Geneva University - Superconducting flux quantum bits: fabricated quantum objects
2007-01-01
Ecole de physique Département de physique nucléaire et corspusculaire 24, Quai Ernest-Ansermet 1211 GENEVE 4 Tél: (022) 379 62 73 Fax: (022) 379 69 92 Lundi 29 janvier 2007 COLLOQUE DE LA SECTION DE PHYSIQUE 17 heures - Auditoire Stueckelberg Superconducting flux quantum bits: fabricated quantum objects Prof. Hans Mooij / Kavli Institute of Nanoscience, Delft University of Technology The quantum conjugate variables of a superconductor are the charge or number of Cooper pairs, and the phase of the order parameter. In circuits that contain small Josephson junctions, these quantum properties can be brought forward. In Delft we study so-called flux qubits, superconducting rings that contain three small Josephson junctions. When a magnetic flux of half a flux quantum is applied to the loop, there are two states with opposite circulating current. For suitable junction parameters, a quantum superposition of those macroscopic states is possible. Transitions can be driven with resonant microwaves. These quantum ...
Flux Exclusion Superconducting Quantum Metamaterial: Towards Quantum-level Switching
Savinov, V.; Tsiatmas, A.; Buckingham, A. R.; Fedotov, V. A.; de Groot, P. A. J.; Zheludev, N. I.
2012-01-01
Nonlinear and switchable metamaterials achieved by artificial structuring on the subwavelength scale have become a central topic in photonics research. Switching with only a few quanta of excitation per metamolecule, metamaterial's elementary building block, is the ultimate goal, achieving which will open new opportunities for energy efficient signal handling and quantum information processing. Recently, arrays of Josephson junction devices have been proposed as a possible solution. However, they require extremely high levels of nanofabrication. Here we introduce a new quantum superconducting metamaterial which exploits the magnetic flux quantization for switching. It does not contain Josephson junctions, making it simple to fabricate and scale into large arrays. The metamaterial was manufactured from a high-temperature superconductor and characterized in the low intensity regime, providing the first observation of the quantum phenomenon of flux exclusion affecting the far-field electromagnetic properties of the metamaterial. PMID:22690319
Phase-controlled superconducting heat-flux quantum modulator
Giazotto, F.; Martínez-Pérez, M. J.
2012-09-01
We theoretically put forward the concept of a phase-controlled superconducting heat-flux quantum modulator. Its operation relies on phase-dependent heat current predicted to occur in temperature-biased Josephson tunnel junctions. The device behavior is investigated as a function of temperature bias across the junctions, bath temperature, and junctions asymmetry as well. In a realistic Al-based setup the structure could provide temperature modulation amplitudes up to ˜50 mK with flux-to-temperature transfer coefficients exceeding ˜125 mK/Φ0 below 1 K, and temperature modulation frequency of the order of a few MHz. The proposed structure appears as a promising building-block for the implementation of caloritronic devices operating at cryogenic temperatures.
Yi, H. R.; Zhang, Y; Schubert, J.; Zander, W.; Zeng, X. H.; Klein, N
2000-01-01
This article describes three planar layouts of superconducting multiturn flux transformers integrated with a coplanar resonator for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. The best magnetic field noise values of 22 and 11.5 fT/Hz(1/2) in the white noise regime were obtained for the layout with two input coils and the layout with the labyrinth resonator, respectively. Excess low-frequency noise (about 200 fT/Hz(1/2) at 10 Hz) was present. Compute...
Yi, H. R.; Zhang, Y.; Schubert, J.; Zander, W.; Zeng, X. H.; Klein, N.
2000-11-01
This article describes three planar layouts of superconducting multiturn flux transformers integrated with a coplanar resonator for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. The best magnetic field noise values of 22 and 11.5 fT/Hz1/2 in the white noise regime were obtained for the layout with two input coils and the layout with the labyrinth resonator, respectively. Excess low-frequency noise (about 200 fT/Hz1/2 at 10 Hz) was present. Computer simulation showed that the loss in this trilayer system was dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The rf coupling coefficient krf between the resonator and the flip-chip-coupled SQUID was also estimated. The values krf2≈14×10-3 obtained for the layout with two input coils, and krf2≈45×10-3 for the layout with the labyrinth resonator were considerably higher than the typical value of krf2≈7×10-3 for the single-layer coplanar resonator. These high coupling coefficients have compensated the somewhat degraded unloaded quality factor of the resonator, thus securing the optimum operation of the rf SQUID.
