Hyperradiance from Soliton Oscillators Synchronized by Capacitive or Inducitve Coupling

The output power from coupled Josephson oscillators is investigated when the junctions are operated in their single fluxon mode. We demonstrate that both inductive and capacitive coupling mechanisms can give rise to hyperradiance when the power is coupled out through a boundary resistor. Analytical expressions are derived from adiabatic perturbation theory and excellent agreement is found between the analytical expression and numerical simulations

Chaos and Thermal Noise in a Josephson Junction Coupled to a Resonant Tank

Selected dynamical modes are investigated for the autonomous system formed from a dc biased Josephson junction which is resistively coupled to a resonant tank. A hysteretic zone in the current-voltage characteristic is shown to result from coexisting chaotic and periodic states. The detailed features of these states, including the geometrical structure of the attractors and their basins of attraction, as well as thermally induced transitions between them, are explored

Interactions Between Charged Rods Near Salty Surfaces

Using both theoretical modeling and computer simulations we study a model system for DNA interactions in the vicinity of charged membranes. We focus on the polarization of the mobile charges in the membranes due to the nearby charged rods (DNA) and the resulting screening of their fields and inter-rod interactions. We find, both within a Debye-Huckel model and in Brownian dynamics simulations, that the confinement of the mobile charges to the surface leads to a qualitative reduction in their ability to screen the charged rods to the degree that the fields and resulting interactions are not finite-ranged as in systems including a bulk salt concentration, but rather decay algebraically and the screening effect is more like an effective increase in the multipole moment of the charged rod

On the Classical Model for Microwave Induced Escape from a Josephson Washboard Potential

We revisit the interpretation of earlier low temperature experiments on Josephson junctions under the influence of applied microwaves. It was claimed that these experiments unambiguously established a quantum phenomenology with discrete levels in shallow wells of the washboard potential, and macroscopic quantum tunneling. We here apply the previously developed classical theory to a direct comparison with the original experimental observations, and we show that the experimental data can be accurately represented classically. Thus, our analysis questions the necessity of the earlier quantum mechanical interpretation.Comment: 4 pages, one table, three figures. Submitted for publication on December 14, 200

Phase Locking Between Fiske and Flux-Flow Modes in Coupled Sine-Gordon Systems

We investigate nonlinear resonant modes in coupled sine-Gordon systems with open boundary conditions. The system models coupled Josephson junctions with boundary conditions representing the situation where an external magnetic field is applied. The so-called Fiske modes are found to exist in phase-locked states where the equivalent voltages across the individual coupled Josephson junctions are either identical or identical with opposite signs. The analysis covers all Fiske modes including the flux-flow region. We present a comprehensive comparison between results on analytical treatment and direct numerical simulations of the coupled field equations

A classical statistical model for distributions of escape events in swept-bias Josephson junctions

We have developed a model for experiments in which the bias current applied to a Josephson junction is slowly increased from zero until the junction switches from its superconducting zero-voltage state, and the bias value at which this occurs is recorded. Repetition of such measurements yields experimentally determined probability distributions for the bias current at the moment of escape. Our model provides an explanation for available data on the temperature dependence of these escape peaks. When applied microwaves are included we observe an additional peak in the escape distributions and demonstrate that this peak matches experimental observations. The results suggest that experimentally observed switching distributions, with and without applied microwaves, can be understood within classical mechanics and may not exhibit phenomena that demand an exclusively quantum mechanical interpretation.Comment: Eight pages, eight figure

Investigation of low temperature quantum crossover in Josephson junctions

The evidence for macroscopic quantum tunneling (MQT) in Josephson junctions at low temperatures has been reassessed. Swept bias escape distributions have been modeled with an algorithm-based simulation and the results compared with data from representative published experiments. Signatures expected of a crossover to MQT are not found in the analyzed data.Comment: 7 pages, 6 figure

π\pi-kinks in strongly ac driven sine-Gordon systems

We demonstrate that $\pi$-kinks exist in non-parametrically ac driven sine-Gordon systems if the ac drive is sufficiently fast. It is found that, at a critical value of the drive amplitude, there are two stable and two unstable equilibria in the sine-Gordon phase. The pairwise symmetry of these equilibria implies the existence of a one-parameter family of $\pi$-kink solutions in the reduced system. In the dissipative case of the ac driven sine-Gordon systems, corresponding to Josephson junctions, the velocity is selected by the balance between the perturbations. The results are derived from a perturbation analysis and verified by direct numerical simulations.Comment: 4 pages, 2 figures, revte

Hyperradiance from Phase-Locked Soliton Oscillators

We show that the power emitted from phase-locked soliton oscillators can exceed the upper limit given by the theory for superradiance from phase-locked point oscillators. As an experimenta11y relevant example, we consider two magnetically coupled long Josephson junctions, operated in single-fluxon modes. Analytical results indicate that the coupling between the two oscillators enables the phase-locked modes to localize in space thereby creating the possibility of an enhancement of the power level beyond the point-oscillator limit. Good agreement is found between analytical results and numerical simulations, and with recently published experimental data