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A novel principle of low-noise voltage measurement based on microelectromechanical systems (MEMS) is introduced and experimentally demonstrated. The method is based on parametric conversion of voltage via electromechanical force to the amplitude of the RF signal of the capacitive measurement circuit that detects the displacement of a moving-plate MEMS capacitor. Both theory and experiments show that the noise of voltage measurement can be considerably decreased by biasing the MEMS device near its pull-in point. Experimental results are in agreement with theoretical predictions and they indicate the potential of the method as a competitor of state-of-the-art low-noise voltmeters in special applications.

We show that electromechanical feedback in MEMS sensors can be used to eliminate the noise of the readout electronics near the pull-in point, at which the force-to-displacement gain of the system becomes infinite. Displacement bias through electrical feedback instead of voltage bias allows stable operation up to and above the pull-in point. Experimentally, the electronics contribution to system resolution was suppressed by an order of magnitude, reaching the intrinsic resolution of the MEMS microphone. The technique allows the use of standard integrated electronics with noise-critical MEMS sensors, such as microphones, pressure sensors and accelerometers.

At the pull-in point, a capacitive MEMS sensor becomes infinitely sensitive to applied force as the effective spring constant goes to zero because of electromechanical feedback We show that this phenomenon can be used to fully eliminate the noise contribution of readout electronics. Experimentally, we show that the electronics noise and interference contribution to system resolution could be suppressed by an order of magnitude, reaching the intrinsic resolution of the MEMS microphone. Experiments are in good agreement with a theory based on a small signal model of a harmonic MEMS oscillator. The technique allows the use of standard integrated electronics with noise-critical MEMS sensors, such as microphones, pressure sensors and accelerometers.

The electrical properties of random networks of single-wall carbon nanotubes (SWNTs) obtained by inkjet printing are studied. Water-based stable inks of functionalized SWNTs (carboxylic acid, amide, poly(ethylene glycol), and polyaminobenzene sulfonic acid) were prepared and applied to inkjet deposit microscopic patterns of nanotube films on lithographically defined silicon chips with a back-side gate arrangement. Source-drain transfer characteristics and gate-effect measurements confirm the important role of the chemical functional groups in the electrical behavior of carbon nanotube networks. Considerable nonlinear transport in conjunction with a high channel current on/off ratio of approximately 70 was observed with poly(ethylene glycol)-functionalized nanotubes. The positive temperature coefficient of channel resistance shows the nonmetallic behavior of the inkjet-printed films. Other inkjet-printed field-effect transistors using carboxyl-functionalized nanotubes as source, drain, and gate electrodes, poly(ethylene glycol)-functionalized nanotubes as the channel, and poly(ethylene glycol) as the gate dielectric were also tested and characterized.

We developed a simple and direct thermo-compression method for integrating single-walled carbon nanotube (SWCNT) mats of adjustable thicknesses, transparency and conductivity into polymer films. Produced SWCNT/polyethylene composite films have exhibited good optical transparency and conductivity as well as high mechanical flexibility. It was found that the electrical conductivity of the SWCNT mats could be significantly improved by ethanol densification. SWCNT/polyethylene thin films demonstrated excellent cold electron field emission properties.

A superconducting thermal detector (bolometer) of THz (sub-millimeter) wave radiation based on sensing the change in the amplitude or phase of a resonator circuit, consisting of a capacitor (Csh) and a superconducting temperature dependent inductor where the said inductor is thermally isolated from the heat bath (chip substrate) by micro-suspensions. The bolometer design includes a thin film inductor located on the membrane, a single or/and multi-layered thin film capacitor, and a thin film absorber of incoming radiation. The bolometer design can also include a lithographic antenna with antenna termination and/or a back reflector beneath the membrane for optimal wavelength detection by the resonance circuit. The superconducting thermal detector (bolometer) and arrays of these detectors operate in a temperature range from 1 Kelvin to 10 Kelvin.Patent family as of 22.10.2021EP2965054 A1 20160113 EP20140719807 20140304US10145743 BB 20181204 US20140773359 20140304 US2016018267 AA 20160121 US20140773359 20140304 WO14135749 A1 20140912 WO2014FI50158 20140304Link to current patent family on right

