Secret key distillation from shielded two-qubit states

TL;DR

This paper investigates conditions for secret key distillation from shielded two-qubit quantum states, demonstrating that bound entangled states can yield secret keys under broader circumstances and analyzing the impact of noise on distillation protocols.

Contribution

It derives new conditions for secret key distillation from shielded two-qubit states, expanding the range of bound entangled states that can be used for secure key generation.

Findings

Secret keys can be distilled from bound entangled states under broader conditions.

Classical distillation protocols remain effective despite added white noise.

Recurrence protocol fails with noise, but advantage distillation persists.

Abstract

The quantum states corresponding to a secret key are characterized using the so-called private states, where the key part consisting of a secret key is shielded by the additional systems. Based on the construction, it was shown that a secret key can be distilled from bound entangled states. In this work, I consider the shielded two-qubit states in a key-distillation scenario and derive the conditions under which a secret key can be distilled using the recurrence protocol or the two-way classical distillation, advantage distillation together with one-way postprocessing. From the security conditions, it is shown that a secret key can be distilled from bound entangled states in a much wider range. In addition, I consider the case that in which white noise is added to quantum states and show that the classical distillation protocol still works despite a certain amount of noise although the recurrence protocol does not.