Kempf, Sebastian; Ferring, Anna; Enss, Christian
2016-10-01
The comprehensive analysis of low-frequency excess flux noise both in terms of magnetic flux noise S Φ , 1 / f and energy sensitivity ɛ1/f of 84 superconducting quantum devices studied at temperatures below 1 K reveals a universal behavior. When analyzing data in terms of ɛ1/f, we find that noise spectra of independent devices cross each other all at certain crossing frequencies fc. Besides this main result of our paper, we further show that superconducting quantum interference device (SQUID) arrays systematically feature higher noise exponents than single SQUIDs and give evidence for a material and device type dependence of low-frequency excess flux noise. The latter results facilitate to engineer the shape of magnetic flux noise spectra and thus to experimentally modify key properties such as coherence or measurement times of superconducting quantum devices.
Coupled superconducting flux qubits
Plantenberg, J.H.
2007-01-01
This thesis presents results of theoretical and experimental work on superconducting persistent-current quantum bits. These qubits offer an attractive route towards scalable solid-state quantum computing. The focus of this work is on the gradiometer flux qubit which has a special geometric design, t
Coupled superconducting flux qubits
Plantenberg, J.H.
2007-01-01
This thesis presents results of theoretical and experimental work on superconducting persistent-current quantum bits. These qubits offer an attractive route towards scalable solid-state quantum computing. The focus of this work is on the gradiometer flux qubit which has a special geometric design, t
Nakanishi, Masakazu
2010-09-01
It is theoretically explained that a response of a superconducting quantum interference device (SQUID) is periodically dependent on total magnetic flux coupling to the SQUID ring (Φ) and its period is a flux quantum (Φ(o)=h/2e, where h and e, respectively, express Planck's constant and elementary charge). For example, the voltage of an electromagnetically oscillated rf-SQUID or a current biased dc-SQUID is thought to be periodically dependent on Φ with a period of Φ(o). In this paper, we propose an accurate method to check the periodicity of a SQUID response by using a set of sensing coils covered with a superconducting sheath. As a demonstration, we measured periodicity of a commercially available thin-film type rf-SQUID response in magnetic flux ranging up to approximately 4300Φ(o). Its flux dependence was periodic below about 3400Φ(o).
Quantum information transfer with superconducting flux qubits coupled to a resonator
Yang, Chui-Ping
2010-01-01
We propose a way for implementing quantum information transfer with two superconducting flux qubits, by coupling them to a resonator. This proposal does not require adjustment of the level spacings or uniformity in the device parameters. Moreover, neither adiabatic passage nor a second-order detuning is needed by this proposal, thus the operation can be performed much faster when compared with the previous proposals.
Institute of Scientific and Technical Information of China (English)
刘当婷; 田野; 赵士平; 任育峰; 陈赓华
2015-01-01
We discuss a simple relation between the input and output signals of a superconducting quantum interference device magnetometer operating in flux locked mode in a cosine curve approximation. According to this relation, an original fast input signal can be easily retrieved from its distorted output response. This technique can be used in some areas such as sensitive and fast detection of magnetic or metallic grains in medicine and food security checking.
Superconducting wires and fractional flux
Sá de Melo, C. A. R.
1996-05-01
The quantization of flux quanta in superconductors is revisited and analyzed in a new geometry. The system analyzed is a superconducting wire. The geometry is such that the superconducting wire winds N times around an insulating cylinder and that the wire has its end connected back to its beginning, thus producing an N-loop short circuited solenoid. The winding number N acts as a topological index that controls flux quantization. In this case, fractional flux quanta can be measured through the center of the insulating cylinder, provided that the cylinder radius is small enough. The Little-Parks experiment for an identical geometry is discussed. The period of oscillation of the transition temperature of the wire is found to vary as 1/N in units of flux Φ relative to the flux quantum Φ0. When a SQUID is made in such a geometry the maximal current through the SQUID varies with period Φ0/N.
Silicon superconducting quantum interference device
Energy Technology Data Exchange (ETDEWEB)
Duvauchelle, J. E.; Francheteau, A.; Marcenat, C.; Lefloch, F., E-mail: francois.lefloch@cea.fr [Université Grenoble Alpes, CEA - INAC - SPSMS, F-38000 Grenoble (France); Chiodi, F.; Débarre, D. [Université Paris-sud, CNRS - IEF, F-91405 Orsay - France (France); Hasselbach, K. [Université Grenoble Alpes, CNRS - Inst. Néel, F-38000 Grenoble (France); Kirtley, J. R. [Center for probing at nanoscale, Stanford University, Palo Alto, California 94305-4045 (United States)
2015-08-17
We have studied a Superconducting Quantum Interference Device (SQUID) made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the gas immersion laser doping technique. The SQUID is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations.
