One-mode quantum Gaussian channels: Structure and quantum capacity
Problems of Information Transmission
Strong NP-hardness of the quantum separability problem
Quantum Information & Computation
Information capacity of a quantum observable
Problems of Information Transmission
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In the first part of the paper we give a representation for entanglement-breaking channels in separable Hilbert space that generalizes the "Kraus decomposition with rank-one operators" and use it to describe complementary channels. We also note that coherent information for antidegradable channel is always nonpositive. In the second part, we give necessary and sufficient condition for entanglement breaking for the general quantum Gaussian channel. Application of this condition to one-mode channels provides several new cases where the additivity conjecture holds in the strongest form.