Transparent and conductive patterns of carboxyl functionalized single-walled carbon nanotubes (SWCNT-COOHs) and the composites of those with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) were deposited on various substrates by inkjet printing. For low print repetitions, the PEDOT-PSS/SWCNT-COOH composite patterns show enhanced conductance as compared to the corresponding PEDOT-PSS conductors. The results suggest a decreased percolation threshold for the printed composite since the nanotubes establish electrical interconnections between the separate PEDOT-PSS (conductive phase) islands being dispersed in the insulating PSS-phase. However, the interaction between PEDOT-PSS and SWCNTs becomes insignificant and the conductivity is not enhanced by the nanotubes, when the amount of PEDOT-PSS is sufficient to form a continuous conducting phase. Up to now, patterns having sheet resistivities as low as ∼1 kΩ/□ could be achieved. Though there is a trade-off between transparency and conductivity – we achieved highly transparent patterns (∼90%) with a reasonably low resistivity of ∼10 kΩ/□. The ink and printing method proposed here offer new alternatives of conventional transparent conductive materials based on either polymers or indium oxides; and pose scaleable production of cost-effective transparent electronics. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have built a room temperature amplifier based on Si JFETs (junction field effect transistors) intended for ac-coupled SQUID (superconducting quantum interference device) readouts, such as in frequency-domain multiplexed transition-edge sensor systems. The amplifier operates at 5M Hzcentre frequency where it has the measured noise temperature of 27 K for a 60 � load, which includes the noise from the active termination and the room temperature transformer. When it was driven from a SQUID with an on-chip matching transformer, flux noise of 0.45 µ� 0 Hz −1/2 was obtained. Additionally, w ec onsider the potential o ft he recently introduced SiGe bipolar transistors for the same application. The dynamic range considerations for SQUID multiplexers, which require the use of an amplifier with a low noise temperature, are briefly discussed. (Some figures in this article are in colour only in the electronic version)

We have developed a simple room-temperature readout for superconducting bolometers and calorimeters. Due to electro-thermal feedback, the bolometer can be noise-matched with the readout amplifier. The constructed amplifier consists of low-noise field-effect transistors, and voltage bias is actively provided by electrical feedback. According to our measurements on superconducting vacuum-bridge bolometers, the total noise is limited by the bolometer phonon and Johnson noise characterized by a critical temperature of 8.5 K. We show that, with proper sensor design, it is possible to reach the photon noise limit in video-rate submillimetre imaging applications.

An AC voltage standard is being developed based on phase sensitive detection of the amplitude of the fundamental frequency component of the output of a programmable Josephson voltage array. The setup is described and requirements for relative uncertainties less than 10/sup -7/ at 1 kHz and 1 V are discussed. According to preliminary experiments, the constructed current bias is able to drive the array from -1 to +1 V within less than 100 ns.

Radiometric sub-millimeter imaging is a candidate technology especially in security screening applications utilizing the property of radiation in the band of 0.2 - 1.0 THz to penetrate through dielectric substances such as clothing. The challenge of the passive technology is the fact that the irradiance corresponding to the blackbody radiation is very weak in this spectral band: about two orders of magnitude below that of the infrared band. Therefore the role of the detector technology is of ultimate importance to achieve sufficient sensitivity. In this paper we present results related to our technology relying on superconducting kinetic inductance detectors operating in a thermal (bolometric) mode. The detector technology is motivated by the fact that it is naturally suitable for scalable multiplexed readout systems, and operates with relatively simple cryogenics. We will review the basic concepts of the detectors, and provide experimental figures of merit. Furthermore, we will discuss the issues related to the scale-up of our detector technology into large 2D focal plane arrays.