Castellano, Maria Gabriella; Grönberg, Leif; Carelli, Pasquale; Chiarello, Fabio; Cosmelli, Carlo; Leoni, Roberto; Poletto, Stefano; Torrioli, Guido; Hassel, Juha; Helistö, Panu
2006-08-01
In order to integrate superconducting qubits with rapid-single-flux-quantum (RSFQ) control circuitry, it is necessary to develop a fabrication process that simultaneously fulfils the requirements of both elements: low critical current density, very low operating temperature (tens of millikelvin) and reduced dissipation on the qubit side; high operation frequency, large stability margins, low dissipated power on the RSFQ side. For this purpose, VTT has developed a fabrication process based on Nb trilayer technology, which allows the on-chip integration of superconducting qubits and RSFQ circuits even at very low temperature. Here we present the characterization (at 4.2 K) of the process from the point of view of the Josephson devices and show that they are suitable to build integrated superconducting qubits.
Wen, Xueda; Yu, Yang
2009-01-01
Recent experiments on Landau-Zener interference in multilevel superconducting flux qubits revealed various interesting characteristics, which have been studied theoretically in our recent work by simply using rate equation method [PRB 79, 094529, (2009)]. In this note we extend this method to the same system but with larger driving amplitude and higher driving frequency. The results show various anomalous characteristics, some of which have been observed in a recent work.
Coherence properties in superconducting flux qubits
Energy Technology Data Exchange (ETDEWEB)
Spilla, Samuele
2015-02-16
The research work discussed in this thesis deals with the study of superconducting Josephson qubits. Superconducting qubits are solid-state artificial atoms which are based on lithographically defined Josephson tunnel junctions properties. When sufficiently cooled, these superconducting devices exhibit quantized states of charge, flux or junction phase depending on their design parameters. This allows to observe coherent evolutions of their states. The results presented can be divided into two parts. In a first part we investigate operations of superconducting qubits based on the quantum coherence in superconducting quantum interference devices (SQUID). We explain experimental data which has been observed in a SQUID subjected to fast, large-amplitude modifications of its effective potential shape. The motivations for this work come from the fact that in the past few years there have been attempts to interpret the supposed quantum behavior of physical systems, such as Josephson devices, within a classical framework. Moreover, we analyze the possibility of generating GHZ states, namely maximally entangled states, in a quantum system made out of three Josephson qubits. In particular, we investigate the possible limitations of the GHZ state generation due to coupling to bosonic baths. In the second part of the thesis we address a particular cause of decoherence of flux qubits which has been disregarded until now: thermal gradients, which can arise due to accidental non equilibrium quasiparticle distributions. The reason for these detrimental effects is that heat currents flowing through Josephson tunnel junctions in response to a temperature gradient are periodic functions of the phase difference between the electrodes. The phase dependence of the heat current comes from Andreev reflection, namely an interplay between the quasiparticles which carry heat and the superconducting condensate which is sensitive to the superconducting phase difference. Generally speaking
Cai, Xinxin
Sr2RuO4, the only layered perovskite known to become superconducting without the presence of Cu, was predicted to be an odd-parity, spin-triplet superconductor shortly after its superconductivity was discovered in 1994. Sr2RuO4 was found to feature exotic vortex physics including half-flux quanta trapped in doubly connected samples and the formation of vortex lattices at low fields. In this dissertation, I present low-temperature magnetoresistance oscillation measurements on micronsized, doubly connected cylinders of Sr2RuO4 to explore the free energy modulation of the half-flux quantum state, inspired by the Little-Parks experiment, following a similar path taken in the original experiments for the establishment of fluoxid quantization. We fabricated transport devices of micron-sized superconducting cylinders of Sr2RuO4 on mechanically exfoliated single crystals. We carried out magnetoresistance oscillation measurements over a wide range of temperatures and magnetic fields for various samples. Magnetoresistance oscillations with an unexpected large amplitude were observed, suggesting a vortex-crossing origin of the magnetoresistance oscillations rather than a conventional Little-Parks effect. In thin-wall cylinders of Sr2RuO4, a large number of pronounced quantum oscillations with a conventional period of the full-flux-quantum were found. For cylinders with a thick wall, two distinct periods of oscillations were found in high- and low-field regimes, respectively, providing insight into the unconventional vortex physics in Sr2RuO4. No evidence for half-flux-quantum resistance oscillations were identified in any sample measured without the presence of an in-plane field. We demonstrated the tunability of the free energy of the superconducting Sr2RuO4 cylinders using various parameters, including an in-plane magnetic field, the measurement current, and structural factors. Distinct dips on magnetoresistance peaks were found, which we argue to be related to the
Fractional flux quanta in superconducting solenoids
Sá de Melo, C. A. R.
