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199

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Introduction

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November 1987 - April 1991

## Publications

Publications (199)

We report experimental studies of quantum-matter heterostructures based on a ferromagnet/normal metal multilayer proximitized by Nb superconducting electrodes to form a novel Josephson weak-link device that is highly sensitive to magnetic fields. The device is a single Josephson junction containing Al/Ni or Al/Py (Py: Ni
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A review of the theory of bi-SQUIDs and the experimental studies of bi-SQUID-based devices is presented. The reported output voltage linearity of the fabricated devices ( ∼ 40 to 45 dB) is much higher than that observed for dc SQUIDs ( ∼ 20 dB). Recent numerical simulation evidence indicates that the linearity can be further improved to at least 60...

We report on the measurement results of the superconducting-ferromagnetic transistors (SFTs). The devices were made at Northwestern University and Hypres (SeeQC), Inc. (Nevirkovets
et al
., 2014; 2015). SFT is a multiterminal device with the SIS′FIFS (or SFIFS′IS) structure (where S, I, and F denote a superconductor, an insulator, and a ferromagn...

2020, The Author(s). One of the most challenging obstacles to realizing exascale computing is minimizing the energy consumption of L2 cache, main memory, and interconnects to that memory. For promising cryogenic computing schemes utilizing Josephson junction superconducting logic, this obstacle is exacerbated by the cryogenic system requirements th...

The use of Josephson junctions (JJs) as switching elements in digital circuits have attracted a significant attention due to their high switching speed, low power dissipation, and the ability to be interconnected via lossless, low-dispersion superconducting lines.

We report the fabrication and characterization at 4.2 K of superconducting-ferromagnetic (SIFS) switching devices that are configured in an injection-controlled weak link geometry (ICWL). Here, S, I, and F denote a superconductor (Nb), an insulator (Al/AlO
<sub>x</sub>
), and a ferromagnetic material [Ni or Ni
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The ability to localize defects in order to understand failure mechanisms in complex superconducting electronics circuits, while operating at low temperature, does not yet exist. This work applies thermally-induced voltage alteration (TIVA), to a biased superconducting electronics (SCE) circuit at ambient temperature. TIVA is a commonly used, laser...

A model of superconducting computer memory exploiting the orthogonal spin transfer (OST) in the pseudospin valve (PS) that is controlled by the three-terminal Josephson superconducting-ferromagnetic transistor (SFT) is developed. The building blocks of the memory are hybrid PS and SFT structures. The memory model is formulated in terms of the equat...

One of the most challenging obstacles to realizing exascale computing is minimizing the energy consumption of L2 cache, main memory, and interconnects to that memory. For promising cryogenic computing schemes utilizing Josephson junction superconducting logic, this obstacle is exacerbated by the cryogenic system requirements that expose the technol...

Josephson junctions drive the operation of superconducting qubits and they are the key for the coupling and the interfacing of superconducting qubit components with other quantum platforms. They are the only means to introduce non linearity in a superconducting circuit and offer direct solutions to tune the properties of a superconducting qubit, th...

A model of superconducting computer memory exploiting the orthogonal spin transfer (OST) in a pseudo-spin-valve (PSV) that is controlled by a three-terminal Josephson superconducting-ferromagnetic transistor (SFT) is developed. The building blocks of the memory are hybrid PSV and SFT structures. The memory model is formulated in terms of the equati...

We report the fabrication and testing, at 4.2 K, of four-terminal SIS′F1IF2S devices, where S(S′) denotes a superconductor (Nb), F1,2 denotes a ferromagnetic material (Ni and permalloy (Py), respectively), and I denotes an insulator (AlOx). The F1IF2 junction plays the role of a pseudo-spin valve, in which the magnetization vector of the Py layer c...

As superconducting quantum processors increase in size and complexity, the scalability of standard techniques for qubit control and readout becomes a limiting factor. Replacing room temperature analog components with cryogenic digital components could allow for the realization of systems well beyond the current state-of-the-art qubit arrays with te...

We developed and experimentally tested a Symmetric Traveling Wave Parametric Amplifier (STWPA) based on Three-Wave Mixing, using the new concept of a Symmetric rf- SQUID. This allows to fully control the second and third order nonlinearities of the STWPA by applying external currents. In this way, the optimal bias point can be reached, taking into...

Loading impact on the bi-SQUID output signal linear-ity has been studied. As the load impedance decreases, the maxi-mum attainable linearity drops. This effect is minimized when the impedance is approximately the same at both signal and Josephson oscillation frequencies. The impedance value is allowed to be as low as
$4R_N$
to
$R_N$
(normal Jos...

