Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y34: Superconducting Devices and Applications |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Galen O'Neil and Robert Horansky, National Institute of Standards and Technology Room: 404 |
Friday, March 20, 2009 8:00AM - 8:12AM |
Y34.00001: Designing electron refrigerators for improved cooling with an expanded thermal model Galen O'Neil, Erik Larson, Joel Ullom Normal-metal/insulator/superconductor (NIS) tunnel junctions can act as refrigerators below 1K. ~Biasing the junction such that only thermally excited electrons have energy higher than the superconducting gap causes selective tunneling which cools the normal metal electrode. ~Because of their small size, low mass, and absence of moving parts, NIS refrigerators are an attractive cooling technology for space and industrial applications. ~We have demonstrated temperature reductions of 100mK from bath temperatures near 300mK. ~For example, we operated a superconducting x-ray detector at 160mK with a cryostat bath temperature of 260mK by using NIS junctions for the additional cooling. ~We will show a more complete thermal model of a large area NIS refrigerator accounting for quasiparticle injection, diffusion, and imperfect trapping. Using this model to guide NIS refrigerator design we expect to achieve our goal of cooling from 300mK to 100mK. [Preview Abstract] |
Friday, March 20, 2009 8:12AM - 8:24AM |
Y34.00002: ABSTRACT WITHDRAWN |
Friday, March 20, 2009 8:24AM - 8:36AM |
Y34.00003: Nanomechanical parametric amplification and oscillation via electrostatic coupling to Cooper-pair box Junho Suh, Matt LaHaye, Pierre Echternach, Keith Schwab, Michael Roukes Nanomechanical resonator coupled to a Cooper-pair box exhibits frequency modulation as a function of the gate voltage when the qubit is adiabatically tuned. We utilize this effect to demonstrate mechanical degenerate parametric amplification and oscillation. Gain above 30dB and self-oscillation is observed. This technique would provide an efficient way to enhance the force sensitivity in the measurement of coupled dynamics of nanomechanical resonanator modes and a solid state qubit. [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y34.00004: Back-action and self-oscillation in the Double Pump Josephson Parametric Amplifier (DPA) Archana Kamal, Adam Marblestone, Michel H. Devoret Josephson Parametric amplifiers are the most promising candidates for reaching the quantum limit of amplification at RF frequencies. The DPA employs 2 pumps. The dual pumps ensure separation between the signal and the pump frequencies, which is necessary to observe delicate effects, such as self-oscillations. We present the model of the DPA. Our calculations are based on Input-Output Theory, and can easily be generalized to any coupled system involving parametric interactions. We analyze the operation of the device, taking into account the feedback introduced by the reaction of the signal amplification on the pump power and we compute various response functions - signal/idler gain, internal gain, and steady state signal response. To account for this back-action between signal and pump, we adopt a mean-field approach and self-consistently explore the boundary between amplification and self-oscillation. The potential of the DPA for quantum-limited measurements and as a squeezer is also discussed. [Preview Abstract] |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y34.00005: Detection and Reset Dynamics of Superconducting Nanowire Single Photon Detectors Anthony Annunziata, Orlando Quaranta, Daniel Santavicca, Joel Chudow, Luigi Frunzio, Aviad Frydman, Michael Rooks, Daniel Prober We investigate the single photon detection and reset mechanisms in superconducting nanowires, which have received recent, widespread attention for use in applications requiring fast optical and near infrared photon counting. These devices are fabricated from ultra-thin Nb and NbN films and read out by measuring short ($\sim $1 ns) transient voltage spikes that result from the localized suppression of superconductivity by an absorbed photon. We find that intrinsic electro-thermal instabilities necessitate a low impedance ($<$50 ohms) readout circuit for stable resetting to the superconducting state after detecting a photon. The actual impedance needed depends on the detailed physical properties of the device. We also investigate the detection mechanism and report the dependence of detection efficiency on the temperature and dc bias current as well as on film disorder, from which we present a model of the detection mechanism. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y34.00006: Measurements of a YBCO superconducting quantum interference filter with planar ion-damaged Josephson junctions Steven M. Anton, Shane A. Cybart, Stephen M. Wu, John Clarke, R.C. Dynes We have fabricated a two dimensional series-parallel array of 565 $\times$28 \linebreak YBa$_2$Cu$_3$O$_{7-\delta}$ thin film ion damage Josephson junctions. The loop areas were varied incommensurately from 28.5 to 90~$\mu$m$^2$ so that the response of the current-biased array to an applied magnetic field is a prominent peak in voltage centered at zero field. We measured voltage versus applied magnetic field characteristics for several static bias currents at different temperatures. Additionally, we measured current-voltage ($I$-$V$) characteristics of the array with no applied magnetic