The role of coherence played in several phenomena in the gamma energy region has not been well recognised until recently. The Mossbauer source nuclei are noncorrelated, but the absorber response has a well-defined phase relation to the instantaneous source radiation within the relaxation time of the nuclear system. By rapidly changing this phase relation with mechanical displacement, new types of coherent transients in gamma regime have been observed. The gamma echo, replicating and amplifying the enchained decay through a thick sample, is perhaps the best known example of these phenomena. In addition, a simple gamma-ray interferometer based on rapid transit through the resonance has been demonstrated. Fast and intense gamma pulses have been obtained with stepwise phase modulation. These and the gamma-NMR double resonance experiments are reviewed in this paper.

We have developed a Nb/Al/AlO‡/Nb trilayer process aimed towards integration of RSFQ and qubit circuits. The emphasis is to provide a process enabling RSFQ operation at sub-100 mK temperatures required for qubit operation. In this paper we describe the main properties of the process. We also present experimental characterization data and in particular introduce a method of determining the critical current density by wafer level room temperature measurements.

This paper describes our work with two applications of microelectromechanical systems (MEMS): a sensitive voltmeter that can be used e.g. as a null detector, and a stand-alone AC voltage reference. Both applications are based on the pull-in effect in a moving-plate capacitor.

We introduce a microwave submillimeter-wave detector based on an integrated micromesh absorber and superconducting kinetic inductance thermometer on a through-wafer released sub-micron thick membrane. Equilibrium operation achieved by thermal isolation through the membrane geometry enables operation at elevated thermal bath temperatures of 5–10 K. The bolometer operates in a phonon-noise limited regime with a measured noise equivalent temperature difference of below 10 mK at 1 s integration time, which is sufficient for radiometric imaging in terrestrial systems. We also measured and analyzed the bolometer frequency response in the band 0.1–1.4 THz. Performance improvements through further dimensional scale-down and temperature dependency are discussed.

We present characterization of a null detector designed for an experiment aimed to close the quantum metrological triangle (QMT). The device is a SQUID amplifier equipped with a large winding-ratio planar input transformer improving the current resolution. We demonstrate equivalent input current noise down to 14 fA/Hz1/2 . Furthermore, operation in a realistic environment of a dry dilution refrigerator hosting the QMT experiment is studied. We discuss particular challenges set by such system as the cryogenics introduces relatively large magnetic interference. We present data from measurements simulating the final QMT experiment and introduce the requirements for the averaging and bias reversal.

Implementation of high resolution passive THz cameras operated at cryogenic temperatures of a few Kelvin benefits from a large number of pixels. At present, building a cryogenic multiplexed read-out circuit represents a challenging task. Here we propose and demonstrate broadband niobium-based tunnel junction bolometers operating in equilibrium regime at 4 K, and read out with a room temperature amplifier with feedback. The implemented scheme allows independent impedance matching for the THz antenna and for the readout. Electrical feedback in the readout scheme eliminates the need for magnetic fields to suppress the supercurrent of the junction. We present electrical and preliminary optical measurements of the detectors. We also analyze a possible scheme for time-domain multiplexing.

Contactless read-out of inkjet printed programmable memory is demonstrated. The memory is arranged as a conducting comb pattern consisting of parallel lines adjacent to a common electrode. The information content of the memory is stored in memory bits, which modulate the electrical surface-area of the lines. The data is read-out capacitively by sweeping the tip of a printed circuit board over the memory. The memory bits were printed using silver nanoparticle ink and switched from an initial, high-resistance state to a low-resistance state using rapid electrical sintering, and furthermore, from the low-resistance state to an open-circuit state via fuse-like action. This read-out approach offers potential for low-cost memory applications as well as e.g. resistance-change sensors.

