Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session Z4: Rydberg Atoms and Coherent Control |
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Chair: Thomas Gallagher, University of Virginia Room: Knoxville Convention Center 301D |
Saturday, May 20, 2006 9:00AM - 9:12AM |
Z4.00001: Time Dependence of Many-Body Interactions in Ultra-cold Rydberg Atom Samples of Different Geometries Thomas Carroll, Cordelia Ochis, Michael Noel Ultra-cold highly-excited atoms in a magneto-optical trap are strongly coupled by the dipole-dipole interaction. We have investigated the importance of many-body effects by controlling the dimensionality and density of the excited sample and by varying the time during which the atoms are allowed to interact. We excited Rydberg atoms in two different geometries: a nearly one dimensional column with a diameter on the order of the typical interatomic spacing and a more three dimensional column with a diameter a few times larger than the typical spacing. In each volume, the interaction time was varied from 0 to 8~$\mu$s. Many-body effects are seen to be important in the time development of the three-dimensional system, while they are suppressed in the one dimensional case. This work was supported by the National Science Foundation under Grant No. 0134676. [Preview Abstract] |
Saturday, May 20, 2006 9:12AM - 9:24AM |
Z4.00002: Coherence conditions for groups of Rydberg atoms Jesus Hernandez, Francis Robicheaux We investigate the excitation of a collection of cold atoms to Rydberg states. By direct numerical solution of Schr\"odinger's equation, we are able to compute various interesting properties of the many body wave function. The high polarizability of Rydberg atoms allows them to support large dipole moments which in turn can interact over long ranges. If the interaction energy between two excited atoms is large enough the resultant energy shift will move the two excitation state out of resonance, thus effectively blocking a two excitation state form occurring. One particular topic investigated is the quantum phase gate, where both groups of atoms are within a blockade radius and subjected to a $\pi -2\pi -\pi$ sequence of pulses. We examine the regime where the groups are neither totally within nor totally outside the blockade radius. Testing the conditions for coherence will help establish constraints for quantum information. If time permits, counting statistics as related to the Mandel $Q$ parameter will be used to measure blockade effectiveness. [Preview Abstract] |
Saturday, May 20, 2006 9:24AM - 9:36AM |
Z4.00003: Many-body effects in strongly interacting systems of Rydberg atoms Jovica Stanojevic, Robin C\"ot\'e We investigate the effects of strong interactions in ultracold Rydberg gases. Strong Rydberg-Rydberg interactions have been proposed to entangle large numbers of atoms, which can be used to implement fast quantum gates. The laser excitation of a macroscopic sample of ultracold atoms to high-lying Rydberg states can be dramatically suppressed by their strong long-range interactions. This leads to a local blockade effect, where a single excited Rydberg atom prevents excitation of its neighbors. Recently, large inhibitions of Rydberg excitations due to van der Waals interactions have been observed. We explore the dynamics of strongly interacting systems with many excited atoms. Including many-body correlations is essential for such systems. Besides the inhibition of Rydberg excitation, we are particularly interested in the conditions for collective oscillations. These oscillations should be much faster than the ordinary Rabi flopping for isolated atoms and should depend on the number of atoms in the sample. We discuss different analytical and numerical techniques used for solving the many-body Hamiltonian. [Preview Abstract] |
Saturday, May 20, 2006 9:36AM - 9:48AM |
Z4.00004: Ionic Dipole and Quadrupole Matrix Elements from Non Adiabatic Core Polarization Edward Shuman, Tom Gallagher The radial matrix elements connecting the ionic Ba$^+$ state to low lying excited $6p$ and $5d$ states can be extracted from the K splittings of the bound $6sn\ell$ states. We develop an expression for the K splitting by a pair of expansions. Comparison of the contributions from different ionic states confirms that all but the lowest two may be safely ignored. Finally we extract the radial Ba$^+$ matrix elements $\left<6s|r|6p\right>$ and $\left<6s|r^2|5d\right>$. [Preview Abstract] |
Saturday, May 20, 2006 9:48AM - 10:00AM |
