Bulletin of the American Physical Society
39th Annual Meeting of the APS Division of Atomic, Molecular, and Optical Physics
Volume 53, Number 7
Tuesday–Saturday, May 27–31, 2008; State College, Pennsylvania
Session Q3: Focus Session: Quantum Control in AMO |
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Chair: Aephraim Steinberg, University of Toronto Room: Keller Building 104 |
Friday, May 30, 2008 2:00PM - 2:36PM |
Q3.00001: Optimal Control of Large Spin Systems Invited Speaker: Poul Jessen Laboratory techniques to manipulate and observe ultracold atoms make these an attractive platform for testing new ideas in quantum control and measurement. I will discuss recent experiments in which we use tensor AC Stark shifts and magnetic fields to drive non-trivial quantum dynamics of a large spin-angular momentum associated with an atomic hyperfine ground state. The nonlinear spin Hamiltonian is sufficiently general to achieve universal quantum control over the 2F+1 dimensional state space, and allows us to generate arbitrary spin states and perform a full quantum state reconstruction of the result. We have implemented and verified time optimal controls to generate a broad variety of spin states, as well as an adiabatic scheme to generate spin-squeezed states for metrology. Most recently we have used our control and measurement tools to realize a common paradigm for quantum chaos known as the quantum kicked top. Direct observation of the phase space dynamics of this system has given an unprecedented look at quantum/classical correspondence. In the future we hope to use coherent optical feedback on atomic ensembles to extend our toolbox for control and measurement to collective spins. Applications include quantum metrology, quantum information processing and simulations of quantum manybody physics. [Preview Abstract] |
Friday, May 30, 2008 2:36PM - 2:48PM |
Q3.00002: Decoherence-Free Control of Large Spin-Atomic Systems with Coherent Electromagnetic Fields Seth Merkel, Souma Chaudhury, Poul Jessen, Ivan Deutsch Cold atomic systems provide a excellent testing ground for quantum control protocols due to their isolation from their environment and the availability of high precision fields from the ``quantum optics toolbox''. ~We consider controlling the 16-dimensional ground state hyperfine manifold of 133Cs through microwaves and rf-magnetic fields. ~These fields allow for essentially decoherence-free control of a system with non-trivial dynamics. ~We analyze the controllability of the system and numerically study the performance of a protocol for performing state preparation, mapping a fiducial state to an arbitrary target state.~ [Preview Abstract] |
Friday, May 30, 2008 2:48PM - 3:00PM |
Q3.00003: Controlled transport of atoms in optical lattices Brian Mischuck, Ivan Deutsch The coherent transport of atoms in optical lattices is essential for quantum computation and quantum simulations involving controlled collisions between the atoms. Such coherence is typically limited by inhomogeneities and background fields. By applying the techniques of quantum control, we study protocols for robustly evolving the motional wave function in the ground band using applied external fields, and well-designed lattices. [Preview Abstract] |
Friday, May 30, 2008 3:00PM - 3:12PM |
Q3.00004: Coherent Control of Wannier-Stark States in a Tilted-Washboard Potential Chao Zhuang, Samansa Maneshi, XiaoXian Liu, Ardavan Darabi, Luciano Cruz, Aephraim Steinberg We study the coupling of Wannier-Stark states of $^{85}$Rb atoms trapped in a one-dimensional tilted-washboard potential. The tilted-washboard potential is formed by a vertical optical lattice plus the gravitational potential. Two methods are used to couple the states. The first one is a combination of lattice displacements and time delays, or phase modulation (PM). The second method is a modulation of the lattice depth, or amplitude modulation (AM). The efficiencies of different PM pulses in coupling the lowest two states are compared. The PM pulses we studied include a single shift; two single shifts with a time delay; displacements with Gaussian time profiles; displacements with sinusoidal time profiles; and displacements with frequency-chirped sinusoidal time profiles, to implement adiabatic rapid passage. Finally, we studied simultaneous PM at $\omega$ and AM at 2$\omega$, where absorption of 2 PM quanta or 1 AM quantum could lead to the same final state. We demonstrate interference between these processes, leading to quantum control of the transfer efficiency to different Wannier-Stark levels. [Preview Abstract] |
