Search

The Center for Axion and Precision Physics Research at the Institute for Basic Science is searching for axion dark matter using ultralow temperature microwave resonators. We report the exclusion of the axion mass range 10.7126–10.7186 μeV with near Kim-Shifman-Vainshtein-Zakharov (KSVZ) coupling sensitivity and the range 10.16–11.37 μeV with about 9 times larger coupling at 90% confidence level. This is the first axion search result in these ranges. It is also the first with a resonator physical temperature of less than 40 mK.

The experimental non-observation of charge-parity (CP) symmetry violation in quantum chromodynamics is commonly referred to as the strong CP problem. The axion, a hypothetical elementary pseudoscalar, is expected to solve the strong CP problem and is also a promising candidate for dark matter. The most sensitive axion search experiments operate at millikelvin temperatures and hence rely on instrumentation that carries signals from a system at cryogenic temperatures to room temperature instrumentation. One of the biggest limiting factors affecting the parameter scanning speed of these detectors is the noise added by the components in the signal detection chain. Since the first amplifier in the chain limits the minimum noise, low-noise amplification is of paramount importance. This paper reports on the operation of a flux-driven Josephson parametric amplifier (JPA) operating at around 2.3 GHz with added noise approaching the quantum limit. The JPA was employed as a first stage amplifier in an experimental setting similar to the ones used in haloscope axion detectors. By operating the JPA at a gain of 19 dB and cascading it with two cryogenic amplifiers operating at 4 K, noise temperatures as low as 120 mK were achieved for the whole signal detection chain.

The paper proposes a method of passive leak detection for underwater pipelines by means of phased antenna arrays. It implies element-wise multiplication and addition of the output signals of individual array transducers. The proposed method provides a twofold increase in the resolution of the detection system in comparison with that obtained by conventional signal processing techniques and a high detection rate. The array pattern has been calculated numerically. The paper presents a version of the inspection system that implements the proposed method of signal processing using a phased antenna array, and the experimental results obtained.

We report results of our development of two types of microwave amplifiers based on Superconducting quantum interference devices (SQUIDs) for CAPP (Center for Axion and Precision Physics Research) axion search experiments. The first amplifier, Microstrip SQUID Amplifier (MSA) has a wide bandwidth. Power dissipation in resistive shunts results in a device overheating and limits the MSA performances. A thermal models of shunt cooling processes is developed and recommendations for a future design is provided. The second amplifier, Josephson Parametric Amplifier (JPA), at limited bandwidth showed a low noise near the standard quantum limit (SQL) of 196 mK. Implementation of a JPA in CULTASK (CAPP's Ultra-Low Temperature Axion Search in Korea) experiment is planned in the end of 2019.

The construction of an axial 8-coil system based on Helmholtz coils is described, which enables a magnetic field with a nonuniformity of not more than 0.1% to be produced at a distance of half the radius from the center of the coil system. The results obtained are confirmed by experimental investigations.

This paper presents the design and simulation of a microelectromechanical gyroscope that simultaneously determines two components of angular velocity. In this device, the silicon sensor is started by an electrostatic actuator to perform a linear harmonic motion at a controlled speed. The movable masses of the sensor move in two directions, orthogonal to the primary vibrations of the sensor under the action of Coriolis forces. This paper considers how temperature influences eigenfrequencies and informative vibrational magnitudes of the micromechanical angular velocity sensor. The parameters that have the greatest impact on the sensor output behavior are determined by a finite-element analysis method. Techniques to stabilize vibration eigenfrequencies of the sensing element are suggested.

The paper presents a new lock-in amplifier with a differential input. The lock-in amplifier has a high common-mode rejection ratio of 200 dB at 1 kHz and 160 dB in the frequency range of 20 Hz to 100 kHz. A method for extending the dynamic range of comparing signals is suggested. The experimental results of metrological characteristic tests are discussed.

The paper describes the design of axial 8-coils system based on Helmholtz coils, which allows to create a magnetic field with inhomogeneity is not more than 0.1% at a distance of half the radius of the geometric center of the coils system. The obtained results are confirmed by experiment.

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present Four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO4 and simultaneous measurement of phonons and scintillation light is in preparation. (C) 2000 Elsevier Science B.V. All rights reserved.