Classical phase-modulation theory is applied to describe the interference of the recoil-free gamma-radiaton fields emitted by a M\"ossbauer source and a resonant absorber in forward-scattering geometry. During the exponential decay of the excited state in the source the resonant absorber develops and emits a coherent field, which interferes destructively with the source field. A stepwise phase change of the source field relative to the absorber field is introduced by a fast mechanical displacement of the source. As a result, an intense pulse of gamma rays is observed in the time dependence of the resonantly filtered radiation. This coherent transient phenomenon is called a gamma echo. The time reference of the gamma-echo experiment is the moment of formation of the excited state in the source. This is in contrast to earlier transient M\"ossbauer experiments in which the measurements were synchronized to the phase of the modulation and averaging occurred over all possible times of formation of the excited state. By choosing a suitable shape for the phase-modulation function in the echo experiment, short pulses of gamma radiation with desired duration and amplitude can be generated within a time frame defined by the lifetime of the excited nuclear state. Here, a detailed description of the experimental and theoretical aspects of stepwise phase modulation in a coincidence scheme is given. Theoretical results are presented in a general form, taking into account the experimental nonidealities. The properties of the mechanical drive system are discussed in detail. Gamma-echo data are presented. Good agreement between the theoretical calculations and the experimental data has been established.

Scaling down the dimensions of thermoacoustic sound sources (thermophones) improves efficiency by means of reducing speaker heat capacity. Recent experiments with nanoscale thermophones have revealed properties which are not fully understood theoretically. We develop a Green’s function formalism which quantitatively explains some observed discrepancies, e.g., the effect of a heat-absorbing substrate in the proximity of the sound source. We also find a generic ultimate limit for thermophone efficiency. We verify the theory with experiments and finite difference method simulations which deal with thermoacoustically operated suspended arrays of nanowires. The efficiency of our devices is measured to be 1 order of magnitude below the ultimate bound. At low frequencies this mainly results from the presence of a substrate. At high frequencies, on the other hand, the efficiency is limited by the heat capacity of the nanowires. Measured sound pressure level and efficiency are in good agreement with simulations. We discuss the feasibility of reaching the ultimate limit in practice.

At present, the imaging of concealed weapons and contraband is primarily carried out at a relatively short stand-off range of a few meters mainly because of spatial resolution considerations. In order to maintain a reasonable aperture size, there is a desire to extend the operating frequency towards 1 THz. In this paper we report the progress on a video-rate THz camera demonstrator which utilizes broadband antenna-coupled microbolometers as detectors, operated within a turnkey commercial closed-cycle cryocooler. A full system has been integrated consisting of 64 parallel sensors and readout electronics, and reflective Schmidt camera optics incorporating a conical scanner for real time imaging.

We demonstrate that a suspended metal wire array can be used to produce high-pressure sound waves over a wide spectrum using the thermoacoustic effect. We fabricated air-bridge arrays containing up to 2×105 wires covering an area of a few square centimeters. The supporting silicon wafer was isotropically plasma etched to release the wires thereby avoiding heat contact with the substrate. Sound pressure levels reaching 110 dB at a distance of 8 cm were demonstrated near 40 kHz in free field. The devices are also able to reproduce music and speech. They have potential for applications especially in the ultrasound range.

Over the past several years, many groups have developed both millimeter-wave as well as terahertz imaging systems for concealed weapons detection. Typically, systems operating at the millimetre-wave range benefit from good transmission of these frequencies through common clothing materials, but provide only modest spatial resolving power at distances larger than a few meters for practical aperture sizes (dap < 1 m). Hence, these existing systems fall in the category of anomaly detectors, i.e. they intrinsically lack the performance to discriminate threat items from innocuous objects, such as cell phones, mp3 players and the like. Moreover, the radiometric performance of a passive imager has to be better than 0.5 K per frame for sufficient signal-to-noise ratio. In this joint Euro-American effort, we are developing a passive ~0.3 THz - 1 THz camera demonstrator capable of sub-Kelvin thermal resolution at video frame rates. The cryogen-free system utilizes a linear array of cryogenic antenna-coupled vacuum-bridge microbolometers, coupled to innovative all-reflective conical scanning optics and room temperature read-out electronics. First imaging results from the video rate system will be presented.

