On Concurrence and Entanglement of Rank Two Channels
arXiv:quant-ph/0605103
Abstract
Concurrence and further entanglement quantifyers can be computed explicitly for channels of rank two if representable by just two Kraus operators. Almost all details are available for the subclass of rank two 1-qubit-channels. There is a simple geometric picture beyond, explaining nicely the role of anti-linearity.
20 pages. An appendix is added. An error in (45) - (47) and known (to me) misspellings are corrected