Although it is well known that CaWO4 is a scintillator it is not often used. mainly because it has a slow light response. However, a high Z and a good light output make this crystal a candidate for use in direct dark matter search experiments. The Cryogenic Rare Event Search using Superconducting Thermometers (CRESST II) experiment looks. for hypothetical massive elementary particles called Weakly Interacting Massive Particles (WIMPs). In an elastic collision of WIMPs with ordinary matter a WIMP transfers part of its energy to a nucleus. Such nuclear recoils are the signals dark matter searches look for. CRESST is using CaWO4 crystals with coincident detection of phonons and scintillation light to suppress radioactive background. Light output and energy resolution of different CaWO4 samples were systematically measured. Best samples have an energy resolution at the Cs-137; line (661 keV) < 8%. As CRESST is a rare event search experiment it has to prevent the background caused by natural radioactivity; therefore, a study of the radiopurity of CaWO4 crystals has been performed. X-ray luminescence properties of crystal samples. in the temperature range 77-500 K, will be presented. (C) 2004 Published by Elsevier B.V.

Controllable adiabatic evolution of a multi-qubit system can be used for adiabatic quantum computation (AQC). This evolution ends at a configuration where the Hamiltonian of the system encodes the solution of the problem to be solved. As a first steps towards realization of AQC we have investigated two, three and four flux qubit systems. These systems were characterized by making use of a radio-frequency method. We designed two-qubit systems with coupling energies up to several kelvins. For the three-flux-qubit systems we determined the complete ground-state flux diagram in the three dimensional flux space around the qubits common degeneracy point. We show that the system`s Hamiltonian can be completely reconstructed from our measurements. Our concept for the implementation of AQC, by making use of flux qubits, is discussed., Comment: 6 pages, 7 figures, Applied Superconductivity Conference 2006

The CRESST Phase II experiment at Gran Sasso is using 300 g scintillating CaWO4 crystals as absorbers for direct WIMP (weakly interactive massive particles) detection. The phonon signal in the CaWO4 crystal is registered in coincidence with the light signal, which is measured with a separate cryogenic light detector. The absorber crystal and the silicon light detector are read out by tungsten superconducting phase transition thermometers (W-SPTs). As a result an active discrimination of the electron recoils against nuclear recoils is achieved. Results on the properties of the detector modules and on the WIMP sensitivity are presented. (C) 2005 Published by Elsevier B.V.

CRESST-II detector modules rely on the ability to actively discriminate electron recoils from nuclear recoils via simultaneous measurement of phonons and scintillation light. The scintillation light produced in each target crystal is detected via an associated calorimeter consisting of a thin silicon wafer read out by a tungsten phase transition thermometer deposited on its surface. About 1% of the energy deposited in CaWO4 is detected as scintillation light; therefore, the sensitivity of the light detector is crucial for the discrimination of electron recoils from nuclear recoils at energies relevant for WIMP searches. We report the detector performance obtained using a thermometer geometry characterized by phonon collectors and a thin film thermal coupling to the heat sink (Fig. 1). This concept allows a high sensitivity by decoupling the area required for the collection of non-thermal phonons and the heat capacity of the sensor. With a 30×30×0.45 mm3 light detector, energy thresholds below 5 keV referred to energy deposition in CaWO4 have been obtained. Results achieved will be presented and an overview on further possibilities of development will be given.

Entanglement lies at the core of quantum algorithms designed to solve problems that are intractable by classical approaches. One such algorithm, quantum annealing (QA), provides a promising path to a practical quantum processor. We have built a series of scalable QA processors consisting of networks of manufactured interacting spins (qubits). Here, we use qubit tunneling spectroscopy to measure the energy eigenspectrum of two- and eight-qubit systems within one such processor, demonstrating quantum coherence in these systems. We present experimental evidence that, during a critical portion of QA, the qubits become entangled and that entanglement persists even as these systems reach equilibrium with a thermal environment. Our results provide an encouraging sign that QA is a viable technology for large-scale quantum computing., Comment: 13 pages, 8 figures, contact corresponding author for Supplementary Information

We have developed massive cryogenic particle detectors to be used in the CRESST dark matter search. Each detector is made of a sapphire crystal and a tungsten superconducting phase transition thermometer. In this paper, we report on the results obtained with four 262 g detectors, which show energy thresholds as low as 350 eV and good energy resolution at low energies. The shape of the experimental pulses, the linearity of the detector response and the energy dependence of the resolution are discussed.

We report on simultaneous detection of phonons and scintillation light using a cryogenic calorimeter composed of a scintillating CaWO 4 crystal and a separate light detector, both instrumented with a tungsten superconducting phase transition thermometer operating at about 12 mK. Clear discrimination between electron and nuclear recoils was demonstrated by irradiating the detector with electrons, photons and neutrons. The shape of the nuclear recoil energy spectrum induced by the neutrons could be well reproduced by simulations.

