38 research outputs found
Frequency pulling and mixing of relaxation oscillations in superconducting nanowires
Many superconducting technologies such as rapid single flux quantum computing
(RSFQ) and superconducting quantum interference devices (SQUIDs) rely on the
modulation of nonlinear dynamics in Josephson junctions for functionality. More
recently, however, superconducting devices have been developed based on the
switching and thermal heating of nanowires for use in fields such as single
photon detection and digital logic. In this paper, we use resistive shunting to
control the nonlinear heating of a superconducting nanowire and compare the
resulting dynamics to those observed in Josephson junctions. We show that
interaction of the hotspot growth with the external shunt produces high
frequency relaxation oscillations with similar behavior as observed in
Josephson junctions due to their rapid time constants and ability to be
modulated by a weak periodic signal. In particular, we use a microwave drive to
pull and mix the oscillation frequency, resulting in phase locked features that
resemble the AC Josephson effect. New nanowire devices based on these
conclusions have promising applications in fields such as parametric
amplification and frequency multiplexing
Bridging the gap between nanowires and Josephson junctions: a superconducting device based on controlled fluxon transfer across nanowires
The basis for superconducting electronics can broadly be divided between two
technologies: the Josephson junction and the superconducting nanowire. While
the Josephson junction (JJ) remains the dominant technology due to its high
speed and low power dissipation, recently proposed nanowire devices offer
improvements such as gain, high fanout, and compatibility with CMOS circuits.
Despite these benefits, nanowire-based electronics have largely been limited to
binary operations, with devices switching between the superconducting state and
a high-impedance resistive state dominated by uncontrolled hotspot dynamics.
Unlike the JJ, they cannot increment an output through successive switching,
and their operation speeds are limited by their slow thermal reset times. Thus,
there is a need for an intermediate device with the interfacing capabilities of
a nanowire but a faster, moderated response allowing for modulation of the
output. Here, we present a nanowire device based on controlled fluxon
transport. We show that the device is capable of responding proportionally to
the strength of its input, unlike other nanowire technologies. The device can
be operated to produce a multilevel output with distinguishable states, which
can be tuned by circuit parameters. Agreement between experimental results and
electrothermal circuit simulations demonstrates that the device is classical
and may be readily engineered for applications including use as a multilevel
memory
BioWires: Conductive DNA Nanowires in a Computationally-Optimized, Synthetic Biological Platform for Nanoelectronic Fabrication
DNA is an ideal template for a biological nanowire-it has a linear structure several atoms thick; it possesses addressable nucleobase geometry that can be precisely defined; and it is massively scalable into branched networks. Until now, the drawback of DNA as a conducting nanowire been, simply put, its low conductance. To address this deficiency, we extensively characterize a chemical variant of canonical DNA that exploits the affinity of natural cytosine bases for silver ions. We successfully construct chains of single silver ions inside double-stranded DNA, confirm the basic dC-Ag+-dC bond geometry and kinetics, and show length-tunability dependent on mismatch distribution, ion availability and enzyme activity. An analysis of the absorbance spectra of natural DNA and silver-binding, poly-cytosine DNA demonstrates the heightened thermostability of the ion chain and its resistance to aqueous stresses such as precipitation, dialysis and forced reduction. These chemically critical traits lend themselves to an increase in electrical conductivity of over an order of magnitude for 11-base silver-paired duplexes over natural strands when assayed by STM break junction. We further construct and implement a genetic pathway in the E. coli bacterium for the biosynthesis of highly ionizable DNA sequences. Toward future circuits, we construct a model of transcription network architectures to determine the most efficient and robust connectivity for cell-based fabrication, and we perform sequence optimization with a genetic algorithm to identify oligonucleotides robust to changes in the base-pairing energy landscape. We propose that this system will serve as a synthetic biological fabrication platform for more complex DNA nanotechnology and nanoelectronics with applications to deep space and low resource environments
A superconducting nanowire spiking element for neural networks
As the limits of traditional von Neumann computing come into view, the
brain's ability to communicate vast quantities of information using low-power
spikes has become an increasing source of inspiration for alternative
architectures. Key to the success of these largescale neural networks is a
power-efficient spiking element that is scalable and easily interfaced with
traditional control electronics. In this work, we present a spiking element
fabricated from superconducting nanowires that has pulse energies on the order
of ~10 aJ. We demonstrate that the device reproduces essential characteristics
of biological neurons, such as a refractory period and a firing threshold.
Through simulations using experimentally measured device parameters, we show
how nanowire-based networks may be used for inference in image recognition, and
that the probabilistic nature of nanowire switching may be exploited for
modeling biological processes and for applications that rely on stochasticity.Comment: 5 main figures; 7 supplemental figure
Multilayered Heater Nanocryotron: A Superconducting-Nanowire-Based Thermal Switch
We demonstrate a multilayer nanoscale cryogenic heater-based switch (M-hTron) that uses a normal-metal heater overlapping a thin-film superconductor separated by a thin insulating layer. The M-hTron eliminates leakage current found in three-terminal superconducting switches and applies heat locally to the superconductor, reducing the energy required to switch the device. Modeling using the energy-balance equations and the acoustic mismatch model demonstrates reasonable agreement with experiment. The M-hTron is a promising device for digital superconducting electronics that require high fan-out and offers the possibility of enhancing readout for superconducting-nanowire single-photon detectors
Cryogenic Memory Architecture Integrating Spin Hall Effect based Magnetic Memory and Superconductive Cryotron Devices
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 technology's lack of high-density,
high-speed and power-efficient memory. Here we demonstrate an array of
cryogenic memory cells consisting of a non-volatile three-terminal magnetic
tunnel junction element driven by the spin Hall effect, combined with a
superconducting heater-cryotron bit-select element. The write energy of these
memory elements is roughly 8 pJ with a bit-select element, designed to achieve
a minimum overhead power consumption of about 30%. Individual magnetic memory
cells measured at 4 K show reliable switching with write error rates below
, and a 4x4 array can be fully addressed with bit select error rates
of . This demonstration is a first step towards a full cryogenic
memory architecture targeting energy and performance specifications appropriate
for applications in superconducting high performance and quantum computing
control systems, which require significant memory resources operating at 4 K.Comment: 10 pages, 6 figures, submitte