title: Decoherence-free quantum information processing with four-photon entangled states.
abstract: Decoherence-free states protect quantum information from collective noise, the predominant cause of decoherence in current implementations of quantum communication and computation. Here we demonstrate that spontaneous parametric down conversion can be used to generate four-photon states which enable the encoding of one qubit in a decoherence-free subspace. The immunity against noise is verified by quantum state tomography of the encoded qubit. We show that particular states of the encoded qubit can be distinguished by local measurements on the four photons only.
authors.affiliation: Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Bourennane
authors.forename: Manfred
authors.initials: M
authors.lastname: Eibl
authors.forename: Sascha
authors.initials: S
authors.lastname: Gaertner
authors.forename: Christian
authors.initials: C
authors.lastname: Kurtsiefer
authors.forename: Adán
authors.initials: A
authors.lastname: Cabello
authors.forename: Harald
authors.initials: H
authors.lastname: Weinfurter