title: Useful multiparticle entanglement and sub-shot-noise sensitivity in experimental phase estimation.
abstract: We experimentally demonstrate a general criterion to identify entangled states useful for the estimation of an unknown phase shift with a sensitivity higher than the shot-noise limit. We show how to exploit this entanglement on the examples of a maximum likelihood as well as of a Bayesian phase estimation protocol. Using an entangled four-photon state we achieve a phase sensitivity clearly beyond the shot-noise limit. Our detailed comparison of methods and quantum states for entanglement enhanced metrology reveals the connection between multiparticle entanglement and sub-shot-noise uncertainty, both in a frequentist and in a Bayesian phase estimation setting.
authors.affiliation: Fakultät für Physik, Ludwig-Maximilians Universität München, D-80799 München, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Krischek
authors.forename: Christian
authors.initials: C
authors.lastname: Schwemmer
authors.forename: Witlef
authors.initials: W
authors.lastname: Wieczorek
authors.forename: Harald
authors.initials: H
authors.lastname: Weinfurter
authors.forename: Philipp
authors.initials: P
authors.lastname: Hyllus
authors.forename: Luca
authors.initials: L
authors.lastname: Pezzé
authors.forename: Augusto
authors.initials: A
authors.lastname: Smerzi