Martijn Wubs (1), Roland Doll (2), Sigmund Kohler (2), and Peter Hanggi (2)

(1) The Niels Bohr Institute, University of Copenhagen
(2) Institut fuer Physik, Universitaet Augsburg

In the first part of this presentation I will report about our study of the initial dephasing of solid-state qubits in the independent-boson model, which describes well
recent experiments on quantum dot (QD) excitons both in bulk and in substrates of reduced geometry such as nanotubes. Using explicit expressions for the exact coherence dynamics, we identify a minimal quantum error-correction rate in terms of the error threshold, temperature, and qubit-environment coupling strength. This allows us to systematically study the benefit of a current trend towards substrates with reduced dimensions. The second part will be about the entanglement dynamics of spatially separated qubits, all coupled to the same bosonic bath. The focus will
be on two Bell states which for vanishing separation are known as robust and fragile entangled states, and on the N-qubit generalization of the former, the W
states. The usual master equation does not capture the exact dynamics even qualitatively. I will propose instead our causal master equation, which performs much better.

[1] Roland Doll, Martijn Wubs, Peter Hanggi, Sigmund Kohler, Europhys. Lett. 76, 547 (2006).
[2] Roland Doll, Martijn Wubs, Peter Hanggi, Sigmund Kohler, Phys. Rev. B 76, 045317 (2007).
[3] Roland Doll, Peter Hanggi, Sigmund Kohler, Martijn Wubs, ArXiv:cond-mat/0807.2555v1 (2008).