title: Beating the standard quantum limit with four-entangled photons.
abstract: Precision measurements are important across all fields of science. In particular, optical phase measurements can be used to measure distance, position, displacement, acceleration, and optical path length. Quantum entanglement enables higher precision than would otherwise be possible. We demonstrated an optical phase measurement with an entangled four-photon interference visibility greater than the threshold to beat the standard quantum limit-the limit attainable without entanglement. These results open the way for new high-precision measurement applications.
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812, Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Nagata
authors.forename: Ryo
authors.initials: R
authors.lastname: Okamoto
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: O'brien
authors.forename: Keiji
authors.initials: K
authors.lastname: Sasaki
authors.forename: Shigeki
authors.initials: S
authors.lastname: Takeuchi