Z4.00005: Weak signal detection using quantum interference Mevan Gunawardena, D.S. Elliott We demonstrate a powerful technique for detecting weak atomic or molecular transitions that is based on homodyning two atomic transition amplitudes. The scheme is tested on a weak Stark-induced transition in cesium by exciting its ground 6s $^{2}$S$_{1/2}$ state to the 8s $^{2}$S$_{1/2}$ excited state by a 411 nm laser field. The strong local oscillator signal is a two-photon transition excited by an 822 nm laser field that connects the same ground and exited states. The Stark-induced transition can be regulated by controlling a DC field across a Cs cell. The simultaneous excitation of the two pathways results in a quantum interference that can be controlled by phase modulating either of the driving laser fields. The change in the relative phase between the laser fields results in a change in the relative phase between the transition amplitudes of the two paths. Thus, phase modulating one of the beams gives rise to an amplitude modulation of the net excitation rate. The amplitude of this modulation allows a quantitative measure of the weak transition rate. [Preview Abstract] |
Saturday, May 20, 2006 10:00AM - 10:12AM |
Z4.00006: Observation of channel phase lag in asymmetric photoelectron angular distributions in the vicinity of autoionizing resonances Rekishu Yamazaki, D.S. Elliott We report the results of channel phase lag measurements in the photoionization of atomic barium. We ionize the 6s6p $^{1}$P$_{1}$ excited state via a coherent laser field consisting of two frequencies, $\omega $ and 2$\omega $, to excite the atom to an autoionizing resonance in the series converging on the 5d$_{5/2}$ threshold. We present the channel phase lag observed for the asymmetric angular distribution for different ionization product states at different locations of the autoionizing resonances. [Preview Abstract] |
Saturday, May 20, 2006 10:12AM - 10:24AM |
Z4.00007: Measurement of the phase difference between even and odd continuum waves in photoionization of atomic rubidium. C.A. Rupley, Rekishu Yamazaki, D.S. Elliott We report improved measurements of asymmetric photoelectron angular distributions resulting from photoionization of atomic rubidium through coherent one-photon and two-photon interactions. Analysis of the asymmetry allows us to determine the phase difference between even- and odd-parity continuum wavefunctions. We discuss calibration of the phase, including field propagation phase shifts and the phase shift upon frequency doubling in a nonlinear crystal. [Preview Abstract] |
Saturday, May 20, 2006 10:24AM - 10:36AM |
Z4.00008: Observation of high-order quantum resonances in the delta kicked rotor M. Partlow, J.F. Kanem, S. Maneshi, C. Zhuang, A.M. Steinberg, M. Spanner Quantum resonances in the delta kicked rotor\footnote{F.L. Moore, J.C. Robinson, C.F. Bharucha, B. Sundaram, M.G. Raizen, {\it Phys. Rev. Lett.} \textbf{75} 4598 (1995). } are characterized by a dramatically increased energy absorption rate in direct contradiction to the momentum localization generally observed. These resonances exist where the scaled Planck's constant $\tilde{\hbar}=\frac{r}{s}\cdot4\pi$, for integers $r$ and $s$. However only the $\tilde{\hbar}=r\cdot2\pi$ resonances are easily observable. We report on the observation of high-order quantum resonances ($s>2$) utilizing a sample of low temperature, non-condensed atoms and a pulsed optical standing wave. Resonances are observed for $\tilde{\hbar}=\frac{r}{16}\cdot4\pi$ for integers $r=2-6$. The behavior of the resonances with variation of kick number and kick strength is examined. Quantum numerical simulations suggest that our observation of high-order resonances indicates a much longer spatial coherence than expected from an initially thermal atomic sample. [Preview Abstract] |
Saturday, May 20, 2006 10:36AM - 10:48AM |
Z4.00009: Coherent Control of Strong Field Dynamics. Carlos Trallero, Thomas Weinacht, Jayson Cohen We present experimental results on coherent control of multi-photon transitions in the strong field limit. A learning algorithm is capable of discovering shaped laser pulses which can compensate for dynamic Stark shifts and greatly outperform an unshaped laser pulse. We provide a comparison between experiments that use a spontaneous emission signal as feedback for the learning algorithm and ones that make use of a stimulated emission signal. Our experimental results are compared with calculations of the strong field dynamics. [Preview Abstract] |
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