Superconducting Quantum Interference in Nb-Pt-Nb Josephson Junction Arrays

好弘 刑部, 佐藤 茂雄, 武 小野美 +2 more

S. E. Hebboul, J. C. Garland

We have measured the rf-bias-current dependence of the \ensuremath{\nu}/2 subharmonic spectral response of planar 300\ifmmode\times\else\texttimes\fi{}300 Nb-Au-Nb proximity-coupled Josephson-junction arrays. The \ensuremath{\nu}/2 subharmonic voltage spectrum was examined at two rf-bias frequencies, \ensuremath{\nu}/${\ensuremath{\nu}}_{\mathit{c}}$\ensuremath{\approxeq}1.4, 2.0 (${\ensuremath{\nu}}_{\mathit{c}}$\ensuremath{\approxeq}120 MHz), and in applied magnetic fields corresponding to f=0,1/2 flux quantum per plaquette. The measurements were compared to analytical predictions for an rf-biased asymmetric superconducting quantum interference device with non-negligble loop inductance and large rf-bias-current amplitudes, based on the resistively shunted Josephson-junction model. Reasonable agreement was found between experiment and theory, suggesting that a possible origin for the observed subharmonic behavior in arrays involves an interplay between array plaquette inductances and junction critical-current variations.

Matteo Cirillo, Susan R. Pace, S. Pagano +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.

Steven M. Anton, Shane A. Cybart, Stephen Wu +2 more

M. Khabipov, Brigitte Mackrodt, R. Dolata +2 more

Motivated by the realization of bifurcation regimes of operation, we report on experiments with superconducting microwave resonators comprising short serial arrays of Nb/AlO x /Nb SIS Josephson junctions and low-inductance SQUIDs. These elements provide sufficiently large Josephson inductance L J ∝ N (N is the number of elements in the chain) enabling nonlinear dynamics of the circuits and detection of low power signals.