Phase-locking in strongly coupled SQUID cells

Donald G. McDonald

S. A. Belonogov, Oleg V. Snigirev, S.S. Tinchev +1 more

V. K. Kaplunenko, J. Mygind, N. F. Pedersen +1 more

We report on synchronous operation of series arrays of inductively coupled superconducting quantum interference devices (SQUIDs). Each array consisted of N=3 or 11 dc SQUIDs with common inductances providing a strong interaction between neighboring cells. Externally shunted (βc≊1) trilayer Nb—AlOx—Nb Josephson junctions were used. Coherent radiation was detected in the frequency range f=67–73 GHz while the array voltage was VN=NfΦ0 (Φ0=2.07×10−15 V s). The stability of the coherent state was influenced by the external dc magnetic field. The linewidth depended on the external loading. For small loading it was N times smaller than expected for a single cell. The influence of the inductive coupling mechanism on the operation of discrete Josephson junction circuits and the similarity to the coupling in layered structures of long Josephson junctions is discussed.

B. Frank, Wolfram Krech, K. Yu. Platov

We present a theoretical analysis of the dynamics of multijunction superconducting quantum interference devices (SQUIDs). The small inductance approximation allows to get analytical expressions for the Josephson phases and voltages, taking into account a finite value of the inductance of the SQUID cells. Contrary to most theoretical investigations which exploited the first-harmonic approximation approach, our results describe the behavior of the circuit for small values of the Josephson frequency as well. Analytical results have been shown to be in a good agreement with numerical simulations.

J. Pleikies, Horst Rogalla, Jakob Flokstra

Jørn Bindslev Hansen

We have investigated phase-locking and voltage-locking in systems consisting of two planar dc-SQUIDs* located close together in the same superconducting film. The locking strength was found to be strongly dependent on the fluxoid state of both SQUIDs. We present a simple model for the inductive coupling between such two dc-SQUIDs and compare the prediction of the model with the experimental results.