title: Light-induced collective pseudospin precession resonating with Higgs mode in a superconductor.
abstract: Superconductors host collective modes that can be manipulated with light. We show that a strong terahertz light field can induce oscillations of the superconducting order parameter in NbN with twice the frequency of the terahertz field. The result can be captured as a collective precession of Anderson's pseudospins in ac driving fields. A resonance between the field and the Higgs amplitude mode of the superconductor then results in large terahertz third-harmonic generation. The method we present here paves a way toward nonlinear quantum optics in superconductors with driving the pseudospins collectively and can be potentially extended to exotic superconductors for shedding light on the character of order parameters and their coupling to other degrees of freedom.
authors.affiliation: Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan. matsunaga@thz.phys.s.u-tokyo.ac.jp shimano@phys.s.u-tokyo.ac.jp.
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Matsunaga
authors.affiliation: Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Tsuji
authors.affiliation: Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Fujita
authors.affiliation: Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan.
authors.forename: Arata
authors.initials: A
authors.lastname: Sugioka
authors.affiliation: Kobe Advanced Research Center, National Institute of Information and Communications Technology, Hyogo 651-2492, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Makise
authors.affiliation: National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Uzawa
authors.affiliation: Kobe Advanced Research Center, National Institute of Information and Communications Technology, Hyogo 651-2492, Japan.
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Terai
authors.affiliation: Kobe Advanced Research Center, National Institute of Information and Communications Technology, Hyogo 651-2492, Japan.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan. High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Aoki
authors.affiliation: Department of Physics, University of Tokyo, Hongo, Tokyo, 113-0033, Japan. Cryogenic Research Center, University of Tokyo, Yayoi, Tokyo 113-0032, Japan. matsunaga@thz.phys.s.u-tokyo.ac.jp shimano@phys.s.u-tokyo.ac.jp.
authors.forename: Ryo
authors.initials: R
authors.lastname: Shimano