Quantum optimal control of unbounded molecular dynamics: Application to NaI predissociation

科研費報告書収録論文(課題番号:13640497・基盤研究(C)(2) ・H13～H14/研究代表者:藤村, 勇一/光化学異性化反応の量子制御

Optimal control for maximally creating and maintaining a superposition state of a two-level system under the influence of Markovian decoherence

Reducing decoherence is an essential step toward realizing general-purpose quantum computers beyond the present noisy intermediate-scale quantum (NISQ) computers. To this end, dynamical decoupling (DD) approaches in which external fields are applied to qubits are often adopted. We numerically study DD using a two-level model system (qubit) under the influence of Markovian decoherence by using quantum optimal control theory with slightly modified settings, in which the physical objective is to maximally create and maintain a specified superposition state in a specified control period. An optimal pulse is numerically designed while systematically varying the values of dephasing, population decay, pulse fluence, and control period as well as using two kinds of objective functionals. Although the decrease in purity due to the decoherence gives rise to the upper limit of the target expectation value, i.e., the saturated value, the optimally shaped pulse effectively deals with the decoherence by gradually creating the target superposition state to realize the saturated value as much as possible.Comment: 20 pages, 12 figures, and 34 reference

Optimal control for manipulating vibrational wave packets through polarizability interactions induced by non-resonant laser pulses

On the basis of optimal control theory, we numerically study how to optimally manipulate molecular vibrational dynamics by using cycle-averaged polarizability interactions induced by mildly intense non-resonant laser (NR) pulses. As the essential elements to be controlled are the probability amplitudes, namely, the populations and the relative phases of the vibrational eigenstates, we consider three fundamental control objectives: selective population transfer, wave packet shaping that requires both population control and relative-phase control, and wave packet deformation suppression that solely requires relative-phase control while avoiding population redistribution. The non-trivial control of wave packet deformation suppression is an extension of our previous study on wave packet spreading suppression. Focusing on the vibrational dynamics in the B state of I2 as a case study, we adopt optimal control simulations and model analyses under the impulsive excitation approximation to systematically examine how to achieve the control objectives with shaped NR pulses. Optimal solutions are always given by NR pulse trains, in which each pulse interval and each pulse intensity are adjusted to cooperate with the vibrational dynamics to effectively utilize the quantum interferences to realize the control objectives with high probability.Comment: 30 pages, 12 figure

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

科研費報告書収録論文(課題番号:15550002・基盤研究(C)(2)・15～16/研究代表者:藤村, 勇一/光駆動分子モーターの量子制御

Engineering quantum wave-packet dispersion with a strong nonresonant femtosecond laser pulse

A nondispersing wave packet has been attracting much interest from various scientific and technological viewpoints. However, most quantum systems are accompanied by anharmonicity, so that retardation of quantum wave-packet dispersion is limited to very few examples only under specific conditions and targets. Here we demonstrate a conceptually universal method to retard or advance the dispersion of a quantum wave packet through “programmable time shift” induced by a strong nonresonant femtosecond laser pulse. A numerical simulation has verified that a train of such retardation pulses stops wave-packet dispersion

Monotonically convergent algorithms for solving quantum optimal control problems described by an integrodifferential equation of motion

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