title: Switchable ultrastrong coupling in circuit QED.
abstract: We propose different designs of switchable coupling between a superconducting flux qubit and a microwave transmission line. They are based on two or more loops of Josephson junctions which are directly connected to a closed (cavity) or open transmission line. In both cases the circuit induces a coupling that can be modulated in strength, reaching the so-called ultrastrong coupling regime in which the coupling is comparable to the qubit and photon frequencies. Furthermore, we suggest a wide set of applications for the introduced architectures.
authors.affiliation: Instituto de Física Fundamental, CSIC, Serrano 113-bis, 28006 Madrid, Spain.
authors.forename: B
authors.initials: B
authors.lastname: Peropadre
authors.forename: P
authors.initials: P
authors.lastname: Forn-Díaz
authors.forename: E
authors.initials: E
authors.lastname: Solano
authors.forename: J J
authors.initials: JJ
authors.lastname: García-Ripoll