Regenerative processes in a radio-frequency Josephson interferometer

Dario Gerace, Hakan E. Türeci, Ataç İmamoğlu +2 more

Alexander S. Averkin, Lyudmila V. Filippenko

Radio frequency superconducting quantum interferometers (RF-SQUIDs) are structural elements of nonlinear media used in superconducting metamaterials and superconducting low-noise parametric amplifiers. An expression for the effective Josephson inductance as a function of the external microwave signal power in a two-tone excitation mode is derived. This formula is applied to calculate the effective inductance of a Josephson junction embedded in an RF-SQUID under microwave radiation. The analytically calculated dependences of the resonant frequency and effective Josephson inductance of a non-hysteresis RF-SQUID on microwave power are in good agreement with experimental results.

E. O. Schulz-DuBois, P. Wolf

C. Granata, B. Ruggiero, M. Russo +3 more

We present niobium-based Josephson devices as prototypes for applications to quantum computation with flux qubits. The most interesting feature of this device is the use of a Josephson vertical interferometer for a fine tuning of flux qubit and interquibit coupling. These devices allow a control of the off-diagonal Hamiltonian terms of flux qubit and of the flux transfer function of a superconducting transformer. In the vertical interferometer, the Josephson current is precisely modulated from a maximum to zero with fine control and precision by a small transversal magnetic field parallel to the radio-frequency superconducting loop plane and to the flux transformer.

Yoshikazu Hayashi, Toshihiro Omodaka

The temperature dependence of radio frequency noise emission from the Nb–Nb superconducting point contact near the critical current is investigated. An anomalous temperature dependence of the RF emission intensity is observed above 7 K; a dip in the RF emission intensity is observed above 8 K. Strong temperature variation of the RF resistance associated with an anomaly in the cos φ term of the Josephson junction is considered to be one of the possible origin for the decrease of the emission intensity near the critical temperature.

Carmine Granata, CORATO V., Longobardi L. +3 more