We present the fabrication and characterization of logic elements (transistors and interconnects) built using our recently developed inkjet-printer-controlled deposition of single-wall carbon nanotube network films. The method requires no preselection of ``metallic'' or ``semiconducting'' nanotubes. By selecting the number of prints on a specified region, it is possible to have low-density, nonlinear, gate-voltage controllable transistors or high-density, linear, high-current-throughput metallic interconnects without any gate-voltage response. Intermediate steps drive the films between the nonlinear and linear regimes with precise controllability. The transport mechanism in these films as a function of bias, gate voltage, and temperature dependence have been investigated and analyzed using junction properties of metal-semiconductors in the context of networks of carbon nanotubes.

We propose a mesoscopic kinetic-inductance radiation detector based on a long superconductor--normal metal--superconductor Josephson junction. The operation of this proximity Josephson sensor (PJS) relies on large kinetic inductance variations under irradiation due to the exponential temperature dependence of the critical current. Coupled with a dc SQUID readout, the PJS is able to provide a signal to noise (S/N) ratio up to ~10^3 in the THz regime if operated as calorimeter, while electrical noise equivalent power (NEP) as low as ~7x10^{-20} W(Hz)^(-1/2) at 200 mK can be achieved in the bolometer operation. The high performance together with the ease of fabrication make this structure attractive as an ultrasensitive cryogenic detector of THz electromagnetic radiation., 4 pages, 3 figures

In this paper, plans and progress of a Finnish collaboration towards direct closure of the quantum metro- logical triangle are presented. The experimental concept and the present status of the main components, including two possibilities of the single charge transport device, Bloch oscillating transistor (BOT) based null detector, and a thin-film cryoresistor, are described.

Ink jet printing has matured to a state where it can be used easily and precisely to print soluble electronic materials in order to produce complete circuits. Here we will show results of printed electronic components and a rectifier circuit intended be used in low-cost RFID tags. Commercial materials and a commercial research ink jet printer were used. Materials were deposited on pre-patterned aluminium electrodes. As the dielectric, poly-vinylphenol (PVPh) with poly-(melamine-co-formaldehyde) PMF cross linker was chosen. P3HT was used as the semiconductor, and finally PEDOT:PSS and ANP silver ink were used as top electrodes and wiring. Resulting capacitors and Schottky diodes were measured and an APLAC simulation model was constructed. There are trap states in forbidden gap of the semiconductor in the organic Schottky diode. Measurement result of frequency dependence of capacitance shows that different trap states induce different time constants. In the APLAC simulation, we used 8 diodes parallel which had different time constants to simulate the influence of the trap states. The results of the currentvoltage and capacitance-frequency simulations show that our model fits the measurement data well. We will use this model as functional component in our rectifier circuit simulation. The antenna circuit and load will be tuned according to simulation results. The measurement and simulation results for the whole circuit will be presented.

We present ultrawideband imagery obtained with modular, 8-element, superconducting Nb microbolometer arrays. Conically scanned images are presented and compared with raster-scanned images obtained on the same arrays and from similar NbN arrays at VTT. Statistical data on detector non-uniformity, and methods for mitigating and compensating it are described. Low-noise readout is accomplished with room-temperature electronics using the transimpedance scheme of Pentilla et al. Characterization of spatial resolution, noise-equivalent temperature difference, and spectral response is done using metrology tools - standard targets, mm-wave blackbodies, and variable filters - that have been developed at NIST for this purpose.

Passive imaging of concealed objects at stand-off distances in excess of a few meters requires both excellent spatial, thermal and temporal resolution from the terahertz imaging system. The combination of these requirements while keeping the overall system cost at a reasonable level has been the motivation for this joint work. The THz imaging system under development is capable of sub-Kelvin NETD at video frame rates. In this paper we report the first imaging results from a 16-pixel array of superconducting antenna-coupled NbN vacuum-bridge microbolometers, operated within a cryogen-free, turn-key refrigerator. In addition to the system overview, we shall also address the uniformity of the detectors and present passive indoors raster-scanned imagery.

