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Yukiyoshi Ohtsuki

Publications and source records attributed to Yukiyoshi Ohtsuki.

5 recordsLinked to original sources
PubMed2005

Quantum control of a chiral molecular motor driven by laser pulses.

"Molecular motors or machines" are one of the hot subjects in chemistry because they play an important role in molecular devices. We have theoretically demonstrated that unidirectional rotations of a chiral molecular motor can be driven by using tailored linearly polarized laser pulses. The findings obtained here serve as a theoretical basis for control of functions such as gearing or acceleration of molecular motors.

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PubMed2004

Optimal laser control of ultrafast photodissociation of I2- in water: mixed quantum/classical molecular dynamics simulation.

A linearized optimal control method in combination with mixed quantum/classical molecular dynamics simulation is used for numerically investigating the possibility of controlling photodissociation wave packets of I(2)(-) in water. Optimal pulses are designed using an ensemble of photodissociation samples, aiming at the creation of localized dissociation wave packets. Numerical results clearly show the effectiveness of the control although the control achievement is reduced with an increase in the internuclear distance associated with a target region. We introduce effective optimal pulses that are designed using a statistically averaged effective dissociation potential, and show that they semiquantitatively reproduce the control achievements calculated by using optimal pulses. The control mechanisms are interpreted from the time- and frequency-resolved spectra of the effective optimal pulses.

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PubMed2004

Optimal control of quantum non-Markovian dissipation: reduced Liouville-space theory.

An optimal control theory for open quantum systems is constructed containing non-Markovian dissipation manipulated by an external control field. The control theory is developed based on a novel quantum dissipation formulation that treats both the initial canonical ensemble and the subsequent reduced control dynamics. An associated scheme of backward propagation is presented, allowing the efficient evaluation of general optimal control problems. As an illustration, the control theory is applied to the vibration of the hydrogen fluoride molecule embedded in a non-Markovian dissipative medium. The importance of control-dissipation correlation is evident in the results.

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PubMed2004

Generalized monotonically convergent algorithms for solving quantum optimal control problems.

A wide range of cost functionals that describe the criteria for designing optimal pulses can be reduced to two basic functionals by the introduction of product spaces. We extend previous monotonically convergent algorithms to solve the generalized pulse design equations derived from those basic functionals. The new algorithms are proved to exhibit monotonic convergence. Numerical tests are implemented in four-level model systems employing stationary and/or nonstationary targets in the absence and/or presence of relaxation. Trajectory plots that conveniently present the global nature of the convergence behavior show that slow convergence may often be attributed to "trapping" and that relaxation processes may remove such unfavorable behavior.

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