Dissertations / Theses: 'Superconducting Nanowire Single Photon Detectors'

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Fitzpatrick, Catherine Rose. "Single-photon metrology with superconducting nanowire single-photon detectors." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2633.

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Single-photon sources and detectors underpin the development of quantum photonic technologies. This thesis presents research into single-photon devices with a focus on telecom wavelengths. A two-channel superconducting nanowire single-photon detector (SNSPD) system was constructed and characterised. It provides free-running single-photon detection at telecom wavelengths with low dark counts and timing jitter below 90 ps FWHM. The system detection e ciency at 1310 nm is 1 % with a 1 kHz dark count rate, which was competitive when the SNSPD was built in 2009. In this work, the low timing jitter of the SNSPD was bene cial to the development of a two-photon interference experiment. Experiments were carried out with single-photon sources based on self-assembled InAs/GaAs quantum dots in micropillar cavities. Preliminary measurements of the second-order correlation function gave g(²)(τ=0) = 0.12 ± 0.04 with above-band excitation and g(²)( τ = 0) = 0:07 ± 0:05 with near-resonant excitation. These values agree with recent papers reporting improved measurements with near-resonant excitation. Irreparable damage to the sample prevented further investigation. This thesis also presents the design, construction and characterisation of a highresolution single-photon spectrometer for telecom wavelengths. The instrument, a scanning Fabry-Perot interferometer, was optimised for the characterisation of quantum photonic sources. It has a spectral resolution of 550 MHz and a free spectral range of (119.0 ± 0.4) GHz.

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Dauler, Eric A. (Eric Anthony) 1980. "Multi-element superconducting nanowire single photon detectors." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46377.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 140-148).
Single-photon-detector arrays can provide unparalleled performance and detailed information in applications that require precise timing and single photon sensitivity. Such arrays have been demonstrated using a number of single-photon-detector technologies, but the high performance of superconducting nanowire single photon detectors (SNSPDs) and the unavoidable overhead of cryogenic cooling make SNSPDs particularly likely to be used in applications that require detectors with the highest performance available. These applications are also the most likely to benefit from and fully utilize the large amount of information and performance advantages provided by a single-photon-detector array.Although the performance advantages of individual superconducting nanowire single photon detectors (SNSPDs) have been investigated since their first demonstration in 2001, the advantages gained by building arrays of multiple SNSPDs may be even more unique among single photon detector technologies. First, the simplicity and nanoscale dimensions of these detectors make it possible to easily operate multiple elements and to closely space these elements such that the active area of an array is essentially identical to that of a single element. This ability to eliminate seam-loss between elements, as well as the performance advantages gained by using multiple smaller elements, makes the multi-element approach an attractive way to increase the general detector performance (detection efficiency and maximum counting rate) as well as to provide new capabilities (photon-number, spatial, and spectral resolution). Additionally, in contrast to semiconductor-based single-photon detectors, SNSPDs have a negligible probability of spontaneously emitting photons during the detection process, eliminating a potential source of crosstalk between array elements.
(cont.) However, the SNSPD can be susceptible to other forms of crosstalk, such as thermal or electromagnetic interactions between elements, so it was important to investigate the operation and limitations of multi-element SNSPDs. This thesis will introduce the concept of a multi-element SNSPD with a continuous active area and will investigate its performance advantages, its potential drawbacks and finally its application to intensity correlation measurements.This work is sponsored by the United States Air Force under Contract #FA8721-05-C-0002. Opinions, interpretations, recommendations and conclusions are those of the authors and are not necessarily endorsed by the United States Government.
by Eric Dauler.
Ph.D.

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Sunter, Kristen Ann. "Optical Modeling of Superconducting Nanowire Single Photon Detectors." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13106421.

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Superconducting nanowire single photon detectors (SNSPDs) can detect single photons or low levels of infrared light in applications that require high speed and low timing jitter, such as integrated circuit analysis. Most applications also require a high device detection efficiency (DDE), but the DDE of SNSPDs is limited by many factors. A good optical design with an integrated optical cavity and dielectric layers can increase the absorptance of 1550-nm light in the active area to over 90%. Therefore, optical modeling using the transfer matrix method was used to guide the design and fabrication of high-efficiency detectors with a measured DDE of over 70%. In addition, finite element analysis was used to simulate the effect of adding different types of optical antennas to SNSPD designs to increase their active area without compromising their speed, and the fabrication of antennas integrated with nanowires achieved sub-10 nm gaps between features. Thin films of niobium nitride, the starting material of the SNSPDs, were investigated using several techniques for thin film characterization, including x-ray diffraction, Auger electron spectroscopy and x-ray photoelectron spectroscopy. Optical setups based on reflectometry and transmittometry were built to determine the film thickness more accurately than deposition time for optical modeling and to provide feedback on the deposition conditions. The optical setups are able to provide reproducible and precise thickness measurements to within 0.1 nm.
Engineering and Applied Sciences

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Bellei, Francesco. "Superconducting nanowire single photon detectors for infrared communications." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109008.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-120).
The ever-increasing data sharing demands of modern technologies forces scientists to adopt new methods that can surpass the approaching limits of classical physics. Quantum optical communications and information, based on single-photon detectors offer the most promising possibility to reach new levels of data rate and communication security. Superconducting nanowire single-photon detectors (SNSPDs) have already been used in the past to demonstrate new protocols of quantum key distribution and are currently the best single-photon detection technology to enable quantum optical communication. With the goal of creating a global quantum communication network, both optical fiber and free-space optical communication technologies have been explored. In addition, the scientific community started pursuing smaller and cheaper cryogenic solutions to enable the use of SNSPDs on a large scale. In this thesis, I describe the design and development of a cryogenic SNSPD receivers in free-space and optical-fiber configurations for 1550-nm-wavelength. The first configuration was created with the goal of enabling optical communication in the mid-IR. I present future steps to achieve this goal. The second configuration was designed to enable a compact and scalable integration of multiple SNSPD channels in the same system. Our approach has the potential of enabling SNSPD systems with more than 64 channels.
by Francesco Bellei.
Ph. D.

