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Physical Review A

Laser control of a multilevel quantum system as static parameter optimization with the help of effective decomposition

Michihiko Sugawara

Published Jan 22, 2010• 0 citations
Publisher

Abstract

A quantum control scheme for multilevel systems utilizing effective decomposition is proposed. In this method, a subsystem chosen for control target is effectively isolated by irradiating intense continuous-wave laser fields onto the complimentary space. By choosing the control target space consisting of small number of eigenstates, effective dressed states for the isolated space are analytically given, which makes it possible to express the performance index defined in the target space as an explicit function of laser parameters. Then, designing the control field can be treated as a static parameter optimization. The present scheme makes it possible not only to optimize the laser parameters but also to investigate the parameter search space, which clarifies the physics of the control process.

DOI
10.1103/physreva.81.013410

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A quantum control scheme for multilevel systems utilizing effective decomposition is proposed. In this method, a subsystem chosen for control target is effectively isolated by irradiating intense continuous-wave laser fields onto the complimentary space. By choosing the control target space consisting of small number of eigenstates, effective dressed states for the isolated space are analytically given, which makes it possible to express the performance index defined in the target space as an explicit function of laser parameters. Then, designing the control field can be treated as a static parameter optimization. The present scheme makes it possible not only to optimize the laser parameters but also to investigate the parameter search space, which clarifies the physics of the control process.
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.
We propose a new scheme for quantum dynamics control of multilevel system using intense lasers. To do so, we apply intense CW lasers to create a strongly coupled subsystem with which one can make the complementary space effectively isolated, and we apply the established control schemes to the isolated subsystem. We have also obtained an effective Hamiltonian for the target subsystem with the help of the second-order perturbation theory. Numerical demonstrations on model systems show that the present decomposition scheme effectively works for population dynamics control. It is also found that relaxation processes can be suppressed under the proposed scheme.
Abstract This paper proposes a numerical approach to the problem of inverse quantum control with a focus on the automated formation of external laser control fields that ensure high-precision and controlled population transfer in multilevel quantum systems. The method is based on optimizing the parameters of control pulses using gradient algorithms in combination with automatic differentiation, which allows for effective control of the physical characteristics of laser fields and increases the stability of the transfer process. The obtained results provide a foundation for the development of more general quantum control methods focused on experimental implementation on real physical platforms.
A gradient-based optimization approach combined with automatic differentiation is employed to ensure high accuracy and scalability when working with high-dimensional parameter spaces. Numerical simulations confirm the effectiveness of the proposed method: the population is reliably transferred to the target state with minimal occupation of intermediate levels, while the control pulses remain smooth and physically implementable. The developed framework serves as a universal and experimentally applicable tool for automated control pulse design in quantum systems. It is particularly useful in scenarios where analytical methods or manual parameter tuning--such as standard schemes like STIRAP--prove to be inefficient or inapplicable.
This paper proposes a numerical approach to the problem of inverse quantum control with a focus on the automated formation of external laser control fields that ensure highprecision and controlled population transfer in multilevel quantum systems. The method is based on optimizing the parameters of control pulses using gradient algorithms in combination with automatic differentiation, which allows for effective control of the physical characteristics of laser fields and increases the stability of the transfer process. The obtained results provide a foundation for the development of more general quantum control methods focused on experimental implementation on real physical platforms.
The control of quantum dynamics via specially tailored laser pulses is a long-standing goal in physics and chemistry. Partly, this dream has come true, as sophisticated pulse-shaping experiments allow us to coherently control product ratios of chemical reactions. The theoretical design of the laser pulse to transfer an initial state to a given final state can be achieved with the help of quantum optimal control theory (QOCT). This tutorial provides an introduction to QOCT. It shows how the control equations defining such an optimal pulse follow from the variation of a properly defined functional. We explain the most successful schemes to solve these control equations and show how to incorporate additional constraints in the pulse design. The algorithms are then applied to simple quantum systems and the obtained pulses are analysed. Besides the traditional final-time control methods, the tutorial also presents an algorithm and an example to handle time-dependent control targets.