We have designed and tested a parallel 8-bit ERSFQ arithmetic logic unit (ALU). The ALU design employs wave-pipelined instruction execution and features modular bit-slice ar-chitecture that is easily extendable to any number of bits and adaptable to current recycling. A carry signal synchronized with an asynchronous instruction propagation provides...

Energy-efficient rapid single flux quantum (ERSFQ) circuits have become a viable alternative for the implementation of superconducting circuits due to a large amount of static power consumption in RSFQ circuits. ERSFQ circuits are built upon the popular RSFQ logic circuits by replacing the power-dissipating resistor bias network with a bias network...

We have designed and tested a parallel 8-bit ERSFQ arithmetic logic unit (ALU). The ALU design employs wave-pipelined instruction execution and features modular bit-slice architecture that is easily extendable to any number of bits and adaptable to current recycling. A carry signal synchronized with an asynchronous instruction propagation provides...

We have designed and tested a parallel 8-bit ERSFQ arithmetic logic unit (ALU). The ALU design employs wave-pipelined instruction execution and features modular bit-slice architecture that is easily extendable to any number of bits and adaptable to current recycling. A carry signal synchronized with an asynchronous instruction propagation provides...

As research in superconducting electronics matures, it is necessary to have failure analysis techniques to identify parameters that impact yield and failure modes in the fabricated product. However, there has been significant skepticism regarding the ability of laser-based failure analysis techniques to detect defects at room temperature in superco...

In this work we give a characterization of the RF effect of memory switching on Nb-Al/AlOx-(Nb)-Pd$_{0.99}$Fe$_{0.01}$-Nb Josephson junctions as a function of magnetic field pulse amplitude and duration, alongside with an electrodynamical characterization of such junctions, in comparison with standard Nb-Al/AlOx-Nb tunnel junctions. The use of micr...

We report fabrication and testing at 4.2 K of four-terminal SF1IF2S1IS2 devices, where S denotes a superconductor (Nb), F1,2 denote ferromagnetic material (permalloy (Py) and Ni respectively), and I denotes an insulator (AlOx). The F1IF2 structure plays a role of a pseudo-spin valve, in which the magnetization vector of the Py layer can be switched...

We consider conditions allowing attending the highly linear voltage response of a bi-SQUID, taking into consideration the inductances of both loops and their shared inductance. The existence of the small latter one allows improving the law of the flux to phase transformation and essential enlarging margins of the high-linearity response. The report...

We test the effect of an external RF field on the switching processes of magnetic Josephson junctions (MJJs) suitable for the realization of fast, scalable cryogenic memories compatible with Single Flux Quantum logic. We show that the combined application of microwaves and magnetic field pulses can improve the performances of the device, increasing...

We present test results for parallel data communication ERSFQ circuits with clock recovery. We experimentally study on-chip and chip-to-chip parallel data communication circuits with 4-, 8-and 16-bit word lengths. The largest circuit is a 16-bit chip-to-chip communication test circuit embedded into a testbed with clock distributed over a combinatio...

Field-programmable gate arrays (FPGA) provide a significantly cheaper solution for various applications in traditional semiconductor electronics. Single flux quantum (SFQ) technologies are developing rapidly and the availability of SFQspecific FPGA will be very useful. Towards developing such an SFQ-specific FPGA, new designs of FPGA subcircuits fo...

We report the observation of an oscillatory behavior of the critical current versus magnetic field dependence in Nb/(Al/Py)5/Al/AlOx/(Al/Py)6/Al/Nb Josephson tunnel junctions at 4.2 K. The oscillations resemble those that occur in superconducting quantum interference devices. Since the oscillations occur in the junctions without any superconducting...

We present a fabrication process for a fully superconducting multichip module (MCM), compatible with superconducting qubit technology, to allow a 3D integration of quantum circuits while preserving qubit coherence. In particular, this MCM can be used to couple a Nb-based Single Flux Quantum classical coprocessor for the integrated control and reado...

We describe an approach to the integrated control and measurement of a large-scale superconducting multiqubit circuit using a proximal coprocessor based on the Single Flux Quantum (SFQ) digital logic family. Coherent control is realized by irradiating the qubits directly with classical bitstreams derived from optimal control theory. Qubit measureme...

Abstract New type of broadband active Electrically Small Antennas (ESA) based on Superconducting Quantum Arrays has been proposed and developed. These antennas are capable of providing both sensing and amplification of broadband electromagnetic signals with a very high Spurious-Free Dynamic Range (SFDR) up to 100 dB (and even more) with high sensit...

