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Photon number resolving detectors find space in many fields, such as quantum optics, boson sampling, and fluorescence spectroscopy. In particular, the reconstruction of the input photon distribution is essential in quantum communications to detect photon-number-splitting attacks. In this work, we discuss the operation configurations of a photon number resolving detector based on superconducting nanostrips at a wavelength of 1550 nm from a temporal point of view. We set a time binning and acquired the number of recorded pulses per bin by means of a time-to-digital converter. We studied the predictions of two theoretical models and compared them to the experimental data in order to analyze their operation regimes depending on the binwidth and to employ them for the reconstruction of the input photon distribution. We applied this method to a continuous-wave laser source, showing that the former can be used for the characterization of nonpulsed light sources, even with a photon emission rate so low that the dark count rate of a superconducting nanostrip is not negligible.

We report the fabrication of superconducting nanowire single-photon detector (SNSPD, SSPD) based on molybdenum nitride (MoN) film with and without a cavity structure. Ultrathin polycrystalline γ-Mo2N films with a Tc about 6 K were obtained by reactive DC magnetron sputtering. The absorption efficiency of the device was calculated by the finite-difference time-domain (FDTD) method using the optical constants of MoN determined by ellipsometry measurements. The SNSPD with a meander of 150-nm-width and 7-nm-thick nanowire showed a long saturation plateau in the bias current dependence of the system detection efficiency (SDE) at visible wavelength. The SNSPD with a cavity structure showed an SDE of 37% and a timing jitter of 79 ps at a wavelength of 1560 nm. The results show that MoN is a promising alternative to amorphous superconductors for high-performance SNSPD. [ABSTRACT FROM AUTHOR]

A configuration of integrated optical superconducting single photon detectors on lithium niobate substrates based on conventional titanium in-diffused waveguides with hybrid waveguide structures for enhancing the detector efficiency is proposed and analyzed. The sensing element in the form of a meander-like superconducting nanowire from niobium nitride is covered with an additional hybrid waveguide from a dielectric material with a higher refractive index than the LiNbO3 substrate to increase the light absorption. A special mode converter in the region free from a superconducting nanostructure is used to excite a localized mode with the maximum absorption coefficient that strongly interacts with the superconductive nanostructure. Silicon and titanium dioxide are considered and compared as suitable materials for the hybrid waveguide structures. Silicon based structures give a higher light concentration and, hence, a higher absorption coefficient. However, they are very demanding to the technological accuracy. Titanium dioxide structures potentially can be produced by the standard thin-film deposition technique and contact photolithography. The estimated absorption coefficient of 1.31 dB/μm is four orders of magnitude higher than that for the detectors with a standard titanium in-diffused waveguide, and a high transformation mode efficiency opens a way for fabrication of integrated optical superconducting single photon detectors with the efficiency comparable with other competing material platforms.

A configuration of integrated optical superconducting single photon detectors on lithium niobate substrates based on conventional titanium in-diffused waveguides with hybrid waveguide structures for enhancing the detector efficiency is proposed and analyzed. The sensing element in the form of a meander-like superconducting nanowire from niobium nitride is covered with an additional hybrid waveguide from a dielectric material with a higher refractive index than the LiNbO3 substrate to increase the light absorption. A special mode converter in the region free from a superconducting nanostructure is used to excite a localized mode with the maximum absorption coefficient that strongly interacts with the superconductive nanostructure. Silicon and titanium dioxide are considered and compared as suitable materials for the hybrid waveguide structures. Silicon based structures give a higher light concentration and, hence, a higher absorption coefficient. However, they are very demanding to the technological accuracy. Titanium dioxide structures potentially can be produced by the standard thin-film deposition technique and contact photolithography. The estimated absorption coefficient of 1.31 dB/μm is four orders of magnitude higher than that for the detectors with a standard titanium in-diffused waveguide, and a high transformation mode efficiency opens a way for fabrication of integrated optical superconducting single photon detectors with the efficiency comparable with other competing material platforms. [ABSTRACT FROM AUTHOR]

Practical superconducting materials and technologies have been enabled with availability for large scale devices and applications. Various large scale and strong magnetic field applications of superconductors have been developed, and a series of those applications are explored with technical details mainly including i) applied superconducting materials and their characteristics; ii) superconducting magnets and their techniques; iii) large and advanced electromagnetic devices and applications. The applied superconductivity, application technology, and availability are especially focused and verified with the trend of large scale applications’ development prospection. [ABSTRACT FROM AUTHOR]

