A Superconducting Bolometer Antenna-Coupled to Terahertz Waves

The electrical performances and the optical response of a superconducting hotspot air-bridge bolometer (SHAB) coupled through a planar antenna to Terahertz waves and operating in vacuum at about 4.2 K, have been measured. The SHAB consists of a narrow Nb air bridge, voltage biased to form, in the middle of the suspended Nb stripe, a resistive hotspot, whose volume is modulated by the incoming radiation. The signal resulting from the coupled optical power and the device noise performance have been measured by using a home made transimpedance amplifier operating at room temperature, resulting in an electrical NEP of about 40 fW/Hz^1/2. Passive detection of the 300 K blackbody radiation at frequency lower than 1.6 THz, band limited by a low-pass optical filters, has been successfully carried out by using a SHAB.     

Norton-Corrected Measurement of Complex Impedances of a Large Format Bolometer Array

We report on our efforts to measure simultaneously a well-calibrated complex impedance of a large number of detectors in a long wavelength bolometer array. The array is described in other presentations. A method for correcting the complex impedance measurements of bolometers and calorimeters has been presented by Lindeman et al. (Rev. Sci. Instrum. 78:043105, [2007]) using a Thévenin equivalent circuit to represent the bias network. We have built on this method for superconducting bolometers with a Norton equivalent circuit and have used it to improve our impedance data. We further describe our method for extracting a Norton-corrected complex impedance as a function of frequency from a stream of multiplexed time-ordered data. This method is well-suited to producing simultaneous complex impedance measurements for a large number of detectors.      

GISMO, a 2 mm Bolometer Camera Optimized for the Study of High Redshift Galaxies

The 2 mm spectral range provides a unique terrestrial window enabling ground based observations of the earliest active dusty galaxies in the universe and thereby allowing a better constraint on the star formation rate in these objects. We have built GISMO (the Goddard-IRAM Superconducting 2-Millimeter Observer), a 2 mm, 128 element superconducting Transition Edge Sensor (TES) based bolometer camera for the IRAM 30 m telescope in Spain. The camera uses an 8×16 planar array of multiplexed TES bolometers, which incorporates our recently designed Backshort Under Grid (BUG) architecture, described elsewhere. The optical design incorporates a 100 mm (4 inches) diameter silicon lens cooled to 4 K, which provides the required fast beam of 0.9 λ/D. With this spatial sampling, GISMO will be very efficient at detecting sources serendipitously in large sky surveys, while the capability for diffraction-limited observations is preserved. With the background limited performance of the detectors, the camera provides significantly greater imaging sensitivity and mapping speed at this wavelength than has previously been possible. The major scientific driver for the instrument is to provide the IRAM 30 m telescope with the capability to rapidly observe galactic and extragalactic dust emission, in particular from high-z Ultra Luminous Infrared Galaxies (ULIRGs) and quasars, even in the summer season. The instrument will fill in the SEDs of high redshift galaxies at the Rayleigh-Jeans part of the dust emission spectrum, even at the highest redshifts. Our source count models predict that GISMO will serendipitously detect one galaxy every four hours on the blank sky, and that one quarter of these galaxies will be at a redshift of z 6.5. We expect to install GISMO at the 30 m telescope in the second half of 2007.      

Electrical and Thermal Characterization of Membrane-Isolated, Antenna-Coupled, TES Bolometers for the SPIDER Experiment

We have fabricated and measured the thermal and DC electrical properties of transition-edge sensing (TES) bolometers to be employed on the SPIDER experiment, a balloon-based observatory for studying the polarization of the cosmic microwave background (CMB). The bolometers consist of Al and Ti thermistors in series and a termination resistor which couples to an on-chip, polarization sensitive, 150 GHz slot-array antenna through a superconducting microstrip transmission line. Several important parameters were measured. Transition temperature measurements were performed by measuring the Johnson noise in the Ti thermistor. Current-voltage characteristic measurements were performed at various temperatures allowing for the deduction of the thermal conductance and the temperature coefficient of resistance. Electrical noise equivalent power was measured to sub-Hertz frequencies. Finally, the time constant of the bolometers was measured within the Al and Ti transitions where electrothermal feedback speeds up the bolometer response compared with the natural time constant measured just above the Ti transition temperature. The results of these measurements are within the design specifications for SPIDER.      

