Frequency divider by underdamped Josephson transmission line

A parallel array of coupled short Josephson junctions under boundary ac driving is theoretically investigated. The driving response is monitored via numerical simulations on the associated Frenkel-Kontorova model as an oscillating output current at the other boundary junction. The theoretical analysis is conducted assuming the phase locking of boundary driving with exact stationary solution of sine-Gordon equation that can be represented by a kink (fluxon) motion back and forth in the restricted geometry of the array. As a consequence the results suggest the conception of a device which could switch to the conducting regime not according to intensity range but rather to given (quantized) frequency range. Moreover our findings indicate also a frequency converting scenario by choosing appropriately the system length and injected fluxon number.     

Experimental observation of delay-induced radio frequency chaos in a transmission line oscillator

We report an experimental study of fast chaotic dynamics in a delay dynamical system. The system is an electronic device consisting of a length of coaxial cable terminated on one end with a diode and on the other with a negative resistor. When the negative resistance is large, the system evolves to a steady state. As the negative resistance is decreased, a Hopf bifurcation occurs. By varying the length of the transmission line we observe Hopf frequencies from 7-53 MHz. With the transmission line length fixed, we observe a period doubling route to chaos as the negative resistance is further reduced providing the first experimental confirmation of an existing theoretical model for nonlinear dynamics in transmission line oscillators [Corti et al., IEEE Trans. Circ. Syst., I: Fundam. Theory Appl. 41, 730 (1994)]. However, other experimental results indicate limitations to this model including an inability to predict the Hopf frequency or to produce realistic continuous wave forms. We extend the model to include finite bandwidth effects present in a real negative resistor. The resulting model is a neutral delay differential equation that provides better agreement with experimental results.     

Reflection of fluxons on a Josephson line cavity

A single fluxon on a semi-infinite Josephson line is reflected at a passive or an active termination. By numerical computation we find a single reflected fluxon, an antifluxon, absorption of the incident fluxon, or fission into an arbitrary number of fluxons depending on the boundary condition. For the passive termination an analytical approximation based on energy analysis is developed.     

Flux cloning in Josephson transmission lines

We describe a novel effect related to the controlled birth of a single Josephson vortex. In this phenomenon, the vortex is created in a Josephson transmission line at a T-shaped junction. The "baby" vortex arises at the moment when a "mother" vortex propagating in the adjacent transmission line passes the T-shaped junction. In order to give birth to a new vortex, the mother vortex must have enough kinetic energy. Its motion can also be supported by an externally applied driving current. We determine the critical velocity and the critical driving current for the creation of the baby vortices and briefly discuss the potential applications of the found effect.     

Direct observation of Josephson capacitance

The effective capacitance has been measured in the split Cooper-pair box (CPB) over its phase-gate bias plane. Our low-frequency reactive measurement scheme allows us to probe purely the capacitive susceptibility due to the CPB band structure. The data are quantitatively explained using parameters determined independently by spectroscopic means. In addition, we show in practice that the method offers an efficient way to do nondemolition readout of the CPB quantum state.     

Superconducting vortex line in Josephson junction

The superconducting ring closed with the half infinite plane Josephson junction is considered. The external magnetic flux is introduced in the ring with the external source supplied solenoid.The conditions of stability are found for the superconducting vortex in the plane Josephson junction. The function φ(φ_x) is derived. Here φ is the total magnetic flux in the hole. This function differentiates from the same function in the case of the ring closed. with the point contact.     

Direct observation of dynamical bifurcation in a superfluid Josephson junction

We report a direct observation of dynamical bifurcation between two plasma oscillation states of a superfluid Josephson junction. We excite the superfluid plasma resonance into a nonlinear regime by driving below the natural plasma frequency and observe a clear transition between two dynamical states. We also demonstrate bifurcation by changing the potential well with temperature variations.     

Structure and energy of a line vortex in a three-dimensional ordered Josephson medium

Two possible equilibrium configurations of line vortices in a three-dimensional ordered Josephson medium for any value of structural factor b are considered: the center of the vortex coincides with the center of one of the cells and the center of the vortex is on one of the contacts. Infinite sets of equations describing these configurations are derived. The infinite set can be made finite if currents away from the center are neglected. The assumption b = 0 is shown to be valid if pinning parameter I is less than 0.25. For I > 0.25, the structures and energies of both configurations of line isolated vortices are calculated throughout the range of structural factor b. As structural factor b increases, phase jumps at the contacts, currents in the central part of the vortex, and the total energies of the vortices decrease in both configurations. This leads to a decrease in critical field H _c1. For all values of I and b, the energy of the vortex centered on the contact is higher than that of the vortex centered in the middle of the cell.     