Superconducting quantum arrays (SQAs) capable of providing highly linear voltage response to magnetic signal and high dynamic range have been suggested and developed. Base elements of the arrays, quantum cells, were devised and studied in detail. Using niobium process, SQAs with different number of the cells and prototypes of the SQA-based broadban...

We report on the development of energy-efficient decoders for cryogenic random access memory and register file. To reduce the pitch, area, and energy, our decoder employs a scalable binary tree architecture. We implemented these decoders using ERSFQ logic controlled by magnetically coupled address lines. These lines are driven by energy-efficient d...

We consider and discuss a design map for bi-SQUIDs as devices capable of providing highly linear voltage response to the applied magnetic flux. The response linearity can amount to 90 to 100 dB at the optimally set parameters, the most critically, at the optimally chosen critical current of the third Josephson junction. In this paper, we summarize...

Through experiments and numerical simulations we explore the behavior of rf SQUID (radio frequency superconducting quantum interference device) metamaterials, which show extreme tunability and nonlinearity. The emergent electromagnetic properties of this metamaterial are sensitive to the degree of coherent response of the driven interacting SQUIDs....

Energy efficiency has become the primary parameter for the design of next-generation single flux quantum (SFQ) circuits. This, however, needs to be balanced with optimization for clock speed and bias margins. Here, we experimentally study the tradeoff between circuit activity, energy efficiency, and bias margins for zero static power dissipation ER...

A focused ion beam (FIB) was used to obtain cross-sectional specimens from both magnetic multilayer and Nb/Al- AlOx/Nb Josephson junction devices for characterization by scanning transmission electron microscopy (STEM) and energy dispersive x-ray spectroscopy (EDX). Automated multivariate statistical analysis of the EDX spectral images produced che...

We report the results of a study of the current gain in high-jc superconducting-ferromagnetic transistors (SFTs) with the SISFIFS structure (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (permalloy, Py), respectively). The Nb/AlOx/Nb trilayer, which serves as the acceptor (SISF) junction, is estim...

We report on the detail analysis of thermal noise, critical current spread and parasitic elements influences on the bi-SQUID voltage response and its linearity. These results together with the results of our previous studies serve as a useful guidance in designing high-performance bi-SQUIDs and bi- SQUID arrays implemented in low-temperature superc...

We performed an in-depth numerical analysis of high inductance bi-SQUIDs with normalized inductance of its one-junction loop l >> 1. This is desired for better coupling with the external signals and for the high temperature superconductor implementations. Typically the high linearity (up to 90 dB) can be achieved in bi-SQUIDs at l ≤ 1 at which its...

We report experimental and theoretical results on the current gain in superconductor-ferromagnetic transistors (SFTs) with the SISFIFS structure (where S, I, and F denote a superconductor (Nb), an insulator (AlO $_{x}$ ), and a ferromagnetic material (Ni), respectively). The Josephson critical current density, $j_{\hbox{ca}}$ , of the acceptor (SIS...

We report a theoretical and experimental study on the use of nonequilibrium tunneling injection to control the local Cooper pair amplitude ΦS in an SF sandwich involving superconducting (S) and ferromagnetic (F) layers coupled by the proximity effect. In an SISFIFS structure (where I is an insulator), this same SF sandwich serves as the acceptor el...

Active electrically small antennas (ESAs) based on superconducting quantum arrays (SQAs) exhibit similar sensitivity to the polarization direction as conventional magnetic ESAs. While active ESAs produce an output voltage independent of the size-to-wavelength ratio with respect to both the quantum cell and the SQA, distinct dimensional effects can...

We describe how to use correctly an active electrically small antenna (ESA) based on Superconducting Quantum Array (SQA) to ensure a highly linear voltage output of the antenna. An interface to the antenna ought to realize strongly mismatched loading of the active ESA. To provide the optimal conjugation of the antenna with the load device such as a...

Narrow-band invisibility in an otherwise opaque medium has been achieved by
electromagnetically induced transparency (EIT) in atomic systems. The quantum
EIT behaviour can be classically mimicked by specially engineered metamaterials
via carefully controlled interference with a "dark mode". However, the narrow
transparency window limits the potenti...

Despite the fact that active an electrically small antenna based on Superconducting Quantum Array forms output voltage which is independent of the antenna size to wavelength ratio, a small size effect can appear and limit the antenna output linearity with the ratio increase. We analyze the size effect in the active antennas of both transformer and...

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There has been a significant progress in the development of broadband superconductor sensors / amplifiers capable of providing high Spurious-Free Dynamic Range for applications in broadband receiving systems with direct digitization of rf signals. This paper is to review our theoretical and experimental results on Su...