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Najafi, Faraz. "Timing performance of superconducting nanowire single-photon detectors." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97816.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 83-89).
Superconducting nanowire single-photon detectors (SNSPDs) are becoming increasingly popular for applications in quantum information and long-distance communication. While the detection efficiency of SNSPDs has significantly improved over time, their timing performance has largely remained unchanged. Furthermore, the photodetection process in superconducting nanowires is still not fully understood and subject to ongoing research. In this thesis, I will present a systematic study of the timing performance of different types of nanowire single-photon detectors. I will analyze the photodetection delay histogram (also called instrument response function IRF) of these detectors as a function of bias current, nanowire width and wavelength. The study of the IRF yielded several unexpected results, among them a wavelength-dependent exponential tail of the IRF and a discrepancy between experimental photodetection delay results and the predicted value based on the electrothermal model. These results reveal some shortcomings of the basic models used for SNSPDs, and may include a signature of the initial process by which photons are detected in superconducting nanowires. I will conclude this thesis by presenting a brief introduction into vortices, which have recently become a popular starting point for photodetection models for SNSPDs. Building on prior work, I will show that a simple image method can be used to calculate the current flow in presence of a vortex, and discuss possible implications of recent vortex-based models for timing jitter.
by Faraz Najafi.
S.M.

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Natarajan, Chandra Mouli. "Superconducting nanowire single-photon detectors for advanced photon-counting applications." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2432.

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The ability to detect infrared photons is increasingly important in many elds of scienti c endeavour, including astronomy, the life sciences and quantum information science. Improvements in detector performance are urgently required. The Superconducting Nanowire Single-Photon Detector (SNSPD/SSPD) is an emerging single-photon detector technology o ering broadband sensitivity, negligible dark counts and picosecond timing resolution. SNSPDs have the potential to outperform conventional semiconductor-based photon-counting technologies, provided the di culties of low temperature operation can be overcome. This thesis describes how these important challenges have been addressed, enabling the SNSPDs to be used in new applications. A multichannel SNSPD system based on a closed-cycle refrigerator has been constructed and tested. E cient optical coupling has been achieved via carefully aligned optical bre. Fibre-coupled SNSPDs based on (i) NbN on MgO substrates and (ii) NbTiN on oxidised Si substrates have been studied. The latter give enhanced performance at telecom wavelengths, exploiting the re ection from the Si=SiO2 interface. Currently, the detector system houses four NbTiN SNSPDs with average detection e ciency >20% at 1310 nm wavelength. We have employed SNSPDs in the characterisation of quantum waveguide circuits, opening the pathway to operating this promising platform for optical quantum computing for the first time at telecom wavelengths.

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Najafi, Faraz. "Superconducting nanowire single-photon detectors : new detector architectures and integration with photonic chips." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99836.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 153-161).
Superconducting nanowire single-photon detectors (SNSPDs) are a promising technology for long-distance optical communication and quantum information processing. Recent advances in single-photon generation, storage and detection technologies have spurred interest in integration of these components onto a single microchip, which would act as a low-power non-classical optical processor. In this thesis, I will present a method for the scalable integration of SNSPDs with photonic chips. I will show that, using a micron-scale flip-chip process, waveguide-coupled SNSPDs can be integrated onto a variety of material systems with high yield. This technology enabled the assembly of the first photonic chip with multiple adjacent SNSPDs with average system detection efficiencies beyond 10%. Using this prototype, we will show the first on-chip detection of non-classical light. I will further demonstrate optimizations to the detector design and fabrication processes. These optimizations increased the direct fabrication yield and improved the timing jitter to 24 ps for detectors with high internal efficiency. Furthermore, I will show a novel single-photon detector design that may have the potential to reach photodetection dead times below 1ns.
by Faraz Najafi.
Ph. D.

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O'Connor, John Alexander. "Nano-optical studies of superconducting nanowire single-photon detectors." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2515.

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uperconducting single-photon detectors based on superconducting nanowires offer broadband single-photon sensitivity, from visible to mid-infrared wavelengths. They have attracted particular attention due to their promising performance at telecommunications wavelengths. The additional benefits of superconducting nanowire single-photon detectors (SNSPDs) include low dark count rates (Hz) and low timing jitter (sub 100 ps). SNSPDs have been employed in practical photon-counting applications such as quantum key distribution (QKD), operation of quantum waveguide circuits and quantum emitter characterisation. Major challenges in the development of SNSPDs are the improvement of device uniformity and achieving efficient optical coupling. Nano-optical techniques such as confocal microscopy can be used to image localised areas of SNSPDs providing a direct measurement of the device uniformity. The work in this thesis describes both initial nano-optical testing at visible wavelengths in liquid helium and the construction of a fibre based miniature confocal microscope configuration operating at telecommunications wavelengths for use in a closed cycle refrigerator. In both cases localised areas of SNSPDs can be studied whilst maintaining efficient optical coupling. The miniature confocal microscope configuration has sub-nanometre position resolution over a 30 μm x 30 μm area by way of a piezoelectric X-Y scanner. A full width at half maximum (FWHM) optical resolution of 1305 nm at a wavelength of 1550 nm is achieved. SNSPDs based upon niobium nitride (NbN) nanowires fabricated on magnesium oxide (MgO) have been studied. The microscope system has allowed us to map the temporal response (timing jitter and output pulse timing delay) of constricted (non-uniform) SNSPDs. By fitting to a theoretical model, the variations in output pulse timing delay have been shown to be caused by variations in hotspot resistances across the device. This observation has provided insights into the underlying physics of SNSPDs and especially the origins of timing jitter in SNSPDs. This provides a pathway to exploitation of this effect in next-generation device designs for applications such as imaging.

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Zhu, Di S. M. Massachusetts Institute of Technology. "Superconducting nanowire single-photon detectors on aluminum nitride photonic integrated circuits." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108974.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 85-91).
With recent advances in integrated single-photon sources and quantum memories, onchip integration of high-performance single-photon detectors becomes increasingly important. The superconducting nanowire single-photon detector (SNSPD) is the leading single-photon counting technology for quantum information processing. Among various waveguide materials, aluminum nitride (AlN) is a promising candidate because of its exceptionally wide bandgap, and intrinsic piezoelectric and electro-optic properties. In this Master's thesis, we developed a complete fabrication process for making high-performance niobium nitride SNSPDs on AlN, and demonstrated their integration with AlN photonic waveguides. The detectors fabricated on this new substrate material have demonstrated saturated detection efficiency from visible to near-IR, sub-60-ps timing jitter, and ~6 ns reset time. This work will contribute towards building a fully integrated quantum photonic processor.
by Di Zhu.
S.M.

