Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session P13: Focus Session: Ultrafast and Ultrahigh Field Chemistry II: Quantum Control |
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Sponsoring Units: DCP Chair: Kenji Ohmori, Institute of Molecular Science Japan Room: Baltimore Convention Center 305 |
Wednesday, March 15, 2006 11:15AM - 11:51AM |
P13.00001: Quantum Control with Nonclassical Light Invited Speaker: Most of the experimental advances in coherent quantum control in recent years have involved ultrashort pulses and pulse shaping techniques. These pulses have been an excellent source of coherent light with precise phase relationship between the various frequency components. In several recent works we have investigated the possibility of using broadband nonclassical light, generated by down-conversion of narrow-band lasers, for coherent control. Such light, for most purposes, exhibit the properties of a broadband thermal noise, but also unique quantum correlations between spectral mode pairs at the signal and idler frequencies that are required for quantum control. We have investigated both the single-photon limit, when the light was composed of individual entangled photon-pairs, and the large signal limit, when the light is not weak but does exhibit nonclassical phase correlations. In the high-intensity limit, we have shown that coherent control of two-photon absorption can be performed with incoherent non-classical light. We showed that the signal-idler phase correlations cause the spectral quantum interference to be completely constructive for two-photon interactions that have a final state energy equal to the pump laser frequency. Consequently, even though the broadband down converted light is neither coherent nor pulsed, it induces two-photon absorption just like a coherent ultrashort pulse, and may likewise be coherently controlled by pulse-shaping techniques. We also demonstrated that pulse shaping techniques can be used in the single-photon limit, where we shape the two-photon correlation function. We demonstrate control of the quantum interference of photons at a beam-splitter, and the generation of Bell-states using polarization pulse-shaping techniques. We believe that the combination of quantum control techniques with quantum optics could add an important ingredient to the toolbox of quantum information and computing. [Preview Abstract] |
Wednesday, March 15, 2006 11:51AM - 12:03PM |
P13.00002: Bell state generation in the presence of complicated entangling interactions Kenji Mishima, Koichi Yamashita We present theoretical investigations on the entanglement generation of bipartite two- and three-level systems interacting with complicated entangling interactions and external electromagnetic fields. The theoretical method employed is based on rotating wave approximation (RWA). By using the partitioning of the complicated entangling interaction matrix, we propose a method of creating the Bell state from the initial separable state in bipartite two-level systems. In addition, by using the bipartite three-level model systems, we show how to create decoherence-free subspace when the Bell state is to be generated. The present work will be useful for realization of entanglement manipulation in the presence of complicated entangling interactions in molecular systems. [Preview Abstract] |
Wednesday, March 15, 2006 12:03PM - 12:15PM |
P13.00003: High-Precision Coherent Control of Molecular Wave Packets Hiroyuki Katsuki, Kouichi Hosaka, Hisashi Chiba, Kenji Ohmori The quantum interference of two vibrational wave packets has been precisely controlled in the electronically excited state of a diatomic molecule by using a pair of fs laser pulses whose relative phase $\phi $ is locked within the attosecond time scale, and the real time evolution of that interference has been observed by another fs probe pulse. The real-time evolution shows a clear dependence on $\phi $. We have also measured a population code, which is a population ratio among the vibrational eigenstates within a WP. The population code also shows a clear dependence on $\phi $. The ordinary frequency domain interpretation based on the spectral interference of locked pulses may be useful to elucidate $\phi $ dependence of population codes, but is no longer suitable for the present real-time observation. The combination of a population code and real-time evolution is useful to obtain both phase and amplitude information stored in a WP. [Preview Abstract] |
Wednesday, March 15, 2006 12:15PM - 12:27PM |
P13.00004: Nanolocalized Nonlinear Electron Photoemission under Coherent Control Mark Stockman We theoretically show that two-photon coherent control yields electron photoemission from metal nanostructures that is localized in nano-size hot spots whose positions are controllable on a nanometer scale, in agreement with recent experiments. We propose to use silver V-shapes as taylored nanoantennas for which the position of the coherently controllable photoelectron-emission hot spot can be deterministically predicted. We predict that the low-frequency, high-intensity (quasistationary) excitation of the photoemission leads to an exponentially high contrast of the coherent control. REFERENCES M. I. Stockman and P. Hewageegana, ``Nanolocalized Nonlinear Electron Photoemission under Coherent Control'', Nano Lett. 5(11), 2325-2329 (2005) [Preview Abstract] |