Very Low Noise Multiplexing with SQUIDs and SiGe Heterojunction Bipolar Transistors for Readout of Large Superconducting Bolometer Arrays

This paper presents an ultra low noise instrumentation based on a standard BiCMOS SiGe 0.35 μm ASIC operating at cryogenic temperatures. The main functions of the electronic circuit are the readout and the multiplexing of SQUIDs/TES. We report the cryogenic operation of the ASIC dedicated to the readout of a 2×4 pixel demonstrator array. We particularly emphasize on the development and the test phases of an ultra low noise ( ) cryogenic amplifier designed with two multiplexed inputs. The cryogenic SiGe amplifier coupled to a SQUID in a FLL operating at 4.2 K is also presented.     

Performance Measurement of the 8-Input SQUIDs for TES Frequency Domain Multiplexing

We report on performance of 8-input superconducting quantum interference devices (SQUIDs) for multiplexing transition-edge sensor signals by using frequency-domain multiplexing. We found the typical critical current and the flux noise to be 17–19 μA and 0.7–1.1 μ , respectively. We also measured the crosstalk current between the input coils of the SQUIDs, and found that the mutual inductance was consistent with the design value, 800 pH. We confirmed that the cross talk current due to the mutual inductance was reduced by the flux-locked-loop (FLL) feedback, and its reduction rate was consistent with 1/(1+ℒ), where ℒ is the FLL feedback gain. We also show the result of 2-channel DC-driven TES signals readout using the 8-input SQUIDs.      

Development of a Digital Signal Readout System for Large TES Arrays

We are developing a digital signal readout system for arrays of high-resolution gamma and fast-neutron detectors based on superconducting transition edge sensors (TESs). The readout system allows for real time data acquisition and analysis at count rates exceeding 100 Hz for pulses with several ∼ms decay times with minimal loss of energy resolution compared to optimum filtering. This digital signal processing system had originally been developed for gamma-ray analysis with HPGe detectors, and we have modified the hardware and firmware to accommodate the slower TES signals. Parameters of the filtering algorithm have been optimized to maximize either resolution or throughput. Here we present a summary of the digital signal processing hardware and discuss its initial performance.      

Heat Capacity Setup for Superconducting Bolometer Absorbers below 400 mK

A calorimeter set up with very low heat capacity ( $\sim $ 20 nJ/K at 100 mK) has been designed using commercial Carbon based resistors. This calorimeter is used to determine the heat capacity of small samples of superconducting bolometer absorbers. In particular, we present heat capacity studies of Tin, a bolometer candidate for Neutrinoless Double Beta Decay in $^{124}$ Sn, in the temperature range of 60–400 mK.     

Design of the Cryogen-Free Cryogenic System for the CUORE Experiment

We present here the final design of the cryogenic system where the CUORE detector will be installed in 2010. It is a large cryogen-free cryostat cooled by pulse tubes and by a high-power dilution refrigerator. To avoid radioactive background, about 15000 kg of lead will be cooled to below 1 K and only few construction materials are acceptable. The detector assembly will have a total mass of about 1500 kg and must be cooled to less than 10 mK in a vibration-free environment. We discuss the adopted technical solutions, the results of the preliminary thermal analysis of the system, and its expected performance.      

On the Role of Polarization of Oxygen Ions and Mechanism of Superconductivity in Cuprate Superconductors

A new approach to the valence electron state in cuprate superconductors leading to a new mechanism of high-temperature superconductivity is considered. The approach takes into account specific features of the outer electron shells of the compound-forming elements and polarization of anions by cations. The polarization of anions by copper cations results in sharing of a valence electron by every two neighboring ions, which gives rise to a highly correlated state of the valence electrons and formation of a localized spin-ordered electron lattice responsible for dielectric and magnetic properties of an undoped material. It is also shown that asymmetric polarization of an anion by cations with inert gas shells transforms an unshared anion electron pair into a superconducting one by exciting it into a hybrid state. The superconducting state of the material itself results from formation and delocalization of one-dimensional Wigner crystals of the excited pairs.     

