Control of a quantum dynamics by a locally optimized laser field. II. Application to a system with dissipation

Quantum Localization of Coherent π-Electron Angular Momentum in (P)-2,2'-Biphenol

Controlling π-electrons with delocalized character is one of the fundamental issues in femtosecond and attosecond chemistry. Localization of π-electron rotation by using laser pulses is expected to play an essential role in nanoscience. The π-electron rotation created at a selected aromatic ring of a single molecule induces a local intense electromagnetic field, which is a new type of ultrafast optical control functioning. We propose a quantum localization of coherent π-electron angular momentum in (P)-2,2'-biphenol, which is a simple, covalently linked chiral aromatic ring chain molecule. The localization considered here consists of sequential two steps: the first step is to localize the π-electron angular momentum at a selected ring of the two benzene rings, and the other is to maintain the localization. Optimal control theory was used for obtaining the optimized electric fields of linearly polarized laser pulses to realize the localization. The optimal electric fields and the resultant coherent electronic dynamics are analyzed.

A new quantum control scheme for multilevel systems based on effective decomposition by intense laser fields

A new quantum control scheme for general multilevel systems using intense laser fields is proposed. In the present scheme, the target subspace consisting of several quantum levels is effectively isolated by applying intense cw lasers with specific conditions. The formulation is carried out using the Green function with the help of projection operator method. Dynamics of the isolated target subspace is governed by an effective Hamiltonian. The developed scheme is applied to the quantum control of dissipative four- and five-level systems. It is clarified that the present method makes it possible not only to manipulate the coherent population dynamics but also to suppress the dissipative dynamics.

Quantum dynamics driven by continuous laser fields under measurements: Towards measurement-assisted quantum dynamics control

We study quantum system dynamics driven by continuous laser fields under the measurement process. In order to take into account the system transition due to the measurement, we define the superoperator which eliminates the coherence relevant to the measured quantum states. We clarify that the dynamics of the measured states is frozen in the frequent measurement limit, while the space spanned by unmeasured states is isolated from the original system. We also derive the effective Liouvillian which governs incoherent population dynamics under the condition, in which measurements are frequently applied. We apply the formulation to two-level and Lambda-type three-level systems and clarify how the quantum measurements hinder the coherent population dynamics driven by the continuous laser fields in practical examples. Analysis on the laser field amplitude dependency of the final distribution in the t-->infinity limit suggests the possibility of the measurement-assisted quantum control.

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.