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 $F_{\text{max}}$ between the stationary entangled state, ${\rho }_{\infty }$, and the maximally entangled state, ${\rho }_m$, can be about $2/3\approx \text{max}\left\{\text{tr}\left({\rho }_{\infty }{\rho }_m\right)\right\}=F_{\text{max}}$, corresponding to a maximum stationary concurrence, $C_{\text{max}}$, of about $1/3\approx C\left({\rho }_{\infty }\right)=C_{\text{max}}$. 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.

• Received 22 August 2008

DOI:https://doi.org/10.1103/PhysRevA.79.052308