Locking vs private capacity of quantum channels
Prof. Andreas Winter
Universitat Autònoma de Barcelona
Guha et al. [arXiv:1307.5368] have recently defined the locking capacity of a quantum channel as the largest rate of a uniformly distributed bit string, which Alice can share with Bob over the channel while an eavesdropper, Eve, who has access to the channel environment, can only gain negligible accessible information about the string. We show that this relaxation of the private capacity of a channel, can be much larger than the latter; in fact, if a sub-linear size key is shared between Alice and Bob, there are channels with zero private capacity but positive locking capacity. This gives a quantitative meaning to the information locking effect [DiVincenzo et al., PRL 92:067902, 2004], and answers an open question of Guha et al. The difference between private and locking capacity can also be related to non-zero discord, at least in some cases. [Based on arXiv:1403.6361, J. Cryptol. 2017].
Andreas Winter was born in Altötting, a small rural town near Munich, known also as the Heart of Bavaria. After developing an infatuation with science early on, and in particular with mathematics, he decided to study this subject in Konstanz and Berlin. He graduated in 1997 from the Freie Universität Berlin, and went on to obtain a doctorate in mathematics from the Universität Bielefeld in 1999, with the late Rudolf Ahlswede. In 2001 he joined the quantum information group in Bristol as a postdoc, became Lecturer in Applied Mathematics there in 2003, and Professor of the Physics of Information in 2006. In 2012 he left Bristol after 11 years, to move to the Universitat Autònoma de Barcelona as ICREA Research Professor, where he is now part of the quantum information group.