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Yang, Joel K. (Joel Kwang wei). "Superconducting nanowire single-photon detectors and sub-10-nm lithography." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53307.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 155-169).
Superconducting nanowire single-photon detectors (SNSPDs) are useful in applications such as free-space optical communications to achieve high-speed data transfer across vast distances with minimum transmission power. In this and other applications, SNSPDs with high detection efficiencies are required. To this end, we designed and fabricated an integrated optical cavity and anti-reflection coating that enhanced the detection efficiency of SNSPDs by almost threefold to current record values of 57% at 1550 nm wavelength. We also improved our understanding of SNSPDs by modeling the electro-thermal response of the detector. This model showed that, beyond the initial formation of a photon-induced resistance across the nanowire, Joule heating results in the growth of the resistive segment. While simple, this model was useful in designing SNSPDs that reset more quickly, and also in explaining an undesirable behavior of the SNSPDs where the devices latch into a resistive state and fail to reset. Like many other devices, such as transistors, SNSPDs would benefit from device miniaturization: SNSPDs with narrower nanowires have higher detection efficiencies and increased sensitivity to low-energy photons. In this thesis, we investigated the resolution performance of electron-beam lithography (EBL) by first improving the contrast performance of hydrogen silsesquioxane (HSQ) negative-tone resist. The contrast of HSQ was improved by adding NaCl salt to an aqueous NaOH developer solution. With this improvement, we achieved a high-resolution electron-beam lithography process capable of patterning structures at 9-nm-pitch dimensions.
(cont.) The ability to pattern sub-10-nm structures is useful for fabricating future high-performance SNSPDs, nanoimprint lithography molds, prototypes of next generation transistors and storage media, and templates for controlling the self-assembly of block copolymers (BCPs). While this EBL process affords high-resolution, it is inherently a low-throughput process due to the serial nature of the pattern exposure. As a result, EBL is not cost effective in fabricating densely-patterned devices in large volumes. However, coin-bining this top-down EBL process with bottom-up BCP self-assembly techniques, we can simultaneously achieve high resolution without sacrificing throughput or pattern registration. We demonstrated that high-throughput fabrication of a hexagonally-ordered array of posts could be achieved by patterning only a sparse array of posts with EBL and using block copolymers to complete the missing structures.
by Joel K. Yang.
Ph.D.

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Sidorova, Mariia. "Timing Jitter and Electron-Phonon Interaction in Superconducting Nanowire Single-Photon Detectors (SNSPDs)." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22296.

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Die vorliegende Doktorarbeit beschäftigt sich mit der experimentellen Studie zweier miteinander verbundener Phänomene: Dem intrinsischen Timing-Jitter in einem supraleitendenden Nanodraht-Einzelphotonen-Detektor (SNSPD) und der Relaxation der Elektronenenergie in supraleitenden Filmen. Supraleitende Nanodrähte auf einem dielektrischen Substrat als mikroskopische Grundbausteine jeglicher SNSPDs stellen sowohl für theoretische als auch für experimentelle Studien komplexe Objekte dar. Die Komplexität ergibt sich aus der Tatsache, dass SNSPDs in der Praxis stark ungeordnete und ultradünne supraleitende Filme verwenden, die eine akustische Fehlanpassung zu dem zugrundeliegenden Substrat aufweisen und einen Nichtgleichgewichts-Zustand implizieren. Die Arbeit untersucht die Komplexität des am weitesten in der SNSPD Technologie verbreiteten Materials, Niobnitrid (NbN), indem verschiedene experimentelle Methoden angewandt werden. Als eine mögliche Anwendung der SNSPD-Technologie wird ein Prototyp eines dispersiven Raman-Spektrometers mit Einzelphotonen-Sensitivität demonstriert.
This Ph.D. thesis is based on the experimental study of two mutually interconnected phenomena: intrinsic timing jitter in superconducting nanowire single-photon detectors (SNSPDs) and relaxation of the electron energy in superconducting films. Microscopically, a building element of any SNSPD device, a superconducting nanowire on top of a dielectric substrate, represents a complex object for both experimental and theoretical studies. The complexity arises because, in practice, the SNSPD utilizes strongly disordered and ultrathin superconducting films, which acoustically mismatch with the underlying substrate, and implies a non-equilibrium state. This thesis addresses the complexity of the most conventional superconducting material used in SNSPD technology, niobium nitride (NbN), by applying several distinct experimental techniques. As an emerging application of the SNSPD technology, we demonstrate a prototype of the dispersive Raman spectrometer with single-photon sensitivity.

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Hu, Xiaolong Ph D. Massachusetts Institute of Technology. "Efficient superconducting-nanowire single-photon detectors and their applications in quantum optics." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/63073.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 123-131).
Superconducting-nanowire single-photon detectors (SNSPDs) are an emerging technology for infrared photon counting and detection. Their advantages include good device efficiency, fast operating speed, low dark-count rate, low timing jitter, free running mode, and no afterpulsing. The challenges to be addressed prior to real applications are cryogenic operations, small active areas, and efficiency-speed tradeoffs. This thesis presents the effort to address these challenges. A fiber-coupled SNSPD system with a large-area detector in a closed-cycle cryocooler has been built, demonstrating 24% system detection efficiency with a darkcount rate of -1000 counts/sec. As a result, the SNSPD system becomes a convenient tool with a single-mode fiber as the input channel and an SMA cable as the output channel. This system has enabled high-quality polarization-entanglement distribution at the wavelength of 1.3 tm. The 99.2% visibility in Hong-Ou-Mandel (HOM) interference measured in this experiment is the highest HOM visibility that has ever been reported for waveguide-based photon-pair sources. After entanglement is distributed, a pair rate of 5.8 pairs/sec at a pump power of 25 iW and two-photon quantum interference visibility of 97.7% have been measured. On the other hand, increasing the active area of the detector does decrease its speed. To address the issue of efficiency-speed tradeoff, SNSPDs have been integrated with optical nano-antennae. A 9- im-by-9- tm detector with 47% device efficiency and 5-ns reset time has been demonstrated. In terms of active area, device efficiency and speed, this SNSPD has the record performance among single-element SNSPDs. Finally, waveguide-integrated SNSPDs have been proposed and designed. The device structure permits efficient coupling of photons into a short nanowire, and thus, efficient and fast SNSPDs. This structure is compatible with on-chip photonic technologies, including inverse-taper couplers and ring resonators, that have been developed in recent years.
by Xiaolong Hu.
Ph.D.

