Please join us on Wednesday, March 12 at 4pm in the Time room for a quantum information seminar by Debbie Leung.

Title:  Maximal Privacy Without Coherence
Speaker: Debbie Leung (IQC)

Abstract:  Privacy and coherence have long been considered closely related properties of a quantum state.  Indeed, a coherently transmitted quantum state is inherently private.  Surprisingly, coherent quantum communication is not always required for privacy: there are quantum channels that are too noisy to transmit quantum information but it can send private classical information.  Here, we ask how different the private classical and the quantum capacities can be.  We present a class of channels N_d with input dimension d^2, quantum capacity Q(N_d) <= 1, and private classical capacity P(N_d) = log d.  These channels asymptotically saturate an interesting inequality P(N) <= (log d_A + Q(N))/2 for any channel N with input dimension d_A, and capture the essence of privacy stripped of the confounding influence of coherence.