### Session N4: Quantum and Non-Linear Optics

Chair: David Phillips, Harvard-Smithsonian for Astrophysics
Room: Knoxville Convention Center 301E

 Thursday, May 18, 2006 1:30PM - 1:42PM N4.00001: Stored light optimization in Rb vapor cells Irina Novikova , David Phillips , Ronald Walsworth We present an experimental study of stored light in Rb vapor cells under conditions of electromagnetically induced transparency (EIT). We study the technical and fundamental limitations to storage lifetimes, efficiency, and fidelity, and propose optimization schemes. Thursday, May 18, 2006 1:42PM - 1:54PM N4.00002: Influence of EIT coherence on laser phase-noise to intensity-noise conversion Yanhong Xiao , David Phillips , Cindy Hancox , Irina Novikova , Ronald Walsworth Laser phase-noise can induce intensity-noise through interactions with atoms. We report an experimental study of the influence of EIT coherence in Rb vapor on this noise conversion process. Enhancement of the intensity-noise is observed as the EIT coherence is varied via two-photon Raman detuning. We attribute this enhancement to the correlation of phase fluctuations created in EIT. Potential implications for CPT atomic clocks will be discussed. Thursday, May 18, 2006 1:54PM - 2:06PM N4.00003: Light storage in coated vapor cells Michael Hohensee , Mason Klein , David Phillips , Irina Novikova , Ronald Walsworth Rubidium vapor cells with walls coated with paraffins such as tetracontane can have very long coherence times due to the suppression of decoherence during wall collisions by the coating.  We discuss behavior of characteristic ultra-narrow EIT spectra and the corresponding slow light in coated cells.  Based on dynamical simulations we consider optimal conditions for storage and retrieval of optical information. Thursday, May 18, 2006 2:06PM - 2:18PM N4.00004: Negative refraction without absorption in the optical regime Juergen Kaestel , Michael Fleischhauer , Susanne F. Yelin , Ron L. Walsworth We show that interference phenomena such as electromagnetically induced transparency together with local field effects can lead to negative refraction with strongly suppressed absorption in the optical regime. For this chirality induced by the coherent coupling of a magnetic dipole transition to a nearly degenerate electric dipole transition in a $V$-type configuration is employed. In this way negative refraction can be obtained without the need of negative permeabilities, thus substantially reducing the requirements on density and magnetic dipole strength. Furthermore while leading to a constructive interference of the cross-coupling and thus to an enhancement of chirality, the coherent coupling also causes a destructive interference in the imaginary part of the electric susceptibility and thus to a suppression of absorption. A remarkable amplification of these effects happens when local field corrections become important: While the refractivity of the medium saturates with increasing density, the absorption decreases in an exponential way, leading to very large refraction/absorption ratios. Thursday, May 18, 2006 2:18PM - 2:30PM N4.00005: The N- and CPT- joint resonance: Theory, experiment and implications for novel compact frequency references. Michael Crescimanno , Irina Novikova , Yanhong Xiao , Cindy Hancox , David Phillips , Ron Walsworth There has been considerable recent interest in the use of the hyperfine N-resonance in clock applications. We describe the solution of a quantum optics model of the joint N- and CPT- optical resonance with particular attention to its lineshape and lightshift/detuning shift behavior. Recent experimental progress allows a direct detailed test of aspects of this theory. This has led to a preliminary view of the promise and problems of this approach to compact frequency standards. Thursday, May 18, 2006 2:30PM - 2:42PM N4.00006: Two photon quantum interference of light emitted by two ions P. Maunz , M.J. Madsen , D.L. Moehring , K. Younge , R.N. Kohn, Jr. , C. Monroe Entanglement, which is at the base of all quantum computing algorithms, can now routinely be established through the collective motion of nearby trapped atomic ions. However, entangling remotely-located ions remains a challenge. One possible realization requires the interference of two single photons emitted by the ions. Towards this end, we demonstrate the second order interference of single photons emitted from two cadmium ions trapped in an rf Paul trap. In free space we achieve a visibility of about 60\%. Additionally, using an ultrafast laser pulse, we demonstrate the excitation of a single ion on a time scale much faster than the lifetime of the excited state. The subsequently emitted photons show near-perfect anti-bunching, demonstrating that from a single laser pulse at most