Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session C5: Wavepacket Dynamics, Coherent Control, Quantum and/or Nonlinear Optics |
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Chair: T. F. Gallagher, University of Virginia Room: Burnham Yates Conference Center Arbor |
Wednesday, May 18, 2005 1:30PM - 1:42PM |
C5.00001: Coherence measurement of kicked Rydberg wave packets Joel Murray, Haidan Wen, Santosh Pisharody, Phil Bucksbaum Terahertz half-cycle pulses (HCP) are used to excite Rydberg wave packets. The states of these wave packets can be viewed as a data register, with information stored in the phase differences between the states. We characterize the operation of a weak HCP on the wave packet, observing the changes in phase and amplitude of each state. We have performed a measurement of the mutual coherence between Rydberg states detected in ramped- field ionization, following the operation of the HCP. We find that coherence is retained, but there exist particular times during the evolution of the wave packet when the HCP induces the loss of correlation between some pairs of Rydberg states. Simulations suggest that this apparent decoherence is due to coherent population transfer to other angular momentum manifolds. Since coherence is retained after the HCP, we are able to perform further coherent operations on the register. [Preview Abstract] |
Wednesday, May 18, 2005 1:42PM - 1:54PM |
C5.00002: Collisional decoherence of Rydberg wavepackets C.O. Reinhold, J. Burgdorfer, F.B. Dunning Collisional interactions represent a major source of decoherence for a gas of Rydberg atoms. We investigate the irreversible dephasing of coherently excited Rydberg wavepackets due to decoherence in collisions with ambient rare gas atoms. We show that the rate of decoherence provides a sensitive tool for measuring quasi-elastic electron-atom (or molecule) collisions at energies extending down to micro electron volts. We present proof of principle calculations for $n \simeq 388$ potassium Rydberg wavepackets in an ambient gas of xenon atoms. We propose a scheme centered on the collisional decoherence of Stark Rydberg wavepackets induced by sudden application of a DC field. [Preview Abstract] |
Wednesday, May 18, 2005 1:54PM - 2:06PM |
C5.00003: Interpreting Learning Control of Molecular Fragmentation in Terms of Enhanced Ionization Mark Baertschy, David Cardoza, Thomas Weinacht We interpret a molecular learning control experiment aimed at optimizing the CF$_{3}^{+}$/CH$_{3}^{+}$ ratio during dissociative ionization of trifluoroacetone, CH$_3$COCF$_3$. The experiment makes use of a learning algorithm and shaped ultrafast laser pulses, and our interpretation of the control is in terms of enhanced molecular ionization during dissociation. Our understanding of the physical control mechanism is built upon necessary features in optimal pulse shapes discovered by the learning algorithm, \textit{Ab initio} molecular structure calculations, pump-probe measurements of the molecular fragmentation, and quasi-static tunnel ionization calculations. This control mechanism is quite general, motivating continued studies of a range of molecules in the ketone family. It may also provide for new measurements of molecular relaxation and dissociation rates. [Preview Abstract] |
Wednesday, May 18, 2005 2:06PM - 2:18PM |
C5.00004: Manipulating a Rydberg electron in a classical orbit H. Maeda, D.V.L. Norum, T.F. Gallagher When applying to a Rydberg atom a weak microwave (MW) field whose frequency nearly matches the classical Kepler frequency of the electron, a spatially localized potential well which oscillates in phase with the MW field is produced in the atom due to a combination of Coulomb potential and an external MW field, in which the electron probability distribution is trapped for a long time: An “eternal” non-dispersing wave packet is created which resembles a classical atom since localized wave packet does not manifest dispersion as time evolves and thus follows Ehrenfest’s theorem. By exploiting the synchronization of the electron wave packet with the MW field, which can be said as phase locking of electron’s radial motion based on the corresponding classical dynamics of nonlinear resonance island in phase space, we have demonstrated that the electron’s orbital motion is sped up or slowed down by increasing or decreasing the MW frequency. [Preview Abstract] |
Wednesday, May 18, 2005 2:18PM - 2:30PM |
