Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D2: Focus Session: Quantum Control of Molecular, Nano, and Plasmonic Materials II |
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Sponsoring Units: DCP Chair: Margaret Murnane, University of Colorado Room: 102 |
Monday, March 3, 2014 2:30PM - 2:42PM |
D2.00001: Resonant Pump-dump Quantum Control of Solvated Dye Molecules with Phase Jumps Arkaprabha Konar, Vadim Lozovoy, Marcos Dantus Quantum coherent control of two photon and multiphoton excitation processes in atomic and condensed phase systems employing phase jumps has been well studied and understood. Here we demonstrate coherent quantum control of a two photon resonant pump-dump process in a complex solvated dye molecule. Phase jump in the frequency domain via a pulse shaper is employed to coherently enhance the stimulated emission by an order of magnitude when compared to transform limited pulses. Red shifted stimulated emission from successive low energy Stokes shifted excited states leading to narrowband emission are observed upon scanning the pi step across the excitation spectrum. A binary search space routine was also employed to investigate the effects of other types of phase jumps on stimulated emission and to determine the optimum phase that maximizes the emission. Understanding the underlying mechanism of this kind of enhancement will guide us in designing pulse shapes for enhancing stimulated emission, which can be further applied in the field of imaging. [Preview Abstract] |
Monday, March 3, 2014 2:42PM - 2:54PM |
D2.00002: High-fidelity transformations of the vibrational qubits in thiophosgene molecule Dmytro Shyshlov, Dmitri Babikov In this computational work, we study how to use shaped picosecond laser pulses for controlling state-to-state transitions in thiophosgene molecule (CSCl$_{2}$) with the goal of encoding quantum information into molecular vibrational eigenstates and implementing quantum gates with high fidelity. State-to-state transitions are induced indirectly through the excitation of a gateway state within the excited electronic state so that a UV/vis laser can be employed for control. We optimize shape of the laser pulse using optimal control theory (OCT) and numerical propagation of laser-driven vibrational wavepackets. This optimization was performed for two-qubit gate CNOT and we were able to optimize laser pulses with fidelity exceeding 0.9999. We analyze the high-fidelity pulse in the frequency domain and explore its robustness by reducing the number of available frequency channels. We also intentionally introduce systematic and random errors to the pulse in the frequency domain by modifying the values of amplitudes and of phases for different frequency components. We conclude that the accurate control of the vibrational two-qubit system can still be achieved with a very limited number of frequency channels and in the presence of some amplitude and phase errors. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D2.00003: Excited state dynamics {\&} optical control of molecular motors Ted Wiley, Roseanne Sension Chiral overcrowded alkenes are likely candidates for light driven rotary molecular motors. At their core, these molecular motors are based on the chromophore stilbene, undergoing ultrafast cis/trans photoisomerization about their central double bond. Unlike stilbene, the photochemistry of molecular motors proceeds in one direction only. This unidirectional rotation is a result of helicity in the molecule induced by steric hindrance. However, the steric hindrance which ensures unidirectional excited state rotation, has the unfortunate consequence of producing large ground state barriers which dramatically decrease the overall rate of rotation. These molecular scale ultrafast motors have only recently been studied by ultrafast spectroscopy. Our lab has studied the photochemistry and photophysics of a ``first generation'' molecular motor with UV-visible transient absorption spectroscopy. We hope to use optical pulse shaping to enhance the efficiency and turnover rate of these molecular motors. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D2.00004: Implementation of exact and approximate methods for nonadiabatic quantum molecular dynamics induced by the interaction with the electromagnetic field and their applications to local quantum control Aur\'elien Patoz, Jiri Vanicek we have implemented a general split-operator/Magnus integrator algorithm of arbitrary order in accuracy for exact nonadiabatic quantum dynamics of a molecule interacting with a time-dependent electromagnetic field. Then, we have derived and implemented analogous geometric integrators of arbitrary order of accuracy for several approximations of treating the molecule-field interaction: the time-dependent perturbation theory, separation of time scales, Condon, rotating-wave, and ultrashort, ``extreme ultrashort,'' and ``extremely extreme ultrashort'' pulse approximations. Our general and efficient implementation permits every possible combination of these basic approximations, allowing testing the validity of each approximation under the experimental conditions independently. In addition, a local quantum control scheme has been implemented in the same formalism allowing using the exact method and several of our approximations. The algorithms are applied to the four-dimensional vibronic coupling model of pyrazine in order to compare the exact and approximate descriptions of the photoexcitation process with a single laser pulse of finite length as well as nonadiabatic quantum dynamics induced by pump and probe laser pulses. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D2.00005: Moshe Shapiro's Pioneering Contributions to Quantum Control Tamar Seideman The pioneering contributions of Moshe Shapiro to the field of coherent control will be reviewed, starting with his work in the '80s and noting several highlights of his research. The talk will conclude with the new directions he was pursuing at the time of his untimely death including quantum pattern recognition, coherent chiral separation, and the coherent suppression of spontaneous emission, decoherence and other decay processes. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 4:06PM |