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Sidorova, Mariia [Verfasser]. "Timing Jitter and Electron-Phonon Interaction in Superconducting Nanowire Single-Photon Detectors (SNSPDs) / Mariia Sidorova." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1226153380/34.

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Charaev, Ilya [Verfasser]. "Improving the Spectral Bandwidth of Superconducting Nanowire Single-Photon Detectors (SNSPDs) / Ilya Charaev." Karlsruhe : KIT Scientific Publishing, 2018. http://www.ksp.kit.edu.

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Schmidt, Wolfgang-Gustav Ekkehart [Verfasser]. "Superconducting Nanowire Single-Photon Detectors for Quantum Photonic Integrated Circuits on GaAs / Wolfgang-Gustav Ekkehart Schmidt." Karlsruhe : KIT Scientific Publishing, 2020. http://d-nb.info/1213447836/34.

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Henrich, Dagmar [Verfasser]. "Influence of Material and Geometry on the Performance of Superconducting Nanowire Single-Photon Detectors / Dagmar Henrich." Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.

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Schmidt, Wolfgang-Gustav Ekkehart [Verfasser], and M. [Akademischer Betreuer] Siegel. "Superconducting Nanowire Single-Photon Detectors for Quantum Photonic Integrated Circuits on GaAs / Wolfgang-Gustav Ekkehart Schmidt ; Betreuer: M. Siegel." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/119312672X/34.

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Melbourne, Thomas. "Magnesium Diboride Devices and Applications." Thesis, Temple University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10689307.

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Magnesium diboride MgB₂ is an interesting material that was discovered to be a superconductor in 2001. It has a remarkably high critical temperature of 39 K which is much greater than was previously thought possible for a phonon-mediated superconductor. MgB₂ was also the first material found to exhibit multiple gap superconductivity. It has two energy gaps, the pi gap with a value of 2.3 meV, and the sigma gap with a value of 7.1 meV. Both the high critical temperature and the multiple large energy gaps make MgB₂ an attractive candidate for superconducting devices. While the initial discovery of MgB₂ was accompanied by much excitement, the enthusiasm has mostly disappeared due to the lack of progress made in implementing MgB₂ in practical devices. The aim of this thesis is to attempt to reinvigorate interest in this remarkable material through a study of a variety of practical superconducting devices made with MgB₂ thin films grown by hybrid physical-chemical vapor deposition (HPCVD).

Two different methods of fabricating MgB₂ Josephson junctions are explored. The first is a sandwich type trilayer configuration with a barrier made by magnetron sputtered MgO. Junctions of this sort have been previously studied and implemented in a variety of devices. While they do show some attractive properties, the on-chip spread in critical current due to barrier non-uniformity was too high to be considered a viable option for use in many-junction devices. By developing a fabrication scheme which utilizes electron beam lithography, modest improvements were made in the on-chip parameter spread, and miniaturization of junction size yielded some insight into the non-uniform barriers.

The second approach of creating MgB₂ Josephson junctions utilized a planar geometry with a normal metal barrier created by irradiating nano-sized strips of the material with a focused helium ion beam. The properties of these junctions are investigated for different irradiation doses. This new technique is capable of producing high quality junctions and furthermore the parameter spread is greatly reduced as compared to the sandwich type junctions. While more research is necessary in order to increase the I_cR_n products, these junctions show promise for use in many-junction devices such as RSFQ circuits.

Prior to this work, the largest substrates that could be coated with HPCVD grown MgB₂ were 2" in diameter. A new chamber was designed and constructed which demonstrated the ability to coat substrates as large as 4". This scaled-up system was used to grow MgB₂ films on 1 x 10 cm flexible substrates. A method of fabrication was developed which could pattern these 10 cm long samples into ribbon cables consisting of many high frequency transmission lines. This technology can be utilized to increase the cooling efficiency of cryogenic systems used for RSFQ systems which require many connections between low temperature and room temperature electronics.

Finally, a method of producing MgB₂ films with thicknesses as low as 8 nm was developed. This is achieved by first growing thicker films and using a low angle ion milling step to gradually reduce the film thickness while still maintaining well connected high quality films. A procedure was developed for fabricating meandering nanowires in these films with widths as low as 100 nm for use as superconducting nanowire single photon detectors (SNSPDs). A study of the transport properties of these devices is first presented. Measurements show low values of kinetic inductance which is ideal for high count rates in SNSPDs. The kinetic inductance measurements also yielded the first measurements of the penetration depth of MgB₂ films in the ultra-thin regime. Devices made from these ultra-thin films were found to be photon sensitive by measurements made by our collaborators.

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Hofherr, Matthias [Verfasser]. "Real-time imaging systems for superconducting nanowire single-photon detector arrays / Matthias Hofherr." Karlsruhe : KIT Scientific Publishing, 2014. http://www.ksp.kit.edu.

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Yan, Xiruo. "A NbTiN superconducting nanowire single photon detector (SNSPD) on a silicon-on-insulator substrate." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/60399.