C5.00005: Quantum Coherent Control of Atoms in a Classically Chaotic Regime Jalani Kanem, Samansa Maneshi, Matthew Partlow, Aephraim Steinberg The classical delta-kicked rotor (DKR) exhibits chaotic behaviour in certain parameter regimes, characterized by a linear increase of the energy of the system as a function of time. Applying the DKR to a quantum system however, will eventually result in states that are localized in momentum space. Therefore, the delta kicks can only increase the energy of the system up to a finite limit given by the momentum localization length[1,2]. This localization has been observed in a system of cooled atoms in a pulsed optical lattice, which is mathematically equivalent to the DKR[3]. Recent extensions of the quantum DKR by P. Brumer, J.Gong and H. Woerner predict coherent control of the relaxation of the system into the localized eigenstates through manipulation of the coherence properties of the initial state and spatial phase of the pulsed potential[4][5]. This can result in either a further suppression of diffusion or superheating in which the system absorbs energy faster than classically allowed. In this presentation we present our experimental results of these predictions. [1]Ott ``Chaos in Dynamical Systems'' (Cambridge 1993) [2]Fishman et. al PRL 49 p509 (1982) [3]Moore et. al. PRL 75 p4598 (1995) [4]Gong et. al. PRL 86 p1741 (2001) [5]Gong et. al. PRE 68 026209 (2003) [Preview Abstract] |
Wednesday, May 18, 2005 2:30PM - 2:42PM |
C5.00006: Complete Quantum Characterization of a Pulse echo in an Optical Lattice Samansa Maneshi, Jalani Fox, Matthew Partlow, Aephraim Steinberg Error correction is the major problem facing quantum information science. An ideal tool to characterize quantum errors and corrections is quantum process tomography \footnote {S. Myrskog et.al., {\it quant-ph/0312210}; M. W. Mitchell et. al. {\it PRL}, \textbf{91}, 120402(2003).}(QPT). In previous experiments with cold atoms in optical lattices decoherence has been observed in the center-of-mass motion. We introduce quantum mechanical methods to completely characterize the state of the system (density matrix) and the evolution process (superoperator). We apply these methods to a pulse-echo technique for correction of dephasing errors due to inhomogeneous broadening. Restoration of oscillations is achieved by applying a series of pulses consisting of lattice displacements. We achieve large echo amplitudes compared to amplitudes previously observed in optical lattices\footnote{ F. B. J. Buchkremer et. al., {\it PRL} \textbf{85}, 3121 (2000). }, and use QPT to compare different pulse sequences\footnote{Y.S. Weinstein et. al, {\it J. Chem. Phys. } \textbf{121(13)}, 6117 (2004). }. We study techniques for using QPT data to optimize error-correction protocols. We believe this approach will be essential for devising appropriate error- correction schemes for general quantum information systems with no a priori knowledge of the errors. [Preview Abstract] |
Wednesday, May 18, 2005 2:42PM - 2:54PM |
C5.00007: Analysis of channelization architecture for wide-band slow light Zachary Dutton, Mark Bashkansky, Michael Steiner, John Reintjes We earlier proposed to extend the available bandwidth for ultra- slow light propagation (via electromagnetically-induced transparency (EIT)) in atomic vapors via a ``channelization'' architecture. Wider bandwidths would greatly increase the applicability of ultra-slow light to signal processing applications in telecommunications, radar, etc. In this architecture, the input signal is dispersed in the transverse direction and a spatially varying magnetic field is applied over the atomic cell such that the two-photon resonance necessary for EIT is maintained everywhere. Using this method, the bandwidth can be increased above the levels available in current systems, which are limited to $\sim$1 MHz by laser power constraints, while still maintaining a delay-bandwidth product exceeding unity. In this paper, we extend our previous calculations, accounting for the diffusion of atoms in the presence of a buffer gas with a microscopic model. This model is used to optimize the design of an experimental demonstration of the method and learn the practical limits of the architecture. [Preview Abstract] |
Wednesday, May 18, 2005 2:54PM - 3:06PM |
C5.00008: Single-photon Swap Gate Using Electromagnetically Induced Transparency parency Deniz Yavuz We propose a scheme to swap the quantum states of two different photons at different wavelengths (colors). We consider a four level atomic system interacting with four fields in a double lambda configuration. Two of the fields are strong and form a traditional electromagnetically induced transparency (EIT) scheme. These fields drive the atoms to a dark state and prepare the coherence (off-diagonal density matrix element) of the non-allowed Raman transition. Two single photons, whose frequencies are separated by the frequency of the Raman transition then interact with each other through the established coherence of the atomic system. Under appropriate conditions, the interaction between the two photons becomes identical to a conventional beam-splitter between two spatial modes. The rotation angle of the beam-splitter is determined by the density-length product of the atomic medium. For a specific density-length product, such a system can perform the swap gate between the two photons. The fidelity of the gate is directly related to the magnitude of the established Raman coherence. [Preview Abstract] |
Wednesday, May 18, 2005 3:06PM - 3:18PM |