field at several temperatures. To fit the $I$-$V$ characteristics, we assumed that each parallel section of the array could be modeled as a single resistively shunted junction with critical currents following a normal distribution. Fitting the summed voltage contributions of the parallel sections to measurements of the array, we computed the resistance and critical current mean and spread. The standard deviation of these critical currents was 15~percent at 74~K. [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y34.00007: Cryogenic Broadband Impedance-Matched Absorptive Microwave Filters Daniel Slichter, Ofer Naaman, Irfan Siddiqi We report Johnson noise and S parameter measurements of a broadband impedance-matched low pass microwave filter consisting of a section of lossy stripline transmission line. The thermal noise power generated by the filter was measured in the frequency band of 1.2 GHz - 1.8 GHz at temperatures from 30 mK to 300 mK. The noise power was comparable to that of a 50$\Omega$ reference load held at the same temperature and measured with the same microwave measurement chain using a cryogenic mechanical switch. Transmission measurements on a filter with $f_{3dB}$=1.3 GHz show that the filter's cutoff characteristics remain essentially unchanged between room temperature and 20 mK. The filters are robust to thermal cycling and are simple to manufacture. We have used these filters to obtain low Cooper pair temperatures in high-bandwidth microwave measurements on superconducting devices. [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y34.00008: The Electronic Properties of AlN Tunnel Barriers and the Effect of Oxygen Impurities Yun Li, John Read, Pinshane Huang, Hsin-wei Tseng, Robert Buhrman The use of ultra-thin aluminum nitride (AlN) barrier layers can result in Josephson Junctions (JJ's) with both very high critical current densities and low sub-gap leakage [1-4], demonstrating that AlN is a superior JJ tunnel barrier material in the ultra-thin barrier limit. We have utilized scanning tunneling spectroscopy (STS) and analytical scanning transmission electron microscopy (STEM) with electron energy-loss spectroscopy (EELS) to investigate thin AlN layers formed on Nb/Al bilayers by treating the Al surface with an atomic nitrogen beam. Under optimum nitridation conditions the resultant $\sim $1nm AlN barrier layers have small, $\sim $ 1 eV, but well defined band gaps and stable surfaces in UHV, with the absence of band-tail states extending close to the Fermi energy, which is in sharp contrast to the case for AlO$_{x }$layers formed by thermal oxidation [5]. The AlN barrier layers are however quite sensitive to even low levels of background oxygen (O) exposure, either during or after the nitridation process, which reacts O into the barrier layer and results in the formation of low energy band-tail states and an unstable surface. [1] Zijlstra et al., APL 91, 233102 (2007); [2] Wang et al., APL 64, 2034 (1994); [3] Kleinsasser et al., IEEE TAS 5, 2318 (1995); [4] Kaul et al., JMRS 20, 3047 (2005); [5] Mather et al., APL 86, 242504 (2005) [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y34.00009: Dispersive Microwave Readout of NanoSQUIDs R. Vijay, Aidin Fathalizadeh, Irfan Siddiqi, Michael Hatridge, John Clarke Superconducting quantum interference devices (SQUIDs) based on Josephson tunnel junctions have long been used as sensitive magnetic flux detectors. NanoSQUIDs, which use submicron weak link junctions for enhanced flux coupling,~are~attractive candidates for magnetic measurements of molecules.~ We present a novel~method~for nanoSQUID readout~which involves embedding the SQUID in a superconducting transmission line cavity operating at microwave frequency. The magnetic flux dependence of the total SQUID inductance modulates the cavity resonant frequency; these frequency changes are determined using microwave reflectometry. This dispersive microwave measurement allows detection of changes in magnetic flux at submicrosecond timescales without creating dissipation in the vicinity of the molecule. Moreover, we can exploit the Josephson nonlinearity of the nanoSQUID for bifurcation amplification to~enhance sensitivity. Optimization of the nanoSQUID design and cavity parameters for maximizing detector sensitivity and bandwidth is discussed. We also discuss the various sources of noise in this measurement scheme and how to minimize their impact. This work is supported by AFOSR and USDOE. [Preview Abstract] |
Friday, March 20, 2009 9:48AM - 10:00AM |
Y34.00010: Dispersive microwave magnetometry of single molecule magnet crystals M. Hatridge, J. Clarke, R. Vijay, J.J. Lee, I. Siddiqi, G. Timco, R. Winpenny Dispersive microwave readout of SQUIDs is a promising technique for magnetometry of molecular magnets, as it offers good sensitivity, high bandwidth, and minimal back action. We have fabricated a sample consisting of a 1.5 GHz aluminum coplanar stripline resonator with a quality factor Q=1000, terminated with a Al-AlO$_{x}$-Al unshunted tunnel junction SQUID with loop area 9 $\mu $m$^{2}$. Flux signals coupled to the SQUID loop are detected as changes in the phase of the reflected microwave signal. We present data characterizing the effective flux noise of the detector as a function of microwave drive power and flux bias. By exploiting the enhanced sensitivity when the resonator is operated in the nonlinear regime we achieve a minimum effective flux noise of 0.5-1 $\mu \Phi _{0}$ / rt Hz. This effective flux noise in the nonhysteretic regime is presently limited by our system noise temperature of 10 K. Data showing low field T$_{1}$ dispersion measured on a small crystal of Cr$_{7}$Ni diluted in Cr$_{8}$ will be presented. We acknowledge support from AFOSR and the US DOE. [Preview Abstract] |
