Superconducting Transition Edge Research Articles

Integrated transition edge sensors on titanium in-diffused lithium niobate waveguides

We show the proof-of-principle detection of light at 1550 nm coupled evanescently from a titanium in-diffused lithium niobate waveguide to a superconducting transition edge sensor. The coupling efficiency strongly depends on the polarization, the overlap between the evanescent field, and the detector structure. We experimentally demonstrate polarization sensitivity of this coupling as well as photon-number resolution of the integrated detector. The combination of transition edge sensors and lithium niobate waveguides can open the field for a variety of new quantum optics experiments.

Nanokelvin DC and AC Meissner-transition-edge temperature detectors.

Based upon a superconducting transition edge sensor (TES), the Meissner-TES is a relatively new type of high resolution cryogenic thermometer which employs the magnetic transition of a superconductor to measure temperature. We have improved the signal-to-noise for DC sensing by a factor of 30 compared to our prior effort and developed a new AC mode which uses an oscillating magnetic field and a lock-in technique with much lower magnetic noise than the DC mode. The thermometer was tuned in situ over a range of operating temperatures 10-50 times larger than the transition width of the superconductor, using an applied persistent magnetic field. The DC mode can have sensitivity better than 1 nK for 100 s averaging, and the AC mode has sensitivity better than 120 nK for very small applied magnetic fields near 14 nT and 100 s averaging. The Meissner-TES can be applied to high resolution temperature control, high sensitivity infrared sensing, optical power scale realization, and the study of temperature-dependent phase transitions.

Superconducting transition edge sensors with phononic thermal isolation

The sensitivity of a low-noise superconducting transition edge sensor (TES) is determined by the thermal conductance of the support structure that connects the active elements of the device to the heat bath. Low-noise devices require conductances in the range 0.1 to 10 pW K−1 and so have to rely on diffusive phonon scattering in long, narrow, amorphous SiNx legs. We show that it is possible to manufacture and operate TESs having short, ballistic low-dimensional legs (cross section 0.5 × 0.2 μm) that contain multi-element phononic interferometers and ring resonators. These legs transport heat in effectively just 5 elastic modes at the TES’s operating temperature (<150 mK), which is close to the quantised limit of 4. The phononic filters then reduce the thermal flux further by frequency-domain filtering. For example, a micromachined 3-element ring resonator reduced the flux to 19% of a straight-legged ballistic device operating at the quantised limit and 38% of a straight-legged diffusive reference device. This work opens the way to manufacturing TESs where performance is determined entirely by filtered, few-mode, ballistic thermal transport in short, low-heat capacity legs, free from the artifacts of two level systems.

Mapping TES Temperature Sensitivity and Current Sensitivity as a Function of Temperature, Current, and Magnetic Field with IV curve and Complex Admittance Measurements.

We have specialized astronomical applications for X-ray microcalorimeters with superconducting transition edge sensors (TESs) that require exceptionally good TES performance, but which operate in the small-signal regime. We have therefore begun a program to carefully characterize the entire transition surface of TESs with and without the usual zebra stripes to see if there are reproducible local "sweet spots" where the performance is much better than average. These measurements require precise knowledge of the circuit parameters. Here, we show how the Shapiro effect can be used to precisely calibrate the value of the shunt-resistor. We are also investigating the effects of stress and external magnetic fields to better understand reproducibility problems.

Electrochemical Growth of Bismuth for X-ray Absorbers

Bismuth electroplating and fabrication efforts for its incorporation as an absorber in Superconducting Transition Edge X-ray Sensor devices are summarized. The bismuth films, a few microns thick, are grown using both aqueous and non-aqueous solutions. They are characterized by optical imaging, profilometry, X-ray diffraction, SEM, and by electrical transport (resistivity and Hall Effect) measurements from 30 to 310 K. While aqueous solutions produce an irregular rough and polycrystalline material, with very little chance to tune transport properties, films grown in non-aqueous solvents improve considerably homogeneity, surface roughness, and density. It is also demonstrated how the crystal texture of the films can be controlled with electroplating parameters. This allows orienting anisotropy axes directly during electroplating and thus tune electrical and thermal conductance depending on device requirements. This a significant step toward direct electrodeposition of Bi films with good transport properties, still a significant technological challenge. In order to have reasonable quantitative objectives for physical properties such as surface roughness, crystalline texture, electrical conductivity, etc. Bismuth films are also grown by Physical Vapor Deposition, characterized and compared with the electroplated.

