To investigate the properties of the Josephson junction and its related circuits,a model of Josephson junction in Multisim has been created.Both the DC(Direct Current) Josephson effect and AC(Active Current) Josephson effect are testified using the model in Multisim.Subsequently,we observe a quasi-periodic motion in the Josephson junction by studying chaotic behaviors of the resistively-capacitively-inductively shunted junction.Besides,we investigate the characteristics of Shapiro steps in chaos and its special effect under thermal noises.Finally,rapid single flux quantum circuit is constructed to convert DC pulse to SFQ(Single Flux Quantum).The simulation results show that the model is powerful so that it can produce valuable predictions in the research of the Josephson junction,which plays an important role in analyzing and designing a superconductive device.
To investigate the properties of the Josephson junction and its related circuits,a model of Josephson junction in Multisim has been created.Both the DC(Direct Current) Josephson effect and AC(Active Current) Josephson effect are testified using the model in Multisim.Subsequently,we observe a quasi-periodic motion in the Josephson junction by studying chaotic behaviors of the resistively-capacitively-inductively shunted junction.Besides,we investigate the characteristics of Shapiro steps in chaos and its special effect under thermal noises.Finally,rapid single flux quantum circuit is constructed to convert DC pulse to SFQ(Single Flux Quantum).The simulation results show that the model is powerful so that it can produce valuable predictions in the research of the Josephson junction,which plays an important role in analyzing and designing a superconductive device.
Superconductive electronics is an extensive field covering both low- and high-temperature superconductors (HTS), and their applications in quantum interference devices, power transmission, microwave filters and logic circuits. The microscopic origins of superconductivity are explained by Bardeen–Cooper–Schieffer (BCS) theory whereas a macroscopic treatment is provided by the Ginzburg–Landau theory. The London equations can explain the well-known Meissner effect of exclusion of magnetic induction by superconductors. A widely used device in superconductive electronics is the Josephson junction (JJ). The DC and AC Josephson effects as well as the inverse AC Josephson effects are described. The application of DC and AC superconducting quantum interference devices (SQUIDs) in magnetometry are discussed. Rapid single flux quantum (RSFQ) logic, touted as a competitive beyond-CMOS technology in nanoelectronics, is briefly surveyed.
Josephson junction, as the core nonlinear element underpinning superconducting electronics, is characterized by its current-phase relation (CPR), which fundamentally determines the dynamical properties and functional capabilities of superconducting quantum devices. Traditional Josephson junctions typically exhibit a traditional sinusoidal CPR; however, the junctions characterized by non-sinusoidal CPR have recently attracted considerable attention due to their distinctive physical properties and promising quantum device applications. In this work, a numerical model tailored specifically for junctions exhibiting non-sinusoidal CPR is developed by integrating experimentally measured current-voltage (I-V ) characteristics from Nb/Al-AlOx/Nb junctions into a resistively and capacitively shunted junction (RCSJ) framework. By leveraging this refined model, the influence of CPR skewness on Josephson junction dynamics is systematically investigated. Our results indicate that in underdamped junctions, the critical current significantly diminishes with the increase of CPR skewness, a behavior reminiscent of the adjustable critical currents typically observed in DC superconducting quantum interference devices (SQUIDs). Conversely, in overdamped junctions, the influence of CPR skewness on the I-V characteristics is found to be negligible. However, our numerical simulations under microwave irradiation indicate that nonsinusoidal CPRs readily promote the emergence of half-integer Shapiro steps in overdamped junctions, thereby establishing CPR skewness as a plausible microscopic origin for this phenomenon. In addition, the advanced design system (ADS) simulations is employed to model nonlinear resonators and DC SQUID circuits, offering a detailed investigation into how nonsinusoidal CPRs modulate the Josephson inductance and magnetic flux response. Our findings reveal that engineering the CPR of Josephson junctions provides substantial flexibility in the design of superconducting qubits, parametric amplifiers, and non-magnetic nonreciprocal devices. This tunability underscores significant opportunities for developing next-generation superconducting electronic components. The Josephson junctions with engineered CPR offer expanded functionality for superconducting quantum technologies. This study suggests that customized CPR can enhance control over the dynamical behavior of junctions, and promote the optimized designs of superconducting qubits, parametric amplifiers, and nonmagnetic nonreciprocal devices.