Friday, May 30, 2008 3:12PM - 3:48PM |
Q3.00005: Fast pulses and slow atoms: making microKelvin molecules using femtosecond lasers Invited Speaker: Ian Walmsley We discuss a general approach to the formation of ultracold ground state molecules by synthesis from pairs of cold atoms using shaped ultrashort optical pulses. This method combines an effective and widely applicable control technology to the problem of preparing molecules is the ground state of all their degrees of freedom. The broad bandwidth of femtosecond pulses provides and number of options for removing energy from a pair of colliding atoms, and binding them with little or no vibrational energy. We shall give examples of possible strategies, and report on experiments demonstrating photoassocation using coherent control, and measuring wavepacket dynamics by femtosecond pump probe molecular ionization. Prospects for stabilizing the molecules by protecting them from further collisions, and for increasing the range of internuclear separations that can be associated will be pointed out. This work is funded by the UK EPSRC, and has contributions from J. Petrovic, A. Wyatt, A. Dicks, D. McCabe, D. England, M. Friedman, H. Martay, T. Koehler, C. Foot and collaborations with F. Masnou-Seeuws and J. Mur-Petit. [Preview Abstract] |
Friday, May 30, 2008 3:48PM - 4:00PM |
Q3.00006: Coherent Control of Retinal Isomerization in Bacteriorhodopsin in the High Intensity Regime Andrei Florean, David Cardoza, James White, Janos Lanyi, Roseanne Sension, Philip Bucksbaum We use a learning algorithm to optimize retinal isomerization in bacteriorhodopsin. Excitation fluence levels up to 1.5 x 10$^{17}$ photons/cm$^{2}$ (upper estimate) are employed. At fluences below 0.5 x 10$^{17}$ photons/cm$^{2}$ no sensitivity of the yield with respect to phase is observed. Above this level the learning algorithm consistently finds that a transform-limited (TL) pulse is optimal for maximizing the isomerization yield (13-cis population). For this optimal pulse the yield increases linearly beyond the saturation of the first excited state. To understand these results we performed systematic searches varying the chirp, bandwidth and energy of the pump pulses while monitoring the isomerization yield. The results are modeled including the influence of one-photon and multi-photon transitions. The analysis reveals that phase and intensity impact the wave packet dynamics in each intermediate conformation as well as the final branching ratio between the all-trans and 13-cis isomers. [Preview Abstract] |
Friday, May 30, 2008 4:00PM - 4:12PM |
Q3.00007: Molecular Fragmentation in the CH2XY Family of Halomethanes Sarah Nichols, Brett Pearson, Tamas Rozgonyi, Thomas Weinacht There is substantial interest in controlling wavepacket dynamics in molecular states with ultrafast pulses. We demonstrate control over the dissociation of CH2Br2, CH2BrI, and CH2I2 molecules. Time dynamics of the dissociations show signatures of parent ion vibrations. Ab initio structure calculations confirm these signatures with strong quantitative agreement. We explore wavepacket dynamics on the parent ion potential energy surface, and use them to control population transfer from the bound parent ion to the dissociative states. [Preview Abstract] |
Friday, May 30, 2008 4:12PM - 4:24PM |
Q3.00008: Shaped-Pulse Control of CO$_{2}$ Bending Vibration G.Y. Chen, Z. Wang, G. Minker, S. Iacangelo, W.T. Hill, III Pulse shaping combined with genetic feedback learning algorithms have proven to be a useful approach for controlling dynamics and producing specific products in a molecular system. However, since the optimal waveforms tend to be neither simple nor unique, extracting the physics -- e.g., identifying the internal quantum trajectories taken by the system to the desired solution -- is a daunting if not impossible task. We are making steps towards addressing this problem by focusing on isolatable parameters related to eigenmodes of three-atom systems. Specifically we have exploited Coulomb explosion imaging with shaped pulses to modify the bending, $\nu _2 $, amplitude of CO$_{2}$ by more than 30{\%} relative to the transform limited pulses. The optimal shapes were determined via genetic algorithm were the 2$^{nd}$ through 5$^{th}$ order phase components were the ``genes.'' While the temporal shapes are different for different solutions, the temporal phases can be remarkably similar for some classes of solutions, which is providing insight into the physics. These results, along with our interpretation will be discussed. [Preview Abstract] |
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