Nobuyuki Zen

1 mm ultrafast superconducting stripline molecule detector

Superconducting stripline detectors (SSLDs) are promising for detecting keV molecules at nanosecond response times and with mass-independent detection efficiency. However, a fast response time is incompatible with practical centimeter detector size. A parallel configuration of striplines provides a means to address this problem. Experimental results and simulation for promisingly large 1-mm-square parallel niobium SSLDs show that nanosecond pulses are produced by superconducting-normal transition within only one of the parallel striplines instead of cascade switching of all the parallel striplines. Successful detection of a series of multimers of immunoglobulin G up to 584 kDa supports the mass-independent efficiency for mass spectrometry.

Subnanosecond time response of large-area superconducting stripline detectors for keV molecular ions

A large-area (200×200 μm2) superconducting stripline detector based on a parallel configuration of superconducting Nb nanowires is presented. We show that the parallel configuration provides a smart way to control the physical nonequilibrium state induced by the molecular impacts, which allows realizing large sensitive area and subnanosecond response at the same time. The experiments were carried out with molecular ions radiation in a keV energy range. The observed rise time was below 400 ps and the relaxation time was 500 ps, the best in this class of superconducting molecular detectors.

Thicker, more efficient superconducting strip-line detectors for high throughput macromolecules analysis

Fast detectors with large area are required in time-of-flight mass spectrometers for high throughput analysis of biological molecules. We fabricated and characterized subnanosecond 1×1 mm2 NbN superconducting strip-line detectors. The influence of the strip-line thickness on the temporal characteristics and efficiency of the detector for the impacts of keV accelerated molecules is investigated. We find that the increase of thickness improves both efficiency and response time. In the thicker sample we achieved a rise time of 380 ps, a fall time of 1.38 ns, and a higher count rate. The physics involved in this behavior is investigated.

Titanium Based Transition Edge Microcalorimeters for Optical Photon Measurements

Transition edge sensor microcalorimeters can be used in many optical quantum measurements because of its low dark counts, high quantum efficiency, and high resolving power of a photon number in weak light pulses. In order to increase count rates up to a few MHz, we have developed a titanium transition edge sensor for the optical measurements, and its performances were analysed. Titanium is one of the ideal superconductor because of its higher transition temperature and lower optical reflectance at 1.5 wavelength. Our titanium film was fabricated with electron-beam evaporation, and showed high residual resistance ratio of 3.5. The sharp superconducting transition also was found at 359 mK, which is close to the critical temperature in bulk. The fabricated device showed a fast response to pulsed laser illumination of 1.5 wavelength with the fall time constant of 300 ns. These features are very promising for high-speed single photon detection in many quantum optical measurements.

Soft X-Ray Spectrometer Using 100-Pixel STJ Detectors for Synchrotron Radiation

Fluorescent X‐ray absorption fine structure (XAFS) is an important tool for material analysis, especially for the measurement of chemical states or local structures of elements. Semiconductor detectors are usually used for separating the fluorescent of elements in question from background fluorescence. However, the semiconductor detectors cannot always discriminate K‐lines of light elements and L‐lines of various elements as different X‐ray peaks at an energy range below about 3 keV. Superconducting tunnel junction (STJ) detectors are promising device for the soft X‐ray at synchrotron radiation beam lines because of excellent energy resolution, high detection efficiency, and high counting rate. We are constructing a fluorescent X‐ray spectrometer having 100‐pixel array of STJs with 200 μm square. The array detector is mounted on a liquid cryogen‐free 3He cryostat. The sensitive area is the largest among the superconducting X‐ray spectrometers operating at synchrotron beam lines. Each pixel is connected to...

