Mendl, Christian B. Theory, Max Planck Institute of Quantum Optics, Max Planck Society;
Wolf, Michael M. Theory, Max Planck Institute of Quantum Optics, Max Planck Society;
Mendl, C. B., & Wolf, M. M. (2009). Unital Quantum Channels - Convex Structure and Revivals of Birkhoff's Theorem. Communications in Mathematical Physics, 289(3), 1057-1086. doi:10.1007/s00220-009-0824-2.