40 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
Free space-coupled superconducting nanowire single photon detectors for infrared optical communications
This paper describes the construction of a cryostat and an optical system
with a free-space coupling efficiency of 56.5% +/- 3.4% to a superconducting
nanowire single-photon detector (SNSPD) for infrared quantum communication and
spectrum analysis. A 1K pot decreases the base temperature to T = 1.7 K from
the 2.9 K reached by the cold head cooled by a pulse-tube cryocooler. The
minimum spot size coupled to the detector chip was 6.6 +/- 0.11 {\mu}m starting
from a fiber source at wavelength, {\lambda} = 1.55 {\mu}m. We demonstrated
efficient photon counting on a detector with an 8 x 7.3 {\mu}m^2 area. We
measured a dark count rate of 95 +/- 3.35 kcps and a system detection
efficiency of 1.64% +/- 0.13%. We explain the key steps that are required to
further improve the coupling efficiency.Comment: 16 pages, double-space
Superconducting Heater Cryotron-Based Reconfigurable Logic Towards Cryogenic IC Camouflaging
Superconducting electronics are among the most promising alternatives to
conventional CMOS technology thanks to the ultra-fast speed and ultra-high
energy efficiency of the superconducting devices. Having a cryogenic control
processor is also a crucial requirement for scaling the existing quantum
computers up to thousands of qubits. Despite showing outstanding speed and
energy efficiency, Josephson junction-based circuits suffer from several
challenges such as flux trapping leading to limited scalability, difficulty in
driving high impedances, and so on. Three-terminal cryotron devices have been
proposed to solve these issues which can drive high impedances (>100 k{\Omega})
and are free from any flux trapping issue. In this work, we develop a
reconfigurable logic circuit using a heater cryotron (hTron). In conventional
approaches, the number of devices to perform a logic operation typically
increases with the number of inputs. However, here, we demonstrate a single
hTron device-based logic circuit that can be reconfigured to perform 1-input
copy and NOT, 2-input AND and OR, and 3-input majority logic operations by
choosing suitable biasing conditions. Consequently, we can perform any
processing task with a much smaller number of devices. Also, since we can
perform different logic operations with the same circuit (same layout), we can
develop a camouflaged system where all the logic gates will have the same
layout. Therefore, this proposed circuit will ensure enhanced hardware security
against reverse engineering attacks.Comment: 12 pages, 5 figure
A nanoCryotron comparator can connect single-flux quantum circuits to conventional electronics
Integration with conventional electronics offers a straightforward and
economical approach to upgrading existing superconducting technologies, such as
scaling up superconducting detectors into large arrays and combining single
flux quantum (SFQ) digital circuits with semiconductor logic and memories.
However, direct output signals from superconducting devices (e.g., Josephson
junctions) are usually not compatible with the input requirements of
conventional devices (e.g., transistors). Here, we demonstrate the use of a
single three-terminal superconducting-nanowire device, called the nanocryotron
(nTron), as a digital comparator to combine SFQ circuits with mature
semiconductor circuits such as complementary metal oxide semiconductor (CMOS)
circuits. Since SFQ circuits can digitize output signals from general
superconducting devices and CMOS circuits can interface existing
CMOS-compatible electronics, our results demonstrate the feasibility of a
general architecture that uses an nTron as an interface to realize a
super-hybrid system consisting of superconducting detectors, superconducting
quantum electronics, CMOS logic and memories, and other conventional
electronics