Abstract The pursuit of high-speed response and precise reconstruction of phase reversal within Josephson junction constitutes the principal research objectives for the device model in the superconducting single flux quantum (SFQ) circuits. The proposing of the resistive-capacitive-inductive-shunted junction (RCLSJ) model by incorporating a shunted inductance on the classical resistive-capacitive-shunted junction (RCSJ) model, indeed achieves a more accurate description of the Current–Voltage ( I – V ) characteristics of Josephson junctions. However, the effectiveness of the RCLSJ model in dynamic simulations of SFQ circuits has not yet been verified. We proposed a simple and convenient test structure for D flip-flop (DFF) circuits to obtain the variation of its bias margin over a wide frequency sweep range. Post-simulations using the RCLSJ model were performed for DFF circuits. It was found that there are still matching problems between the simulations and tests, especially in the higher frequency region. Based on the junction area structure and layout application under the SIMIT-Nb03 process, a corrected RCLSJ model, designated as the RCLSJv model, was developed. This model mainly reassigns the parasitic inductance of the junction area and introduces correction coefficients by fitting the test data. The validity of the model has been verified through the comprehensive fitting of multiple sets of DFFs’ test data. In comparation with the RCSJ model, the deviation between the test and simulation results was successfully confined within 3%. Notably, in the frequency range above 60 GHz, the matching degree exhibits a remarkable enhancement, with an improvement factor ranging from 2 to 5 times.
Applications to electronics are mainly based on Josephson junctions special properties. As it was pointed before, a single Josephson junction is a perfect voltage to frequency converter (AC Josephson effect). One example is the application into RF amplifiers where a radiofrequency signal generates a magnetic flux in a circuit coupled to, for example, DC-SQUID. Josephson effect allows converting the flux into the SQUID to an amplified voltage signal, proportional to the number of 0. That is the base of the microwave applications. The SQUID inductance together with the capacitance of the junction, allows also using the device as resonator.
Abstract\nThis diploma work is about Rapid Single Flux Quantum (RSFQ) circuits. This\nsupercoducting digital circuitry has the most promising properties in terms of speed and\npower consumption. The active elements of the RSFQ circuits are Josephson junctions (JJ).\nFor their fabrication low temperature superconducting niobium films are used. Today the\ndesign and fabrication of RSFQ circuits are done in a standardized way with well-defined\ndesign rules. Nevertheless, to design complicated circuits with more than several hundred\njunctions a lot of practical problems must be solved.\nDifferent aspects of the RSFQ circuits design process were investigated in this work.\nIn the theoretical part we propose a new, more realistic model of the Josephson junction for\nphysical simulation (which is necessarily used for design of every RSFQ gate) in order to\nimprove its quality and precision. The new model for the JJ includes additional inductances,\nwhich must reflect a specific environment of the junction layout. The influence of parameter\ndeviations was investigated in the simulation. As sources of the deviation we chose the\nspread of c (the Stewart-McCumber parameter) and that of the inductances. Then the\noperational margins of the basic elements of the RSFQ logic SR flip-flop were determined\nand compared with the prediction of the previously used model. To prove the results of\nsimulations we designed a test structure of the SR flip-flop, with c=1 and c=2 for the wellestablished\nHYPRES technology (USA).\nAnother part of the work is practical measurements. A test chip, containing chains of 100\nJosephson junctions was designed and measured in order to estimate the spread of critical\ncurrents in real technology.
The shunt resistors used in many Josephson junction circuits contain an inductive component that can significantly degrade high-frequency performance. Numerical simulations reveal complex dynamical behaviour, including relaxation oscillations, period-doubling sequences, and chaos, all of which are serious problems for applications as high-frequency sources and detectors. This complex AC behaviour creates features in the simulated DC current-voltage characteristics. Since these simulations closely match experimental data, they can be used to investigate the high-frequency AC behaviour of real junctions. Thus, we are able to use simple DC measurements to observe evidence of complex high-frequency dynamics. The inductance of the shunt branch can be accurately determined by comparing simulations to measurements. Simulations also allow us to map regions of the parameter space which exhibit complicated behaviour. These regions should be avoided when a nearly sinusoidal voltage waveform is desired, as is the case for Josephson junction-based oscillators.