Instituto de Ciencia de Materiales de Madrid
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Incomplete pure dephasing of N-qubit entangled W states

Roland Doll, Martijn Wubs, Peter Hänggi, and Sigmund Kohler
Phys. Rev. B 76, 045317 (2007)

We consider qubits in a linear arrangement coupled to a bosonic field which acts as a quantum heat bath and causes decoherence. By taking the spatial separation of the qubits explicitly into account, the reduced qubit dynamics acquires an additional non-Markovian element. We investigate the exact time evolution of an entangled many-qubit W state, which for vanishing qubit separation remains robust under pure dephasing. For finite separation, by contrast, the dynamics is no longer decoherence-free. On the other hand, spatial noise correlations may prevent complete dephasing. While a standard Bloch-Redfield master equation fails to describe this behavior even qualitatively, we propose instead a widely applicable causal master equation. Here we employ it to identify and characterize decoherence-poor subspaces. Consequences for quantum error correction are discussed.
arXiv:cond-mat/0703075

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last modified: 23.11.2017 by Sigmund Kohler