1996-03-01
The quantization of flux quanta in superconductors is revisited and analyzed in a new topology. The topology is that of a superconducting wire that winds N times around a fixed axis and has its end connected back to its beginning, thus producing an N-loop short circuited solenoid. In this case, fractional flux quanta can be measured through the center of the solenoid, provided that its cross-section radius is small enough. The Little-Parks experiment for an identical topology is discussed. The period of oscillation of the transition temperature of the wire is found to vary as 1/N in units of flux Φ relative to the flux quantum Φ0.
Fraunhofer regime of operation for superconducting quantum interference filters
DEFF Research Database (Denmark)
Shadrin, A.V.; Constantinian, K.Y.; Ovsyannikov, G.A.;
2008-01-01
Series arrays of superconducting quantum interference devices (SQUIDs) with incommensurate loop areas, so-called superconducting quantum interference filters (SQIFs), are investigated in the kilohertz and the gigahertz frequency range. In SQIFs made of high-T-c bicrystal junctions the flux-to-vol...
Superconducting Qubits as Mechanical Quantum Engines
Sachtleben, Kewin; Mazon, Kahio T.; Rego, Luis G. C.
2017-09-01
We propose the equivalence of superconducting qubits with a pistonlike mechanical quantum engine. The work reports a study on the nature of the nonequilibrium work exchanged with the quantum-nonadiabatic working medium, which is modeled as a multilevel coupled quantum well system subject to an external control parameter. The quantum dynamics is solved for arbitrary control protocols. It is shown that the work output has two components: one that depends instantaneously on the level populations and another that is due to the quantum coherences built in the system. The nonadiabatic coherent dynamics of the quantum engine gives rise to a resistance (friction) force that decreases the work output. We consider the functional equivalence of such a device and a rf-SQUID flux qubit.
Superradiance with an ensemble of superconducting flux qubits
Lambert, Neill; Matsuzaki, Yuichiro; Kakuyanagi, Kosuke; Ishida, Natsuko; Saito, Shiro; Nori, Franco
2016-12-01
Superconducting flux qubits are a promising candidate for realizing quantum information processing and quantum simulations. Such devices behave like artificial atoms, with the advantage that one can easily tune the "atoms" internal properties. Here, by harnessing this flexibility, we propose a technique to minimize the inhomogeneous broadening of a large ensemble of flux qubits by tuning only the external flux. In addition, as an example of many-body physics in such an ensemble, we show how to observe superradiance, and its quadratic scaling with ensemble size, using a tailored microwave control pulse that takes advantage of the inhomogeneous broadening itself to excite only a subensemble of the qubits. Our scheme opens up an approach to using superconducting circuits to explore the properties of quantum many-body systems.
Superconducting Qubits and Quantum Resonators
Forn-Díaz, P.
2010-01-01
Superconducting qubits are fabricated "loss-free" electrical circuits on a chip with size features of tens of nanometers. If cooled to cryogenic temperatures below -273 °C they behave as quantum elements, similar to atoms and molecules. Such a qubit can be manipulated by fast-oscillating magnetic fi
Low-frequency Flux Noise in SQUIDs and Superconducting Qubits
Sendelbach, Steven; Hover, David; Kittel, Achim; Mueck, Michael; McDermott, Robert
2008-03-01
Superconducting qubits are a leading candidate for scalable quantum information processing. In order to realize the full potential of these qubits, it is necessary to develop a more complete understanding of the microscopic physics that governs dissipation and dephasing of the quantum state. In the case of the Josephson phase and flux qubits, the dominant dephasing mechanism is an apparent low-frequency magnetic flux noise with a 1/f spectrum. The origin of this excess noise is not understood. We report the results of SQUID measurements that explore the dependence of the excess low-frequency flux noise on SQUID inductance, geometry, materials, and temperature. We discuss contributions to the measured noise from temperature fluctuations, trapped vortices in the superconducting films, and surface magnetic states in the native oxides of the superconductors. We discuss implications of our measurements for qubit dephasing.
Superconducting Quantum Circuits
Majer, J.B.
2002-01-01
This thesis describes a number of experiments with superconducting cir- cuits containing small Josephson junctions. The circuits are made out of aluminum islands which are interconnected with a very thin insulating alu- minum oxide layer. The connections form a Josephson junction. The current trough
Quantum Memristors with Superconducting Circuits
Salmilehto, J.; Deppe, F.; di Ventra, M.; Sanz, M.; Solano, E.
