Berlin 2005 – scientific programme
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TT: Tiefe Temperaturen
TT 10: Superconductivity - Tunneling, Josephson Junctions, SQUIDs
TT 10.7: Talk
Saturday, March 5, 2005, 10:00–10:15, TU H104
Josephson junctions with nonlinear damping for qubit-RSFQ circuit applications — •A. B. Zorin, M. I. Khabipov, D. V. Balashov, R. Dolata, F.-I. Buchholz, and J. Niemeyer — Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
The overdamped Josephson tunnel junctions with resistive shunts are the key elements of the Rapid Single-Flux-Quantum (RSFQ) circuits enabling processing of information presented in quantized leaps of the Josephson phase. The normal metal shunts generate significant current noise even in the quiescent (zero-voltage) state of the Josephson junctions, so an application of such circuits for readout of a Josephson qubit is problematic because of dramatic dephasing. We demonstrate that shunting of tunnel junctions by Superconductor-Insulator-Normal metal (S-I-N) structures having pronounced nonlinear I-V characteristics can ensure both sufficient damping for proper functioning of the circuit and negligibly small noise in the quiescent state. Superconducting Nb/AlOx/Nb junctions shunted by Nb/AlOx/AuPd junctions of S-I-N type were fabricated and, in agreement with our model, exhibited non-hysteretic I-V characteristics at temperatures down to at least 1.4 K.