title: Experimental extraction of secure correlations from a noisy private state.
abstract: We report experimental generation of a noisy entangled four-photon state that exhibits a separation between the secure key contents and distillable entanglement, a hallmark feature of the recently established quantum theory of private states. The privacy analysis, based on the full tomographic reconstruction of the prepared state, is utilized in a proof-of-principle key generation. The inferiority of distillation-based strategies to extract the key is exposed by an implementation of an entanglement distillation protocol for the produced state.
authors.affiliation: Institute of Physics, Nicolaus Copernicus University, ul Grudziadzka 5/7, 87-100 Toruń, Poland.
authors.forename: K
authors.initials: K
authors.lastname: Dobek
authors.forename: M
authors.initials: M
authors.lastname: Karpiński
authors.forename: R
authors.initials: R
authors.lastname: Demkowicz-Dobrzański
authors.forename: K
authors.initials: K
authors.lastname: Banaszek
authors.forename: P
authors.initials: P
authors.lastname: Horodecki