2017-02-01
Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. For realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methods to quantify memory retention in the system.
Quantum Memristors with Superconducting Circuits
Salmilehto, J.; Deppe, F.; Di Ventra, M.; Sanz, M.; Solano, E.
2017-01-01
Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. For realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methods to quantify memory retention in the system. PMID:28195193
2015-03-26
initial value problem L-C inductor -capacitor MATLAB Matrix Laboratory MHz megahertz MRI magnetic resonance imaging NDE non-destructive examination ODE...theory of operation ( Type I and Type II superconductors), by critical temperature (high and low temperature superconductors), or by the material itself...superconducting research is focused on critical temperatures below 77 K. There are several material types that are used for this temperature range with Niobium as
Superconducting quantum circuits theory and application
Deng, Xiuhao
Superconducting quantum circuit models are widely used to understand superconducting devices. This thesis consists of four studies wherein the superconducting quantum circuit is used to illustrate challenges related to quantum information encoding and processing, quantum simulation, quantum signal detection and amplification. The existence of scalar Aharanov-Bohm phase has been a controversial topic for decades. Scalar AB phase, defined as time integral of electric potential, gives rises to an extra phase factor in wavefunction. We proposed a superconducting quantum Faraday cage to detect temporal interference effect as a consequence of scalar AB phase. Using the superconducting quantum circuit model, the physical system is solved and resulting AB effect is predicted. Further discussion in this chapter shows that treating the experimental apparatus quantum mechanically, spatial scalar AB effect, proposed by Aharanov-Bohm, can't be observed. Either a decoherent interference apparatus is used to observe spatial scalar AB effect, or a quantum Faraday cage is used to observe temporal scalar AB effect. The second study involves protecting a quantum system from losing coherence, which is crucial to any practical quantum computation scheme. We present a theory to encode any qubit, especially superconducting qubits, into a universal quantum degeneracy point (UQDP) where low frequency noise is suppressed significantly. Numerical simulations for superconducting charge qubit using experimental parameters show that its coherence time is prolong by two orders of magnitude using our universal degeneracy point approach. With this improvement, a set of universal quantum gates can be performed at high fidelity without losing too much quantum coherence. Starting in 2004, the use of circuit QED has enabled the manipulation of superconducting qubits with photons. We applied quantum optical approach to model coupled resonators and obtained a four-wave mixing toolbox to operate photons
Coherent oscillations in a superconducting flux qubit without microwave pulses
Energy Technology Data Exchange (ETDEWEB)
Poletto, Stefano; Lisenfeld, Juergen; Lukashenko, Alexander; Ustinov, Alexey V. [Physikalisches Institut III, Universitaet Erlangen-Nuernberg (Germany); Castellano, Maria Gabriella; Chiarello, Fabio [Istituto di Fotonica e Nanotecnologie del CNR, Roma (Italy); Cosmelli, Carlo [Dipartimento di Fisica and INFN, Universita' di Roma La Sapienza (Italy); Carelli, Pasquale [Universita' degli Studi dell' Acquila (Italy)
2008-07-01
We report on observation of coherent oscillations in a superconducting flux qubit by using no microwave excitation but only nanosecond-long dc flux pulses. The investigated circuit is a double-SQUID consisting of a superconducting loop interrupted by a small dc-SQUID, which we control via two bias fluxes {phi}{sub c} and {phi}{sub x}. The potential energy profile of the qubit has the shape of a double well, where the flux {phi}{sub c} controls the height of the barrier between the two minima and the flux {phi}{sub x} changes the potential symmetry. The two computational states of the qubit are identified with the two energy minima and physically correspond to clockwise or anticlockwise circulating currents in the double-SQUID main loop. We observed coherent oscillations, in the frequency range between 8 and 20 GHz, induced by fast pulses of the control flux {phi}{sub c} modulating the barrier between the two potential wells. The quantum dynamics that leads to this kind of oscillations is composed of a non-adiabatic and adiabatic evolution of the two lowest energy states.
Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Makise, Kazumasa; Wang, Zhen
2012-07-15
We demonstrate the successful operation of a multielement superconducting nanowire single-photon detector (SSPD) array integrated with a single-flux-quantum (SFQ) readout circuit in a compact 0.1 W Gifford-McMahon cryocooler. A time-resolved readout technique, where output signals from each element enter the SFQ readout circuit with finite time intervals, revealed crosstalk-free operation of the four-element SSPD array connected with the SFQ readout circuit. The timing jitter and the system detection efficiency were measured to be 50 ps and 11.4%, respectively, which were comparable to the performance of practical single-pixel SSPD systems.