Wednesday, March 15, 2006 12:27PM - 12:39PM |
P13.00005: Monitoring Molecular Dynamics using Coherent Electrons from High-Harmonic Generation Nick Wagner, Andrea W\"uest, Ivan Christov, Tenio Popmintchev, Xibin Zhou, Margaret Murnane, Henry Kapteyn In this talk, we will discuss the first observation of intramolecular vibrational dynamics using electrons rescattered during the process of high-order harmonic generation. We excite coherent vibrations in SF$_{6}$ using impulsive Raman scattering with a short laser pulse. A second, more-intense laser pulse generates high-order harmonics of the fundamental laser, at wavelengths of $\sim $ 20-50 nm. The high-order harmonic yield is observed to oscillate, at frequencies corresponding to all the Raman-active modes of SF$_{6}$, with an asymmetric mode most visible. This is in contrast to conventional impulsive stimulated Raman spectroscopy where only the symmetric breathing mode of the molecule is easily observed. The data also show evidence of relaxation dynamics following impulsive excitation of the molecule. Our results indicate that high harmonic generation is a sensitive probe of vibrational dynamics and may yield more information simultaneously than conventional ultrafast spectroscopic techniques. Since the de Broglie wavelength of the recolliding electron is on the order of interatomic distances, i.e. $\sim $ 1.5 {\AA}, small changes in the shape of the molecule lead to large changes in the high harmonic yield. This work therefore demonstrates a new spectroscopic technique for probing ultrafast internal dynamics in molecules that uniquely combines ultrafast time resolution with atomic-scale structural information. [Preview Abstract] |
Wednesday, March 15, 2006 12:39PM - 1:15PM |
P13.00006: Observation and control of ultrafast quantum interferences in atoms and molecules. Invited Speaker: I will present several examples of ultrafast interferences in atoms and molecules, at the femtosecond and picosecond time scale. In a two level atom, real-time quantum state holography is performed through interferences between quantum states created by a reference pulse and a chirped pulse resulting in coherent transients. A sequence of several measurements allows one to measure the real and imaginary parts of the excited state wave function. These measurements are performed during the interaction with the ultrashort laser pulse. The extreme sensitivity of this method to the pulse shape provides a tool for electric field measurement. In a molecule, the transient interferences between two oscillating wave-packets have been observed and controlled. In a first experiment, a vibrational wave packet is created in the iodine B state. Due to anharmonicity, the wave-packet spreads and recombines in one single wave packet (revival time) or two wave-packets (half revival time). When these two wave packets cross, they transiently create a stationary wave which is observed. In a second experiment, the same situation is created by launching two wave packets in the same potential well with an ultrastable relative phase. The delay, set to 1.5 vibrational periods, is stabilized with sub 100 attosecond precision. The same transient interference pattern is observed. Moreover, the relative phase between the counterpropagating wave packets can now be controlled by scanning the interpulse delay on an optical period. [Preview Abstract] |
Wednesday, March 15, 2006 1:15PM - 1:27PM |
P13.00007: Final resolution of the step-wise versus concerted mechanism controversy for excited-state double proton transfer in the 7-azaindole dimer in the gas phase Hiroshi Sekiya, Kenji Sakota, Chie Okabe, Nobuyuki Nishi The excited-state double-proton transfer (ESDPT) reaction in the 7-azaindole dimer has been extensively studied by spectroscopic methods in the gas phase and in solution. Two ESDPT mechanisms, stepwise and concerted mechanisms, have been proposed so far. However, a definite conclusion has not been provided due to a lack of clear evidence. We provide final resolution of the stepwise versus concerted mechanism controversy for the ESDPT reaction in the 7-azaindole dimer by electronic spectroscopy and picosecond-time resolved spectroscopy in the gas phase (K. Sakota, C. Okabe, N. Nishi, H. Sekiya, J. Phys. Chem. A, 109, 5245 (2005)). The ESDPT reaction in the 7-azaindole dimer proceeds via the concerted mechanism. We propose a dynamic cooperative effect, where the motions of the two transferring protons couple with each other through the electronic reorganization (K. Sakota ,H. Sekiya, J. Phys. Chem. A, 109, 2718 (2005); 109,2722 (2005)). [Preview Abstract] |
