Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U9: Superconductivity: Squid Instruments |
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Sponsoring Units: DMP Chair: Mike Osofsky, Naval Research Laboratory Room: Colorado Convention Center Korbel 1D |
Thursday, March 8, 2007 8:00AM - 8:12AM |
U9.00001: Closing the Quantum Metrological Triangle M. Paalanen, A. Kemppinen, A. Manninen, A. Satrapinski, J. Hassel, P. Helisto, A.O. Niskanen, Heikki Seppa, P. Hakonen, Mikko Mottonen, Jukka Pekola, Juha Vartiainen Quantum Metrological Triangle is made out of Josephson voltage standard, Quantum Hall resistance standard and an accurate current pump. Closing the Triangle consists of applying Ohm's law with great accuracy on the three devices, based on fundamental physical phenomena and quantities, such as Planck's constant and electron charge. The first two devices are already accepted international metrological standards. Recently we have made progress in developing the missing components for the closing experiments, i.e. a differential low-noise amplifier for comparing small currents and a current pump. Both of these new devices are based on superconducting single electronics. We will describe our plans for closing the Triangle along with the expected uncertainties and also report on the progress in developing the low noise current amplifier and the current pump. [Preview Abstract] |
Thursday, March 8, 2007 8:12AM - 8:24AM |
U9.00002: A low-field SQUID MRI system: design, performance and characterization. Byeong Ho Eom, Konstantin Penanen, Inseob Hahn A low-field MRI system with SQUID detector and gradiometer sense coil readout is being developed for clinical imaging. The system is compact and low-weight and operates in minimally shielded environment. An in-vivo image of human hand with sensitive field of view of 3cm, in-plane resolution of 1mm and 4mm slice width can be acquired in $\sim $5 minutes. We discuss the system design, optimization, noise characteristics~and imaging performance of the~apparatus.~ [Preview Abstract] |
Thursday, March 8, 2007 8:24AM - 8:36AM |
U9.00003: Optimization of sensing coil geometry for low-field SQUID MRI and MEG. Konstantin Penanen, Byeong Ho Eom, Inseob Hahn The performance of low-field MRI and MEG systems critically depends on the noise-limited sensitivity of the SQUID input subsystem. Optimization tradeoffs between the sensing coil field sensitivity, extraneous field rejection and self-inductance, as well as geometrical and fabrication constraints need to be considered. In addition to coil geometry optimizations, it is beneficial to optimize the shape of the wire loops the coil is wound with. We present the results of such optimization study in configurations typical for SQUID MEG and MRI sensing coils. A significant improvement over the circular cross-section wire can be achieved when flat washer wire is used.~ [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U9.00004: Noise Temperature of the Microstrip SQUID Amplifier with Cooling Fins Darin Kinion, John Clarke Microwave amplifiers, based on washer-type niobium dc SQUIDs with integrated input coils that act as a microstrip resonator operate at frequencies between 50 MHz and 2 GHz, and in principle are capable of reaching the Standard Quantum Limit (SQL) for linear amplifiers. In practice, heating of the shunt resistors may increase their Johnson noise thereby limiting the ultimate noise temperature before the SQL is reached. To reduce this noise contribution, we measure the noise temperature by cooling the devices to 25-500 mK in a dilution refrigerator, and by attaching large-area cooling fins to the shunts to minimize hot-electron effects. We have previously measured the noise temperature as a function of both frequency and physical temperature. At 800 MHz, the minimum noise temperature was 47 $\pm$ 4 mK (within 20\% of the SQL) at a physical temperature of 90 mK, with no further improvement upon cooling. This limiting behavior could be an indication of either the SQL or of hot- electron effects in the shunts. We will present results of separate flux-noise measurements at 140 kHz where similar limiting behavior below 100 mK should be caused only by hot- electron effects, thus resolving the ambiguity. [Preview Abstract] |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U9.00005: Cavity Josephson Bifurcation Amplifier: an improved microwave readout for a superconducting qubit Michael Metcalfe, Etienne Boaknin, Vladimir Manucharyan, rajamani Vijayaraghavan, Luigi Frunzio, Michel Devoret Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasiveness. We have developed a new type of dispersive bifurcating amplifier, which consists of a Josephson junction imbedded in a microwave on-chip resonator. In contrast with the Josephson bifurcation amplifier [1,2,3], which has an on-chip capacitor shunting a junction, the resonator is based on a simple coplanar waveguide imposing a pre-determined frequency and whose other RF characteristics like the quality factor are easily controlled and optimized. Furthermore, readout frequencies ranging from 1 to 10GHz have been realized. Under proper microwave irradiation conditions, the resonator has two metastable states. Which state is adopted by the resonator depends on the state of a qubit coupled to the readout junction. We present the characterization of the Cavity Bifurcation Amplifier and demonstrate its application as a readout for the Quantronium qubit. \newline [1] I. Siddiqi et al. Phys. Rev. Lett 93, 207002 (2004) \newline [2] I. Siddiqi et al. Phys. Rev. Lett. 