Feedback control of superconducting quantum circuits
Ristè, D.
2014-01-01
Superconducting circuits have recently risen to the forefront of the solid-state prototypes for quantum computing. Reaching the stage of robust quantum computing requires closing the loop between measurement and control of quantum bits (qubits). This thesis presents the realization of feedback contr
Effect of mutual inductance coupling on superconducting flux qubit decoherence
Institute of Scientific and Technical Information of China (English)
Yanyan Jiang; Hualan Xu; Yinghua Ji
2009-01-01
In the Born-Markov approximation and two-level approximation, and using the Bloch-Redfield equation, the decoherence property of superconducting quantum circuit with a flux qubit is investigated. The influence on decoherence of the mutual inductance coupling between the circuit components is complicated. The mutual inductance coupling between different loops will decrease the decoherence time. However, the mutual inductance coupling of the same loop, in a certain interval, will increase the decoherence time. Therefore, we can control the decoherence time by changing the mutual inductance parameters such as the strength and direction of coupling.
Controlling superconductivity by tunable quantum critical points.
Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson
2015-03-04
The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5.
Emulation of complex open quantum systems using superconducting qubits
Mostame, Sarah; Huh, Joonsuk; Kreisbeck, Christoph; Kerman, Andrew J.; Fujita, Takatoshi; Eisfeld, Alexander; Aspuru-Guzik, Alán
2017-02-01
With quantum computers being out of reach for now, quantum simulators are alternative devices for efficient and accurate simulation of problems that are challenging to tackle using conventional computers. Quantum simulators are classified into analog and digital, with the possibility of constructing "hybrid" simulators by combining both techniques. Here we focus on analog quantum simulators of open quantum systems and address the limit that they can beat classical computers. In particular, as an example, we discuss simulation of the chlorosome light-harvesting antenna from green sulfur bacteria with over 250 phonon modes coupled to each electronic state. Furthermore, we propose physical setups that can be used to reproduce the quantum dynamics of a standard and multiple-mode Holstein model. The proposed scheme is based on currently available technology of superconducting circuits consist of flux qubits and quantum oscillators.
Improved superconducting quantum interference devices by resistance asymmetry
Testa, G.; Pagano, S.; Sarnelli, E.; Calidonna, C. R.; Furnari, M. Mango
2001-10-01
Direct current superconducting quantum interference devices made by Josephson junctions with asymmetric shunt resistances have been numerically investigated in the low temperature regime. When combined with a damping resistance, the asymmetry leads to a flux to voltage transfer coefficient several times larger than the one typical of symmetric devices, together with a lower magnetic flux noise. These results show that this type of asymmetric device may replace the standard ones in a large number of magnetometric applications, improving the sensitivity performance. The large transfer coefficient may also simplify the readout electronics allowing a direct coupling of asymmetric devices to an external preamplifier, without the need of an impedance matching flux transformer.
Probing quantum coherence in arrays of superconducting qubits
Energy Technology Data Exchange (ETDEWEB)
Liguori, Alexandra; Rivas, Angel; Huelga, Susana; Plenio, Martin [Institut fuer Theoretische Physik, Universitaet Ulm, D-89069 Ulm (Germany)
2011-07-01
In the mid-80's the so-called phenomenon of dynamic localization was shown for a charged particle moving under the influence of a sinusoidally-varying time-dependent electric field, and more recently similar resonances in the conduction were found to be present also in ion channels. In this work we study the conditions under which this dynamic localization can be found in arrays of superconducting qubits. This phenomenon can serve as a signature of quantum coherence in such systems and moreover could be checked experimentally by various groups constructing arrays of superconducting flux qubits.
Quantum Magnetomechanics with Levitating Superconducting Microspheres
Romero-Isart, O; Navau, C; Sanchez, A; Cirac, J I
2011-01-01
We show that by magnetically trapping a superconducting microsphere close to a quantum circuit, it is experimentally feasible to perform ground state cooling and to prepare quantum superpositions of the center-of-mass motion of the microsphere. Due to the absence of clamping losses and time dependent electromagnetic fields, the mechanical motion of micrometer-sized metallic spheres in the Meissner state is predicted to be extremely well isolated from the environment. Hence, we propose to combine the technology of magnetic mictrotraps and superconducting qubits to bring relatively large objects to the quantum regime.