D2.00006: Electron dynamics and its control in molecules Invited Speaker: Regina de Vivie-Riedle The accessibility of few femtosecond or even attoseconds pulses opens the door to direct observation of electron dynamics. The idea to steer chemical reactions by localization of electronic wavepackets is intriguing, since electrons are directly involved in bond breaking and formation. The formation of a localized electronic wavepacket requires the superposition of two or more appropriate electronic states. Its guidance is only possible within the coherence time of the system and has to be synchronized with the vibrational molecular motions. In theoretical studies we elucidate the role of electron wavepacket motion for the control of molecular processes. We give three examples with direct connection to experiments. From our analysis, we extract the systems requirements defining the time window for intramolecular electronic coherence, the basis for efficient control. Based on these findings we map out a photoreaction that allows direct control by guiding electronic wavepackets. The carrier envelope of a femtosecond few cycle IR pulse is the control parameter that steers the photoreaction through a conical intersection.\\[4pt] References:\\[0pt] [1] I. Znakovskaya, P. von den Hoff, S. Zherebtsov, A. Wirth, O. Herrwerth, M. J. J. Vrakking, R. de Vivie-Riedle, and M. F. Kling, Phys. Rev. Lett., 103 (2009), 103002.\\[0pt] [2] P. von den Hoff, I. Znakovskaya, M. F. Kling and R. de Vivie-Riedle, Chem. Phys. , 366 (2009), 139.\\[0pt] [3] P. von den Hoff, M. Kowalewski, R. Siemering and R. de Vivie-Riedle, IEEE Journal of Selected Topics in Quantum Electronics, 18 (2012), 119-129.\\[0pt] [4] T. Bayer, H. Braun, C. Sarpe, R. Siemering, P. von den Hoff, R. de Vivie-Riedle, T. Baumert, and M. Wollenhaupt, Phys. Rev. Lett. 110 (2013), 123003.\\[0pt] [5] M. Kling, P. von den Hoff, I. Znakovskaya, and R. de Vivie-Riedle, Phys. Chem. Chem. Phys. 15 (2013), 9448-9467. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D2.00007: Optical Control of Internal Conversion in Pyrazine Grant Barry, Sima Singha, Zhan Hu, Tamar Seideman, Robert Gordon We apply quantum control schemes previously reserved for atoms and small molecules to more complex polyatomic molecules. Pyrazine was chosen as a model polyatomic molecule for its well-studied conical intersection seam between the S1 and S2 potential energy surfaces (PESs). Using shaped ultraviolet femtosecond laser pulses, we demonstrate optical control of the excited state dynamics of this molecule under collisionless conditions. This was achieved in a pump-probe experiment by employing a genetic algorithm programmed to suppress ionization of the pyrazine molecules at a preselected time. Our findings indicate that the optimized pulses localize the wave packet for times up to 1.5 ps at a location on the coupled S1/S2 PESs where ionization is energetically forbidden. Our approach is general and does not require knowledge of the molecular Hamiltonian. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D2.00008: Chemical control of cyclohexadiene photochemistry Brenden Arruda, Broc Smith, Kenneth Spears, Roseanne Sension The photoinduced ring-opening reaction 1,3-cyclohexadiene (CHD) chromophores is a common motif in optical switches, photochromic materials, and biological systems. The topology of the excited state potential energy surface makes these systems an important paradigm for coherent optical control. Altering substitution patterns on the CHD backbone can lead to different dynamics for the same reactive chromophore, as evidenced by the fluorescence quantum yield of CHD (10$^{\mathrm{-6}})$ compared with the highly substituted Provitamin D$_{\mathrm{3}}$ (2 x 10$^{\mathrm{-4}})$. CHD derivatives such as the 1,4-disubstituted $\alpha $-terpinene and the 2,5-disubstituted $\alpha $-phellandrene, offer model systems to bridge the gap between these two regimes of excited state dynamics. Recently our lab has used ultrafast spectroscopy to characterize the excited state dynamics of these CHD-based systems. Our broadband probe provides additional information about the ground state relaxation and conformational distribution of the photoproducts. An overview of the factors that govern the landscape of the excited state potential energy surface and ground state conformational distribution will be provided based on experimental measurements and electronic structure calculations. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 5:06PM |
D2.00009: Control of Strong Field Molecular Ionization with Shaped Ultrafast Laser Pulses Invited Speaker: Thomas Weinacht Strong field molecular ionization can prepare molecules in superpositions of multiple ionic states, generating an electron hole wave packet. We demonstrate control over which ionic states are populated via strong field ionization by varying the shape of the ionization pulse. Calculations allow us to interpret the control and determine the role of resonances in the neutral molecule and cation. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:42PM |
D2.00010: Molecular dissociation dynamics driven by strong-field multiple ionization Invited Speaker: Philip Bucksbaum We have studied and compared the dynamics of small molecules that have been multiply ionized and dissociated by strong ultrafast infrared lasers or by strong x-ray lasers. In both regimes we find that multiple ionization can occur on time scales comparable to the fastest interatomic motion, and therefore lead to dissociation patterns that can be related to the transient structure and internal motion of the molecules. The mechanisms that produce multiply charged ions are very different in these two cases. Infrared lasers induce field-ionization, while x-ray lasers induce core-ionization followed by Auger relaxation. This affects the dissociation dynamics. In experiments studying the dissociation of 1,3-cyclohexadiene we find that infrared laser-induced multiple ionization is greatly enhanced by transient processes that occur in the vicinity of conical intersections [Bucksbaum and Petrovic, \textit{Faraday Discussions} \textbf{163}, 475 (2013); Petrovic et al., \textit{J.Chem. Phys}. \textbf{139}, (2013)] When strong x-rays are used as the exciting source, the molecular geometry can influence the Auger process and change the fragment relative abundances [Petrovic et al., \textit{Phys. Rev. Letters} \textbf{108}, 253006 (2012)]. We will discuss recent experiments in deuterated acetylene, which employed x-ray pulse-pairs to explore the x-ray fragmentation process in greater detail. [Preview Abstract] |
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