Single photon detectors (SPD) are largely used when the signal to be measured is particularly low or if high accuracy, timing resolution and low noise are required. About twenty years ago, a new type of SPD based on superconducting materials appeared, and today these devices present the best performances in terms of efficiency, noise, counting rate, detectable wavelength, dead time, and timing jitter. In this work, we first describe the working principle of Superconducting Nanostrips Single Photon Detectors (SNSPDs) and provide a brief overview of the main properties and applications. Then, we present the results of the fabrication and characterization of Molybdenum Silicide SNSPDs with a cover layer of a thin Aluminium film (MoSi/Al). MoSi has already been adopted to fabricate SNSPDs, and in this work, we prove that the additional Al layer enhances the operating conditions without compromising the detection likelihood and leaving unaltered the properties of the device, even over a temporal window of two years and after several thermal cycles. [ABSTRACT FROM AUTHOR]

The general-purpose circuit simulator analysis program for linear active circuits (APLAC) is not widely known within the superconductor circuit community, regardless of its built-in Josephson junction model and capability of modeling the superconductive phase transition with controlled sources. We review the use of APLAC to model, e.g., noisy dc SQUIDs and transition-edge sensors. Based on an APLAC simulation, we also comment on the preference of voltage bias over current bias in dc SQUIDs in applications where large dynamic range and high bandwidth are simultaneously required. [ABSTRACT FROM AUTHOR]

Superconducting Nanowire Single Photon Detectors (SNSPDs) have demonstrated timing and efficiency properties that have placed them at the frontier in single photon sensing applications (e.g. photon counting, deep space optical communications, quantum communication, and quantum encryption). Properties such as timing jitter as low as 3 ps, dark counts under 90 counts per day, high detection efficiency ($>90\%$), short dead time and sensitivity over a wide range of photon energies (UV to IR). SNSPDs have a cutoff energy where the photon does not have enough energy to trigger the detection mechanism. In this paper, we lay out the framework and experimental setup to explore a modified approach in detecting photons below the cut off energy typical in an SNSPD. Leveraging the nanowire's change in kinetic inductance from photon absorption, the resulting voltage pulse is measured through a coupled quantum-noise-limited parametric amplifier. We consider nanowires with widths less than the vortex entry limit of w $< 4.4\xi$ , where $\xi$ is the coherence length, limiting the sources of noise. [ABSTRACT FROM AUTHOR]

Excess heat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time constants.  The Mo/Au bilayer transition edge sensor (TES) bolometric detectors initially fabricated for the high resolution mid-infrared spectrometer (HIRMES) exhibited two response thermalization scales, one of which is a few times longer than estimates based upon the properties of the bulk materials employed in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional to the pixel area, which ranges between ∼0.3 and 2.6 mm2.  Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant.  Additional information about the nature of this excess heat capacity is gleaned from glancing incidence X-ray diffraction, which reveals the presence of molybdenum silicides near the silicon surface which is a consequence of the bi-layer deposition.  Quantitative analysis of the concentration of excess molybdenum, estimated with secondary ion mass spectroscopy, is commensurate to the additional heat capacity needed to explain the anomalous time response of the detectors. [ABSTRACT FROM AUTHOR]

Based on early phenomenological ideas about the operation of superconducting single-photon detectors (SSPD or SNSPD), it was expected that materials with a lower superconducting gap should perform better in the IR range. The plausibility of this concept could be checked using two popular SSPD materials - NbN and WSi films. However, these materials differ strongly in crystallographic structure (polycrystalline B1 versus amorphous), which makes their dependence on disorder different. In our work we present a study of the single-photon response of SSPDs made from two disordered B1 structure superconductors - vanadium nitride and niobium nitride thin films. We compare the intrinsic efficiency of devices made from films with different sheet resistance values. While both materials have a polycrystalline structure and comparable diffusion coefficient values, VN films show metallic behavior over a wide range of sheet resistance, in contrast to NbN films with an insulator-like temperature dependence of resistivity, which may be partially due to enhanced Coulomb interaction, leading to different starting points for the normal electron density of states. The results show that even though VN devices are more promising in terms of theoretical predictions, their optimal performance was not reached due to lower values of sheet resistance. [ABSTRACT FROM AUTHOR]

With a growing demand for detecting light at the single-photon level in various fields, researchers are focused on optimizing the performance of superconducting single-photon detectors (SSPDs) by using multiple approaches. However, input light coupling for visible light has remained a challenge in the development of efficient SSPDs. To overcome these limitations, we developed a novel system that integrates NbN superconducting microwire photon detectors (SMPDs) with gap-plasmon resonators to improve the photon detection efficiency to 98% while preserving all detector performance features, such as polarization insensitivity. The plasmonic SMPDs exhibit a hot-belt effect that generates a nonlinear photoresponse in the visible range operated at 9 K (∼0.64 T c ), resulting in a 233-fold increase in phonon-electron interaction factor (γ) compared to pristine SMPDs at resonance under CW illumination. These findings open up new opportunities for ultrasensitive single-photon detection in areas like quantum information processing, quantum optics, imaging, and sensing at visible wavelengths.

