Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 28: Transport - Poster Session

TT 28.20: Poster

Thursday, March 29, 2007, 14:00–17:45, Poster A

Limitation of entanglement due to spatial qubit separation — •Roland Doll, Martijn Wubs, Peter Hänggi, and Sigmund Kohler — Institut für Physik, Universität Augsburg, Universitätsstrasse 1, 86135 Augsburg

We consider spatially separated qubits coupled to a thermal bosonic field which acts as a heat bath and, thus, causes decoherence. By taking the spatial separation of the qubits explicitly into account, the reduced qubit dynamics becomes intrinsically non-Markovian. For pure dephasing we solve the dynamics exactly and explicitly. We first focus on the entanglement of two Bell states which for vanishing separation are known as robust and fragile entangled states. The robustness of two-qubit decoherence-free subspaces depends on temperature, qubit-field coupling strength, and qubit separation. Our exact results are then generalized to an arbitrary number of qubits. We show for weak qubit-bath coupling that a standard Bloch-Redfield approach fails to describe the reduced dynamics even at long times and predicts spurious decoherence-free subspaces. We derive a master equation that does not suffer from such deficiencies. It allows us to directly attribute the observed non-Markovian features to spatial bath correlations.

[1] R. Doll, M. Wubs, P. Hänggi, and S. Kohler, Europhys. Lett. 76, 547 (2006).