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[en] It has recently been explained why I-V curves of rf-driven overdamped junctions exhibit three distinct regions and two kinds of Shapiro steps when the rf frequency is smaller than the characteristic frequency ωc=2eRIc/ℎ of the junction. This paper shows that these results can be extended to underdamped junctions for rf frequencies smaller than 1/RC. (orig.)
[en] The effect of thermal noise on chaotic behavior in the rf-biased Josephson junction is studied through digital simulations. In instances for which chaotic behavior occurs in the noise-free system, it is found that the dynamics of the system are almost unchanged by the addition of thermal noise unless the level of thermal noise exceeds that of the chaotic state. In instances for which the only stable states of the noise-free system are periodic solutions, small amounts of thermal noise can induce the junction to hop between two different dynamical states, producing a low-frequency noise level much higher than that of the thermal noise. Such noise-induced hopping can occur either between two periodic solutions or between a periodic solution and a metastable chaotic solution. When a metastable chaotic state is involved, temperatures somewhat higher than those which produce hopping can destablize the periodic solution to the point where the system spends virtually all of its time in the metastable chaotic state, creating noise-induced chaos. The similarities between chaotic behavior at zero temperature and noise-induced chaos are sufficiently strong that it may be difficult to distinguish the two cases experimentally
[en] RF-driven underdamped Josephson junctions are expected to exhibit chaotic behavior in the rf frequency range roughly defined by ωRC< or approx.ω< or approx.ωp where ωRC=1/RC and ωp=(2cIc/ℎC)1/2. Numerical simulations of the I-V curves are presented as the rf frequency is increased from 0.1 ωRC to 2 ωp. The effect of chaos on the I-V curves is strongly dependent on the rf frequency. (orig.)
[en] We report on the functionality of a Nb-based superconducting single flux quantum (SFQ) toggle flip-flop (TFF) circuit, comprising a complementary superconductor-ferromagnet-superconductor (SFS) Josephson π-junction. The SFS junction was used as a phase shifting element inserted in the storage loop of the TFF. The fabricated circuits demonstrated correct functionality with the operation parameter ranges of ± 20%. The application of SFS π-junctions makes the SFQ circuits very compact, may substantially improve their stability, and may also be suitable for integration with Josephson quantum circuits (qubits).
[en] A system using a Josephson series array capable of developing voltages of up to 1.3 V is described. The array system has been compared to Volt NRC with good agreement. At 1.018 V, the difference between the array system and VNRC which is referenced to an existing single junction system is 0.008 +- 0.035 μV