one photon is scattered by the atom. Improving the visibility of the two-photon interference and combining it with the readily available methods of state detection of a trapped ion may allow two ions to be entangled without involving their motion. Thursday, May 18, 2006 2:42PM - 2:54PM N4.00007: Quantum State Reconstruction of a Large Angular Momentum by Continuous Weak Meaurement Poul Jessen , Greg Smith , Andrew Silberfarb , Ivan Deutsch We show experimentally that an optical probe measurement can be used to acquire complete information about the angular momentum density matrix for an ensemble of Cs atoms in the $F$ = 3 hyperfine ground manifold. We do this by measuring a single atomic observable (e. g. a spin component), while driving the system so that it explores the entire spin state space. The quantum state can then be estimated from the measurement record in the presence of the known system dynamics. We show that high fidelity estimates can be achieved for a wide variety of test states, including squeezed- and similar non-classical states generated by the action of the tensor light shift. The procedure is non-destructive, in the sense that the ensemble is available in a known quantum state at the end of the estimation. It can also -- in principle -- be performed in real time, though our implementation does not reach that limit. This suggests that the procedure may serve as the starting point for a new type of feedback that involves partial or complete knowledge of the ensemble quantum state. Thursday, May 18, 2006 2:54PM - 3:06PM N4.00008: Large Cross-Phase Modulation between Slow Co-propagating Weak Pulses in $^{87}$Rb Z.B. Wang , K.-P. Marzlin , B.C. Sanders Strong optical cross-phase modulation (XPM) for weak fields is tremendously important, e.g.~for optical quantum information processing and for all-optical switches in classical communication. Several proposals based on electromagnetically induced transparency (EIT) have been brought forward, but XPM remains experimentally challenging. One problem is to achieve equal slow group velocities (double EIT) for both signal pulses to maximize the interaction time. \\ We present a scheme that exploits the best features of previous proposals and adds some new techniques, thereby optimizing the large XPM parameter. We propose a feasible procedure to prepare the atomic initial state such that double EIT with a single atomic species can be achieved, and present a specific implementation of the scheme for $^{87}$Rb with a single pump laser and a homogeneous magnetic field. Furthermore, we study the nonlinear evolution of the two weak signal pulses and present a new upper bound on the maximal XPM phase shift achievable for two Gaussian single-photon pulses. Thursday, May 18, 2006 3:06PM - 3:18PM N4.00009: Cavity-Aided Single Atom Detection on an Atom Chip Igor Teper , Yu-ju Lin , Vladan Vuletic We will present the results in detecting and counting small numbers of rubidium atoms, down to one atom, in a microscopic magnetic trap. We employ a 2.5 cm long, near-confocal cavity with a finesse of 8600 mounted on the atom chip that generates the microtrap. Both fluorescence and absorption techniques are used for the detection. In the fluorescence scheme, 2.0(2) photons per atom are collected, which achieves a quantum efficiency of 75{\%} for single atom detection with a probability of 7{\%} of false counting due to background photons, while the attenuation of transmission through the cavity is 2.0(3){\%} per atom. The cavity can also potentially be used for spin squeezing by measuring the atom-induced cavity frequency shift, and we expect that 20dB of squeezing can be achieved with N= 5x10$^{5}$ atoms. Spin squeezing would allow for an atomic clock operated below the standard quantum limit (shot noise limit). Thursday, May 18, 2006 3:18PM - 3:30PM N4.00010: Coherent Interactions with Rubidium Atoms Confined in a Hollow-Core Photonic Band-Gap Fiber Saikat Ghosh , Amar Bhagwat , Christopher Kyle Renshaw , Shireen Goh , Alexander Gaeta , Brian Kirby The creation of a significant density of alkali atoms within a hollow-core fiber offers significant promise for applications in extremely low-light level nonlinear optics. However, such a system has proven to be challenging to realize experimentally. We use the phenomenon of light-induced atomic desorption in a surface-modified hollow-core photonic bandgap fiber to produce a significant density of Rubidium atoms throughout its length. A theoretical analysis of the system is in good agreement with our experimental observations. We use this system to demonstrate electromagnetically induced transparency in the fiber with control field powers as low as 20 nW. Issues regarding decoherence and optical delays are studied experimentally and theoretically.