title: Protected Josephson Rhombus chains.
abstract: We have studied the low-energy excitations in a minimalistic protected Josephson circuit which contains two basic elements (rhombi) characterized by the π periodicity of the Josephson energy. Novel design of these elements, which reduces their sensitivity to the offset charge fluctuations, has been employed. We have observed that the lifetime T1 of the first excited state of this quantum circuit in the protected regime is increased up to 70  μs, a factor of ∼100 longer than that in the unprotected state. The quality factor ω01T1 of this qubit exceeds 106. Our results are in agreement with theoretical expectations; they demonstrate the feasibility of symmetry protection in the rhombus-based qubits fabricated with existing technology.
authors.affiliation: Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Bell
authors.affiliation: Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: Paramanandam
authors.affiliation: Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA and LPTHE, CNRS UMR 7589, 4 place Jussieu, 75252 Paris, France.
authors.forename: Lev B
authors.initials: LB
authors.lastname: Ioffe
authors.affiliation: Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Gershenson