Southwest Quantum Information and Technology

Universal limitations on quantum key distribution over a network

Presenting Author: Siddhartha Das, Universite libre de Bruxelles
Contributing Author(s): Stefan Baeuml, Marek Winczewski, Karol Horodecki

Secure communication is at the heart of hopes for a quantum-based internet. Such a network would use principles of quantum physics to generate secret encryption keys that are, in principle, unbreakable. But many questions remain with regards to security criteria for these systems and the rate at which they can generate secure keys. We introduce the most general form of a quantum network channel, which we call as a quantum multiplex channel. We determine fundamental limitations on secret key distribution over quantum multiplex channels against a quantum eavesdropper while using the most general adaptive strategy. Trusted parties are allowed to perform local operations and classical communication between channel uses. The essential step in our multifaceted project was to show that any entanglement-based protocol used to distribute cryptographic keys among many parties must distill a genuinely multipartite entangled state. Using this finding, we provide bounds on the secret key rates among an arbitrary number of trusted parties over a network. These bounds are in terms of quantities that measure the potential for entanglement generation of quantum multiplex channels. The generic structure of our protocol and bounds allows us to determine limitations on quantum key repeaters and rates of measurement-device-independent quantum key distribution. Furthermore, for certain cases of interest, we determine the maximum rates at which a secret key can be shared among trusted parties.

Read this article online: https://arxiv.org/abs/1912.03646

(Session 5 : Thursday from 12:00pm-2:00 pm)