Article is written in collaboration with Tomas Rybara and Mario Zimana,b, deals with rather interesting properties of two-qubit channels and is now available at arXiv:1110.3757v1 [quant-ph]
a Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia (RCQI)
b Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland
We address the problem of the robustness of entanglement of bipartite systems (qubits) interacting with dynamically independent environments. In particular, we focus on characterization of so-called local entanglement-annihilating two-qubit channels, which set the maximum permissible noise level allowing to perform entanglement-enabled experiments. The differences, but also subtle relations between entanglement-breaking and local entanglement-annihilating channels are emphasized. A detailed characterization of latter ones is provided for a variety of channels including depolarizing, unital, (generalized) amplitude-damping, and extremal channels. We consider also the convexity structure of local entanglement-annihilating qubit channels and introduce a concept of entanglement-annihilation duality.