We demonstrate the first implementation of a GaN-based infrared photodetector epitaxially grown on silicon. The device is a GaN/AlGaN quantum cascade detector that consists of layered quantum well structure grown by plasma-assisted molecular beam epitaxy on a 4-in Si (111) substrate. The design, simulations, growth process, optical measurements and device performance are presented and discussed. The photosignal, centered at a wavelength of 4.4 $\mu \text{m}$ , is resolved up to 150 K. The zero bias responsivity is $44~\mu \text{A}$ /W at 19 K and the detectivity is $2\times 10^{8}$ Jones. [ABSTRACT FROM AUTHOR]

Singlet oxygen luminescence dosimetry (SOLD) is a highly promising direct monitoring method for photodynamic therapy (PDT) in the treatment of cancer. Early SOLD systems have been hampered by inefficient excitation, poor optical collection and immature infrared single photon detection technology. We report carefully engineered improvements addressing all of these deficiencies. We use a supercontinuum source with a tunable filter to precisely target the peak absorption wavelength of the chosen photosensitizer; we have designed a compact and versatile optical package for precise alignment; we have successfully employed state-of-the-art superconducting photon counting technologies. Through these improvements, we can achieve histogram acquisition from a photosensitizer in solution test sample. This setup opens the pathway to physiological SOLD studies for PDT dosimetry. [ABSTRACT FROM AUTHOR]

Resonant mode splitting phenomenon can be observed in the terahertz transmission spectrum of a finite superconducting photonic crystal (SD) N S, where S and D denote a superconducting layer and a dielectric layer, respectively. In this structure, each D-layer in (SD) N S constitutes a Fabry-Perot cavity. The original single resonant mode at N  = 1 can then be split into N resonant modes for N  > 1 due to the time-coupling effect coming from N cavities. Within the framework of the coupled mode theory, we successfully employ synchronized time-coupling theory to analytically explain the number of split resonant peaks, the resonant frequencies, and the frequency intervals between peaks. Additionally, it is found that the coupling coefficient is an increasing function of the original resonant frequency, which, in turn, indicates that the split frequencies and interval can be tuned by the thickness of layer D. Application of this synchronized time-coupling theory to elucidate similar splitting phenomena in plasma photonic crystals and metamaterial photonic crystals is also discussed. [ABSTRACT FROM AUTHOR]

In this study, we focus on the preparation of a nanocarbon and ZnO based hybrid with the incorporation of nitrogen to form diamond nanowires (N-DNW) and ZnO nanotubes (ZNTs) using simple routes. The potential of the carbon enriched hybrid material for application as UV photodetectors (PDs) or electron field emitters (EFE) is evaluated. Firstly, the ZNT/N-DNW based UV PDs with their multifinger anode cathode configuration offer a high photoresponse ratio of 1930, which is superior to that of bare ZnO PDs (12.6). The obtained photoresponse values also have greatly enhanced stability and photoresponsivity of 49.2 AW −1 compared with the ZNRs (0.4 AW −1 ). In addition, EFE study of the ZNT/N-DNW hybrid device reveals an electron emission at voltage as low as 2.59 V/μm with a high current density of 5.2 mA/cm 2 . This striking improvement in the multifunctional measurements of the annealed ZNT/N-DNW - based device can be attributed to its fast adsorptivity and oxygen vacancies. Moreover, the respective band model of this hybrid structure was also proposed to demonstrate its heterostructure. Furthermore, the outstanding feature of this combination are its cost-effective synthesis routes, reliability, and long-term stability, which makes it a potential applicant for multifunctional opto-electronic devices. [ABSTRACT FROM AUTHOR]

