title: Efficient entanglement distillation without quantum memory.
abstract: Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution.
authors.affiliation: Institut für Laserphysik, Universität Hamburg, Hamburg 22761, Germany.|Institut für Gravitationsphysik, Leibniz Universität Hannover and Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut), Hannover 30167, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Abdelkhalek
authors.affiliation: Institut für Gravitationsphysik, Leibniz Universität Hannover and Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut), Hannover 30167, Germany.
authors.forename: Mareike
authors.initials: M
authors.lastname: Syllwasschy
authors.affiliation: Quantum Information and Communication, Ecole Polytechnique de Bruxelles, CP 165, Université libre de Bruxelles, Brussels 1050, Belgium.
authors.forename: Nicolas J
authors.initials: NJ
authors.lastname: Cerf
authors.affiliation: Department of Optics, Palacký University, Olomouc 77146, Czech Republic.
authors.forename: Jaromír
authors.initials: J
authors.lastname: Fiurášek
authors.affiliation: Institut für Laserphysik, Universität Hamburg, Hamburg 22761, Germany.|Institut für Gravitationsphysik, Leibniz Universität Hannover and Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut), Hannover 30167, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Schnabel