Large-scale computing system characteristics vary by application class, but power and energy use has become a major problem for all classes. Superconducting computing may be able to serve the needs of these systems significantly better than conventional technology. Recent developments in single flux quantum circuit technology for digital logic include variants with greatly improved energy efficiency. Concepts were investigated for computing systems capable of performance in the range from 1 to 1000 PFLOP/s. The concept systems were constrained to use existing commercial cryogenic refrigerators and Nb superconducting technology. In order to meet the performance goals, cache and main memory capable of operating at cryogenic temperatures will be required. Superconducting computing is shown to be potentially competitive on the basis of power and energy efficiency if key component technologies can meet specific goals. Potential advantages of superconducting computing are identified as well as areas requiring further development.

Energy-Efficient Superconducting Computing—Power Budgets and Requirements

During the past 15 years a new field has emerged, which combines superconductivity and spintronics, with the goal to pave a way for new types of devices for applications combining the virtues of both by offering the possibility of long-range spin-polarized supercurrents. Such supercurrents constitute a fruitful basis for the study of fundamental physics as they combine macroscopic quantum coherence with microscopic exchange interactions, spin selectivity, and spin transport. This report follows recent developments in the controlled creation of long-range equal-spin triplet supercurrents in ferromagnets and its contribution to spintronics. The mutual proximity-induced modification of order in superconductor-ferromagnet hybrid structures introduces in a natural way such evasive phenomena as triplet superconductivity, odd-frequency pairing, Fulde-Ferrell-Larkin-Ovchinnikov pairing, long-range equal-spin supercurrents, [Formula: see text]-Josephson junctions, as well as long-range magnetic proximity effects. All these effects were rather exotic before 2000, when improvements in nanofabrication and materials control allowed for a new quality of hybrid structures. Guided by pioneering theoretical studies, experimental progress evolved rapidly, and since 2010 triplet supercurrents are routinely produced and observed. We have entered a new stage of studying new phases of matter previously out of our reach, and of merging the hitherto disparate fields of superconductivity and spintronics to a new research direction: super-spintronics.

https://iopscience.iop.org/article/10.1088/0034-4885/78/10/104501/pdf

Spin-polarized supercurrents for spintronics: a review of current progress.

Figures of merit connecting processing capabilities with power dissipated (OpS/Watt, Joule/bit, etc.) are becoming dominant factors in choosing technologies for implementing the next generation of computing and communication network systems. Superconductivity is viewed as a technology capable of achieving higher energy efficiencies than other technologies. Static power dissipation of standard RSFQ logic, associated with dc bias resistors, is responsible for most of the circuit power dissipation. In this paper, we review and compare different superconductor digital technology approaches and logic families addressing this problem. We present a novel energy-efficient single flux quantum logic family, ERSFQ/eSFQ. We also discuss energy-efficient approaches for output data interface and overall cryosystem design.

/pdf/energy-efficient-single-flux-quantum-technology-144o6vu2zy.pdf

Energy-Efficient Single Flux Quantum Technology

We investigate the recovery of superconducting NbN-nanowire photon counters after detection of an optical pulse at a wavelength of 1550nm, and present a model that quantitatively accounts for our observations. The reset time is found to be limited by the large kinetic inductance of these nanowires, which forces a tradeoff between counting rate and either detection efficiency or active area. Devices of usable size and high detection efficiency are found to have reset times orders of magnitude longer than their intrinsic photoresponse time.

Kinetic-inductance-limited reset time of superconducting nanowire photon counters

We have observed well-defined phase slips between quantized persistent current states around a toroidal atomic (23Na) Bose-Einstein condensate. These phase slips are induced by a weak link (a localized region of reduced superfluid density) rotated slowly around the ring. This is analogous to the behavior of a superconducting loop with a weak link in the presence of an external magnetic field. When the weak link is rotated more rapidly, well-defined phase slips no longer occur, and vortices enter into the bulk of the condensate. A noteworthy feature of this system is the ability to dynamically vary the current-phase relation of the weak link, a feature which is difficult to implement in superconducting or superfluid helium circuits.

Driving phase slips in a superfluid atom circuit with a rotating weak link.

Ultrafast switching speed, low power, natural quantization of magnetic flux, quantum accuracy, and low noise of cryogenic superconductor circuits enable fast and accurate data conversion between the analog and digital domains. Based on rapid single-flux quantum (RSFQ) logic, these integrated circuits are capable of achieving performance levels unattainable by any other technology. Two major classes of superconductor analog-to-digital converters (ADCs) are being developed - Nyquist sampling and oversampling converters. Complete systems with digital sampling at rates of /spl sim/20 GHz and above have been demonstrated using low-temperature superconductor device technology. Some ADC components have also been implemented using high-temperature superconductors. Superconductor ADCs have unique applications in true digital-RF communications, broadband instrumentation, and digital sensor readout. Their designs, test results, and future development trends are reviewed.

/pdf/superconductor-analog-to-digital-converters-5db83fuox2.pdf

Superconductor analog-to-digital converters

This paper presents the development of an Analog-to-Digital Converter (ADC) based on a low-temperature superconductor (Nb) chip and room-temperature interface modules for applications in digital receivers for communications, radars, and electronic warfare. The ADC design, MATLAB/sup TM/ simulations, and experimental results of single- and two-tone tests are described.

A superconductor high-resolution ADC

Digital RF correlation based signal processing arrangements allow for the development of software—controlled radio reception without the need for down-conversion to IF frequencies. Various arrangements are implemented using superconducting RSFQ logic enabling the clock and processing speeds required.

Digital RF correlator for multipurpose digital signal processing

We have designed, fabricated and tested the second-generation (2G) design of a high-resolution, dynamically programmable analog-to-digital converter (ADC) for radar and communications applications. The ADC chip uses the phase modulation–demodulation architecture and on-chip digital filtering. The 2G ADC design has been substantially enhanced. Both ADC front-end modulator and demodulator, as well as decimation digital filter, have been redesigned for operation at 20 GHz. Test results of this 6000 Josephson junction 2G ADC chip at clock frequencies up to 19.6 GHz are described. These test results were compared to the results of ADC functional simulation using MATLAB.

High-resolution ADC operation up to 19.6 GHz clock frequency

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 comparator with at least one MJJ. Selected X and Y-directional write lines in their combination are capable of switching the magnetization of the MJJ. A superconducting device includes a first and a second junction in a stacked configuration. The first junction has an insulating layer barrier, and the second junction has an insulating layer sandwiched in-between two ferromagnetic layers as barrier. An electrical signal inputted across the first junction is amplified across the second junction.

Superconducting devices with ferromagnetic barrier junctions

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