Using numerical simulation, we investigate the output power and loading tradeoffs for Superconducting Quantum Arrays (SQAs) suggested for the implementation of broadband radio-frequency systems, including active electrically small antennas capable of providing highly linear transfer characteristics with a high dynamic range. Standard matching loads...

We present an analysis of microwave dynamics of Superconducting Quantum Cell (SQC) in microwave field performed by means of 3D numerical simulations using a two-plate model. The simulations are necessary for realization of the active Electrically Small Antennas (ESA) based on Superconducting Quantum Arrays (SQA) composed of SQCs. It was found that...

We report experimental results on characteristics of SFIFS junctions and multiterminal SFIFSIS and SISFIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (Ni), respectively). The SFIFS (SFIS) junctions serve as injectors in the SFIFSIS (SISFIS) devices, which have transistorlike properties;...

We have designed and tested energy-efficient single flux quantum (eSFQ) circuits suitable for wave-pipelined architectures. The high energy-efficiency of eSFQ circuits combined with the sequential nature of SFQ logic makes eSFQ especially suitable for energy-efficient variants of highly-pipelined circuits such as modern arithmetic logic units (ALUs...

We designed, fabricated, and demonstrated an energy-efficient ERSFQ 4-bit decoder. The first version of the decoder is designed and fabricated using HYPRES legacy 1.0-μm four-layer 4.5-kA/cm2 process. It occupies an area of 700 μm × 1800 μm, which is to be reduced to 160 μm × 400 μm once fabricated using HYPRES's RIPPLE-2 0.25-μm six-layer process....

A superconducting memory cell includes a magnetic Josephson junction (MJJ) with a ferromagnetic material, having at least two switchable states of magnetization. The binary state of the MJJ manifests itself as a pulse appearing, or not appearing, on the output. A superconducting memory includes an array of memory cells. Each memory cell includes a...

There have been three great movements in the development of the Josephson digital logic: latching logic, single flux quantum (SFQ) logic, and low-energy logic. This chapter introduces the basic principles of the implementation of samplers and analog-to-digital converters (ADC) devices with superconductors. Furthermore, it addresses the recent state...

A superconducting quantum interference devices (SQUID) comprises a superconducting inductive loop with at least two Josephson junction, whereby a magnetic flux coupled into the inductive loop produces a modulated response up through radio frequencies. Series and parallel arrays of SQUIDs can increase the dynamic range, output, and linearity, while...

Multi-loop arrays of Josephson Junctions (JJ) with non-uniform area distributions, which are known as Superconducting Quantum Interference Filters (SQIF), are the most highly sensitive sensors of changes in applied magnetic field as well as the absolute magnitude of magnetic fields. The non-uniformity of the loop sizes allows the array to produce a...

We present an improved analytic theory, numerical simulation, and analysis of noise characteristics of a bi-SQUID in comparison with those of a dc SQUID in an open loop configuration. The analytic theory which had been developed earlier, neglecting a pulse component of the difference of the phases of Josephson junctions, is now completed taking int...

We report experimental results on characteristics of SFIFS junctions and
multi-terminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb),
an insulator (AlOx), and a ferromagnetic material (Ni), respectively). The
SFIFS junctions serve as injectors in the SFIFSIS devices which have
transistor-like properties; for this reason we call t...

Several critical applications of superconducting electronics that have been successful-ly commercialized are the Josephson voltage standard, superconducting quantum interference device (SQUID) magnetometers, superconductor?insulator?supercon-ductor (SIS) mixers, and analog filters [1]?[4]. More recently, digital and mixed-sig-nal circuits based on...

Superconducting Quantum Arrays (SQAs) based on integration of quantum cells each consisting of two Josephson-junction parallel arrays [Differential Quantum Cell (DQC)] are analyzed for applications in broadband radio frequency systems. These SQAs are capable of providing highly linear magnetic signal to voltage transfer with high dynamic range. Bot...

The sixteen articles in this special section were presented at the 2013 International Superconductive Electronics Conference (ISEC). The 14th ISEC (ISEC 2013) was held in Cambridge, MA, USA, from July 7??11, 2013. For the first time, ISEC was held as an IEEE conference, sponsored by the IEEE Council on Superconductivity. ISEC 2013 covered rapidly d...

We report experimental results on the dc and ac characterization of multiterminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlOx), and a ferromagnetic material (Ni), respectively), which display transistor-like properties. We investigated two types of such superconducting-ferromagnetic transistors (SFTs): ordina...