Friday, March 20, 2009 10:00AM - 10:12AM |
Y34.00011: Single-artificial-atom lasing using a voltage-biased superconducting charge qubit Robert Johansson, Sahel Ashhab, Alexandre Zagoskin, Franco Nori We consider a system composed of a single artificial atom coupled to a cavity mode. The artificial atom is biased such that the most dominant relaxation process in the system takes the atom from its ground state to its excited state, thus ensuring population inversion. Even under this condition, lasing action can be suppressed if the `relaxation' rate, i.e. the pumping rate, is larger than a certain threshold value. Using simple transition-rate arguments and a semiclassical calculation, we derive analytic expressions for the lasing suppression condition and the state of the cavity in both the lasing and suppressed-lasing regimes. The results of numerical calculations agree very well with the analytically derived results. Our analysis and results are relevant to the recently realized superconducting artificial-atom laser. [arXiv:0803.1209] [Preview Abstract] |
Friday, March 20, 2009 10:12AM - 10:24AM |
Y34.00012: A scanning SQUID microscope for imaging high-frequency magnetic fields C. P. Vlahacos, F. C. Wellstood, J. Matthews We have developed a large-bandwidth scanning SQUID microscope in order to spatially image high frequency magnetic fields. By using a hysteretic Nb dc-SQUID and a pulsed sampling technique, rather than a non-hysteretic SQUID and a flux-locked loop, we have overcome the bandwidth limitations of existing scanning SQUID microscopes, which typically only image below about 1 MHz. The microscope allows for non-contact time-varying magnetic field images to be taken of room temperature samples with time steps down to 50 ps and spatial resolution ultimately limited by the size of the SQUID to about 10 $\mu $m. Towards this end, results will be presented on the design, development, and operation of a cryo-cooled 4.2 K scanning SQUID microscope with a bandwidth of dc to 3 GHz and a sensitivity of about 52.4 nT per sample. [Preview Abstract] |
Friday, March 20, 2009 10:24AM - 10:36AM |
Y34.00013: The Josephson Microwave Photomultiplier Brendan Osberg, Jay Gambetta, Frank Wilhelm The current lack of single microwave photon counters -as opposed to microwave amplifiers- has become a problematic omission in the toolkit of available circuit QED devices. Hence, we propose a microwave photo-multiplier based on a modified phase qubit. Such a system, trapped in the metastable state, can be activated over its potential energy barrier by an incoming photon, creating an avalanche effect analogous to current photo-diodes. Linear coupling of the junction flux with the radiation field, in the weak damping regime, permits photodetection from an arbitrary quantum source in the GHz range. We model this device theoretically and investigate its sensitivity, bandwidth, efficiency, and dark-count rate using the Langevine stochastic differential equations and a path integral approach. [Preview Abstract] |
Friday, March 20, 2009 10:36AM - 10:48AM |
Y34.00014: Transport Properties of a Hybrid SET-SQUID Device in Tunable Dissipative Environment. Shuchao Meng, Jeffrey Quilliam, Chas Mugford, Andy Sachrajda , Jan Kycia We will present measurements of transport properties of a new type of superconducting device, designed to allow a fully adjustable Hamiltonian with charge term, Josephson coupling term, and dissipation term. This device consists of a superconducting Single Electron Transistor (sSET) and two Superconducting Quantum Interference Devices (SQUIDs). A 2D electron gas embedded 90nm below the substrate surface provides a tunable dissipative environment. A small magnetic field can be applied to drive this hybrid device from the strong Josephson coupling regime to the SET regime. Dissipation and temperature dependence of the switching current out of the zero-voltage state show different characteristics for different settings of competition between Josephson coupling and charging energy. [Preview Abstract] |
Friday, March 20, 2009 10:48AM - 11:00AM |
Y34.00015: Cooper Pair Wavefunction Approach to SNS Junctions Yong-Jihn Kim Recently we introduced a Cooper pair wavefunction approach to the Josephson effects [1]. The approach led to the discovery of threshold resistance in the SIS junctions and more accurate temperature dependence of the DC supercurrent. We apply the approach to the SNS junctions. The Cooper pair wavefunction in the superconductor penetrates into the normal metal, leading to proximity-effect-induced Josephson coupling. The resulting Josephson coupling energy and the supercurrents are calculated from the overlap of the Cooper pair wavefunction of the superconductor and the induced Cooper pair wavefunction of the normal metal near the interface. We calculate the magnitude of the superccurrent at 0K and the temperature dependence of the supercurrent. We compare our theoretical results with experiments. [1] Yong-Jihn Kim, J. Appl. Phys. Vol. 103, 103902 (2008). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700