94 research outputs found
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
Infrared Transmissometer to Measure the Thickness of NbN Thin Films
We present an optical setup that can be used to characterize the thicknesses
of thin NbN films to screen samples for fabrication and to better model the
performance of the resulting superconducting nanowire single photon detectors.
The infrared transmissometer reported here is easy to use, gives results within
minutes and is non-destructive. Thus, the thickness measurement can be easily
integrated into the workflow of deposition and characterization. Comparison to
a similar visible-wavelength transmissometer is provided.Comment: 6 pages, 8 figure
Budd-Chiari syndrome recurring in a transplanted liver
A patient with Budd-Chiari syndrome who underwent orthotopic liver transplantation and developed recurrent disease is described. The immediate postoperative period was complicated by multiple thrombotic episodes, followed by a period of apparent remission associated with the initiation of coumadin and persantine therapy. After discontinuation of such antithrombotic therapy in order to biopsy the liver, the patient experienced another series of clinically overt vascular thromboses and ultimately died of sepsis 15 mo posttransplantation after a prolonged and complicated terminal hospital course. At autopsy, recurrent Budd-Chiari syndrome as well as thromboses in numerous other organs was demonstrated. © 1983
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
Universal scaling of the critical temperature for thin films near the superconducting-to-insulating transition
Thin superconducting films form a unique platform for geometrically-confined,
strongly-interacting electrons. They allow an inherent competition between
disorder and superconductivity, which in turn enables the intriguing
superconducting-to-insulator transition and believed to facilitate the
comprehension of high-Tc superconductivity. Furthermore, understanding thin
film superconductivity is technologically essential e.g. for photo-detectors,
and quantum-computers. Consequently, the absence of an established universal
relationships between critical temperature (), film thickness () and
sheet resistance () hinders both our understanding of the onset of the
superconductivity and the development of miniaturised superconducting devices.
We report that in thin films, superconductivity scales as . We
demonstrated this scaling by analysing the data published over the past 46
years for different materials (and facilitated this database for further
analysis). Moreover, we experimentally confirmed the discovered scaling for NbN
films, quantified it with a power law, explored its possible origin and
demonstrated its usefulness for superconducting film-based devices.Comment: 100 pages, 37 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
- …