Superconducting photoinjectors have a potential to be the optimal solution for moderate and high current cw operating free electron lasers. For this application, a superconducting lead (Pb) cathode has been proposed to simplify the cathode integration into a 1.3 GHz, TESLA-type, 1.6-cell long purely superconducting gun cavity. In the proposed design, a lead film several micrometres thick is deposited onto a niobium plug attached to the cavity back wall. Traditional lead deposition techniques usually produce very non-uniform emission surfaces and often result in a poor adhesion of the layer. A pulsed plasma melting procedure reducing the non-uniformity of the lead photocathodes is presented. In order to determine the parameters optimal for this procedure, heat transfer from plasma to the film was first modelled to evaluate melting front penetration range and liquid state duration. The obtained results were verified by surface inspection of witness samples. The optimal procedure was used to prepare a photocathode plug, which was then tested in an electron gun. The quantum efficiency and the value of cavity quality factor have been found to satisfy the requirements for an injector of the European-XFEL facility. [ABSTRACT FROM AUTHOR]

In superconducting single-photon detectors (SSPD), the efficiency of local suppression of superconductivity and hot-spot formation is controlled by diffusivity and electron–phonon interaction time. Here, we selected a material, 3.6-nm-thick MoN${}_{x}$ film, which features diffusivity close to those of NbN traditionally used for SSPD fabrication, but with electron–phonon interaction time an order of magnitude larger. In MoN${}_{x}$ detectors, we study the dependence of detection efficiency on bias current, photon energy, and strip width, and compare it with NbN SSPD. We observe nonlinear current-energy dependence in MoN ${}_{x}$ SSPD and more pronounced plateaus in dependences of detection efficiency on bias current, which we attribute to longer electron–phonon interaction time. [ABSTRACT FROM PUBLISHER]

We are developing a new technique to apply transition-edge sensors (TESs) to X-ray spectroscopy of exotic atoms, especially of kaonic atoms. To demonstrate the feasibility of this pioneering project, performance of a TES-based X-ray detector was evaluated in pion- and kaon-beam environments at particle accelerators. We successfully observed X-rays from pionic-carbon atoms with a resolution as good as 7 eV FWHM at 6 keV. Also at a kaon beamline, we confirmed that the TES spectrometer will be able to achieve our resolution goal, 6 eV, in our first scientific campaign to measure X-rays from kaonic-helium atoms. [ABSTRACT FROM AUTHOR]

We propose a novel design of superconducting nanowire avalanche photodetectors (SNAPs), which combines the advantages of multistage avalanche SNAPs to lower the avalanche current IAV and that of series-SNAPs to reduce the reset time. As proof of principle, we fabricated 800 devices with large detection area (15 μm × 15 μm) and five different designs on a single silicon chip for comparison, which include standard SNSPDs, series-3-SNAPs, and our modified series-SNAPs with double-stage avalanche structure 2*2-SNAPs, 2*3-SNAPs, and 3*3-SNAPs. The former three types of the detectors demonstrate fully saturated device detection efficiencies of ∼20% while the latter two types are latching at larger bias currents. In addition, the IAV of 2*2-SNAPs is only 64% of the switching current ISW that is lower than series-3-SNAPs (74%) and well below that of 4-SNAPs (84%) reported elsewhere. We also measure that the exponential decay times of the detectors are proportional to 1/ n^2 due to the lack of external choke inductors. In particular, the decay time of 3*3-SNAPs is only 0.89 ns compared to the standard SNSPDs’ 63.2 ns, showing the potential to attain GHz counting rates. [ABSTRACT FROM PUBLISHER]

We report a broadband superconducting nanowire single-photon detector for the near-infrared waveband. The optical absorptance in this band is enhanced by utilizing a reflective aluminum mirror and a SiO2 layer as an optical cavity. A broadband system detection efficiency (SDE) over 50% from 950 to 1600 nm with a low dark count rate of 10 Hz is realized by coupling a HI 1060 FLEX single-mode fiber. The SDEs reaches 78.3%, 70.9%, and 57.7% at the wavelengths of 1064, 1310, and 1550 nm, respectively. A system timing resolution (jitter) of 83 ps at 1550 nm is obtained. The detector may be useful for broadband applications such as earth observation, environment monitoring, and biomedicine. [ABSTRACT FROM PUBLISHER]

We investigated the suitability of AlN as a buffer layer for NbN superconducting nanowire single-photon detectors (SNSPDs) on GaAs. The NbN films with a thickness of 3.3–20 nm deposited onto GaAs substrates with an AlN buffer layer demonstrate a higher critical temperature, critical current density, and lower residual resistivity in comparison to films deposited onto bare substrates. Unfortunately, the thermal coupling of the NbN film to the substrate weakens. SNSPDs made of 4.9-nm-thick NbN films on buffered substrates (in comparison to detectors made from NbN films on bare GaAs) demonstrate three orders of magnitude lower dark count rates and about ten times higher detection efficiency at 900 nm being measured at 90% of the critical current. The system timing jitter of SNSPDs on buffered substrates is 72 ps, which is 36 ps lower than those on bare substrate. However, a weaker thermal coupling of NbN nanowire to the buffered substrate leads to a latching effect at bias currents > 0.97 I C. [ABSTRACT FROM PUBLISHER]

