Limitation of entanglement due to spatial qubit separationR. Doll, M. Wubs, P. Hänggi and S. Kohler
Institut für Physik, Universität Augsburg - Universitätsstraße 1 D-86135 Augsburg, Germany
received 23 August 2006; accepted in final form 27 September 2006
published online 18 October 2006
We consider spatially separated qubits coupled to a thermal bosonic field that causes pure dephasing. Our focus is on the entanglement of two Bell states which for vanishing separation are known as robust and fragile entangled states. The reduced two-qubit dynamics is solved exactly and explicitly. Our results allow us to gain information about the robustness of two-qubit decoherence-free subspaces with respect to physical parameters such as temperature, qubit-bath coupling strength and spatial separation of the qubits. Moreover, we clarify the relation between single-qubit coherence and two-qubit entanglement and identify parameter regimes in which the terms robust and fragile are no longer appropriate.
03.65.Yz - Decoherence; open systems; quantum statistical methods.
03.67.Mn - Entanglement production, characterization, and manipulation.
© EDP Sciences 2006