title: Equivalence between two-qubit entanglement and secure key distribution.
abstract: We study the problem of secret key distillation from bipartite states in the scenario where Alice and Bob can perform measurements only at the single-copy level and classically process the obtained outcomes. Even with these limitations, secret bits can be asymptotically distilled by the honest parties from any two-qubit entangled state, under any individual attack. Our results point out a complete equivalence between two-qubit entanglement and secure key distribution: a key can be established through a one-qubit channel if and only if it allows one to distribute entanglement. These results can be generalized to a higher dimension for all those states that are one-copy distillable.
authors: GAP-Optique, University of Geneva, 20, Rue de l'Ecole de Médecine, CH-1211 Geneva 4, Switzerland.
authors: Antonio
authors: A
authors: Acín
authors: Lluis
authors: L
authors: Masanes
authors: Nicolas
authors: N
authors: Gisin