Experimental progress of a 4K VM/PT hybrid cryocooler for pre-cooling 1K sorption cooler

Sub-kelvin refrigerator has many applications in space detector and manned space station, such as for the transition-edge superconducting (TES) bolometers operated in the 50 mK range. In order to meet the requirement of space applications, the high efficient, vibration free and high stability refrigerator need to be designed. VM/PT hybrid cryocooler is a new type cryocooler capable of attaining temperature below 4K. As a low frequency Stirling type cryocooler, it has the advantages of high stability and high efficiency. Combined with the vibration free sorption cooler and ADR refrigerator, a novel sub-kelvin cooling chain can be designed for the TES bolometer. This paper presents the recent experimental progress of the 4K VM/PT hybrid cryocooler in our laboratory. By optimizing of regenerators, phase shifters and heat exchangers, a lowest temperature of 2.6K was attained. Based on this cryocooler, a preliminary sorption cooler could be designed.

Thermal elastic-wave attenuation in low-dimensional SiNx bars at low temperatures

At low temperatures, <200 mK, the thermal flux through low-dimensional amorphous dielectric bars, <2 μm wide and 200 nm thick, is transported by a small number of low-order elastic modes. For long bars, L > 400 μm, it is known that the conductance scales as 1/L, where L is the length, but for short bars, 1 μm < L < 400 μm, the length dependence is poorly known. Although it is assumed that the transport must exhibit a diffusive to ballistic transition, the functional form of the transition and the scale size over which the transition occurs have not, to our knowledge, been measured. In this paper, we use ultra-low-noise superconducting Transition Edge Sensors to measure the heat flux through a set of SiNx bars to establish the characteristic scale size of the ballistic to diffusive transition. For bars supporting 6 to 7 modes, we measure a thermal elastic-wave attenuation length of 20 μm. The measurement is important because it sheds light on the scattering processes, which in turn are closely related to the generation of thermal fluctuation noise. Our own interest lies in creating patterned phononic filters for controlling heat flow and thermal noise in ultra-low-noise devices, but the work will be of interest to others trying to isolate devices from their environments and studying loss mechanisms in micro-mechanical resonators.

Characterization of a Free-Standing Membrane Supported Superconducting Ti Transition Edge Sensor

Superconducting transition edge sensors (TES) based on a Ti microbridge on Si substrate have demonstrated a very low noise equivalent power. Their effective response time, however, is in the order of microseconds due to relatively high transition temperature (i.e., 300–400 mK) of the Ti microbridge, making it difficult to read out the signal of a large Ti TES array with a SQUID-based multiplexer. We propose a twin-slot antenna coupled superconducting Ti microbridge separated from the antenna feed and supported by a free-standing membrane. Its resistive transition (R-T) and current-voltage (I–V) curves are measured before and after KOH wet etching of the Si substrate underneath the Ti microbridge. The free-standing membrane supported Ti TES with a thickness of 40 nm shows slightly lower transition temperature and higher normal resistance. Its thermal conductance is reduced to ∼800 pW/K from ∼3000 pW/K. In addition, its effective response time measured with a current pulse signal is about 5 μ s. The uniformity of the 8 × 8 TES array is studied by measuring the distribution of normal resistance and critical temperature. In order to improve the uniformity, we increase the Ti film thickness to 64 nm, and characterize its thermal and electrical features.