The so-called “optimal filter” analysis of a microcalorimeter's x-ray pulses is statistically optimal only if all pulses have the same shape, regardless of energy. However, the shapes of pulses from a nonlinear detector can and do depend on the pulse energy. A pulse-fitting procedure that we call “tangent filtering” accounts for the energy dependence of the shape and should, therefore, achieve superior energy resolution. We take a geometric view of the pulse-fitting problem and give expressions to predict how much the energy resolution stands to benefit from such a procedure. We also demonstrate the method with a case study of K-line fluorescence from several 3d transition metals. The method improves the resolution from 4.9 to 4.2 eV at the Cu K $\alpha$ line (8.0 keV). [ABSTRACT FROM PUBLISHER]

Implementation of the unipolar barrier detector concept in HgCdTe-based compound semiconductor alloys is a challenging problem, primarily because practical lattice-matched materials that can be employed as the wide bandgap barrier layer in HgCdTe nBn structures present a significant valence band offset at the n-type/barrier interface, thus impeding the free flow of photogenerated minority carriers. However, it is possible to minimize the valence band offset by replacing the bulk HgCdTe alloy-based barrier with a CdTe–HgTe superlattice barrier structure. In this paper, an $8 \times 8$ k.p Hamiltonian combined with the nonequilibrium Green’s function formalism has been employed to numerically demonstrate that the single-band effective mass approximation is an adequate numerical approach, which is valid for the modeling, design, and optimization of band alignment and carrier transport in HgCdTe-based nBn detectors incorporating a wide bandgap superlattice barrier. [ABSTRACT FROM PUBLISHER]

In this paper, we developed a simple method to fabricate an indium-doped ZnO nanostructure ultraviolet (UV) photodetector (PD) on a glass substrate. Through the aqueous chemical solution method, the indium-doped ZnO nanostructure uniformly grew on a glass substrate. The average length and diameter were 3.06 \mu \textm and 38 nm, respectively. At 1 V bias, the photo-to-dark current ratio of the indium-doped ZnO PD was 740 under UV light irradiation (365 nm). The sample exhibited fast response and recovery time. The increase and decrease times were 3.02 and 1.53 s, correspondingly. When irradiated at 360 nm, the UV-visible rejection ratio of the indium-doped ZnO nanostructure PD was approximately 312. The indium-doped ZnO nanostructure PD exhibited high sensitivity, fast response and recovery times, and good orientation properties. [ABSTRACT FROM PUBLISHER]

We use an external magnetic field to probe the detection mechanism of a superconducting nanowire singlephoton detector. We argue that the hot belt model (which assumes partial suppression of the superconducting order parameter Δ across the whole width of the superconducting nanowire after absorption of the photon) does not explain observed weak-held dependence of the photon count rate (PCR) for photons with λ = 450 nm and noticeable decrease of PCR (with increasing the magnetic field) in a range of the currents for photons with wavelengths λ = 450-1200 nm. Found experimental results for all studied wavelengths can be explained by the vortex hot spot model (which assumes partial suppression of Δ in the area with size smaller than the width of the nanowire) if one takes into account nucleation and entrance of the vortices to the photon induced hot spot and their pinning by the hot spot with relatively large size and strongly suppressed Δ. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) photodetectors were fabricated with low temperature (<150 °C) solution-processed zinc oxide (ZnO) layers. A polydimethylsiloxane (PDMS) layer was used as the encapsulation to protect the devices from ambient effects. Current-voltage ( I-V) characteristics, transient characteristics, and the encapsulation effect were compared for ohmic and Schottky contact devices that were formed with aluminum and silver electrodes, respectively. Schottky contact devices were shown to be able to achieve rapid response with the recovery time not affected by the encapsulation. [ABSTRACT FROM AUTHOR]