In the CRESST-II experiment, scintillating CaWO4 crystals are used as absorbers for direct weakly interacting massive particles (WIMP) detection. Nuclear recoils can be discriminated against electron recoils by measuring phonons and scintillation light simultaneously. The absorber crystal and the silicon light detector are read out by tungsten superconducting phase transition thermometers. Results on the sensitivity of the phonon and the light channel, radiopurity, the scintillation properties of CaWO4, and on the WIMP sensitivity are presented. (C) 2003 Elsevier B.V. All rights reserved.

We report on a newly developed detector based on a Superconducting-Phase-Transition Thermometer which is used in a Time-of-flight mass spectrometer for heavy molecules. It exhibits a sensitive area of 3.0×3.0 mm 2 and a time resolution of approximately 1.1 μs . First measurements with our setup on heavy proteins up to 150,000 amu are presented.

Efforts to develop useful quantum computers have been blocked primarily by environmental noise. Quantum annealing is a scheme of quantum computation that is predicted to be more robust against noise, because despite the thermal environment mixing the system's state in the energy basis, the system partially retains coherence in the computational basis, and hence is able to establish well-defined eigenstates. Here we examine the environment's effect on quantum annealing using 16 qubits of a superconducting quantum processor. For a problem instance with an isolated small-gap anticrossing between the lowest two energy levels, we experimentally demonstrate that, even with annealing times eight orders of magnitude longer than the predicted single-qubit decoherence time, the probabilities of performing a successful computation are similar to those expected for a fully coherent system. Moreover, for the problem studied, we show that quantum annealing can take advantage of a thermal environment to achieve a speedup factor of up to 1,000 over a closed system.

We describe a quantum tunneling spectroscopy technique that requires only low-bandwidth control. The method involves coupling a probe qubit to the system under study to create a localized probe state. The energy of the probe state is then scanned with respect to the unperturbed energy levels of the probed system. Incoherent tunneling transitions that flip the state of the probe qubit occur when the energy bias of the probe is close to an eigenenergy of the probed system. Monitoring these transitions allows the reconstruction of the probed system eigenspectrum. We demonstrate this method on an rf SQUID flux qubit.

We report on the development of a SQUID read-out for a fast cryogenic detector with superconducting phase transition thermometer. To avoid the usual transformer matching and modulation–demodulation technique we are using a second SQUID to amplify the signal of a first stage input SQUID. A bandwidth of 2 MHz and a slew rate of 2×105 Φ0 s−1 were achieved. The system is developed for the detection of large protein molecules in a time of flight mass spectrometer.

Superconducting circuits have played an essential role in realizing quantum mechanical phenomena in macroscopic systems. One such example is the observation of macroscopic resonant tunneling (MRT) of magnetic flux between the lowest energy states of single rf-SQUID flux qubits, as demonstrated by several groups [1–4]. These measurements provide both a clear signature of quantum mechanics in a macroscopic circuit at a finite temperature and in the presence of noise and a direct means of determining the tunneling energy between states. Theoretical descriptions of the MRT rate have been presented [5, 6] and indicate a direct connection between the profile of the MRT rate peaks and properties of the environment. Analogous measurements of the tunneling of magnetization in nanomagnets [7, 8] suggest that MRT is responsible for dynamics in these materials as well. In this work, we extend measurements of MRT to inductively coupled pairs of flux qubits. We present experimental observations of tunneling between the two lowest energy states of the coupled system for several coupling strengths. These data yield two-qubit energy gaps that match those predicted by the independently calibrated Hamiltonian of the coupled system. Moreover, measurements of the two-qubit energy gap are used to infer sin

