@article{KubBra18, title = {Two-qubit causal structures and the geometry of positive qubit-maps}, author = {K{\"u}bler, J. M. and Braun, D.}, journal = {New Journal of Physics}, volume = {20}, number = {8}, pages = {083015}, year = {2018}, doi = {10.1088/1367-2630/aad612}, url = {http://stacks.iop.org/1367-2630/20/i=8/a=083015} }