"All-versus-nothing" nonlocality test of quantum mechanics by two-photon hyperentanglement

We report the experimental realization and the characterization of polarization and momentum hyperentangled two photon states, generated by a new parametric source of correlated photon pairs. By adoption of these states an "all versus nothing" test of quantum mechanics was performed. The two photon hyperentangled states are expected to find at an increasing rate a widespread application in state engineering and quantum information. PACS: 03.65.Ud, 03.67.Mn, 42.65. LmComment: Replaced with published versio

Erratum: Connection between entanglement and the speed of quantum evolution

PACS number s : 03.67.Mn, 89.70. c, 03.65. w, 02.50. r, 99.10.CdErratum: Connection between entanglement and the speed of quantum evolution [Phys. Rev. A 72, 032337 (2005)]Peer reviewe

Effects of frequency correlation in linear optical entangling gate operated with independent photons

Bose-Einstein coalescence of independent photons at the surface of a beam splitter is the physical process that allows linear optical quantum gates to be built. When distinct parametric down-conversion events are used as an independent photon source, distinguishability arises form the energy correlation of each photon with its twin. We find that increasing the pump bandwidth may help in improving the visibility of non-classical interference and reaching a level of near perfect indistinguishability. PACS: 03.67.Mn, 42.65.Lm, 42.50.St.Comment: Replaced with published versio

Entanglement in a first-order quantum phase transition

4 págs.; 3 figs.; PACS number(s): 03.65.Ud, 03.67.Mn, 73.43.NqThe entanglement properties of the ground state for a system of spins half embedded in a magnetic field were investigated. A first-order transition was obtained at zero field. It was found that two-spin entanglement displays a jump at the transition point. It was shown that the symmetries of the Hamiltonian allow to simplify the diagnolization.Peer Reviewe

Entanglement in Finitely Correlated Spin States

We derive bounds for the entanglement of a spin with an (adjacent and non-adjacent) interval of spins in an arbitrary pure finitely correlated state (FCS) on a chain of spins of any magnitude. Finitely correlated states are otherwise known as matrix product states or generalized valence-bond states. The bounds become exact in the limit of the entanglement of a single spin and the half-infinite chain to the right (or the left) of it. Our bounds provide a proof of the recent conjecture by Benatti, Hiesmayr, and Narnhofer that their necessary condition for non-vanishing entanglement in terms of a single spin and the ``memory'' of the FCS, is also sufficient . Our result also generalizes the study of entanglement in the ground state of the AKLT model by Fan, Korepin, and Roychowdhury. Our result permits one to calculate more efficiently, numerically and in some cases even analytically, the entanglement of arbitrary finitely correlated quantum spin chains.Comment: PACS 03.67.Mn, 05.50.+q. Minor typos in v1 corrected. In v2: expanded Introduction and Discussion. Simplified proof of the main resul