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The variations of the critical current ${I}_{c}$ across the layers as a function of the parallel magnetic field $H$ have been studied on small area stacked junctions fabricated from perfect single crystal B${\mathrm{i}}_{2}$S${\mathrm{r}}_{2}$CaC${\mathrm{u}}_{2}$${\mathrm{O}}_{8}$ whiskers. Intrinsic dc Josephson effect has been clearly demonstrated on structures with in-plane size $L$ less than $20\ensuremath{\mu}\mathrm{m}$. With $L$ increases, a dimensional crossover to monotonic size independent behavior of ${I}_{c}(H)$ has been observed. ${I}_{c}(H)$ decrease in this region is proportional to $\sqrt{H}$ in accordance with the Fistul-Giuliani theory.

Device-independent protocols use nonlocality to certify that they are performing properly. This is achieved via Bell experiments on entangled quantum systems, which are kept isolated from one another during the measurements. However, with present-day technology, perfect isolation comes at the price of experimental complexity and extremely low data rates. Here we argue that for device-independent randomness generation -- and other device-independent protocols where the devices are in the same lab -- we can slightly relax the requirement of perfect isolation, and still retain most of the advantages of the device-independent approach, by allowing a little cross-talk between the devices. This opens up the possibility of using existent experimental systems with high data rates, such as Josephson phase qubits on the same chip, thereby bringing device-independent randomness generation much closer to practical application., Comment: 6 pages, 2 figures

In arrays of globally coupled Josephson junctions, antiphase states have high multiplicity in phase space. For an array of [ital N] oscillators, there are ([ital N][minus]1) distinct antiphase states. In this Letter we show, using the modern ideas of controlling a saddle on a basin boundary, how to switch from one antiphase state to another. The cases of three and four Josephson junctions are explicitly considered. The method we present is directly applicable to real experiments of globally coupled oscillators.

We argue that the vacuum polarization by the virtual electron-positron pairs can be measured by studying a Josephson junction in a strong magnetic field. The vacuum polarization results in a weak dependence of the Josephson constant on the magnetic field strength which is within the reach of the existing experimental techniques., 4 pages, 2 figures, LaTeX

We study the ac Josephson effect in a superconductor-ferromagnet heterostructure with a variable magnetic configuration. The system supports triplet proximity correlations whose dynamics is coupled to the magnetic dynamics. This feedback dramatically modifies the behavior of the junction. The current-phase relation becomes double periodic at both very low and high Josephson frequencies ${\ensuremath{\omega}}_{J}$. At intermediate frequencies, the periodicity in ${\ensuremath{\omega}}_{J}t$ may be lost.

We report on the interlayer far infrared response for a series of ${\mathrm{L}\mathrm{a}}_{2\ensuremath{-}x}{\mathrm{S}\mathrm{r}}_{x}{\mathrm{C}\mathrm{u}\mathrm{O}}_{4}$ crystals with $0.08lxl0.20$ focusing on the survey of the Josephson plasmon resonance (JPR). The analysis of the JPR mode provides information on the local variation of the superfluid density within the ${\mathrm{C}\mathrm{u}\mathrm{O}}_{2}$ planes thus empowering one with a tool for ``microscopy'' on the superconducting condensate. Our results uncover the presence of regions with characteristic length of $\ensuremath{\sim}100--200\text{ }\text{ }\AA{}$ within which superconductivity is strongly depressed or completely depleted. An examination of the doping trends suggests that development of superconducting inhomogeneities is triggered by the formation of the unidirectional spin density wave state in ${\mathrm{L}\mathrm{a}}_{2\ensuremath{-}x}{\mathrm{S}\mathrm{r}}_{x}{\mathrm{C}\mathrm{u}\mathrm{O}}_{4}$ at $x=1/8$.

Well-defined zigzag-shaped ramp-type Josephson junctions between YBa2Cu3O7 and Nb have been studied. The magnetic field dependencies of the critical currents provide evidence for d-wave?induced alternations in the direction of the Josephson current between neighboring sides of the zigzag structure. The arrays present controllable model systems to study the influences of ? facets in high-angle high- Tc grain boundaries. From the characteristics, we estimate a possible imaginary s-wave admixture to the order parameter of the YBa2Cu3O7 to be below 1%.

The intermittent-type chaos occurring in rf- and dc-current-driven Josephson junctions is investigated. A simple physical model is proposed and is used for an analytic calculation of the power spectrum. The latter has a broadband part which decays algebraically at high frequencies. Comparison with numerical results shows good agreement. Further application and generalizations of this approach are outlined.

A quasiparticle-current-fluctuation contribution to the radiation emitted by Josephson tunnel junctions is calculated. The result is combined with Stephen's result for the pair-current-fluctuation contribution and compared with experimental linewidth data for Sn-I-Sn and Pb-I-Pb junctions.

Using the ac Josephson effect we have demonstrated experimentally that $\frac{2e}{h}$ is identical in lead, tin, and indium to within 1 part in ${10}^{8}$.

The proximity-induced Josephson effect is studied microscopically by analysis of the quasiclassical transport equations in a sandwich geometry. The main Shapiro step is found at $V=\frac{h\ensuremath{\nu}}{4e}$. It is thus concluded that the proximity-induced Josephson effect is not seen in a recent experiment by Han et al.