Direct observation of tunneling and nonlinear self-trapping in a single bosonic Josephson junction

We report on the first realization of a single bosonic Josephson junction, implemented by two weakly linked Bose-Einstein condensates in a double-well potential. In order to fully investigate the nonlinear tunneling dynamics we measure the density distribution in situ and deduce the evolution of the relative phase between the two condensates from interference fringes. Our results verify the predicted nonlinear generalization of tunneling oscillations in superconducting and superfluid Josephson junctions. Additionally, we confirm a novel nonlinear effect known as macroscopic quantum self-trapping, which leads to the inhibition of large amplitude tunneling oscillations.     

Parametric frequency transformation in a superconducting waveguide line with an integrated Josephson oscillator

The parametric frequency division in a coplanar waveguide line with an integrated single-contact rf SQUID (Josephson oscillator) is discussed. It is assumed that the oscillator is excited by pump pulses whose carrier frequency can be a multiple of the plasma frequency of the oscillator. It is shown that the Josephson oscillator excited at the pump frequency can induce frequency division by emitting subharmonics that are multiples of the fundamental frequency (fractional resonances). Parameters for which parametric frequency transformation occurs are determined. The possible generalization of this effect to the quantum case in which correlated microwave photons (entangled photon states) can be generated is discussed.     

Performance robustness of a noise-assisted transmission line

In this paper we analyze the stochastic-resonant behavior of a chain of forward-coupled bistable overdamped oscillators used as a transmission line with possible applications to neurophysiology, information transmission and storage. We drive the line with a random sequence of non-return-to-zero bits and each oscillator is independently perturbed by noise. The line is analyzed for varying coupling strengths that lead to different regimes, ranging from noise-supported to coupling-supported transmission. We characterize the transmission performance by parameters such as output bit error rate and delivered signal-to-noise ratio, and show them to improve and remain flat for a broad range of noise intensities in all coupling regimes. In particular, we found that this system exhibits an enhanced robustness as compared to a linear transmission channel impaired only by additive noise.     

Acoustical characteristics of a multichannel transmission line

The properties of an acoustic system called by the author ”a multichannel transmission line” (MTL) are considered. Analytical expressions are derived for the following main acoustical characteristics of an MTL consisting of an arbitrary number N of single lines: the input impedance, the resonance frequencies, the reflection and transmission factors for an MTL-insulator, and the reflection factor for an MTL-absorber. For these quantities, numerical calculations are performed, and their frequency dependences are presented for different parameters of the constituent lines in the cases N=2 and 3. It is shown that the acoustical characteristics of MTL-insulators and MTL-absorbers have considerable advantages over the characteristics of similar systems designed on the basis of single lines.     

Direct observation of the transition from the conventional superconducting state to the pi state in a controllable Josephson junction

We measure the full supercurrent-phase relation of a controllable pi junction around the transition from the conventional 0 state to the pi state. We show that around the transition the Josephson supercurrent-phase relation changes from I(sc) approximately I(c)sin((phi) to I(sc) approximately I(c)sin((2phi). This implies that, around the transition, two minima in the junction free energy exist, one at phi=0 and one at phi=pi, whereas only one minimum exists at the 0 state (at phi=0) and at the pi state (at phi=pi). Theoretical calculations based on the quasiclassical theory are in good agreement with the observed behavior.     

介观耗散传输线的量子化

从耗散传输线的经典运动方程出发,将传输线中的单模信号进行量子化,研究了传输线在激发相干态下的量子效应.结果表明,传输线的量子涨落不仅与电路参数和电路的状态有关,还与传输线的位置有关. 关键词： 介观传输线 耗散 单模 激发相干态     

磁绝缘传输线振荡器中的次级电子倍增现象

根据磁绝缘传输线振荡器(MILO)的结构特点，建立了一个单边次级电子倍增(multipactor)模型，通过对敏感曲线、相位聚焦的计算，分析了MILO中发生multipactor的物理图象.结果表明：从聚焦区域大小看，单边发生multipactor 比双边要严重.在MILO中发生的multipactor都属于单边模式，并且有出现电子掠入射金属表面的大量机会，因此它发生multipactor比O型器件严重. 关键词： 磁绝缘传输线振荡器 次级电子倍增效应 脉冲缩短