C5.00009: The Effect of Doppler Broadening on Electromagnetically Induced Transparency and Autler-Townes splitting in Molecular Cascade Excitation Scheme Ergin Ahmed, Angelos Lazoudis, Marjatta Lyyra We present here a theoretical analysis and interpretation of our recent experimental results on a molecular Electromagnetically Induced Transparency (EIT) and Autler-Townes (AT) splitting in a three-level cascade excitation scheme. We demonstrate analytical expressions for the Doppler broadened excitation spectra from the intermediate and upper levels in the limit of a weak coupling field, as is the case in all our experimental results. On the basis of these expressions we had investigated the critical role of Doppler averaging for observing EIT and AT-splitting in molecules. For example, for the AT effect we show that in Doppler broadened media there is a threshold coupling Rabi frequency above which the splitting can be observed experimentally and that the splitting is not only a function of the coupling Rabi frequency as is the case in homogenously broadened media, but also strongly depends on the ratio of the wavelengths of the coupling and probe lasers. [Preview Abstract] |
Wednesday, May 18, 2005 3:18PM - 3:30PM |
C5.00010: Influence of atomic coherence diffusion on EIT and stored light Yanhong Xiao, Irina Novikova, David Phillips, Ronald Walsworth We report an experimental study of the effect of atomic coherence diffusion on electromagnetically induced transparency (EIT) and stored light in Rb vapor cells. Due to diffusion of ground state coherence over the full volume of the cell -- i.e., beyond the laser beam volume -- we observe much longer storage times than expected from the time scale associated with the lowest order diffusion mode through the laser beam, as well as the retrieval of multiple pulses when long intervals are used between retrievals. [Preview Abstract] |
Wednesday, May 18, 2005 3:30PM - 3:42PM |
C5.00011: Slow and stored light in tetracontane-coated vapor cells Mason Klein, Irina Novikova, David Phillips, 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. Here we report on the use of such cells (with an intrinsic coherence time of ground-state hyperfine and Zeeman transitions longer than 10 milliseconds) for slow- and stored- light. While spin-exchange reduces the ground-state coherence time in the measurements reported here, millisecond coherence lifetimes are observed in stored light measurements. Ongoing studies to optimize stored light efficiency in such cells will be presented. [Preview Abstract] |
Wednesday, May 18, 2005 3:42PM - 3:54PM |
C5.00012: Trojan wavepackets in quantum mechanics equivalent to classical mechanics Matt Kalinski We formulate the theory of wavepackets moving on classical circular orbits in Hydrogen atom in rotating electromagnetic wave within the quantum mechanics equivalent to classical mechanics [1]. Unlike within the true quantum mechanics the wavepackets spreads during the time comparable with the time of full quantum revival within true quantum mechanics. Numerical solutions of the nonlinear Schrodingers equation are provided using non-linear split operator method for this equation. \newline [1] D. Shay, Phys. Rev A, {\bf 13}, 2261 (1976). [Preview Abstract] |
Wednesday, May 18, 2005 3:54PM - 4:06PM |
C5.00013: Improving coherent population amplitudes in open $\Lambda$-systems Vishal Shah, Svenja Knappe, Peter Schwindt, Leo Hollberg, John Kitching A novel scheme based on optical pumping for transforming open $\Lambda $-systems to closed $\Lambda $-systems is proposed and is experimentally implemented on a sample of $^{87}$Rb atoms confined in a vapor cell. A seven-fold improvement in the amplitude of a coherent population trapping (CPT) resonance is observed at sufficient light intensities. The density matrix formalism is used to derive an analytic expression that highlights the differences between a closed and an open $\Lambda $-system in CPT and its consequences on the performance of atomic clocks are discussed. [Preview Abstract] |
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C5.00014: Cartesian-Hyperspherical Hartree-Fock method for numerical observation of stabilized Langmuir states Matt Kalinski Based on the fact that hyperspherical radial dynamics of the Helium atom can be slow comparing to other coordinates we formulate adiabatic Hartree-Fock equations for the Hydrogen atom in both circularly polarized and the magnetic fields for the Langmuir states both in the circularly polarized and magnetic fields. The time-dependent Hartree-Fock equations are solved as functions of the effective parameter $z$ (approximately the hyperspherical radius of the suspected configuration) and then the time-averaged energy is minimized to obtained the electron equilibrium in third spatial direction. The transverse part of the wave function is then found by solving two-dimensional Schr{\"o}dinger equation with the effective potential found from the minimalization. [Preview Abstract] |
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