Wednesday, March 15, 2006 1:27PM - 1:39PM |
P13.00008: On the Control of Product Yields in the Photofragmentation of Deuteriumchlorid Ions (DCl$^{+})$ -- Cl + D$^{+} \quad <$ - - DCl$^{+}$ - - $>$ Cl$^{+}$ + D. Karl-Michael Weitzel, Georg Breunig, Alexandra Lauer, Mikhail Korolkov We have investigated the prospect of controlling the photofragmentation of deuterium chloride ions (DCl$^{+})$ via ultra short IR laser pulses both by experiments and by numerical solution of coupled Schr\"{o}dinger equations. The calculations provide evidence that the ratio of product ion yields Cl$^{+}$ versus D$^{+}$ can be manipulated by appropriate choice of laser pulse parameters, in particular central laser wavelength, pulse duration, intensity and chirp [1]. The analysis of time dependent populations reveals phase sensitive competition between intra- and inter-electronic state excitation. Complementary, we have performed one- and two-color fs experiments looking at the dissociation of DCl$^{+}$ ions at 800 nm [2] and in the range from 3.5$\mu $m to 7.5$\mu $m (2857cm$^{-1}$ to 1333cm$^{-1})$ [3]. In particular we show, that the ratio of product yields D$^{+}$/Cl$^{+}$ can be controlled via the chirp of the laser pulse at 4.5$\mu $m. References [1] M.V. Korolkov, K.-M. Weitzel, J. Chem. Phys. 123, 164308, (2005) [2] H.G. Breunig, A. Lauer, K.-M. Weitzel, Proceedings of the Femtochemistry VII (2005) [3] H.G. Breunig, K.-M. Weitzel, in preparation. [Preview Abstract] |
Wednesday, March 15, 2006 1:39PM - 1:51PM |
P13.00009: Femtosecond pulse shaping in the mid infrared region using a Dazzler Takamasa Momose, Masaaki Tsubouchi, Yuki Miyamoto We present a method to produce programmable phase- and amplitude-modulated femtosecond laser pulses in the mid infrared region (MIR: 3 -- 10 $\mu $m) by difference-frequency generation (DFG). The signal output (NIR: 1.1 -- 1.5 $\mu $m) of an optical parametric amplifier was shaped with an acousto-optic programmable dispersive filter (Dazzler), and mixed in a AgGaS$_{2}$ crystal with the idler pulse temporary stretched by passing a dispersion block to generate MIR pulses. A Dazzler provides convenient and precise way of shaping femtosecond pulses in NIR region. It is, however, not well understood how the phase and amplitude modulations are transferred from a NIR pulse to a MIR pulse via DFG process. We will discuss the analysis of the shaped NIR and MIR pulses using a frequency-resolved optical gating (FROG) and an FT-IR [Preview Abstract] |
Wednesday, March 15, 2006 1:51PM - 2:03PM |
P13.00010: Fast Transient Electron Magnetic Resonance at 240 GHz Johan van Tol The zero-field splitting of the excited triplet states of organic molecules often is of the order of 1 GHz or less, and transient EPR at X-band is generally sufficient for the determination of the zero-field splitting and kinetic parameters in these type of molecules. However, information on the g-factor and g-anisotropy cannot be obtained at conventional EPR frequencies, and interpretations of the data in terms of electronic structure are mostly limited to symmetry considerations. On the other hand information of the g-anisotropy provides additional clues with respect to electronic structure, while a direct comparison with radical-ion forms of the molecules becomes possible. Experimental data of transient EPR at 240 GHz will be presented for a variety of system (fullerene-based and porphyrin-based). EPR at these very high frequencies can accurately determine the g-anisotropy and in some cases the orientation of the g-tensor with respect to the ZFS tensor. Also at these high frequencies sub nanosecond processes can be measured. Examples will be given. [Preview Abstract] |
Wednesday, March 15, 2006 2:03PM - 2:15PM |
P13.00011: Response of Dipicolinic Acid ($C_{5}H_{5}N(COOH)_{2}$) to Ultrafast Laser Pulses Petra Sauer, Roland Allen Dipicolinic acid (DPA) and its salts are common constituents of bacterial spores, including those of anthrax. It has been proposed that such spores can be detected via spectroscopic techniques which employ ultrashort laser pulses. The development of these techniques should be enhanced by a detailed understanding of the microscopic processes that transpire when a molecule is subjected to femtosecond-scale pulses of various intensities, durations, and polarizations. We have recently developed a model that can be used to perform realistic simulations of the electronic and nuclear dynamics of biological molecules (containing carbon, hydrogen, oxygen and nitrogen) when they are subjected to such pulses. The bond lengths and vibrational frequencies for a variety of test molecules are in reasonable agreement with those obtained in experiment and \textit{ab initio} calculations. Here we report results of simulations for DPA responding to femtosecond-scale laser pulses, with an analysis of the vibrational modes and electronic states which are most relevant for various choices of the laser pulse parameters. [Preview Abstract] |
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