PhD Defense: Roberto Ferrara

 Title: An Information-Theoretic Framework for Quantum Repeaters


Quantum communication and quantum entanglement achieve tasks that are beyond the reach of classical mechanics. One of these tasks is the sharing of perfect key between two distant parties. Surprisingly, there exist quantum communication so noisy that quantum information cannot be transmitted without errors while perfect key can be transmitted reliably, which is formalized in arbitrarily large gaps between distillable key and distillable entanglement. In the future quantum parties will be distributed in a network, where the entanglement will be generated between quantum repeater stations and then teleported to the interested parties, and it is thus natural to ask whether the separation persists if we insert a repeater station. In this thesis, we show the first bounds on the distillable key in quantum repeaters in terms of the distillable entanglement between the nodes for states that provide perfect key between the nodes, pointing toward the intuition that the distillable entanglement is the only relevant resource that survives the relay of quantum information.

Supervisor: Prof. Mathias Christandl, MATH, University of Copenhagen

Assessment Committee

Ass. Prof. (Chairman), Laura Mančinska, University of Copenhagen.

Ass. Prof. Peter Harremoës, Niels Brock, Copenhagen Business College.

Prof. Michał Horodecki, University of Gdansk