Generating stationary entangled states in superconducting qubits

When a two-qubit system is initially maximally entangled, two independent decoherence channels, one per qubit, would greatly reduce the entanglement of the two-qubit system when it reaches its stationary state. We propose a method on how to minimize such a loss of entanglement in open quantum systems. We find that the quantum entanglement of general two-qubit systems with controllable parameters can be controlled by tuning both the single-qubit parameters and the two-qubit coupling strengths. Indeed, the maximum fidelity F{sub max} between the stationary entangled state, {rho}{sub {infinity}}, and the maximally entangled state, {rho}{sub m}, can be about 2/3{approx_equal}max(tr({rho}{sub {infinity}}{rho}{sub m}))=F{sub max}, corresponding to a maximum stationary concurrence, C{sub max}, of about 1/3{approx_equal}C({rho}{sub {infinity}})=C{sub max}. This is significant because the quantum entanglement of the two-qubit system can be produced and kept, even for a long time. We apply our proposal to several types of two-qubit superconducting circuits and show how the entanglement of these two-qubit circuits can be optimized by varying experimentally controllable parameters.

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