Many interesting but practically intractable problems can be reduced to that of finding the ground state of a system of interacting spins. It is believed that the ground state of some naturally occurring spin systems can be effectively attained through a process called quantum annealing. Johnson et al. use quantum annealing to find the ground state of an artificial Ising spin system comprised of an array of eight superconducting flux qubits with programmable spin–spin couplings. With an increased number of spins, the system may provide a practical physical means to implement quantum algorithms, possibly enabling more effective approaches towards solving certain classes of hard combinatorial optimization problems. Many interesting but practically intractable problems can be reduced to that of finding the ground state of a system of interacting spins; however, finding such a ground state remains computationally difficult1. It is believed that the ground state of some naturally occurring spin systems can be effectively attained through a process called quantum annealing2,3. If it could be harnessed, quantum annealing might improve on known methods for solving certain types of problem4,5. However, physical investigation of quantum annealing has been largely confined to microscopic spins in condensed-matter systems6,7,8,9,10,11,12. Here we use quantum annealing to find the ground state of an artificial Ising spin system comprising an array of eight superconducting flux quantum bits with programmable spin–spin couplings. We observe a clear signature of quantum annealing, distinguishable from classical thermal annealing through the temperature dependence of the time at which the system dynamics freezes. Our implementation can be configured in situ to realize a wide variety of different spin networks, each of which can be monitored as it moves towards a low-energy configuration13,14. This programmable artificial spin network bridges the gap between the theoretical study of ideal isolated spin networks and the experimental investigation of bulk magnetic samples. Moreover, with an increased number of spins, such a system may provide a practical physical means to implement a quantum algorithm, possibly allowing more-effective approaches to solving certain classes of hard combinatorial optimization problems.

A novel rf-SQUID flux qubit that is robust against fabrication variations in Josephson junction critical currents and device inductance has been implemented. Measurements of the persistent current and of the tunneling energy between the two lowest lying states, both in the coherent and incoherent regime, are presented. These experimental results are shown to be in agreement with predictions of a quantum mechanical Hamiltonian whose parameters were independently calibrated, thus justifying the identification of this device as a flux qubit. In addition, measurements of the flux and critical current noise spectral densities are presented that indicate that these devices with Nb wiring are comparable to the best Al wiring rf-SQUIDs reported in the literature thusfar, with a $1/f$ flux noise spectral density at $1 $Hz of $1.3^{+0.7}_{-0.5} \mu\Phi_0/\sqrt{\text{Hz}}$. An explicit formula for converting the observed flux noise spectral density into a free induction decay time for a flux qubit biased to its optimal point and operated in the energy eigenbasis is presented., Comment: 20 pages, 16 figures

A highly sensitive galvanometer operating at liquid-nitrogen temperature for direct and low-frequency current measurements was developed on the basis of a HTSC SQUID. The direct-current sensitivity of the galvanometer is approximately 0.5 nA at an internal resistance of about 20 Ω. Its energy resolution in the white noise region is 2 × 10−21 J/Hz.

A method to stabilize cryogenic detectors with superconducting phase transition thermometers in their operating point is presented. Measurements of X-ray lines emitted by an 55 Fe X-ray fluorescence source showed an improvement in energy resolution from 230 to 133 eV on the 1.5 keV aluminium line with this technique. Furthermore the required set-up allows to simulate real events by injecting heat pulses into the thermometer and in this way to calibrate the detector and to monitor its long-term stability.

Diffusion of quasiparticles over distances up to 4 mm has been observed in various superconducting films. The quasiparticles were created by X-ray absorption in film strips with critical temperatures near 1 K and were detected in two superconducting phase transition thermometers at the ends of each strip. Position and energy of the absorbed X-rays as well as diffusion constants and lifetimes of the quasiparticles were determined. Very long lifetimes up to 9 ms allow the realization of large area phonon collector films on massive cryogenic particle detectors. Recently, with a first such detector a high efficiency of the phonon collection could be demonstrated.

Cryogenic calorimeters with superconducting phase transition (SPT) thermometers are extremely sensitive particle detectors. Some characteristics of SPT calorimeters such as linearity and dynamic range often suffer from the superconducting transition shape. The common way to improve the performances is to use the voltage bias to operate the SPT calorimeter in strong electrothermal feedback mode. This method does not allow us to optimize the noise, linearity and dynamic properties simultaneously. We have developed a novel SQUID circuit with thermal feedback which allows to improve the linearity, dynamic range and speed of the SPT calorimeter. Results obtained with a cryogenic calorimeter based on a tungsten thermometer are presented.

The results of an investigation of YBa2Cu3O7-x Josephson contacts applied to practical devices are reported. The ceramics preparation technology, the fabrication method of stable Josephson contacts with low critical currents and experimental methods and techniques are described. An estimate of the limiting energy resolution of the superconducting quantum interferometer, based on described contacts, is given.

