paper

Position-based coding and convex splitting for private communication over quantum channels

arXiv:1703.01733 · doi:10.1007/s11128-017-1718-4

Abstract

The classical-input quantum-output (cq) wiretap channel is a communication model involving a classical sender , a legitimate quantum receiver , and a quantum eavesdropper . The goal of a private communication protocol that uses such a channel is for the sender to transmit a message in such a way that the legitimate receiver can decode it reliably, while the eavesdropper learns essentially nothing about which message was transmitted. The -one-shot private capacity of a cq wiretap channel is equal to the maximum number of bits that can be transmitted over the channel, such that the privacy error is no larger than . The present paper provides a lower bound on the -one-shot private classical capacity, by exploiting the recently developed techniques of Anshu, Devabathini, Jain, and Warsi, called position-based coding and convex splitting. The lower bound is equal to a difference of the hypothesis testing mutual information between and and the "alternate" smooth max-information between and . The one-shot lower bound then leads to a non-trivial lower bound on the second-order coding rate for private classical communication over a memoryless cq wiretap channel.

v2: 31 pages, 1 figure, applies main result to the pure-loss bosonic channel

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