title: Quantum-enhanced optical-phase tracking.
abstract: Tracking a randomly varying optical phase is a key task in metrology, with applications in optical communication. The best precision for optical-phase tracking has until now been limited by the quantum vacuum fluctuations of coherent light. Here, we surpass this coherent-state limit by using a continuous-wave beam in a phase-squeezed quantum state. Unlike in previous squeezing-enhanced metrology, restricted to phases with very small variation, the best tracking precision (for a fixed light intensity) is achieved for a finite degree of squeezing because of Heisenberg's uncertainty principle. By optimizing the squeezing, we track the phase with a mean square error 15 ± 4% below the coherent-state limit.
authors.affiliation: Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Yonezawa
authors.forename: Daisuke
authors.initials: D
authors.lastname: Nakane
authors.forename: Trevor A
authors.initials: TA
authors.lastname: Wheatley
authors.forename: Kohjiro
authors.initials: K
authors.lastname: Iwasawa
authors.forename: Shuntaro
authors.initials: S
authors.lastname: Takeda
authors.forename: Hajime
authors.initials: H
authors.lastname: Arao
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ohki
authors.forename: Koji
authors.initials: K
authors.lastname: Tsumura
authors.forename: Dominic W
authors.initials: DW
authors.lastname: Berry
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Ralph
authors.forename: Howard M
authors.initials: HM
authors.lastname: Wiseman
authors.forename: Elanor H
authors.initials: EH
authors.lastname: Huntington
authors.forename: Akira
authors.initials: A
authors.lastname: Furusawa