A gradiometer based on two ceramic superconducting quantum interference devices (SQUIDs) operating at liquid-nitrogen temperature is developed. The minimum gradient sensitivity is 3.1*10/sup -12/ T/mHz/sup 1/2/ in a white-noise region. The minimum damping coefficient of the external disturbing factors is K=32. The gradiometer consists of two independent magnetometers separated from each other by 9 cm. It was tested by measuring the magnetocardiogram of a human heart. A typical magnetocardiogram was measured simultaneously with the magnetometer, with one lower channel of the gradiometer, and with the described gradiometer. The measurements were carried out with a bandwidth of 60 Hz, in real time, inside the approximately=5-mm-wall aluminum barrel 50-m outside the nearest building. The comparison of these magnetocardiograms shows that the gradiometer considerably suppresses the low-frequency variations of the magnetic field of the Earth, the low-frequency industrial noise, and the influence of cryostat vibration. >

Macroscopic resonant tunneling between the two lowest lying states of a bistable RF-SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian shaped profile that is not peaked at the resonance point, but is shifted to a bias at which the initial well is higher than the target well. The r.m.s. amplitude of the noise, which is proportional to the decoherence rate 1/T_2^*, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low frequency (1/f) flux noise in this device is a quantum mechanical environment in thermal equilibrium., 4 pages 4 figures

We experimentally confirm the functionality of a coupling element for flux-based superconducting qubits, with a coupling strength $J$ whose sign and magnitude can be tuned {\it in situ}. To measure the effective $J$, the groundstate of a coupled two-qubit system has been mapped as a function of the local magnetic fields applied to each qubit. The state of the system is determined by directly reading out the individual qubits while tunneling is suppressed. These measurements demonstrate that $J$ can be tuned from antiferromagnetic through zero to ferromagnetic., Updated text and figures

In the early stages of running of the CRESST dark matter search using sapphire detectors at very low temperature, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time the energy release in fracture has been directly and accurately measured on a microscopic event-by-event basis. The energy threshold corresponds to the breaking of only a few hundred covalent bonds, a sensitivity some orders of magnitude greater than that of previous technique. We report some features of the data, including energy distributions, waiting time distributions, autocorrelations and the Hurst exponent. The energy distribution appear to follow a power law, $dN/dE\propto E^{-\beta}$, similar to the power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain,the waiting time $w$ or gap distribution between events has a power law behavior at small $w$ and an exponential fall-off at large $w,$ and can be fit $\propto w^{-\alpha}e^{-w/w_0}$. The autocorrelation function shows time correlations lasting for substantial parts of an hour. An asymmetry is found around large events, with higher count rates after, as opposed to before,the large event ., Comment: Fig 4 and surrounding discussion changed. References added, langauge clarified, with greater stress on sensitivity and total energy detection. Error in metadata fixed

In the early stages of running of the CRESST dark matter search with sapphire crystals as detectors, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time that the energy release in fracture has been accurately measured on a microscopic event-by-event basis. The energy distributions appear to follow a power law, dN/dE proportional to E-beta, similar to the Gutenberg-Richter power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain, the autocorrelation function shows time correlations lasting for substantial parts of an hour. Some remarks are made concerning the possible role Of Such mechanical stress release processes in the noise of sensitive cryodetectors. (c) 2006 Elsevier B.V. All rights reserved.

We have demonstrated strong antiferromagnetic coupling between two three-junction flux qubits based on a shared Josephson junction, and therefore not limited by the small inductances of the qubit loops. The coupling sign and magnitude were measured by coupling the system to a high-quality superconducting tank circuit. Design modifications allowing to continuously tune the coupling strength and/or make the coupling ferromagnetic are discussed., REVTeX 4, 4 pages, 5 figures; v2: completely rewritten, added finite-temperature results and proposals for ferromagnetic galvanic coupling

We present the first experimental results on a device with more than two superconducting qubits. The circuit consists of four three-junction flux qubits, with simultaneous ferro- and antiferromagnetic coupling implemented using shared Josephson junctions. Its response, which is dominated by the ground state, is characterized using low-frequency impedance measurement with a superconducting tank circuit coupled to the qubits. The results are found to be in excellent agreement with the quantum-mechanical predictions., Comment: REVTeX 4, 5pp., 7 EPS figure files. N.B.: "Alec" is my first, and "Maassen van den Brink" my family name. v2: final published version, with changed title, different sample micrograph, and several clarifications

Cryogenic detectors directly measure the impact energy of any impinging particle independent of its velocity. Thus, a very high, mass-independent, detection efficiency is expected from their application in time-of-flight mass spectrometry. The cryogenic detector applied here is based on a superconducting phase-transition thermometer and was implemented in a dual reflector time-of-flight mass spectrometer (N-geometry). A dilution series, using standard sample preparation procedures, shows that the detection limit for insulin (Mr: 5734) can be decreased by several orders of magnitude, down to 0.5 amol on the MALDI target. Detection limits for rhM-CSF β (Mr: 49,032) and for polyclonal IgG (Mr: ca 150,000) in the high femtomole and low picomole range, respectively, were established.