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Single photon detectors are essential part of most optical quantum information applications. Among all candidates, superconducting nanowire single photon detectors (SNSPD) have the advantages of low jitter, low dark count rates and high maximum count rate. Commercial systems based on these detector elements currently cost on order $50-100K. In this project a circular meander design of a free-space SNSPD is fabricated and tested in house. Although the absolute absorption efficiency of the detector is low, because it was fabricated on a substrate optimized for other applications, the measured and modelled values for both incident polarizations agree within the uncertainties. The bias current dependence is almost constant from 50% to 100% of the breakdown threshold value, which should allow operation at intrinsic dark count rates extrapolated to be < 1 Hz at 2.05 K.
Science, Faculty of
Graduate

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Yang, Joel K. (Joel Kwang wei). "Fabrication of superconducting nanowire single proton detectors." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34355.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
Includes bibliographical references (p. 81-85).
The future NASA Mars project will need an ultra-fast, highly sensitive photodetector to increase the bandwidth of free-space long-range communication, which is now done primarily using RF signals. Our original motivation in fabricating superconducting nanowire single-photon detectors (SN-SPD) is to fulfill this need. The SN-SPD's reported GHz counting rates [1] make it very attractive for this application. A new fabrication process for making SN-SPDs using hydrogen-silsesqioxane (HSQ), a high-resolution electron-beam lithography resist will be presented. An electron-beam proximity-effect correction program was developed to achieve nanowires with uniform linewidths, which is important for device performance. Finally, we present initial test results that show device functionality and performance. Our best device has a detection efficiency of [approx.] 10 % at 1064 nm photon wavelength at 2.1 K and a photon-induced voltage-pulse duration of [approx.] 3 ns.
by Joel K. Yang.
S.M.

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Söderstrand, Alexander. "Models of superconducting nanowire single-photon detection." Thesis, KTH, Fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217346.

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Kirkwood, Robert A. "Superconducting single photon detectors for quantum information processing." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8136/.

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Single photon detectors are a vital part of many emerging technologies which harness the quantum properties of light to benefit the fields of communication, computation and sensing. Superconducting nanowire single photon detectors (SNSPDs) offer high detection efficiency, low dark count rates, low timing jitter, and infrared sensitivity that are required by the most demanding single photon counting applications. This thesis presents SNSPDs fabricated and tested at the University of Glasgow that are integrated with optical structures which enable enhanced detection efficiency and integration with waveguide circuit technology. The monolithic integration of waveguide circuit components presents a route towards realisation of an optical quantum information processor that has the stability and scalability to perform the demanding tasks of quantum computation. A novel process is introduced for incorporating superconducting detectors with single mode gallium arsenide waveguides and quantum dot single photon sources. Together these elements would enable the generation of quantum states of light which could be manipulated and detected on a single chip. Detectors are patterned in NbTiN thin superconducting films on to suspended nanobeam waveguides with better than 50 nm alignment accuracy. Low temperature electrical and optical testing confirms the detectors’ single photon sensitivity under direct illumination as well as to waveguide coupled light. Measured detectors were found to have internal registering efficiencies of 6.8 ± 2.4%. Enhancing absorption of photons into thin superconducting films is vital to the creation of high efficiency superconducting single photon detectors. Fabricating an SNSPD on a dielectric mirror creates a partial cavity that can be tailored to enhance detection of light at specific wavelengths. Devices have been fabricated and tested in this thesis with enhanced detection efficiency at infrared and visible wavelengths for quantum cryptography, remote sensing and life science applications. Detectors fabricated in NbTiN on GaAs/AlGaAs Bragg mirrors exhibited a system detection efficiency of 1.5% at 1500 nm wavelength for the best device measured. SNSPDs were also fabricated in NbN on aperiodic dielectric mirrors with a range of different bandwidths. A peak system detection efficiency of 82.7% at 808 nm wavelength was recorded.

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Jerjen, Iwan. "Superconducting tunnel junctions as energy resolving single photon detectors /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17113.

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Heath, Robert M. "Nano-optical studies of superconducting nanowire devices for single-photon detection." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6132/.

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Superconducting nanowire single photon detectors (SNSPDs) are a rapidly maturing detector technology that offer superior performance relative to competing infrared photon counting technologies. The original experimental work presented here explores three novel methods of improving and analysing detector characteristics, employing low-temperature piezoelectric motors at temperatures below 4 K in a closed-cycle cryostat. Utilizing the low-temperature piezoelectric nanopositioners in tandem with a miniature confocal microscope, this work specifically shows a spatially-separable parallel-wire SNSPD demonstrating one- and two-pixel photon discrimination, with the detector responding more quickly when triggering two pixels. The work demonstrates nanoantenna-coupled SNSPDs, which are simulated, designed, and tested using the same nano-optical setup. In these an increased local absorption into the nanowire is seen at the antennas' resonant wavelengths, enhancing the efficiency of the detector by up to 130 %. Finally, a modified optical setup using a distributed Bragg reflector fibre in place of the microscope to form a tunable cavity around two configurations of SNSPD is demonstrated, improving absorption of the incident light into the nanowire across the whole active area. For these, enhancement in the system detection efficiency of up to 40 % is seen.