Experimental Quantum Randomness Processing Using Superconducting Qubits
Yuan, Xiao; Liu, Ke; Xu, Yuan; Wang, Weiting; Ma, Yuwei; Zhang, Fang; Yan, Zhaopeng; Vijay, R.; Sun, Luyan; Ma, Xiongfeng
2016-07-01
Coherently manipulating multipartite quantum correlations leads to remarkable advantages in quantum information processing. A fundamental question is whether such quantum advantages persist only by exploiting multipartite correlations, such as entanglement. Recently, Dale, Jennings, and Rudolph negated the question by showing that a randomness processing, quantum Bernoulli factory, using quantum coherence, is strictly more powerful than the one with classical mechanics. In this Letter, focusing on the same scenario, we propose a theoretical protocol that is classically impossible but can be implemented solely using quantum coherence without entanglement. We demonstrate the protocol by exploiting the high-fidelity quantum state preparation and measurement with a superconducting qubit in the circuit quantum electrodynamics architecture and a nearly quantum-limited parametric amplifier. Our experiment shows the advantage of using quantum coherence of a single qubit for information processing even when multipartite correlation is not present.
Experimental Quantum Randomness Processing Using Superconducting Qubits.
Yuan, Xiao; Liu, Ke; Xu, Yuan; Wang, Weiting; Ma, Yuwei; Zhang, Fang; Yan, Zhaopeng; Vijay, R; Sun, Luyan; Ma, Xiongfeng
2016-07-01
Coherently manipulating multipartite quantum correlations leads to remarkable advantages in quantum information processing. A fundamental question is whether such quantum advantages persist only by exploiting multipartite correlations, such as entanglement. Recently, Dale, Jennings, and Rudolph negated the question by showing that a randomness processing, quantum Bernoulli factory, using quantum coherence, is strictly more powerful than the one with classical mechanics. In this Letter, focusing on the same scenario, we propose a theoretical protocol that is classically impossible but can be implemented solely using quantum coherence without entanglement. We demonstrate the protocol by exploiting the high-fidelity quantum state preparation and measurement with a superconducting qubit in the circuit quantum electrodynamics architecture and a nearly quantum-limited parametric amplifier. Our experiment shows the advantage of using quantum coherence of a single qubit for information processing even when multipartite correlation is not present.
Quantum State Transfer between Charge and Flux Qubits in Circuit-QED
Institute of Scientific and Technical Information of China (English)
WU Qin-Qin; LIAO Jie-Qiao; KUANG Le-Man
2008-01-01
@@ We propose a scheme to implement quantum state transfer in a hybrid circuit quantum electrodynamics (QED)system which consists of a superconducting charge qubit, a flux qubit, and a transmission line resonator (TLR).It is shown that quantum state transfer between the charge qubit and the flux qubit can be realized by using the TLR as the data bus.
Coherent oscillations in a superconducting tunable flux qubit manipulated without microwaves
Energy Technology Data Exchange (ETDEWEB)
Poletto, S; Lisenfeld, J; Lukashenko, A; Ustinov, A V [Physikalisches Institut, Universitaet Karlsruhe (Thailand), D-76131 Karlsruhe (Germany); Chiarello, F; Castellano, M G; Torrioli, G [Istituto di Fotonica e Nanotecnologie, CNR, 00156 Roma (Italy); Cosmelli, C [Dipartimento Fisica, Universita di Roma La Sapienza, 00185 Roma (Italy); Carelli, P [Dipartimento Ingegneria Elettrica, Universita dell' Aquila, 67040 Monteluco di Roio (Italy)], E-mail: ustinov@physik.uni-karlsruhe.de
2009-01-15
We experimentally demonstrate coherent oscillations of a tunable superconducting flux qubit by manipulating its energy potential with a nanosecond-long pulse of magnetic flux. The occupation probabilities of two persistent current states oscillate at a frequency ranging from 6 GHz to 21 GHz, tunable by changing the amplitude of the flux pulse. The demonstrated operation mode could allow quantum gates to be realized in less than 100 ps, which is much shorter than gate times attainable in other superconducting qubits. Another advantage of this type of qubit is its immunity to both thermal and magnetic field fluctuations.