Design and Fabrication Highlights Enabling a 2 mm, 128 Element Bolometer Array for GISMO

The Backshort-Under-Grid (BUG) superconducting bolometer array architecture is intended to be highly versatile, operating over a large range of wavelengths and background conditions. To validate the basic array design and to demonstrate its applicability for future kilopixel arrays, we will demonstrate a 128-element bolometer array optimized for 2 mm wavelength using a new Goddard Space Flight Center instrument, GISMO (Goddard IRAM Superconducting 2-Millimeter Observer). The design considerations unique to GISMO and laboratory experimental results will be discussed.      

Direct Measurement of the Critical Velocity Above Which a Tuning Fork Generates Turbulence in Superfluid Helium

The dynamics of an electrically-driven 8 kHz quartz tuning fork has been studied experimentally in liquid helium-4 in the temperature range 1.3<T<4.2 K under the saturated vapour pressure. The fork has relatively large dimensions compared to standard 32 kHz fork used in recent investigations. The velocity of the tip of the fork prong is measured by the indirect electromechanical equivalent method and is compared with the velocity of another 8 kHz fork (from the same batch) determined by direct optical measurement of the oscillation amplitude through Michelson interferometry. A comparison of these results has provided absolute values for the critical velocity of the transition to the turbulent state.     

Materials Development for Auxiliary Components for Large Compact Mo/Au TES Arrays

Pursuing the feasibility of scaling conventionally-micromachined transition-edge-sensor (TES) arrays, we have undertaken a study of materials suitable for array integration. A potential limitation of increased pixel count is adequate heatsinking of each detector element to its base temperature. We describe technical approaches for heat sinking large compact TES microcalorimeter arrays and calculate the achievable heatsinking based on measured material parameters. Techniques include backside-deposited thick film copper on arrays with deep-etched wells in the substrates and electroplated gold and copper-filled micro-trenches on the substrate surface. Another limitation is the sensitivity of the thin film circuit elements to applied stress, which can arise in fabrication and mounting of arrays of increasing size. We have explored stress and deposition temperature sensitivity in our molybdenum-based bilayers. Such process parameters can impact options for array heat sinking and electrical interconnects.      

Empirical likelihood confidence intervals for the endpoint of a distribution function

Estimating the endpoint of a distribution function is of interest in product analysis and predicting the maximum lifetime of an item. In this paper, we propose an empirical likelihood method to construct a confidence interval for the endpoint. A simulation study shows the proposed confidence interval has better coverage accuracy than the normal approximation method, and bootstrap calibration improves the accuracy.     

Measurement of the detection efficiency of microchannel plates for 1–15 keV electrons

Measurements of the detection efficiency (ϵ) of microchannel plates (MCP) for electrons with energies between 1 and 15 keV and input angles between 0° and 60° are reported. In addition, saturation effects at intensities up to 4.5 electrons/channel per second and the efficiency increase by a collecting field at the MCP surface are considered.     

Effect of Boron Substitution for Bi on Superconductivity of the Bi-2212 Phase in the Bi-Sr-Ca-Cu-O System

Possibility of boron substitution for Bi and the substitution effect on superconductivity is investigated for the Bi-2212 phase of Bi-Sr-Ca-Cu-O. From X-ray diffraction study, it is found that samples in the (Bi_2?x B _x )Sr₂CaCu₂O _z system are mainly of the single 2212 phase in a composition range of 0.0≤x≤0.6, and both of the lattice parameters a and c change with increasing x up to 0.6. From measurements of the magnetic susceptibility and the electrical resistivity, the superconducting transition temperature is found to increase up to 0.6 with increasing x. These results are considered to show that boron is substitutable for Bi up to x=0.6 in the (Bi_2?x B _x )Sr₂CaCu₂O _z system and that the boron substitution causes the number of hole-carriers to decrease in this system.     

