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Kongzhi yu juece

Lyapunov stabilization strategy of mixed-state quantum systems with ideal conditions

Shuang Cong

Published Jan 1, 2010• 4 citations
OpenAlex

Abstract

Under the ideal conditions that the controlled systems are non-degenerate,transitionally non-degenerate,and fully connected,the stabilization problem of mixed-state quantum systems is studied by using a Lyapunov function with free degrees. Based on the LaSalle's principle,the largest invariant set of the closed-loop systems and the convergent state set associated with any initial state are deduced,and the construction principles of free degrees that ensure the system can be asymptotically stabilized in any equilibrium state contained in the largest invariant set are given. A numerical simulation experiment on a two-level system shows the rationality of the obtained theoretical results.

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Under the ideal conditions that the controlled systems are non-degenerate,transitionally non-degenerate,and fully connected,the stabilization problem of mixed-state quantum systems is studied by using a Lyapunov function with free degrees. Based on the LaSalle's principle,the largest invariant set of the closed-loop systems and the convergent state set associated with any initial state are deduced,and the construction principles of free degrees that ensure the system can be asymptotically stabilized in any equilibrium state contained in the largest invariant set are given. A numerical simulation experiment on a two-level system shows the rationality of the obtained theoretical results.
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A convergent state control strategy of open quantum system based on Lyapunov method is proposed for the target state being a pure state in decoherence-free subspaces. Based on the assumptions of all the transition frequencies being different and all the levels being directly coupled,a sufficient condition is proposed for the observation operator to make that the largest invariant set only contains target state.On the basis of choosing the average of observable operators as a Lyapunov function,the control laws are designed in interaction picture and the largest invariant set of the controlled system is analyzed via Barbalat's Lemma. It is shown that any pure target state in decoherence-free subspace is globally asymptotic stable under the sufficient condition given,and the system controlled could be transferred to target state from arbitrary initial state.Also,a method is provided to construct the observation operator via Schmidt orthogonalization.Numerical experiments on a three-level system verify the validity of the proposed control strategy.
A control strategy of quantum states of open quantum system based on Lyapunov method is proposed. On the basis of choosing the average of observable operators as a Lyapunov function, the control laws are designed in interaction picture. We analyze the largest invariant set of the controlled system via Barbalat's Lemma. Based on some assumptions of Hamiltonians, we propose a sufficient condition of the observable operator to guarantee the convergence of the open quantum system, and proof that the proposed strategy can make any pure target state in decoherence-free subspace be globally asymptotic stable under the sufficient condition. Also, we provide a method to construct the observable operator via Schmidt orthogonalization. Numerical experiments on a three-level system validate the effectiveness of the proposed control strategy.
For closed quantum systems, if controlled systems are strongly regular and all other eigenstates are directly coupled to a target state, then such control systems can be asymptotically stabilized by means of the Lyapunov-based control. However, when the controlled systems are not strongly regular, or when there exists at least one eigenstate that is directly uncoupled to the target state, the situations will become complicated. This paper proposed a method based on an implicit Lyapunov function to overcome these two degenerate cases. Also, the proposed method is suitable for multi-control Hamiltonian systems. The convergence of closed-loop systems is analyzed by the LaSalle invariance principle. Finally, numerical simulation experiments on a 4-level system are done. The experiment results show the effectiveness of the implicit Lyapunov control method for degenerate cases and multi-control Hamiltonians.
We present detailed analysis of the convergence properties and effectiveness of Lyapunov control design for bilinear Hamiltonian quantum systems based on the application of LaSalle's invariance principle and stability analysis from dynamical systems and control theory. For a certain class of Hamiltonians, strong convergence results can be obtained for both pure and mixed state systems. The control Hamiltonians for realistic physical systems, however, generally do not fall in this class. It is shown that the effectiveness of Lyapunov control design in this case is significantly diminished.
A Lyapunov-based unified control method for closed quantum systems is proposed, which can transfer the state of closed quantum system from any initial state to any desired target state. In particular, the proposed control method can work under the conditions that free Hamiltonian of the non-ideal quantum system is not strongly regular, and (or) the Hamiltonian is not fully connected. The simulation experiments of the state transition control between different states of three, four and five qubit systems are carried out to verify that the proposed control method is suitable for all kinds of non-ideal quantum systems and the advantages of Lyapunov-based unified control method. The design process of the proposed method, the calculation process of each parameter in each experiment and the analysis of each experimental result are given in detail.