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Herder, Charles H. (Charles Henry) III. "Designing and implementing a readout strategy for superconducting single photon detectors." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/63024.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 109-112).
Introduction: Photon detection is an integral part of experimental physics, high-speed communication, as well as many other high-tech disciplines. In the realm of communication, unmanned spacecraft are travelling extreme distances, and ground stations need more and more sensitive and selective detectors to maintain a reasonable data rate.[10] In the realm of computing, some of the most promising new forms of quantum computing require consistent and efficient optical detection of single entangled photons.[27] Due to projects like these, demands are increasing for ever more efficient detectors with higher count rates. The Superconducting Nanowire Single-Photon Detector (SNSPD) is one of the most promising new technologies in this field, being capable of counting photons as faster than 100MHz and with efficiencies around 50%. Currently, the leading competition is from the geiger-mode avalanche photodiode, which is capable of ~20- 70% efficiency at a ~5MHz count rate depending on photon energy. In spite of these advantages, the SNSPD is still a brand-new technology and as a result they do not have the same support hardware support as other detectors. As such, SNSPD's are much more difficult to integrate into an existing an experiment. Because of this difficulty, SNSPD's have not been deployed extensively for research or industrial applications. The signal analysis chain that is connected to this detector is one of the key choke points. Each detector count produces a 0.1 mV, 10 nS wide pulse with a maximum count frequency on the order of 100MHz. Currently, this signal is processed outside of the cryostat with a series of RF amplifiers and a high-speed counter. This design works for detector prototyping, but poses a series of problems with actual design implementation. Most importantly, it prevents our design from being scalable. Even though we can fabricate thousands of detectors on a single wafer, it would be extremely difficult to place that many RF lines without crosstalk or other interference. The purpose of this thesis is to build a more robust and scalable readout technology for SNSPDs. First, we will develop intermediate technologies that improve upon current readout technology and will be necessary to develop the final goal. Ultimately, we plan to build circuitry on-chip that will first convert each detector's analog signal to a digital signal and then condense the data from each detector into an externally clocked, single-bit output indicating the presence or absence of a photon at any detector. This will allow simultaneous readout of a large number of detectors on a single wafer. Additionally, our cryogenic will decrease the noise observed by the detector, as the amplifier is no longer operating at room temperature. Finally, our readout will provide a simple hardware API to be interfaced to a computer or embedded processing unit. The catch to this development process is that the entire system must operate at 4.2K or below. As such, one must either use HEMT CMOS or Rapid Single-Flux- Quantum (RSFQ) logic. HEMT CMOS is better suited to analog amplification of the output signal, while RSFQ circuitry is better suited to the construction of the SNSPD interface and digital logic. RSFQ circuitry is better suited as an input stage because input amplification with CMOS is difficult, as one must operate in the linear regime of a HEMT. This requires on the order of 1 mA at 1.8 V minimum, which results in approximately 2 mW per stage. This is to be compared against RSFQ comparators which utilize approximately 0.5 mA at almost no voltage, resulting in muW of dissipation per stage. Given that we are hoping to produce a large number of SNSPD input stages, RSFQ is clearly a better choice. However, we only have a small number of output signals from the cryostat, so it is much more reasonable to use CMOS, as we can attain larger signal amplitudes.
by Charles Henry Herder III.
M.Eng.

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Kahl, Oliver [Verfasser], and M. [Akademischer Betreuer] Wegener. "Superconducting Single-Photon Detectors for Integrated Quantum Optics / Oliver Kahl. Betreuer: M. Wegener." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1093559098/34.

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Lopez, Bruno. "Towards the detection of single photons in the mid-infrared." Thesis, KTH, Tillämpad fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297517.

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In this project, the fabrication of single-photon detectors based on superconducting nanowires is presented, with great focus on extending their operation range to the mid infrared. In particular, Niobium Titanium Nitride (NbTiN) and Molybdenum Silicide (MoSi), superconducting materials with different properties, are presented, studied and used as fabrication platforms. Different approaches are followed, mainly adjusting the nanowire width and thickness to achieve near unity quantum efficiency at mid infrared wavelengths. With the vision of using these devices for atmospheric LIDAR and sensing experiments, saturation at 2050 nm is studied that corresponds to the absorption peak of CO2. For the best device made on NbTiN thin films, unity quantum efficiency is shown at 2050 nm with a time jitter of 116 ps at 1550 nm. Simulations using the transfer matrix method and the commercial software Lumerical are carried out, concluding that the devices made in NbTiN could have 23.1-26.7% system detection efficiency at 2050 nm on a Silicon SiO2/Si platform. Further improvements show that the detection efficiency could reach between 52-62% (for 0.33 and 0.5 fill factor, respectively calculated with FDTD simulations) by engineering optical cavities.
I detta projekt presenteras en fabrikations process för enstaka foton detektorer baserade på supraledande nanotrådar. Fokuset har legat på att utöka våglängds regionen där detektorernas kan detektera till mid-infrarött ljus. Två specifika supraledande material, Niobium Titan (NbTiN) och Molybdenum Silicide (MoSi), med olika egenskaper har studerats och använts som material. Dimensionerna på nanotrådarna, framför allt tjockleken och bredden, har optimerats för att uppnå nära enhetlig kvant-effektivitet vid mid-infraröda våglängder. Med visionen att detektorerna ska användas för atmosfäriska LiDAR mätningar har de studerats för satruering vid 2050 nm som motsvarar ett absorbtions maximum för CO2. Detektorerna tillverkade med NbTinN uppnådde 100% kvant effektivitet för 2050 nm ljus med ett tids jitter på 116 ps vid 1550 nm ljus. Simuleringar med överförings matrisen metoden och den kommersiella mjukvaran Lumerical visar att NbTiN detektorer placerade på en SiO2/Si platform kan ha en 23.1-26.7% effektivitet vid 2050 nm. Ytterligare simuleringas visar att effektiviteten kan nå upp till 52-62% (för 0.33 och 0.5 fyllnadsfaktor, respektive beräknad med FDTD) genom att inkludera optiska kaviteter.

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Keshavarz, Akhlaghi Mohsen. "Nonlinearity and Gating in Superconducting Nanowire Single Photon Detectors." Thesis, 2011. http://hdl.handle.net/10012/6416.

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The quantum properties of electromagnetic radiation at single photon level promise to offer what are classically inaccessible. Single photon sources and detectors are therefore on demand for exploiting these properties in practical applications, including but not limited to quantum information processing and communication. In this thesis, I advance Superconducting Nanowire Single Photon Detectors (SNSPD) both in terms of models describing their operation, and their performance. I report on characterization, semi-empirical modeling, quantum-optical modeling and detector tomography. The results provide more accurate methods and formulations to characterize and mathematically describe the detectors, valuable findings from both application and device points of views. I also introduce the concept of Gated SNSPDs, show how to implement and how to characterize them. Through series of theoretical and experimental investigations, I show performance advantages of Gated SNSPDs in terms of dead time and dark count rate, important figures for many applications like quantum key distribution. The ultimate limitations of gated operation are also explored by physical modeling and simulation steps.

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Allmaras, Jason Paul. "Modeling and Development of Superconducting Nanowire Single-Photon Detectors." Thesis, 2020. https://thesis.library.caltech.edu/13748/8/Allmaras_Thesis_Final.pdf.