Study of TES-Based Microcalorimeters of Different Size and Geometry Under AC Bias

Frequency-division multiplexing (FDM) is the current baseline read-out system for the large array of superconducting transition edge sensors (TES's) under development for the X-ray instrument XIFU ( Athena ). In this multiplexing scheme the sensor operates as amplitude modulator of a MHz carrier. To achieve the best performance with these and similar instruments the detector physics and its interaction with the read-out circuit needs to be better understood. In particular we need an explanation for the dependence of the TES microcalorimeter nonlinear impedance on the bias point, because it directly affects the choice of the detector optimal working point. With the TES microcalorimeters fabricated at NASA-Goddard we observe current steps in the amplitude of the uncalibrated IV characteristics when the detectors are read-out in the frequency domain and are biased in the low-resistance part of the superconducting transition. In this paper, we report on the characterization under FDM of NASA-Goddard TES microcalorimeters under development for the XIFU instrument. We have measured several pixels with different size and geometry in the bias frequency range from 1 to 4 MHz and at different bath temperatures. The results will be discussed within the recently developed weak-link theoretical framework.

Mapping of the resistance of a superconducting transition edge sensor as a function of temperature, current, and applied magnetic field.

We have measured the resistance R(T, I, B ext) of a superconducting transition edge sensor over the entire transition region on a fine scale, producing a 4-dimensional map of the resistance surface. The dimensionless temperature and current sensitivities of the TES resistance have been determined at each point. α and β are closely related to the sensor performance, but show a great deal of complex, large amplitude fine structure over large portions of the surface that is sensitive to the applied magnetic field. We discuss the relation of this structure to the presence of Josephson "weak link" fringes.

基于光子数测量的量子信道物理安全检测

理想的单光子源和高性能的单光子探测器是制约量子密钥分配系统中的密钥安全和码率的两个关键因素。弱相干脉冲作为单光子源，为保证安全性，平均光子数必须少而限制了码率的提高。本文介绍了超导边沿传感器单光子探测器，提出了多端口分束器与多APD结合可用于量子密钥分配系统中检测弱相干脉冲中的光子数。对窃听者的攻击策略进行分析的基础上，基于光子数的检测，指出在保证安全性的前提条件下可以提高弱相干脉冲中的平均光子数，进而提高系统的量子密钥成码率。 The ideal single photon source and high performance single photon detectors are two key factors that restrict the key security and bit rate in quantum key distribution system. As a single photon source, the weak coherent pulse must contain fewer average photon number for the sake of security, thus the quantum bit rate cannot be raised to a high level. Superconducting transition edge sensor for single photon detection has been introduced. It is proposed that multi-port beam splitter combined with many APDs can be used to detect the photon number in weak coherent pulse in quantum key distribution system. The attack tactics of eavesdropper is analyzed, and based on photon number detection, it is proposed that the average photon number in weak coherent pulse can be improved, thus the quantum key bit rate can be improved.

Gain drift compensation with no feedback-loop developed for the X-Ray Integral Field Unit/ATHENA readout chain

The focal plane of the X-Ray Integral Field Unit (X-IFU) instrument of the Advanced Telescope for High-Energy Astrophysics observatory is composed of 3840 microcalorimeters. These sensors, based on superconducting transition edge sensors (TES), are read out through a frequency multiplexer. A “base-band feedback” suppresses all the carriers of the multiplexed signal in the superconducting quantum interference devices input coil (cryogenic readout). However, the loop gain of this feedback is too small (less than 10 in the present baseline of the phase A mission) to strongly compensate the readout gain drifts. An onboard x-ray source is considered to calibrate the gain of the full instrument. However, in-flight calibration time must be minimized, which leads to a requirement on the gain stability larger than 10 − 4 over a long duration (between each calibration) to reach the challenging energy resolution goal of 2.5 eV at 6 keV of the X-IFU. A significant part of this gain is provided by a low-noise amplifier in the warm front-end electronics (WFEE). To reach such gain stability over more than a dozen minutes, this noncooled amplifier has to cope with the temperature and supply voltage variations. Moreover, mainly for noise reasons, a common large loop gain with feedback cannot be used. We propose a new amplifier topology using diodes as loads of a differential amplifier to provide a fixed voltage gain, independent of the temperature and of the bias fluctuations. This amplifier is designed using 350-nm SiGe BiCMOS technology and is part of an integrated circuit developed for the WFEE. Our simulations provide the expected gain and noise performances. Comparison with standard resistive loaded differential pair clearly shows the advantages of the proposed amplifier topology with a gain drift decreased by more than an order of magnitude. Performances of this diode loaded amplifier are discussed in the context of the X-IFU requirements.