Minority carrier lifetimes in undoped and Beryllium-doped Type-2 Ga-free, InAs/InAsSb strained layer superlattices (SLS) with energy gaps as low as 0.165 eV were determined from photoluminescence kinetics. The minority carrier lifetime of 450 ns at 77 K in the undoped SLS confirms a high material quality. In similarly-grown structures that were p-doped to N = 6 × 10 and 3 × 10 cm, electron lifetimes of τ = 45 ns and 8 ns were measured. The 6 × 10 cm doping level is a factor of 6 greater than the typical background doping level in long-wave infrared (LWIR) Ga-containing InAs/GaSb SLS with similar bandgap and electron lifetime. This suggests that LWIR photodetectors with InAs/InAsSb SLS absorbers can be designed with smaller minority carrier concentrations and diffusion dark current densities. A relatively slow decrease of the lifetime with doping suggests a minor role of Auger recombination in the studied Ga-free SLS at T = 77 K with p-doping up to mid-10 cm level. [ABSTRACT FROM AUTHOR]

The nondestructive assay (NDA) of plutonium-bearing materials using gamma-ray spectroscopy supports global nuclear nonproliferation and safeguards efforts. High-purity germanium (HPGe) detectors have been used for this application for decades, but the uncertainty limit remains around 1% relative error for measured isotope ratios, an order of magnitude larger than destructive assay. To lower NDA uncertainty limits, we are pursuing new measurement technology using superconducting microcalorimeter detectors, and assessing the sources of current uncertainty limits. We compare results from analysis of plutonium isotopic standards using HPGe and microcalorimeter detectors, and find lower random error for the microcalorimeter data. Uncertainties in the reference values of constants of nature contribute to the total measurement error. For one particular set of constants, the gamma-ray energies, we find that microcalorimeter analysis is much less sensitive (more than a factor of ten) to the uncertainty in nuclear data than HPGe. [ABSTRACT FROM PUBLISHER]

Digital signatures are widely used to provide security for electronic communications, for example, in financial transactions and electronic mail. Currently used classical digital signature schemes, however, only offer security relying on unproven computational assumptions. In contrast, quantum digital signatures offer information-theoretic security based on laws of quantum mechanics. Here, security against forging relies on the impossibility of perfectly distinguishing between nonorthogonal quantum states. A serious drawback of previous quantum digital signature schemes is that they require long-term quantum memory, making them impractical at present. We present the first realization of a scheme that does not need quantum memory and which also uses only standard linear optical components and photodetectors. In our realization, the recipients measure the distributed quantum signature states using a new type of quantum measurement, quantum state elimination. This significantly advances quantum digital signatures as a quantum technology with potential for real applications. [ABSTRACT FROM AUTHOR]

Microcalorimeter detectors provide unprecedented energy resolution for gamma-ray spectroscopy. One application is measuring the isotopic composition of plutonium-bearing samples by non-destructive gamma-ray spectroscopy to support nuclear safeguards and nonproliferation efforts. When measured with conventional high-purity germanium (HPGe) detectors, data from these samples contain significant peak overlaps requiring spectral deconvolution for analysis. The improved energy resolution of the microcalorimeter detector reduces peak overlaps leading to improvement in the statistical error component of the total measurement uncertainty. In this paper, we describe analysis code that was developed for spectral peak fitting and isotopic content determination from microcalorimeter and HPGe data. We apply the code to data collected from several plutonium standards to quantify the improvement of the statistical error derived from the improved energy resolution. [ABSTRACT FROM PUBLISHER]

High-efficiency photon-number-resolving detectors have been developed using titanium-based transition-edge sensors. Device performances have been evaluated with respect to the response photon distribution, dark count, and timing jitter. In the analysis of the photon statistics, the observed detection probabilities were consistent with Poisson distributions. From a comparison of the measured distribution with theory, 98% detection efficiency was deduced at 850 nm. The dark count probability of the device is less than 10^-6, corresponding to a dark count rate of 0.6 Hz. The timing jitter is 25 ns, the best value ever reported (to our knowledge) in transition-edge sensors used for optical photon measurements. [ABSTRACT FROM AUTHOR]

We have successfully fabricated superconducting niobium nitride thin films on single crystals of magnesium oxide using a pulsed laser deposition technique where 1064 nm (photon energy \sim1.16 eV) laser pulses from an Nd:YAG laser were used for ablation. A correlation between the superconducting transition temperature, the nitrogen base pressure during deposition and the lattice parameter of the produced NbN films was observed. Superconductor–insulator–normal metal junctions fabricated using these NbN films as the superconductor revealed nonlinear electrical characteristics at 4.2 K associated with quasiparticle tunneling. [ABSTRACT FROM AUTHOR]