Data taken by CRESST in 2000 with a cryogenic detector system based on 262 g sapphire crystals is used to place limits on WIMP dark matter in the Galactic Halo. The detector is especially sensitive for low-mass WIMPS with spin-dependent cross sections and improves on existing limits in this region. CRESST is now preparing for a second phase, which will use a 10 kg detector consisting of 300 g CaWO4 crystals with simultaneous detection of phonons and scintillation light to reduce background.

Data taken by CRESST with a cryogenic detector system based on 262 g sapphire crystals has been used to place limits on WIMP dark matter in the Galactic Halo. The experiment was especially sensitive for low-mass WIMPs with spin-dependent cross sections and improves on existing limits in this region. © 2002 Elsevier Science B.V. All rights reserved.

The use of quasiparticle diffusion in a superconducting film has the potential to allow an increase in the size of a cryogenic detector without proportional loss of energy resolution. The quasiparticle lifetime and the diffusion constant are critical parameters which have limited this development. Using W superconducting phase transition thermometers as the sensors and a W/Al bilayer as the diffusion film, we have measured quasiparticle diffusion over a distance of 2 mm and deduced a diffusion constant of D=2.5×10 −4 m 2 / s and a quasiparticle lifetime of τ=9.0 ms , which is, to our knowledge, by far the longest ever observed. With Ir/Au thermometers and an Ir/Au/Al diffusion film we found D=4.6×10 −3 m 2 / s and τ=0.43 ms with diffusion over 4 mm , the longest distance observed to date.

The CRESST experiment seeks hypothetical WIMP particles that could account for the bulk of dark matter in the Universe. The detectors are cryogenic calorimeters in which WIMPs would scatter elastically on nuclei, releasing phonons. The first phase of the experiment has successfully deployed several 262 g sapphire devices in the Gran Sasso underground laboratories. A main source of background has been identified as microscopic mechanical fracturing of the crystals, and has been eliminated, improving the background rate by up to three orders of magnitude at low energies, leaving a rate close to one count per day per kg and per keV above 10 keV recoil energy. This background now appears to be dominated by radioactivity, and future CRESST scintillating calorimeters which simultaneously measure light and phonons will allow rejection of a great part of it., To appear in the proceedings of the CAPP2000 Conference, Verbier, Switzerland, July, 2000 (eds J. Garcia-Bellido, R. Durrer, and M. Shaposhnikov)

We present the current status of CRESST (Cryogenic Rare Event Search using Superconducting Thermometers) project and new results concerning detector development. The basic technique involved is to search for WIMPs by the measurement of non-thermal phonons, as created by WIMP-induced nuclear recoils. Combined with our newly developed method for the simultaneous measurement of scintillation light, strong background discrimination is possible, resulting in a substantial increase in WIMP detection sensitivity.

The critical currents and normal resistances of the small bridges from yttrium-based high-Tc superconducting ceramics have been measured. The characteristic voltage of these bridges was found to be approximately 20 μV. This effect can be explained if, between the ceramic grains, there are contacts of an order of one crystalline cell in size.

A magnetocardiometer based on a single-hole SQUID made from high-Tc YBa2Cu3O7-x ceramic, operating without magnetic shielding is described. It has enabled the authors to measure a magnetocardiogram in real time in a 60 Hz bandwidth. Spectra for the intrinsic noise of the SQUID and the ambient noise of the magnetocardiogram measurement site are given.

Publisher Summary This chapter helps in designing, building and testing a system for experiments with the 1.3 GHz superconducting cavity. The major part of the system is a horizontal cryostat which includes a helium vessel for the cavity, He-gas and LN2-cooled shields, two nodes for RF couplers, a device for mechanical stretching or squeezing the cavity and a control system. Cooling down to 2.0 K and below is performed with saturated superfluid helium pumped by 500 1/s unit. Operation experience collected up to date is discussed in the chapter. The feature of the control system is the usage of 16 channels cold multiplexer to measure temperatures within the liquid helium vessel. Its components are tested for the radiation environment performance. The obtained results are presented for the various dose values. In the environment combining gamma and neutron radiations and cryogenic temperatures, up to the total doses of approximately 10,000 Gy and 3·l013n/cm2, correspondingly, the cold multiplexer based on the HCMOS PC74HC/4067 chips, can be used successfully. To define these boundaries more exactly, further explorations are needed.