title: Observation of Collective Coupling between an Engineered Ensemble of Macroscopic Artificial Atoms and a Superconducting Resonator.
abstract: The hybridization of distinct quantum systems is now seen as an effective way to engineer the properties of an entire system leading to applications in quantum metamaterials, quantum simulation, and quantum metrology. Recent improvements in both fabrication techniques and qubit design have allowed the community to consider coupling large ensembles of artificial atoms, such as superconducting qubits, to a resonator. Here, we demonstrate the coherent coupling between a microwave resonator and a macroscopic ensemble composed of several thousand superconducting flux qubits, where we observe a large dispersive frequency shift in the spectrum of 250 MHz. We achieve the large dispersive shift with a collective enhancement of the coupling strength between the resonator and qubits. These results represent the largest number of coupled superconducting qubits realized so far.
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Kakuyanagi
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Matsuzaki
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: Corentin
authors.initials: C
authors.lastname: Déprez
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: Hiraku
authors.initials: H
authors.lastname: Toida
authors.affiliation: National Institute of Information and Communications Technology, 4-2-1, Nukuikitamachi, Koganei, Tokyo 184-8795, Japan.
authors.forename: Kouichi
authors.initials: K
authors.lastname: Semba
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamaguchi
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: William J
authors.initials: WJ
authors.lastname: Munro
authors.affiliation: NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
authors.forename: Shiro
authors.initials: S
authors.lastname: Saito