Among various discussed ways of explosive detection, the techniques using electromagnetic radiation are considered as having great potential and research activities are recommended in this field. To identify new threats, like liquid explosives, with low rate of false alarms, fast spectral measurements are required in a broad frequency range from microwave to terahertz. We attract attention to a great potential of high-Tc Josephson technology in security applications and present our results in developing high-Tc Josephson junctions for Hilbert spectroscopy and detector arrays. [ABSTRACT FROM PUBLISHER]

Superconducting single-photon detectors (SSPDs) are nanostructured devices made from ultrathin superconducting films. They are typically operated at liquid helium temperature and exhibit high detection efficiency, in combination with very low dark counts, fast response time, and extremely low timing jitter, within a broad wavelength range from ultraviolet to mid-infrared (up to 6 mum). SSPDs are very attractive for applications such as fiber-based telecommunication, where single-photon sensitivity and high photon-counting rates are required. We review the current state-of-the-art in the SSPD research and development, and compare the SSPD performance to the best semiconducting avalanche photodiodes and other superconducting photon detectors. Furthermore, we demonstrate that SSPDs can also be successfully implemented in photon-energy-resolving experiments. Our approach is based on the fact that the size of the hotspot, a nonsuperconducting region generated upon photon absorption, is linearly dependent on the photon energy. We introduce a statistical method, where, by measuring the SSPD system detection efficiency at different bias currents, we are able to resolve the wavelength of the incident photons with a resolution of 50 nm. [ABSTRACT FROM PUBLISHER]

We report on time-resolved, transient photoimpedance measurements performed on current-biased MgB2 microbridges excited by 100-fs wide, 800-nm wavelength, and 76-MHz repetition-rate optical pulses. Our bridges had dimensions of 20 μm by 40 μm and were patterned by conventional photolithography and ion milling from 150-nm-thick, epitaxial MgB2 films grown by a hybrid physical-chemical vapor-deposition technique. For high-speed detection experiments, the microbridges were embedded into coplanar-strip transmission lines and connected to a 20-GHz-bandwidth sampling oscilloscope via a semirigid coaxial cable. The test structures were placed inside an optical cryostat and studies were performed in the temperature range between 15 K and 40 K. At temperatures, e.g., 20 K, far below the bridge critical temperature and under low optical excitation, large and fast (130 ps in duration) photoresponse transients were observed, which we associate with the kinetic-inductive (Cooper-pair breaking) mechanism. At temperatures approaching the MgB2 critical temperature and/or under intense light illumination, an additional slow component of the photoresponse with a nanosecond decay time was measured. We interpret this second photoimpedance component as a resistive response, resulting from the hot-electron heating effect. The observed picosecond kinetic photoresponse makes our MgB2 bridges attractive candidates for fast and efficient optical detectors and photon counters. [ABSTRACT FROM AUTHOR]

Point defects have been introduced into YBa/sub 2/Cu/sub 3/O/sub 7/ through low energy helium ion irradiation in order to probe the origin of dissipation in a current-carrying superconductor. Resistivity, infrared reflectance and x-ray diffraction measurements indicate that the films are not chemically altered and that the induced point defects act as scattering centres. Measured electric field-current density characteristics are found to be well described by a model based on quantum current fluctuations. This description is used to extract the change in the superconducting carrier density with ion damage which agrees well with direct measurements of the same quantity by infrared reflectance. The implications of the relation between dissipation and the superconducting carrier density, or alternatively the magnetic penetration depth, are discussed. [ABSTRACT FROM PUBLISHER]

A novel method of absorption measurements is reported through which we have succeeded in measuring directly the absolute absorptivity of a La-based superconductor in the 100 GHz to 500 THz frequency region using different lasers. We have made transmission measurements on free standing single crystals of the La-based superconductor using a laser and a high sensitivity detector, and succeeded in measuring the transmissivity. For the first time, the surface impedance has been analytically derived from the absorptivity and transmissivity at room temperature. [ABSTRACT FROM PUBLISHER]

We have measured the rf impedance of 10-nm thick superconducting granular NbN meander lines between 5 /spl mu/m and 20 /spl mu/m wide. The complex reflection coefficient was obtained directly using a vector network analyzer. The impedance (at 10 MHz for a 5 /spl mu/m wide line) is dominated by the large kinetic Inductance of the film, with a sheet inductance of order 1 nH, giving a total inductance of 400 nH for a 5 /spl mu/m/spl times/2 mm line. The kinetic inductance diverges as T/spl rarr/T/sub c/=6.5 K, as expected from Ginzburg-Landau theory (GL). Of particular interest is a substantial decrease of measured inductance with increasing dc current, contrary to the dependence expected from GL. This anomalous current dependence is not well understood, but may be related to vortex dynamics and Josephson effects in these granular films, as supported by preliminary Josephson array simulations. These results have important implications for potential devices such as tunable rf phase shifters and kinetic inductance photodetectors. [ABSTRACT FROM PUBLISHER]

