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For a flux qubit described by a two-level system of equations we propose a special time dependent external control field. We show that for a qubit placed in this field there exists a critical value of tunnel frequency. When the tunnel frequency is close to its critical value, the probability value of a definite direction of the current circulating in a Josephson-junction circuit may be kept above 1/2 during a desirable time interval. We also show that such a behavior is not much affected by a sufficiently small dissipation.
We consider dynamical decoupling schemes in which the qubit is continuously manipulated by a control field at all times. Building on the theory of the Uhrig Dynamical Decoupling sequence (UDD) and its connections to Chebyshev polynomials, we derive a
We theoretically study specific schemes for performing a fundamental two-qubit quantum gate via controlled atomic collisions by switching microscopic potentials. In particular we calculate the fidelity of a gate operation for a configuration where a
Exact and nonperturbative quantum master equation can be constructed via the calculus on path integral. It results in hierarchical equations of motion for the reduced density operator. Involved are also a set of well--defined auxiliary density operat
The validity of optimized dynamical decoupling (DD) is extended to analytically time dependent Hamiltonians. As long as an expansion in time is possible the time dependence of the initial Hamiltonian does not affect the efficiency of optimized dynami
We investigate the system constituted by a polarizable atom near a nanosphere under the influence of an external electrostatic field, showing that the attractive dispersive force between them can be overcome by the electrostatic interaction. Therefor