Influence of the Coupling between Two Qubits in an Open Coherent Cavity: Nonclassical Information via Quasi-Probability Distributions

In this paper, we investigate the dynamics of two coupled two-level systems (or qubits) that are resonantly interacting with a microwave cavity. We examine the effects of the intrinsic decoherence rate and the coupling between the two qubits on the non-classicality of different system partitions via quasi-probability functions. New definitions for the partial Q-function and its Wehrl entropy are used to investigate the information and the quantum coherence of the phase space. The amount of the quantum coherence and non-classicality can be appropriately tuned by suitably adopting the rates of the intrinsic-decoherence and the coupling between the two qubits. The intrinsic decoherence has a pronounced effect on the negativity and the positivity of the Wigner function. The coupling between the two qubits can control the negativity and positivity of the quasi-probability functions.

A modified generalized residual method for minimization problems with errors of a known level in weakened norms

Предложен алгоритм численного решения задачи квадратичной минимизации на эллипсоиде, заданном в гильбертовом пространстве компактным оператором. Алгоритм представляет собой определенную трансформацию обобщенного метода невязки, предназначенную для применения в неклассических информационных условиях, когда априорная информация об уровне погрешности в операторе, задающем функционал, доступна лишь в нормах, ослабленных по сравнению с исходными. При этом сходимость алгоритма устанавливается в исходных нормах. Приводятся простейшие вычислительные иллюстрации. An algorithm is proposed for the numerical solution of a quadratic minimization problem on an ellipsoid specified in the Hilbert space by a compact operator. This algorithm is a certain transform of the generalized residual method designed previously for the application in nonclassical information conditions when {\it a priori} information on the error level in an operator defining the cost functional is available only in the norms being weaker than the original ones. At the same time, the convergence of the algorithm is proved in the original norms. A number of simple numerical examples are discussed.