Nb-based superconducting tunnel junctions are being developed as high energy resolution X-ray detectors. Unfortunately, loss of excess quasiparticles at the edges, combined with lateral diffusion, results in an inhomogeneous response. To study this degradation of energy resolution, we manufactured detectors with a Ta trap in the top or bottom electrode away from the tunneling barrier. Excess quasiparticles in this so-called killed electrode will be trapped effectively and thus removed from the tunneling process. The X-ray spectra of the active electrode can be fitted with a model based on classical diffusion of quasiparticles. On junctions with a killed bottom electrode also Low Temperature Scanning Electron Microscopy (LTSEM) measurements have been performed. The X-ray spectra and the LTSEM scans are consistent with each other and with the model. The energy resolution of the junctions presented here is limited by loss of quasiparticles at the edges. [ABSTRACT FROM PUBLISHER]

UV and X-ray astronomy need hyperspectral imaging devices, i.e. large format (1000/spl times/1000) arrays of pixels in which each single-photon event is tagged with spectral information. Such devices permit multicolor imagery and surveys to be obtained with a single camera. Here we discuss the first-stage of development of a new generation of UV/X-ray detectors that will provide 0.1-0.01% energy resolution in an array format. [ABSTRACT FROM PUBLISHER]

We have developed superconducting single-photon imaging X-ray detectors with an energy resolution of 54 eV at 6 keV and a spatial resolution of 1 /spl mu/m over an effective length of 40 /spl mu/m. They utilize a current-sensitive low-noise preamplifier with a dc voltage bias. It has a signal bandwidth of 300 kHz, current noise of i/sub n/=0.26 pA//spl radic/(Hz) and voltage noise of e/sub n/=0.5 nV//spl radic/(Hz) with an input capacitance of 200 pF under operating conditions. Injected pulses with a charge Q=3.7/spl middot/10/sup 6/ electrons have been measured with a standard deviation /spl sigma/Q=3400 electrons, corresponding to an electronic noise of 13 eV at 6 keV. [ABSTRACT FROM PUBLISHER]

Photon counting experiments with Ta/Al superconducting tunnel junctions are presented. Single photon detection is demonstrated in the wavelength range /spl lambda/=200-2000 nn with a resolving power /spl lambda///spl Delta//spl lambda/=22-4. The response of the detector shows good linearity with photon energy. [ABSTRACT FROM PUBLISHER]

We describe SIN (superconductor-insulator-normal) tunnel junctions made by thin-films of Nb/AlOx/Cu and we report on the measurements of their I-V characteristics between 10 K and 0.3 K. The junctions show a strong dependence of the subgap conductance on the temperature, which makes them suitable for the on-chip measurement of the temperature. In this paper we also describe the design of an on-chip electronic refrigerator based on this type of junction. [ABSTRACT FROM PUBLISHER]

In the current generation of high-T/sub c/ bolometers the thermal conductance is often chosen for a short time-constant rather than for optimal sensitivity. We describe a novel bolometer bias and readout scheme that promises to relax this constraint. Voltage bias of the superconductor results in strong negative electrothermal feedback that greatly reduces the time-constant of the bolometer. We estimate that a decrease of more than one order of magnitude in time-constant should be possible with existing high-T/sub c/ thermometers. We give theoretical estimates of the performance gain with voltage bias for several bolometers that have been reported in the literature. We find cases where the sensitivity can be greatly improved (by changing the thermal conductance) while holding the time constant fixed and others where the bolometer can be made much faster while maintaining the sensitivity. [ABSTRACT FROM PUBLISHER]

In this letter, we report the electrical and optical characteristics of a superconducting vacuum-bridge microbolometer with an electrical noise equivalent power of 26fW radicHz and an effective time constant of 380 ns, when operated at a bath temperature of 4K. We employ a novel room temperature external negative feedback readout architecture, that allows for noise matching to the device without bulky stepup transformers or cooled electronics. Both the detector and the readout lend themselves to be scaled to imaging arrays. The directly measured noise equivalent temperature difference over a 100-1000-GHz bandwidth is 125 mK in a 30-ms integration time [ABSTRACT FROM PUBLISHER]