94, 027005 (2005) \newline [3] I. Siddiqi et al. Phys. Rev. B. 73, 0054510 (2006) [Preview Abstract] |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U9.00006: Symmetry of Charge and Thermal Transport in Andreev Interferometers Jeff Weiss, Philippe Jacquod Motivated by recent experiments of Chandrasekhar et al. [Phys. Rev. Lett. 81, 437 (1998); Phys. Rev. B 72, 020502(R) (2005)], we investigate the symmetry of charge and thermal transport through magnetic-field threaded Andreev interferometers. We construct a scattering theory that accounts for multi-terminal geometries with no specific spatial symmetry. We use random matrix theory to calculate both the electrical and thermal four-terminal resistances and the thermopower, focusing on their magnetic flux dependence. Our results on the parity and amplitude of the magnetic field dependence is connected to the experimental results. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:24AM |
U9.00007: Few quasiparticle dynamics with a single-Cooper-pair transistor. Nadia Court, Andrew Ferguson, Robert Clark We employ the single-quasiparticle sensitivity of the single-Cooper-pair transistor (SCPT) to directly measure the quasiparticle population of a small superconducting volume. The SCPT is measured in a radio-frequency configuration allowing $>$ MHz bandwidth and is connected to a quasiparticle trap formed using aluminium bandstructure engineering. Quasiparticles in the trap region tunnel into the SCPT, this interrupts the coherent Cooper-pair transport and is detected by changes in the reflected radio-frequency signal. The quasiparticle population is monitored both in the steady state and under non-equilibrium conditions of quasiparticle injection. In particular, we study the non-equilibrium regime where the quasiparticle recombination time is accessed via the response of the SCPT to pulsed injection. We discuss the application of the SCPT as an ultra sensitive sub-mm photon detector and also as a tool to investigate the statistical mechanics of a few quasiparticle gas. [Preview Abstract] |
Thursday, March 8, 2007 9:24AM - 9:36AM |
U9.00008: High Frequency Flux Sampling SQUID Microscope C.P. Vlahacos, J. Matthews, S.P. Kwon, F.C. Wellstood One important application of scanning SQUID microscopes is to fault detection in integrated circuits and multi-chip modules. However, the present generation of computer processors operate at over 1 GHz, well above the bandwidth of the present generation of SQUID microscopes. We have overcome the bandwidth limitations of traditional scanning SQUID microscopes by removing the main bandwidth limiter -- the conventional flux-locked loop electronics -- and using instead a pulsed sampling technique with a hysteretic dc SQUID. We present time-varying magnetic field images obtained with the 4.2 K cryocooled microscope with a time-resolution below 1 nanosecond, and discuss the advantages and limitations of this method. [Preview Abstract] |
Thursday, March 8, 2007 9:36AM - 9:48AM |
U9.00009: Fast NDE of Superconducting Magnet Wires using a Flow-Through SQUID Microscope with Coaxial Current Injection J. Matthews, F.C. Wellstood, H. Weinstock We have developed a cryocooled high-Tc SQUID microscope for fast non-destructive evaluation (NDE) of long wires, designed for detecting defects in superconducting magnet wire. A feedthrough mechanism pulls the wire at speeds of up to 20 cm/s through a thin mylar tube that separates the room temperature wire from the SQUID. In order to null the magnetic field from bulk current flow the current return path is coaxial with the wire. We present results on test wires and samples of NbTi superconducting wire. By comparison with analytical and numerical models, we extract information from the data, such as defect size and location, and also outline a method for fast automated detection of defects in long wires. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:00AM |
U9.00010: A three-junction single electron transistor as a diffusive, high-speed thermometer: Experiment and simulation Loren Swenson, D.K. Wood, A.N. Cleland Nanoscale calorimetry promises unprecedented sensitivity and temporal resolution for energy measurements in mesoscopic systems. As the size scale and temperature of a calorimeter are reduced, the heat capacity and equilibration time decrease rapidly. Achieving the lowest temperatures at the smallest size scales therefore requires thermometric sensors that can be operated with large measurement bandwidths ($>$ 1 MHz), at low temperatures ($<$ 1 K), and that minimally perturb the calorimeter itself. We have fabricated a unique, three junction single-electron transistor that allows diffusive thermometric sensing of a nanoscale calorimeter, with minimal power dissipation in the calorimeter volume. In this talk, we will describe the experiment, and our development of a Monte Carlo method to simulate the experimental device. Design optimization, sensitivity and practical implementation considerations will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 10:00AM - 10:12AM |
