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 N5: Wavepackets and Control of Molecules and Large Systems |
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Chair: Brett Pearson, SUNY Stony Brook Room: Knoxville Convention Center 301AB |
Thursday, May 18, 2006 1:30PM - 1:42PM |
N5.00001: Controlling Molecular Fragmentation: Charge Transfer in a Dissociating Molecule Brett Pearson, Mark Baertschy, David Cardoza, Thomas Weinacht We investigate control of molecular fragmentation in the halogen-substituted acetone CHBr$_2$COCF$_3$. Feedback experiments can successfully control the CF$_3^+$/CHBr$_2^+$ branching ratio during dissoctiative ionization. Optimal pulse shapes, combined with pump-probe spectroscopy, suggest a control mechanism that transfers electronic charge from the CF$_3$ to the CHBr$_2$ fragment during dissociation. Further tests show that the charge transfer process may be interpreted in terms of adiabatic rapid passage mediated by a dynamic resonance between different electronic states in the dissociating molecule. This control mechanism provides a possibility for measuring the nuclear wave function of the dissociating molecule. [Preview Abstract] |
Thursday, May 18, 2006 1:42PM - 1:54PM |
N5.00002: Imaging Molecular Wavefunctions during Dissociation Mark Baertschy, Brett Pearson, David Cardoza, Thomas Weinacht Recent fragmentation control experiments with CHBr$_2$COCF$_3$ suggest an approach for measuring the dissociating wavepacket. The approach is based on detecting changes in fragmentation yields as the wave packet passes through a spatially dependent resonance. It is possible to measure the quantum mechanical probability density of the dissociating wavepacket directly. Furthermore, phase information about the nuclear wave function can be obtained using molecular wave packet interferometry. It is also possible to directly observe the consequences of entanglement between nuclear and electronic wave functions. This approach is general, and well suited for even large polyatomic molecules as long as they can be driven to dissociate and traverse a dynamic charge transfer resonance during dissociation. [Preview Abstract] |
Thursday, May 18, 2006 1:54PM - 2:06PM |
N5.00003: Coherent control of excited state vibrational coherences of a molecule in solution Andrei Florean, Elizabeth Carroll, Roseanne Sension, Philip Bucksbaum We demonstrate control of excited state wave packets in the laser dye LD690 by spectral and phase shaping of the pump pulses. Excitation by blue detuned, positively chirped pulses slows the dephasing of the excited state vibrational coherences compared to a transform-limited pulse. Negative chirp suppresses the onset of coherent oscillations in the ground state. The high electronic state selectivity achieved with spectral shaping enables us to probe the characteristics of the excited state potential energy surface. We find that the frequency of the dominant vibrational mode is 573 wavenumbers in the excited state, shifted from 586 wavenumbers in the ground state. [Preview Abstract] |
Thursday, May 18, 2006 2:06PM - 2:18PM |
N5.00004: Dynamical coherence transfer in photoelectron diffraction in N$_2$ B. Zimmermann, V. McKoy, B. Langer, U. Becker Coherence is one of the key problems in quantum physics. It is the coherent or incoherent character of matter that separates the quantum from the classical world. However, coherence never disappears but is rather transferred into other systems, in most cases to a complex environment, where the system becomes a classical one. We will show that photoelectron diffraction in homonuclear molecules can be used to investigate this decoherence process. Furthermore, we will show that in this case, in contrast to other decoherence experiments, the coherence transfer is purely dynamic. [Preview Abstract] |
Thursday, May 18, 2006 2:18PM - 2:30PM |
N5.00005: Optimizing impulsive rotational wave packet excitation for molecular phase modulation Omid Masihzadeh, Mark Baertschy, Randy Bartels The full transient macroscopic linear optical susceptibility tensor induced in a transiently aligned molecular gas by a single, linearly polarized intense alignment pulse is studied. We determine the optimal properties of the pulse that forms the rotational wave packet. Significantly, we demonstrate that the optimal pulse for phase modulation differs from the optimal alignment pulse. We are extending our studies of molecular phase modulation to excitation by pulse sequences. Finally, the limited information about rotational wave packets obtained by measuring the linear optical susceptibility can be augmented by also measuring the time-varying nonlinear optical susceptibilities. [Preview Abstract] |
Thursday, May 18, 2006 2:30PM - 2:42PM |
N5.00006: Rotational wave packet dynamics with high energy excitation Mark Baertschy, Omid Masihzadeh, Randy Bartels In recent years molecular phase modulation of light has been vigorously investigated as a method for optical pulse manipulation. To optimize phase modulation, a rotational wave packet is excited by alignment pulses with peak intensities of $\sim 10^{13}$ W cm$^{-2}$ and pulse durations $>$ 100 fs. Interference structures emerge in the angular density matrices for the rotational wave packet excited by these energetic laser pulses. The interference structures emerge with increasing pulse energy. We present a simple physical interpretation relating the observed interferences in the density matrices to dynamics of the rotational wave packets formed by the pulse interaction. [Preview Abstract] |
Thursday, May 18, 2006 2:42PM - 2:54PM |
N5.00007: Optimal Control of Large Spin Systems Seth Merkel, Souma Chaudhury, Andrew Silberfarb, Tobias Herr, Ivan Deutsch, Poul Jessen A quantum system is said to be controllable if the accessible Hamiltonians (as a Lie algebra) generate all unitary operators on Hilbert space. Optimal quantum state control seeks a time-dependent sequence of Hamiltonians that maximize the fidelity with an arbitrary target state given a fixed initial state. We consider optimal control of the spin of a cesium atom restricted to its F=3 ground state hyperfine manifold, with a Hilbert space of dimension 2F+1=7. Control is implemented through time varying magnetic fields in two orthogonal directions along with a quadratic AC-Stark shift created by an off-resonant laser probe. The optimization is performed under several constraints, most importantly a temporal limitation determined by dephasing due to photon scattering and parameter inhomogeneity. [Preview Abstract] |
Thursday, May 18, 2006 2:54PM - 3:06PM |
N5.00008: Control of Landau orbits by electromagnetic vortices Iwo Bialynicki-Birula Electromagnetic beams of radiation endowed with orbital angular momentum have embedded vortex lines. These electromagnetic vortices act as beam guides for charged particles. Exact solutions of the classical (Lorentz) and quantum (Schroedinger and Dirac) equations, derived in Phys. Rev. Lett. 93, 20402 (2004), exhibit such a behavior. In the present contribution, I take my investigation a step further and describe the motion of particles in a combination of an electromagnetic wave with a vortex line and a constant magnetic field. I will show that an electromagnetic wave with a vortex line can be used to control and to transport the cyclotron orbits (Landau orbits in the quantum mechanical setting) across the lines of the constant magnetic field. For that we need electromagnetic beams with moving vortices. Such beams can be produced by taking a superposition of a monochromatic beam having a fixed vortex line with a detuned plane wave. Cyclotron (Landau) orbits will be trapped by the electromagnetic vortex and they will follow a moving vortex. These results are based on new analytic solutions of the Lorentz and the Dirac equations describing the motion of charged particles in the presence of an electromagnetic wave with a vortex line and a constant magnetic field. [Preview Abstract] |
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