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Superconducting nanowire single-photon detectors (SNSPDs) have demonstrated remarkable efficiency, timing resolution, and intrinsic dark count rate properties, but the SNSPD community currently lacks a comprehensive model of the single-photon detection process. In this work, we conduct a detailed examination of the current detection mechanism models and compare their predictions to new experimental measurements of the intrinsic timing properties and polarization dependence of specialized NbN test devices. First, we consider the energy downconversion cascade using the kinetic equations to describe the non-equilibrium electron and phonon systems immediately following photon absorption. These calculations provide estimates for the energy loss and fluctuations during this process, and provide qualitative information about the way energy is partitioned between the electron and phonon systems. To study the suppression of superconductivity following downconversion, we apply the most advanced existing model, that of Vodolazov (2017), but find it inadequate to quantitatively describe the timing properties of these detectors. By extending the model to use the generalized time-dependent Ginzburg-Landau equations, we achieve better quantitative agreement with experiment. However, the generalized model still provides only a qualitative picture of the detection process.

We also conduct an experimental examination of the heat transfer process in WSi nanowires by examining the nanowire reset dynamics, steady-state dissipation, and crosstalk between elements of an array. The results are compared to existing electrothermal models, but these models fail to adequately describe the dynamics of the system. A generalized form of the electrothermal model provides better fitting to experiment, but incorporation of non-equilibrium effects is likely needed to provide a fully quantitative description of the system. These results are directly connected to some of the thermal challenges of SNSPD array development. Informed by the crosstalk results, we demonstrate a new multiplexing technique based on thermal coupling between two active nanowire layers, known as the thermal row-column. This method promises to enable kilopixel to megapixel scale imaging arrays for low photon-flux applications. Finally, we discuss the design and characterization of the ground detector for the Deep Space Optical Communication (DSOC) demonstration mission.

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Orgiazzi, Jean-Luc Francois-Xavier. "Packaging and Characterization of NbN Superconducting Nanowire Single Photon Detectors." Thesis, 2009. http://hdl.handle.net/10012/4453.

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Superconducting nanowire single-photon detectors (SNSPDs) are nanodevices usually made from thin niobium nitride (NbN) films. Operated at liquid helium temperature, they can exhibit high detection efficiency with low dark-counts associated with a fast response time and a low timing jitter. Covering a broad detection range from ultraviolet to mid-infrared, SNSPDs are a very attractive alternative to silicon or gallium arsenide based semiconductor detectors for fiber based telecommunication when single-photon sensitivity and high counting rates are necessary. Efficient packaging and fiber coupling of a SNSPD is in itself a real challenge and is often a limiting factor in reaching high system quantum efficiency. Our approach makes use of a controlled expansion alloy which has been adequately heat treated to enhance its characteristics for cryogenic operation. This insures the integrity of the optical coupling at cryogenic temperatures while done at room temperature. It also provides a good attenuation for electromagnetic interference due to the high relative permeability of the nickel-iron alloy. The small form factor of this pigtailed optical fiber package makes it versatile and could be easily integrated with a commercial cryogen-free system or simply dipped into a standard helium transport Dewar. We report on our theoretical and experimental methodology to evaluate the optical coupling quality and present the optoelectronic characterization of two devices packaged in this way. Electrical simulation is studied to understand the speed limitation factor inherent to these devices and preliminary speed and jitter measurements are reported.

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Eftekharian, Amin. "Plasmonic Superconducting Single Photon Detector." Thesis, 2013. http://hdl.handle.net/10012/7928.

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A theoretical model with experimental verification is presented to enhance the quantum efficiency of a superconducting single-photon detector without increasing the length or thickness of the active element. The basic enhancement framework is based on: (1) Utilizing the plasmonic nature of a superconducting layer to increase the surface absorption of the input optical signal. (2) Enhancing the critical current of the nanowires by reducing the current crowding at the bend areas through optimally rounded-bend implementation. The experimental system quantum efficiency and fluctuation rates per second are assessed and compared to the proposed theoretical model. The model originated from an accurate description of the different liberation mechanisms of the nano-patterned superconducting films (vortex hopping and vortex-antivortex pairing). It is built complimentary to the existing, well-established models by considering the effects of quantum confinement on the singularities' energy states. The proposed model explains the dynamics of singularities for a wide range of temperatures and widths and describe an accurate count rate behavior for the structure. Furthermore, it explains the abnormal behaviors of the measured fluctuation rates occurring in wide nano-patterned superconducting structures below the critical temperature. In accordance to this model, it has been shown that for a typical strip width, not only is the vortex-antivortex liberation higher than the predicted rate, but also quantum tunneling is significant in certain conditions, and cannot be neglected as it has been in previous models. Also it is concluded that to satisfy both optical guiding and photon detection considerations of the design, the width and the thickness of the superconducting wires should be carefully determined in order to maintain the device sensitivity while crossing over from the current crowding to vortex-based detection mechanisms.

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"Development of Superconducting Nanowire Single Photon Detector Technologies for Advanced Applications." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.50584.

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abstract: Measurements of the response of superconducting nanowire single photon detector (SNSPD) devices to changes in various forms of input power can be used for characterization of the devices and for probing device-level physics. Two niobium nitride (NbN) superconducting nanowires developed for use as SNSPD devices are embedded as the inductive (L) component in resonant inductor/capacitor (LC) circuits coupled to a microwave transmission line. The capacitors are low loss commercial chip capacitors which limit the internal quality factor of the resonators to approximately $Qi = 170$. The resonator quality factor, approximately $Qr = 23$, is dominated by the coupling to the feedline and limits the detection bandwidth to on the order of 1MHz. In our experiments with this first generation device, we measure the response of the SNSPD devices to changes in thermal and optical power in both the time domain and the frequency domain. Additionally, we explore the non-linear response of the devices to an applied bias current. For these nanowires, we find that the band-gap energy is $\Delta_0 \approx 1.1$meV and that the density of states at the Fermi energy is $N_0 \sim 10^{10}$/eV/$\mu$m$^3$. We present the results of experimentation with a superconducting nanowire that can be operated in two detection modes: i) as a kinetic inductance detector (KID) or ii) as a single photon detector (SPD). When operated as a KID mode in linear mode, the detectors are AC-biased with tones at their resonant frequencies of 45.85 and 91.81MHz. When operated as an SPD in Geiger mode, the resonators are DC biased through cryogenic bias tees and each photon produces a sharp voltage step followed by a ringdown signal at the resonant frequency of the detector. We show that a high AC bias in KID mode is inferior for photon counting experiments compared to operation in a DC-biased SPD mode due to the small fraction of time spent near the critical current with an AC bias. We find a photon count rate of $\Gamma_{KID} = 150~$photons/s/mA in a critically biased KID mode and a photon count rate of $\Gamma_{SPD} = 10^6~$photons/s/mA in SPD mode. This dissertation additionally presents simulations of a DC-biased, frequency-multiplexed readout of SNSPD devices in Advanced Design System (ADS), LTspice, and Sonnet. A multiplexing factor of 100 is achievable with a total count rate of $>5$MHz. This readout could enable a 10000-pixel array for astronomy or quantum communications. Finally, we present a prototype array design based on lumped element components. An early implementation of the array is presented with 16 pixels in the frequency range of 74.9 to 161MHz. We find good agreement between simulation and experimental data in both the time domain and the frequency domain and present modifications for future versions of the array.
Dissertation/Thesis
Doctoral Dissertation Physics 2018