All Metal Organic Deposited High-T c Superconducting Transition Edge Bolometer on Yttria-Stabilized Zirconia Substrate

We report on the results of a YBa2Cu3O7−x (YBCO) superconductive transition edge bolometer (TEB) fabricated on a Ce0.9La0.1O2−7 (CLO) buffered single crystalline yttria-stabilized zirconia (YSZ) substrate. Metal organic deposition was used for the fabrication of both the YBCO thin film as well as CLO buffer layer, while standard photolithography was applied for TEB preparation. YBCO thin film properties were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), AC susceptibility and resistance versus temperature measurements. Optical response of the TEB in terms of voltage amplitude and phase was analysed and measured through four-probe technique in a liquid nitrogen cooling system. An increase in voltage amplitude response was observed for the fabricated YBCO/CLO/YSZ bolometer compared to previously reported TEBs with similarly deposited YBCO thin film on a SrTiO3 (STO). This increase is assumed to be a result of the lower thermal conductivity and lower specific heat capacity of YSZ compared to STO substrate.

Fabrication and Test of Large Area Spider-Web Bolometers for CMB Measurements

Detecting the primordial ’B-mode’ polarization of the cosmic microwave background is one of the major challenges of modern observational cosmology. Microwave telescopes need sensitive cryogenic bolometers with an overall equivalent noise temperature in the nK range. In this paper, we present the development status of large area (about 1 cm\(^{2})\) spider-web bolometer, which imply additional fabrication challenges. The spider-web is a suspended Si\(_{3}\)N\(_{4}\) 1 \(\upmu \)m-thick and 8-mm diameter with mesh size of 250 \(\upmu \)m. The thermal sensitive element is a superconducting transition edge sensor (TES) at the center of the bolometer. The first prototype is a Ti–Au TES with transition temperature tuned around 350 mK, new devices will be a Mo–Au bilayer tuned to have a transition temperature of 500 mK. We present the fabrication process with micro-machining techniques from silicon wafer covered with SiO\(_{2}\) - Si\(_{3}\)N\(_{4}\) CVD films, 0.3 and 1 \(\upmu \)m- thick, respectively, and preliminary tests.

Cryogenic gamma detectors enable direct detection of 236U and minor actinides for non-destructive assay

We demonstrate the utility of a superconducting transition edge sensor (TES) γ-ray detector with high energy resolution and low Compton background for non-destructive assay (NDA) of a uranium sample from reprocessed nuclear fuel. We show that TES γ-detectors can separate low-energy actinide γ-emissions from the background and nearby lines, even from minor isotopes whose signals are often obscured in NDA with conventional Ge detectors. Superconducting γ-detectors may therefore bridge the gap between high-accuracy destructive assay (DA) and easier-to-use NDA.

