title: Generation of orbital angular momentum Bell states and their verification via accessible nonlinear witnesses.
abstract: The controlled generation of entangled states and their subsequent detection are integral aspects of quantum information science. In this Letter, we implement a simple and precise technique that produces any of the four Bell states in the orbital angular momentum degree of freedom. We then use these states to perform the first experimental demonstration of an accessible nonlinear entanglement witness. Such a witness determines entanglement by using the same measurements as required for a linear witness but can detect, in this case, twice as many states as a single linear witness can. We anticipate that our method of state preparation and nonlinear witnesses will have further uses in areas of quantum science, such as superdense coding and quantum key distribution.
authors.affiliation: Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, K1N 6N5 Canada.
authors.forename: Megan
authors.initials: M
authors.lastname: Agnew
authors.forename: Jeff Z
authors.initials: JZ
authors.lastname: Salvail
authors.forename: Jonathan
authors.initials: J
authors.lastname: Leach
authors.forename: Robert W
authors.initials: RW
authors.lastname: Boyd