Measurement and Estimation of High-Vacuum Effective Thermal Conductivity of Polyimide Foam in the Temperature Range from 160 K to 370 K for Outer Space Applications

Polyimide foam (PF) is a low-thermal conductivity and lightweight material with high resistances against heat, protons, and UV irradiation. A new thermal insulation composed of PFs and multiple aluminized films (PF–MLI) has potential to be used in outer space as an alternative to conventional multilayer insulation (MLI). As fundamental numerical data, the effective thermal conductivity of PF in wide ranges of density and temperature need to be determined. In the present study, thermal-conductivity measurements were performed by both the periodic heating method and the guarded hot-plate method in the temperature range from 160 K to 370 K and the density range from 6.67  \(\mathrm{kg} \cdot \mathrm{m}^{-3}\) to 242.63  \(\mathrm{kg}\cdot \mathrm{m}^{-3}\) . The experiments were carried out in a vacuum and under atmospheric pressure. For confirmation of the validity of the present guarded hot-plate apparatus under atmospheric pressure, the effective thermal conductivity of the lowest-density PF was measured with the aid of the heat flow meter apparatus calibrated by the standard reference material (NIST SRM 1450c) in the temperature range from 303 K to 323 K. In order to cross-check the present experimental results, the temperature and density dependences of the effective thermal conductivity of PF were estimated by means of the lattice Boltzmann method based on a dodecahedron inner microscopic complex structure model which reflects a real 3D X-ray CT image of PF.     

Calibration System with Modulated Polarization Source for Superconducting Detectors at 0.1 K

We developed a calibration system with a modulated polarization source for superconducting detectors at the 0.1-K stage in a dilution cooler. Our target application for this system is detector calibration for observations of the cosmic microwave background polarization. For this application, the calibration system is required to generate a well-characterized polarization signal in a wide frequency range; e.g., 20–300 GHz. The calibration system is attached at the bottom of the 0.1-K stage. Radio absorbers, which are attached to the inner wall of a cylindrical metal shield, emit unpolarized black-body radiation (4.5 K). The radiation reflects off an aluminum mirror at 120 K, which induces a linearly polarized component because of the finite emissivity of the mirror; the magnitude of the polarization is 60 mK in this configuration. The axis of polarization can be varied by rotation of the mirror. Therefore, the detectors measure the modulated polarization; however, unpolarized radiation into the detector is maintained constant. We succeeded in cooling the system properly. The sample stage for setting the detector achieved a temperature below 0.1 K under the 5 K load condition (some of the radiation from the absorbers and the mirror emission, 0.5 K). High-frequency components of emission from the mirror are shielded by using two thermal filters: polytetrafluoroethylene and nylon 66.     

Charged nanoparticles as supramolecular surfactants for controlling the growth and stability of microcrystals

Microcrystals of desired sizes are important in a range of processes and materials, including controlled drug release, production of pharmaceutics and food, bio- and photocatalysis, thin-film solar cells and antibacterial fabrics. The growth of microcrystals can be controlled by a variety of agents, such as multivalent ions, charged small molecules, mixed cationic-anionic surfactants, polyelectrolytes and other polymers, micropatterned self-assembled monolayers, proteins and also biological organisms during biomineralization. However, the chief limitation of current approaches is that the growth-modifying agents are typically specific to the crystalizing material. Here, we show that oppositely charged nanoparticles can function as universal surfactants that control the growth and stability of microcrystals of monovalent or multivalent inorganic salts, and of charged organic molecules. We also show that the solubility of the microcrystals can be further tuned by varying the thickness of the nanoparticle surfactant layers and by reinforcing these layers with dithiol crosslinks.     

Enhancement of Sudden Death of Entanglement for Driven Qubits

We study the recently discovered phenomena of sudden death of entanglement for a system of two qubits, each of them independently longitudinally damped by a reservoir and subjected to a continuous driving. We show that driving produces, in the interaction picture, an effective bath that has elements amounting to various extra sources of noise (transverse, thermal squeezed, thermal longitudinal). As a result, the time of sudden death decreases due to driving, which we verify as well by direct numerical calculation. We suggest that this phenomenon can be studied systematically using superconducting qubits driven by microwave fields.