X-Ray Transmission Characteristic Measurements of Polycapillary Optics Installed in an Analytical Electron Microscope

This paper studies the polycapillary optics that are used to focus and transmit the X-rays emitted by a transmission electron microscope (TEM) specimen to an energy dispersive spectrometer using a superconducting transition edge sensor (TES) microcalorimeter. In this study, X-rays are collected from a TEM specimen and are then focused on a silicon drift detector, from which energy spectrum measurements of the polycapillary optics are taken and used to determine the transmission characteristics of the optics. When the polycapillary optics are used, an increase of 25.9 is seen in the intensity of 4.6 keV X-rays, while an increase of 6.0 is seen for 12.6 keV X-rays. The focal spot sizes of the X-ray beams from the polycapillary optics are found to be 382 μm for the 4.6 keV X-rays and 156 μm for the 12.6 keV X-rays. Further improvement of these characteristics can be achieved by improving the alignment of the optics to the detector and the collimator, which immediately precedes the detector, and by optimizing the collimator width.

Nanobridge SQUIDs as calorimetric inductive particle detectors

Superconducting transition edge sensors (TESs) have made dramatic progress since their invention some 65 years ago (Andrews et al 1949 Phys. Rev. 76 154–155; Irwin and Hilton 2005 Topics Appl. Phys. 99 63–149) until now there are major imaging arrays of TESs with as many as 7588 separate sensors. These are extensively used by astronomers for some ground-breaking observations (Hattori et al 2013 Nucl. Instrum. Methods Phys. Res. A 732 299–302). The great success of TES systems has tended to overshadow other superconducting sensor developments. However there are other types (Sobolewski et al 2003 IEEE Trans. Appl. Supercond. 13 1151–7; Hadfield 2009 Nat. Photonics 3 696–705) which are discussed in papers within this special edition of the journal. Here we describe a quite different type of detector, also applicable to single photon detection but possessing possible advantages (higher sensitivity, higher operating temperature) over the conventional TES, at least for single detectors.

Absolute calibration of a variable attenuator using few-photon pulses.

We demonstrate the ability to calibrate a variable optical attenuator directly at the few-photon level using a superconducting Transition Edge Sensor (TES). Because of the inherent linearity of photon-number resolving detection, no external calibrations are required, even for the energy of the laser pulses, which ranged from means of 0.15 to 18 photons per pulse at the detector. To verify this method, calibrations were compared to an independent conventional calibration made at much higher photon fluxes using analog detectors. In all cases, the attenuations estimated by the two methods agree within their uncertainties.Our few-photon measurement determined attenuations using the Poisson-Influenced K-Means Algorithm (PIKA) to extract mean numbers of photons per pulse along with the uncertainties of these means. The robustness of the method is highlighted by the agreement of the two calibrations even in the presence of significant drifts in the optical power over the course of the experiment.Work of the United States Government. Not subject to copyright.

20 ps Pulsed Laser Irradiation to Current-Biased Kinetic Inductance Detector Made of Nb Nanowires

A current-biased kinetic inductance detector (CB-KID) is a new type of superconducting detector and senses a change in kinetic inductance in the superconducting nanowire biased by weak dc current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> . Kinetic inductance depends on the density of Cooper pairs. Therefore, when Cooper pairs are broken by local energy dissipation, a change in kinetic inductance ΔLk can be obtained by monitoring a voltage V across the CB-KID sensor. The CB-KID has a wide operating temperature regime in the superconducting state whereas a current-biased transition edge detector senses a change in resistance at the superconductive transition edge and operates only at near vicinity of Tc. The confirmation for the validity of the CB-KID idea was preceded by using an MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CB-KID meanderline detector. We extended this CB-KID method to a conventional Nb nanowire. We consider that our Nb-based CB-KID has versatile potentials in the various future applications. It is for the first time that the Nb-based CBKID operates at 4 K and has a capability of submicrometer position resolution.

Mo/Au Bilayer TES Resistive Transition Engineering

We have investigated two types of superconducting transition edge sensor (TES) modified with structures on the surface. One is a Mo/Au TES modified with Nb stripes, which increase the transition temperature and broaden the transition width. Another is a Mo/Au TES modified with Au stripes, which decrease the transition temperature and broaden the transition width. It is experimentally demonstrated that the resistive transition profile of a TES can be desirably engineered with a superconductor and/or a normal metal by properly choosing the width and spacing of the modification stripes on the surface.