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Martinez, Glenn. "Towards saturation of detection efficiency in superconducting single-photon detectors at 4.2 K using local helium ion irradiation." Thesis, 2021. https://hdl.handle.net/2144/43079.

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Superconducting single-photon detectors (SSPDs) are the leading detectors in terms of high-speed single-photon counting and high detection efficiency (DE). One factor that limits the DE is the critical current Ic, which is the maximum current before the superconductor switches to the normal state. Increasing device’s bias current towards the Ic can improve the DE. However, the device’s Ic is reduced due to constriction and current crowding at the edges of the wire. Typically, this is caused by fabrication defects. Locally suppressing superconductivity at these defects can potentially lessen the occurrence of current crowding. In this thesis, we used the beam from the helium ion microscope (HIM) and measured the Ic to observe the effects of locally irradiating specific areas on a SSPD wire. Due to the HIM’s small spot size and high collimation, we can control the superconducting gap precisely at the center and edges of the wire. Suppressing the edges can potentially reduce current crowding and increase the device’s critical current while suppressing the center can improve detection sensitivity for photons incident at that location. Our results showed that the irradiated devices had reduced Ic compared to unirradiated devices for both cases. We then extend this method of local suppression of superconductivity to explore an alternative method of fabricating SSPDs by directly writing the device on the superconducting thin film. This can enable the fabrication of devices without the use of lithography resist. In our experiment, we fabricated a 3 μm wire using optical lithography that was disconnected at the center and connected it by writing a single 1 μm wire with the He+ ion beam. We measured the Ic for samples with and without the 1 μm wire pattern and observed that the Ic decreased as we increased the ion dose. Overall, this work aims to contribute to the continuing investigation of the detection mechanism for SSPDs and the improvement of nanofabrication methods using the HIM.

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Yan, Zhizhong. "Quantum Optoelectronic Detection and Mixing in the Nanowire Superconducting Structure." Thesis, 2010. http://hdl.handle.net/10012/4952.

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The recent advancement of superconducting nano devices has allowed for making a Superconducting Nanowire Single Photon Detector (SNSPD), whose extraordinary features have strongly motivated the research community to exploit it in many practical applications. In this thesis, an experimental setup for testing the SNSPD has been established. It contains an in-house packaging that meets the requirements of RF/microwave and optoelectronic characterizations. The quantum efficiency and detection efficiency measurements have confirmed that our approach is satisfactory. The dark count performance has reached the anticipated level. The factors affecting rise and fall times of the photoresponses are addressed. Based on the successful setup, the characterizations including dc, small signal ac measurements have been undertaken. The measurements are aimed at quantitatively investigating Cooper pair density in the superconducting nanowire. The experimental method involves a two-step, small signal S-parameter measurement either in the presence or absence of optical powers. The subsequent measurements by varying the temperature and dc bias current have achieved remarkable understanding on the physical properties of SNSPD nanowires. Then, the electrically induced nonlinearity is studied via the large signal RF and Microwave measurements. The experiments are a set of one-tone and two-tone measurements, in which either the RF driving power is varied at a fixed frequency, or vice versa. Two major nonlinear microwave circuit analysis methods, i.e. time-domain transient and hybrid-domain harmonic balance analysis, are employed. The simulation result reveals the optimized conditions of reaching the desired nonlinearity. Finally, we have successfully measured the optoelectronic mixing products in an electrically pumped optoelectronic mixer, which has identical structures as that of the SNSPD. The experiments confirm that this mixer is not only sensitive to the classical light intensities, but also to that of the single photon level. Meanwhile, the quantum conversion matrices is derived to interpret the quantum optoelectronic mixing effects.

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Jafari, Salim Amir. "Superconducting Nanostructures for Quantum Detection of Electromagnetic Radiation." Thesis, 2014. http://hdl.handle.net/10012/8431.

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In this thesis, superconducting nanostructures for quantum detection of electromagnetic radiation are studied. In this regard, electrodynamics of topological excitations in 1D superconducting nanowires and 2D superconducting nanostrips is investigated. Topological excitations in superconducting nanowires and nanostrips lead to crucial deviation from the bulk properties. In 1D superconductors, topological excitations are phase slippages of the order parameter in which the magnitude of the order parameter locally drops to zero and the phase jumps by integer multiple of 2\pi. We investigate the effect of high-frequency ﬁeld on 1D superconducting nanowires and derive the complex conductivity. Our study reveals that the rate of the quantum phase slips (QPSs) is exponentially enhanced under high-frequency irradiation. Based on this ﬁnding, we propose an energy-resolving terahertz radiation detector using superconducting nanowires. In superconducting nanostrips, topological ﬂuctuations are the magnetic vortices. The motion of magnetic vortices result in dissipative processes that limit the efficiency of devices using superconducting nanostrips. It will be shown that in a multi-layer structure, the potential barrier for vortices to penetrate inside the structure is elevated. This results in significant reduction in dissipative process. In superconducting nanowire single photon detectors (SNSPDs), vortex motion results in dark counts and reduction of the critical current which results in low efficiency in these detectors. Based on this ﬁnding, we show that a multi-layer SNSPD is capable of approaching characteristics of an ideal single photon detector in terms of the dark count and quantum efficiency. It is shown that in a multi-layer SNSPD the photon coupling efficiency is dramatically enhanced due to the increase in the optical path of the incident photon.

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