U9.00011: Ultra-Sensitive Hot-Electron Detectors of IR/sub-mm Radiation Wei Jian, David Olaya, Sergey Pereverzev, Michael Gershenson, Boris Karasik, Andrew Sergeev We have developed a superconducting nanostructure that enables an ultra-sensitive detection of far infrared (FIR) and sub-mm radiation. The nanostructure consists of a Ti nanobridge with a volume of $\sim $3$\times $10$^{-3}$~$\mu $m$^{3}$ flanked with Nb current leads. The electrons in the nanostructure are thermally isolated from the heat bath due to Andreev reflection from superconducting Nb leads and a weak electron-phonon coupling at mK temperatures. Being driven into the resistive state by the temperature and/or magnetic field, this transition-edge sensor is very sensitive to electron overheating. According to our measurements of the thermal conductance between the electrons in the nanobridge and the heat bath, the expected noise equivalent power and the response time of the detector at T=0.1~K are $\sim $10$^{-20}$~W/Hz$^{1/2}$ and $\sim $1 ms, respectively. Alternatively, this nanostructure with a heat capacity C $\sim $ 10$^{-19}$J/K at T=0.1\textsc{~K} can be used for the calorimetry of photons and phonons with an energy resolution $\sim $~10$^{-21}$~J. This resolution is sufficiently high for the detector to operate in a regime of THz photon counting. [Preview Abstract] |
Thursday, March 8, 2007 10:12AM - 10:24AM |
U9.00012: Microwave Techniques for SQUID Multiplexing John Mates, Kent Irwin, Leila Vale, Gene Hilton, Konrad Lehnert, Manuel Castellanos-Beltran A single Superconducting Quantum Interference Device, or SQUID, is a particularly good low-noise, low impedance amplifier. However, many applications for which SQUID's are well-suited, ranging from astronomical spectroscopy to nuclear non-proliferation verification, require a large array of amplifiers. Large arrays require multiplexing techniques. Our group at NIST has fabricated several multiplexed SQUID arrays, including 1,280 pixel arrays, that use a time-division multiplexing technique. I will report on existing SQUID multiplexing techniques and the development of a SQUID multiplexer operating at microwave frequencies. This new technique uses non- hysteretic, non-dissipative rf-SQUID's to tune microwave resonators, so that, with high enough Q's, potentially tens of thousands of SQUID's could be read out on one coaxial line. I will also report on our initial experimental work, in which we have demonstrated Q's of around 100,000. [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 10:36AM |
U9.00013: Superconducting Tunnel Junctions as Submillimeter Direct Detectors John Teufel, Minghao Shen, Luigi Frunzio, Daniel Prober, Robert Schoelkopf We are developing superconducting tunnel junctions (STJ) as direct detectors for submillimeter astronomy. Photons with energy greater than the superconducting gap of the aluminum absorber break Cooper pairs and generate excess quasiparticles that are then measured as a tunneling current through the STJ. In order to monitor the response of the detector with large readout bandwidth and maximal sensitivity, we have implemented a novel readout which monitors the impedance of the detector via radio frequency (RF) reflectometry. For calibration of the detector, we have also developed a gold microbridge as an on-chip, submillimeter photon source. When biased, high frequency noise from the microbridge couples via a transmission line to the detector. This allows for a calibrated photon source with near unity coupling, fast chopping, and calculable response. We present results in which we measured the ``optical'' properties of the STJ using the microbridge source and RF-STJ readout at 300 mK, demonstrating good responsivity, high sensitivity, and fast response times. [Preview Abstract] |
Thursday, March 8, 2007 10:36AM - 10:48AM |
U9.00014: Single Crystal Superconducting Bolometric Photon Detector Kevin Inderhees, Paul Welander, James Eckstein We have studied bolometric photon detectors made from 10 nm thick single crystal niobium films grown by MBE. The films are atomically flat, have transition temperatures above 7.5 K and residual resistivity ratios $>$10, and can be patterned with uniform cross section, since they are not granular. The critical current density at 4.2 K is greater than 2x10$^{7}$ A/cm$^{2}$. The films are patterned into links between 300 and 500 nm wide. As a function of bias current, the detectivity is sharply peaked near the critical current, which appears to increase the sensitivity. The detected voltage signal has been studied at low frequency so far ($\sim $1MHz), and is linearly dependent on the photon flux. The fact that relatively wide links provide good detectivity is due to the uniform superconducting transport properties of the single crystal niobium. [Preview Abstract] |
Thursday, March 8, 2007 10:48AM - 11:00AM |
U9.00015: Ultra-high resolution alpha particle spectroscopy using cryogenic microcalorimeters R. D. Horansky, J. N. Ullom, J. B. Beall, W. B. Doriese, W. D. Duncan, L. Ferreira, G. C. Hilton, K. D. Irwin, C. D. Reintsema, L. Vale, M. W. Rabin, A.S. Hoover, S. P. Lamont, C. R. Rudy We have built a novel alpha particle detector using a transition edge sensor (TES) thermometer attached to a bulk superconducting absorber and have measured $<$ 2.5~keV resolution at 5.3~MeV . We have used the microcalorimeter to measure a mixture of Pu isotopes and are able to individually resolve peaks corresponding to $^{239}$Pu and $^{240}$Pu which are separated by 12.9~keV. The $^{240}$Pu/$^{239}$Pu activity ratio is a key parameter for determining whether a plutonium sample is weapons or reactor grade. Conventional silicon based detectors achieve resolutions no better than 10~keV, severely limiting current actinide assays. In addition, the microcalorimeter alpha detector has shown significantly better resolution for gamma rays. The origin of the resolution difference for gamma and alpha interactions may be due to lattice damage and is currently under study. [Preview Abstract] |
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