplicity (no resonant cavity) and efficiency (we measure up to 9.5 dB of noise reduction below the standard quantum limit). However, up to now, no microscopic model was proposed for this phenomenon. Here we present for the first time such a model [2] based on the Heisenberg-Langevin input-output formalism [3] and we verify that the classical gain and the quantum correlations are in very good agreement with our experimental datas. A new regime of correlation generation in absence of gain is also proposed. \\[4pt] [1] C.F. McCormick et al., Opt. Lett (2007) vol. 32 p. 178\\[0pt] [2] Q. Glorieux et al., in preparation (2010)\\[0pt] [3] P. Kolchin, Phys. Rev. A (2007) vol. 75 p. 33814