Influence of noise on Josephson junctions dynamics with a BCS theory-based model

We developed a weak-linked Josephson junction time-domain simulation tool based on the Bardeen-Cooper-Schrieffer (BCS) theory to account for the electrodynamics of Cooper pairs and quasiparticles in the presence of thermal noise. The model, based on Werthamer and Harris formalisms, allows us to describe the behavior of Josephson junctions for various current and/or voltage input waveforms, analog or digital, and for any operating temperature below the critical temperature of the superconducting materials. We show a good agreement between experimental and simulated IV curves of Josephson junctions, as well as a relative increase of the grey zone width of an SFQ balanced comparator between 4 and 20% due to the presence of quasiparticles, for McCumber parameters comprised between 0.1 and 1, respectively.Comment: Presented at the European Conference on Applied Superconductivity (EUCAS 2023), Bologna, Italy, 03-07 September 2023. 5 pages, 6 figures, 21 reference

Design of a Superconducting Antenna Integrated with a Diplexer for Radio-Astronomy Applications, Journal of Telecommunications and Information Technology, 2014, nr 3

This paper presents the design of a compact frontend diplexer for radio-astronomy applications based on a self complementary Bow-tie antenna, a 3 dB T-junction splitter and two pass-band fractal lters. The whole diplexer structure has been optimized by using an evolutionary algorithm. In particular the problem of the diplexer design is recast into an optimization one by dening a suitable cost function which is then minimized by mean of an evolutionary algorithm namely the Particle Swarm Optimization (PSO). An X band diplexer prototype was fabricated and assessed demonstrating a good agreement between numerical and experimental results

Study of microwave resonances induced by bias lines of shunted Josephson junctions

Bias lines routed over a ground plane naturally form microstrip lines associated with the presence of a capacitance. This can lead to unwanted resonances when coupled to Josephson junctions. This work presents an electrical model of a shunted Josephson junction with its bias lines and pads, fabricated with the 1 kA/cm$^2$ RSFQ niobium process of the FLUXONICS Foundry. A compact LCL T-model is used to simulate the microwave behavior of the bias line, predict resonances and design resonance-free superconducting circuits. The I-V characteristics of three shunted Josephson junctions have been obtained from time-domain simulations done with JSIM and show a good match with the global behavior and experimentally observed resonance at 230 GHz, measured at 4.2 K. The influence of the position and value of a series resistor placed on bias lines is studied to damp unwanted resonances at the junction.Comment: Presented at ISEC2019 conferenc

Analysis of Internally Shunted Josephson Junctions

partially_open11sìFollowing the ever-rising demand for new functionalities and novel materials in superconducting circuitry, we provide a complete view on the self-shunting problem in Josephson junctions, relating it to specific features of a multichannel weak link between electrodes where averaging over the channels yields a bimodal distribution of transparencies with maxima near unity and zero. We provide two examples of such internally shunted devices, namely, four-layered Nb/Al-Al oxide-Nb junctions with strongly disordered nanometer-thick insulating layers where stochastic distribution of transparencies takes place on a local rather than a global scale and MoRe/W-doped Si-Si-MoRe devices with strongly inhomogeneous silicon interlayers partly doped by metallic nanoclusters where the main charge transport occurs across resonance-percolating trajectories. We show how the predicted universal distribution function of transmission coefficients can be verified experimentally without any fitting parameters and analyze some old and new experimental data from this perspective. We believe that our results can form a base for novel four-layered Josephson junctions with enhanced superconducting properties and, at the same time, well-separated metallic electrodes.partially_openLacquaniti, Vincenzo; Cassiago, Cristina; De Leo, Natascia; Fretto, Matteo; Sosso, Andrea; Febvre, Pascal; Shaternik, Volodymyr; Shapovalov, Andrii; Suvorov, Olexandr; Belogolovskii, Mikhail; Seidel, PaulLacquaniti, Vincenzo; Cassiago, Cristina; DE LEO, Maria; Fretto, MATTEO ANDREA; Sosso, Andrea; Febvre, Pascal; Shaternik, Volodymyr; Shapovalov, Andrii; Suvorov, Olexandr; Belogolovskii, Mikhail; Seidel, Pau

Superconducting computing: a beyond-CMOS solution on the way towards quantum computation (invited)

session: High-performance, energy-efficient computing [I.1]International audienc