Superconducting nano-strip particle detectors

We review progress in the development and applications of superconducting nano-strip particle detectors. Particle detectors based on superconducting nano-strips stem from the parent devices developed for single photon detection (SSPD) and share with them ultra-fast response times (sub-nanosecond) and the ability to operate at a relatively high temperature (2–5 K) compared with other cryogenic detectors. SSPDs have been used in the detection of electrons, neutral and charged ions, and biological macromolecules; nevertheless, the development of superconducting nano-strip particle detectors has mainly been driven by their use in time-of-flight mass spectrometers (TOF-MSs) where the goal of 100% efficiency at large mass values can be achieved. Special emphasis will be given to this case, reporting on the great progress which has been achieved and which permits us to overcome the limitations of existing mass spectrometers represented by low detection efficiency at large masses and charge/mass ambiguity. Furthermore, such progress could represent a breakthrough in the field. In this review article we will introduce the device concept and detection principle, stressing the peculiarities of the nano-strip particle detector as well as its similarities with photon detectors. The development of parallel strip configuration is introduced and extensively discussed, since it has contributed to the significant progress of TOF-MS applications.

Demonstration of single-flux-quantum readout circuits for time-of-flight mass spectrometry systems using superconducting strip ion detectors

We have been developing a superconducting time-of-flight mass spectrometry (TOF-MS) system that consists of a superconducting strip ion detector (SSID) and a single-flux-quantum (SFQ) time-to-digital converter. In this study, we implement a prototype TOF-MS system using an SSID and an SFQ readout circuit in which output signals from the SSID are read out by the SFQ readout circuit and output to room-temperature electronics. The SFQ readout circuit, which consists of a current discriminator, a Josephson transmission line and an SFQ/dc converter, was fabricated using the AIST Nb standard process (STP2), and installed in a 4.2 K cryostat with a meander-shaped NbN SSID measuring 200 μm square. The dark count rate for the SSID was measured as increasing exponentially with the increase in the bias current of the SSID by using the SFQ readout circuit. Mass spectrum measurements of biomolecules, Angiotensin I, which has a molecular weight of 1296 Da, were demonstrated by using the matrix-assisted laser desorption/ionization method, and a clear corresponding peak was observed in the mass spectrum.

Ion-induced dynamical change of supercurrent flow in superconducting strip ion detectors with parallel configuration

Superconducting strip ion detectors are promising for realizing ideal ion detection in time-of-flight mass spectrometry. To realize large sensitive area for practical use, parallel configurations of superconducting strips are mandatory. In a previous parallel configuration design, however, we have found that a non-negligible number of ion impact events were lost because a large number of output current pulses for single ions were fatally small. An alternative parallel configuration design has solved this critical problem. It has been revealed that ion impact events induce dynamical change of bias current flow among parallel superconducting strips. Furthermore, output current distributions of larger bias current have shown another dynamical phenomenon: multi-strip switching triggered by single ion impact.

Improvements in the AIST Cryogenic Radiometer With Superconducting Thermometer

We are developing a cryogenic radiometer (CR) with a superconducting thermometer for the optical laser power calibration. This device consists of a niobium transition edge sensor and an electrical substitution heater on a silicon substrate. The device temperature is locked at the niobium transition temperature with a superconducting quantum interference device amplifier and a proportional-integral-derivative controller. The device successfully determines the absolute optical power in the range from 20 nW to 600 muW, with a fast response of 3 s. The equivalence measurement shows that the response difference between the substitution power and the simulated optical power is less than 0.0034%. These properties are very attractive for next generation of a high-accuracy CR

Biomolecular ion detection using high-temperature superconducting MgB2 strips

Superconducting strip ion detectors (SSIDs) are promising for realization of ideal ion detection with 100% efficiency and nanosecond-scale time response in time-of-flight mass spectrometry. We have detected single biomolecular ions in the keV range using a 10-nm-thick and 250-nm-wide strip of a high temperature superconductor, magnesium diboride (MgB2), at temperatures of up to 13 K. The output pulse shape is explained remarkably well using circuit simulations and time-dependent Ginzburg-Landau simulations coupled with a heat diffusion equation. The simulations show that the hot spot model is applicable to the proposed MgB2-SSIDs and the normal region expansion is completed within 16 ps, which corresponds to a maximum length of 1010 nm.