From source model to quantum key distillation: An improved upper bound

In this paper we derive a new upper bound on the quantum key distillation capacity. This upper bound is an extension of the classical bound of Gohari and Anantharam on the source model problem. Our bound strictly improves the quantum extension of reduced intrinsic information bound of Christandl et al. Although this bound is proposed for quantum settings, it also serves as an upper bound for the special case of classical source model, and may improve the bound of Gohari and Anantharam. The problem of quantum key distillation is one in which two distant parties, Alice and Bob, and an adversary, Eve, have access to copies of quantum systems A, B, E respectively, prepared jointly according to an arbitrary state ρ_ABE. Alice and Bob desire to distill secret key bits that are secure from Eve, using only local quantum operations and authenticated public classical communication (LOPC).