The objective of this program is to demonstrate a system capable of passive indoors detection and identification of concealed threat items hidden underneath the clothing of non-cooperative subjects from a stand-off distance of several meters. To meet this difficult task, we are constructing an imaging system utilising superconducting ultrawideband antenna-coupled microbolometers, coupled to innovative room temperature read-out electronics, and operated within a cryogen-free pulse tube refrigerator. Previously, we have demonstrated that these devices are capable of a Noise Equivalent Temperature Difference (NETD) of 125 mK over a pre-detection bandwidth from 0.2-1 THz using a post-detection integration time of 30 ms. Further improvements on our devices are reducing this number to a few tens of mK. Such an exquisite sensitivity is necessary in order to achieve the undoubtedly stringent requirements for low false positive alarm rate combined with high probability of detection dictated by the application. Our technological approach allows for excellent per frame NETD (objective 0.5 K or below at 30 Hz frame rate), and is also amenable to multispectral (colour) imagery that enhances the discrimination of innocuous objects against real threats. In the paper we present results obtained with an 8-pixel subarray from our linear array of 128 pixels constructed using a modular approach. Two-dimensional imaging will be achieved by the use of conical scanning.

It has been suggested that rapid single flux quantum (RSFQ) devices could be used as the classical interface of superconducting qubit systems. One problem is that the interface acts as a dissipative environment for a qubit. Recently, ways to modify the RSFQ damping to reduce the dissipation have been introduced. One of the solutions is to damp the Josephson junctions by a frequency-dependent linear circuit instead of the plain resistor. The approach has previously been experimentally tested with a simple SFQ comparator. In this paper we perform experiments with a full RSFQ circuit, and thus conclude that in terms of stable operation the approach is applicable to scalable RSFQ circuits. Realization and optimization issues are also discussed.

Josephson arrays are suitable for applications involving mm waves. Realizations of such systems typically involve structures that are large compared to the wavelength. Though many such systems are well established, there has been a shortage of generic modeling techniques, which would be simple enough for practical engineering, while quantitative. In this paper we apply the model we have recently developed to some device examples. We calculate the available output power of an array of unshunted SIS junctions. We also discuss the impact of power generation effects in Josephson voltage standards. We also extend the model to include partial synchronization. The analytic results are compared to simulated and experimental data.

Trabajo presentado como comunicación a la Conferencia "Space Telescopes and Instrumentation 2008: Ultraviolet to Gamma Ray" celebrada en Francia el 23 de Junio del 2008., The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 x 5 pixel array of TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing (FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogenfree cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs, fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital electronics, etc. Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray energy resolution of 1.58 eV at 250 eV and 2.5 eV @ 5.9 keV for the read-out of one TES-pixel only. Next step is deployment of FDM to read-out the full array. Full performance demonstration is expected mid 2009., The authors acknowledge an ESA Technological Research Program contract for the development of TES-arrays and SQUIDs, being a significant support to the EURECA program. Also the recent ESA TRP contract for the development of SQUID-based electronics is of crucial importance for this work.

In the recent years, millimetre wave and THz imaging have received a vast amount of interest due to the interesting possibilities and applications that imaging at these frequencies could enable. Many of the applications that have generated substantial interest (such as stand-off concealed weapons detection) often require exquisite sensitivity, while a low system cost is required. In this paper we discuss one potential candidate for affordable imaging arrays: an antenna-coupled superconducting microbolometer. We show that these devices possess capabilities that are hard to meet with other passive detection schemes. While refrigeration to cryogenic temperatures is required for maximum performance, we show that the devices can be operated within a cryogen-free refrigerator that allows for turn-key operation. Comparison with other detectors is presented.

