Hyperchaotic behaviours and controlling hyperchaos in an array of RCL-shunted Josephson junctions

This paper deals with dynamical behaviours in an array composed of two resistive-capacitive-inductive-shunted （RCL-shunted） Josephson junctions （RCLSJJs） and a shunted resistor. Numerical simulations show that periodic, chaotic and hyperchaotic states can coexist in this array. Moreover, a scheme for controlling hyperchaos in this array is presented by adjusting the external bias current. Numerical results confirm that this scheme can be effectively used to control hyperchaotic states in this array into stable periodic states, and different stable periodic states with different period numbers can be obtained by appropriately choosing the intensity of the external bias current.

Controlling chaos in RCL-shunted Josephson junction by delayed linear feedback

The resistively-capacitively-inductively-shunted （RCL-shunted） Josephson junction （RCLSJJ） shows chaotic behaviour under some parameter conditions. Here a scheme for controlling chaos in the RCLSJJ is presented based on the linear feedback theory. Numerical simulations show that this scheme can be effectively used to control chaotic states in this junction into stable periodic states. Moreover, the different stable period states with different period numbers can be obtained by appropriately adjusting the feedback intensity and delay time without any pre-knowledge of this system required.

Simulation and measurement of millimeter-wave radiation from Josephson junction array

We report the circuit simulations and experiments of millimeter-wave radiation from a high temperature superconducting(HTS) bicrystal Josephson junction(BJJ) array. To study the effects of junction characteristic parameters on radiation properties, new radiation circuit models are proposed in this paper. The series resistively and capacitively shunted junction(RCSJ) models are packaged into a Josephson junction array(JJA) model in the simulation. The current-voltage characteristics(IVCs) curve and radiation peaks are simulated and analyzed by circuit models, which are also observed from the experiment at liquid nitrogen temperature. The experimental radiation linewidth and power are in good agreement with simulated results. The presented circuit models clearly demonstrate that the inconsistency of the JJA will cause a broad linewidth and a low detected power. The junction radiation properties are also investigated at the optimal situation by circuit simulation. The results further confirm that the consistent JJA characteristic parameters can successfully narrow the radiation linewidth and increase the power of junction radiation.

Quadruple-stacked Nb/NbxSi1-x/Nb Josephson junctions for large-scale array application

Large-scale Josephson junction(JJ)arrays are essential in many applications,especially quantum voltage standards application for which hundreds of thousands of junctions are required to realize a high quantum voltage.For almost all applications,high-quality JJ arrays must be realized in a small chip area.This study proposes vertically quadruplestacked Nb/(NbxSi1-x/Nb)4 JJs to increase the integration density of junctions in an array.The current–voltage(I–V)characteristics of a single stack of Nb/(NbxSi1??x/Nb)4 JJs have been measured at 4.2 K.The uniformity of junctions in one stack and the uniformity of several stacks over the entire 2 inches wafer have been analyzed.By optimizing the fabrication parameters,a large-scale quadruple-stacked Nb/(NbxSi1??x/Nb)4 array consisting of 400000 junctions is realized.Good DC I–V characteristics are obtained,indicating the good uniformity of the large-scale array.

Ground state of a superconducting π ring array under external magnetic fields

The ground state of a two-dimensional square superconducting πring array has been investigated. The circulating currents of the π ring array will spontaneously magnetize to the ＇antiferromagnetic＇ arrangement with directions of the nearest-neighbouring currents circulating oppositely in the absence of an external magnetic field. It is found that the external magnetic field could destroy the anti-parallel configuration effectively. The external magnetic field needed to destroy the anti-parallel configuration is related to the superconducting π ring＇s inductance parameter β= 2πLIc/Ф0. For a small β the anti-parallel configuration, which is the lowest-energy ground state of the system, will be fully destroyed and changed to the configuration that the circulating currents have the same direction and parallel to the external magnetic field when the magnetic flux reaches Ф0/4 in each ring. Moreover, the magnetic field needed to destroy the anti-parallel configuration will be very small when β is large enough.