Total insecurity of communication via strong converse for quantum privacy amplification

Understand

Quantum privacy amplification is a central task in quantum cryptography.

• Given shared randomness, which is initially correlated with a quantum system held by an eavesdropper, the goal is to extract uniform randomness which is decoupled from the latter.
• The optimal rate for this task is known to satisfy the strong converse property and we provide a lower bound on the corresponding strong converse exponent.
• In the strong converse region, the distance of the final state of the protocol from the desired decoupled state converges exponentially fast to its maximal value, in the asymptotic limit.