The temperature resolving power (NETD) of millimeter wave imagers based on InP HEMT MMIC radiometers is typically about 1 K (30 ms), but the MMIC technology is limited to operating frequencies below ~ 150 GHz. In this paper we report the first results from a pixel developed for an eight pixel sub-array of superconducting antenna-coupled microbolometers, a first step towards a real-time imaging system, with frequency coverage of 0.2 - 3.6 THz. These detectors have demonstrated video-rate NETDs in the millikelvin range, close to the fundamental photon noise limit, when operated at a bath temperature of ~ 4K. The detectors will be operated within a turn-key cryogen-free pulse tube refrigerator, which allows for continuous operation without the need for liquid cryogens. The outstanding frequency agility of bolometric detectors allows for multi-frequency imaging, which greatly enhances the discrimination of e.g. explosives against innoncuous items concealed underneath clothing.

EURECA (EURopEan Calorimeter Array) is a European-Japanese project that aims to demonstrate technical readiness for a Transition-Edge-Sensor based X-ray imaging spectrometer on ESA's XEUS observatory. EURECA comprises a 5 x 5 pixel TES micro-calorimeter array with an energy resolution aim of 1 - 2 eV for the 0.1 - 3 keV energy range. The small array will be read out by four SQUID channels using frequency domain multiplexing (FDM).

A design of subkelvin single flux quantum (SFQ) circuits with reduced power dissipation and additional cooling of shunt resistors for superconducting qubit control circuits has been developed and characterized. We demonstrate operation of SFQ comparators with current resolution of 40 nA at 2 GHz sampling rate. Due to improved cooling the electron temperature in shunt resistors of a SFQ comparator is below 50 mK when the bath temperature is about 30 mK., Comment: 4 pages, 3 figures

Power generation and synchronization in Josephson junction arrays have attracted attention for a long time stemming both from fundamental interest and from application potential. The authors study the array of junctions coupled to a distributed transmission line either driven by an external microwave signal or in a self-oscillating mode. The authors simplify the theoretical treatment in terms of harmonic analysis and power balance. The model explains large operation margins of superconductor-normal-superconductor and superconductor-insulator-normal-insulator-superconductor junction arrays. The authors also compare theory, experiments, and simulations of self-oscillating externally shunted superconductor-insulator-superconductor junction arrays.

A quantum-based ac voltage standard operating from about 1 Hz up to 10 kHz at 1 V is being developed. The standard is based on relating the output of a stable sine generator to a square wave obtained by biasing a nonhysteretic Josephson junction array alternately at steps n = -2 and n = +2. We have constructed a bias current source and a buffer amplifier connected to the array which enable fast switching between steps. In this paper, we describe the system used for generation of the square wave and present experimental results which show that the accuracy of the fundamental frequency component amplitude of the square wave is sufficient for realization of a standard with accuracy better than 1 /spl times/ 10/sup -6/.

We introduce an optimized Josephson double array generating two independent voltages up to 1.5V using only one microwave input. Such an array, combined with the quantum Hall resistance, can provide the basic traceability for an electricity metrology laboratory from DC voltage to capacitance. We describe the array and present preliminary experimental results from DC measurements. Extending the output voltage up to 10V is discussed

The Bloch oscillating transistor is a new mesoscopic current amplifier with estimated white current noise below 1 fA/Hz 1/2 and potentially low 1/f noise. The operation principle and recent results of the BOT are presented and its potential in closing the quantum metrology triangle is analysed

An AC-voltage standard operating at 1 V level at 1 kHz based on nonhysteretic Josephson junction arrays (JJA) is under development. The electronics connected to the array is now sufficiently fast and noiseless when aiming at a 1-ppm accuracy. Some preliminary results and the current setup and status are reported

We have studied the possibility of realizing AC voltages with metrological accuracy. In this paper we propose two experimental setups for generating accurate sinusoidal voltage waveforms from square-wave biased nonhysteretic programmable Josephson array voltage standards.

A new construction principle of AC current shunts has been applied to a set of shunts for AC currents from 1 A to 20 A, 20 Hz-10 kHz. The completed set will also cover current ranges from 20 mA to 1 A. The shunts are stable and do not show excessive AC-DC amplitude or phase differences and can thus be calibrated to work as AC current and resistance reference standards up to 10 kHz.