Superconducting Transition Edge Sensor Research Articles

Resonant Soft X-Ray Scattering from Stripe-Ordered La2−xBaxCuO4 Detected by a Transition-Edge Sensor Array Detector

Resonant soft x-ray scattering (RSXS) is a leading probe of valence band order in materials best known for detecting charge density wave order in the copper-oxide superconductors. One of the biggest limitations on the RSXS technique is the presence of a severe fluorescence background which, like the RSXS cross section itself, is enhanced under resonant conditions. This background prevents the study of weak signals such as diffuse scattering from glassy or fluctuating order that is spread widely over momentum space. Recent advances in superconducting transition edge sensor (TES) detectors have led to major improvements in energy resolution and detection efficiency in the soft x-ray range. Here, we perform a RSXS study of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ at the Cu $L_{3/2}$ edge (932.2 eV) using a TES detector with 1.5 eV resolution, to evaluate its utility for mitigating the fluorescence background problem. We find that, for suitable degree of detuning from the resonance, the TES rejects the fluorescence background, leading to a 5 to 10 times improvement in the statistical quality of the data compared to an equivalent, energy-integrated measurement. We conclude that a TES presents a promising approach to reducing background in RSXS studies and may lead to new discoveries in materials exhibiting valence band order that is fluctuating or glassy.

Improving Energy Detection Efficiency of Ti-Based Superconducting Transition-Edge Sensors with Optical Cavity

Superconducting transition-edge sensors (TESs) have demonstrated high detection efficiency and photon-number-resolving capability, making TESs attractive in quantum information and astrophysics. Aiming to achieve high energy detection efficiency (i.e., the ratio of the detected energy to incident energy), we integrate the TES in an optical cavity, consisting of 16-layer dielectric reflection mirror and 4-layer antireflection coating. The critical temperature was decreased to 260 mK after deposition of antireflection coating from its original 323 mK. The energy detection efficiency was increased by a factor of two, up to 40%, thanks to the enhancement of photon absorption by adding the optical cavity.

Particle Physics with the Cosmic Microwave Background with SPT-3G

The cosmic microwave background (CMB) encodes information about the content and evolution of the universe. The presence of light, weakly interacting particles impacts the expansion history of the early universe, which alters the temperature and polarization anisotropies of the CMB. In this way, current measurements of the CMB place interesting constraints on the neutrino energy density and mass, as well as on the abundance of other possible light relativistic particle species. We present the status of an on-going 1500 sq. deg. survey with the SPT-3G receiver, a new mm-wavelength camera on the 10-m diameter South Pole Telescope (SPT). The SPT-3G camera consists of 16,000 superconducting transition edge sensors, a 10x increase over the previous generation camera, which allows it to map the CMB with an unprecedented combination of sensitivity and angular resolution. We highlight projected constraints on the abundance of sterile neutrinos and the sum of the neutrino masses for the SPT-3G survey, which could help determine the neutrino mass hierarchy.

Development of a Fast Response Titanium-Gold Bilayer Optical TES With an Optical Fiber Self-Alignment Structure

We developed a Ti/Au bilayer optical superconducting transition edge sensor (TES) laying on an optical fiber self-aligned structure. The bilayer approach enables us to control the superconducting transition temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> , which results in 8-μm-square-sized TES with T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> as high as 314.0 mK. Moreover, the TES device is micro-machined so that it can be easily assembled with an optical fiber via a self-aligned method. Our TES device achieved a system photon detection efficiency (PDE) of 83.6% at 940 nm with an energy resolution of 0.21 eV. Electrical and effective time constants (rise time and decay time) were as short as 74 and 75 ns, respectively. We also theoretically analyzed the imperfect system PDE. According to this analysis, the imperfection originated mainly from misalignment between the TES and the optical fiber, and the system PDE will be increased up to >95% by use of an optical fiber with a smaller mode field diameter.

End-to-End Instrument Performance Simulation System (EIPS) Framework: Application to Satellite Microwave Atmospheric Sounding Systems

This article presents a generic flexible framework for an End-to-end Instrument Performance Simulation System (EIPS) for satellite atmospheric remote sensing instruments. A systematic process for developing an end-to-end simulation system based on Rodgers’ atmospheric observing system design process has been visualised. The EIPS has been developed to support the quantitative evaluation of new satellite instrument concepts in terms of performance simulations, design optimisation, and trade-off analysis. Important features of this framework include: fast radiative transfer simulation capabilities (fast computation and line-by-line like simulations), applicability across the whole electromagnetic (EM) spectrum and a number of integrated retrieval diagnostics. Because of its applicability across the whole EM spectrum, the framework can be usefully applied to synergistic atmospheric retrieval studies. The framework is continually developing and evolving, and finding applications to support and evaluate emerging instrument and mission concepts. To demonstrate the framework’s flexibility in relation to advanced sensor technologies in the microwave range, a novel superconducting transition edge sensor (TES) -based multi-spectral microwave instrument has been presented as an example. As a case study, the performance of existing multi-spectral-type microwave instruments and a TES-technology-based multi-spectral microwave instrument has been simulated and compared using the developed end-to-end simulation framework.

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 (&amp;lt;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.

Calorimetry of Heavy Charged Particle by Superconducting Transition-Edge Sensor

Heavy ion cancer therapy allows the tumors to destroy while sparing surrounding, healthy tissues. By controlling the incident energy of heavy ions, the penetration depth can be adjusted precisely to the tumor area. The ionizing chambers are usually used for the determination of absorbed dose in the heavy ion irradiation fields; however, uncertainty in measurement of these detectors is expected to remain by more than 5%, and this has a negative influence on the therapeutic effect. Now we began to develop the precision heavy ion beam detector applying the superconducting transition-edge sensor (TES). Using the Ir/Au-TES coupled to a tin absorber, we have succeeded to detect the helium ions which were injected from Heavy Ion Medical Accelerator in Chiba. Although pulses are fully saturated because the temperature change is beyond the transition region, the signal length reflects the incident energy of each injected heavy ion. These results indicate the possibility of the precision heavy ion energy detection applying the TES detector.

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.

Effects of Normal Metal Features on Superconducting Transition-Edge Sensors

In transition-edge sensors (TESs), the addition of normal metal stripes on top of the superconducting bilayer, perpendicular to the current direction, is known to globally alter the sensitivity of the resistance R to changes in temperature T and current I. Here, we describe measurements of the dependence of the TES current on magnetic field B, bath temperature and voltage bias in devices with various numbers of stripes. We show that the normal metal features have a profound effect on the appearance of localized regions of very large $$(T/R)\,\hbox {d}R/\hbox {d}T$$ . We associate this with changes in the current distribution and corresponding changes in the oscillatory pattern of I(B). $$140~\upmu \hbox {m}$$ TESs with no stripes are found to have a relatively smooth resistive transition and sufficiently low noise that the measured energy resolution is 1.6 eV for X-rays of 1.5 keV. The predicted energy resolution at 6 keV is better than 2 eV, once the heat capacity is optimized for these higher energies.

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

At low temperatures, &amp;lt;200 mK, the thermal flux through low-dimensional amorphous dielectric bars, &amp;lt;2 μm wide and 200 nm thick, is transported by a small number of low-order elastic modes. For long bars, L &amp;gt; 400 μm, it is known that the conductance scales as 1/L, where L is the length, but for short bars, 1 μm &amp;lt; L &amp;lt; 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.

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.