Two-dimensional lattice gauge theories with superconducting quantum circuits
Energy Technology Data Exchange (ETDEWEB)
Marcos, D., E-mail: david.marcos@me.com [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Widmer, P. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Rico, E. [IPCMS (UMR 7504) and ISIS (UMR 7006), University of Strasbourg and CNRS, 67000 Strasbourg (France); Hafezi, M. [Joint Quantum Institute, NIST/University of Maryland, College Park 20742 (United States); Department of Electrical Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742 (United States); Rabl, P. [Institute of Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Wien (Austria); Wiese, U.-J. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Zoller, P. [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria)
2014-12-15
A quantum simulator of U(1) lattice gauge theories can be implemented with superconducting circuits. This allows the investigation of confined and deconfined phases in quantum link models, and of valence bond solid and spin liquid phases in quantum dimer models. Fractionalized confining strings and the real-time dynamics of quantum phase transitions are accessible as well. Here we show how state-of-the-art superconducting technology allows us to simulate these phenomena in relatively small circuit lattices. By exploiting the strong non-linear couplings between quantized excitations emerging when superconducting qubits are coupled, we show how to engineer gauge invariant Hamiltonians, including ring-exchange and four-body Ising interactions. We demonstrate that, despite decoherence and disorder effects, minimal circuit instances allow us to investigate properties such as the dynamics of electric flux strings, signaling confinement in gauge invariant field theories. The experimental realization of these models in larger superconducting circuits could address open questions beyond current computational capability.
Saito, Shiro; Zhu, Xiaobo; Amsüss, Robert; Matsuzaki, Yuichiro; Kakuyanagi, Kosuke; Shimo-Oka, Takaaki; Mizuochi, Norikazu; Nemoto, Kae; Munro, William J; Semba, Kouichi
2013-09-06
We have built a hybrid system composed of a superconducting flux qubit (the processor) and an ensemble of nitrogen-vacancy centers in diamond (the memory) that can be directly coupled to one another, and demonstrated how information can be transferred from the flux qubit to the memory, stored, and subsequently retrieved. We have established the coherence properties of the memory and succeeded in creating an entangled state between the processor and memory, demonstrating how the entangled state's coherence is preserved. Our results are a significant step towards using an electron spin ensemble as a quantum memory for superconducting qubits.
Toward a superconducting quantum computer. Harnessing macroscopic quantum coherence.
Tsai, Jaw-Shen
2010-01-01
Intensive research on the construction of superconducting quantum computers has produced numerous important achievements. The quantum bit (qubit), based on the Josephson junction, is at the heart of this research. This macroscopic system has the ability to control quantum coherence. This article reviews the current state of quantum computing as well as its history, and discusses its future. Although progress has been rapid, the field remains beset with unsolved issues, and there are still many new research opportunities open to physicists and engineers.
Superconducting Quantum Arrays for Broadband RF Systems
Kornev, V.; Sharafiev, A.; Soloviev, I.; Kolotinskiy, N.; Mukhanov, O.
2014-05-01
Superconducting Quantum Arrays (SQAs), homogenous arrays of Superconducting Quantum Cells, are developed for implementation of broadband radio frequency (RF) systems capable of providing highly linear magnetic signal to voltage transfer with high dynamic range, including active electrically small antennas (ESAs). Among the proposed quantum cells which are bi-SQUID and Differential Quantum Cell (DQC), the latter delivered better performance for SQAs. A prototype of the transformer-less active ESA based on a 2D SQA with nonsuperconducting electric connection of the DQCs was fabricated using HYPRES niobium process with critical current density 4.5 kA/cm2. The measured voltage response is characterized by a peak-to-peak swing of ~100 mV and steepness of ~6500 μV/μT.
Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits.
Marcos, D; Wubs, M; Taylor, J M; Aguado, R; Lukin, M D; Sørensen, A S
2010-11-19
We propose a method to achieve coherent coupling between nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the magnetic coupling can be used to achieve a coherent transfer of quantum information between the flux qubit and an ensemble of NV centers. This enables a long-term memory for a SC quantum processor and possibly an interface between SC qubits and light.
Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits
DEFF Research Database (Denmark)
Marcos, D.; Wubs, Martijn; Taylor, J.M.
2010-01-01
We propose a method to achieve coherent coupling between nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the ma......, the magnetic coupling can be used to achieve a coherent transfer of quantum information between the flux qubit and an ensemble of NV centers. This enables a long-term memory for a SC quantum processor and possibly an interface between SC qubits and light....
Institute of Scientific and Technical Information of China (English)
MAO Hai-yan; WANG Fu-ren; MENG Shu-chao; MAO Bo; LI Zhuang-zhi; NIE Rui-juan; LIU Xin-yuan; DAI Yuan-dong
2006-01-01
A new type of HTc superconducting film combshape resonator for radio frequency superconducting quantum interference devices (RF SQUID) has been designed.This new type of superconducting film comb-shape resonator is formed by a foursquare microstrip line without a flux concentrator.The range of the center frequency of this type of resonator varies from 800 MHz to 1300 MHz by changing the length of the teeth.In this paper,we report on simulating the relationship of the value of the center frequency and the length of the teeth,and testing the noise of HTc RF SQUID coupling this comb-shape resonator.
Tuning the Gap of a Superconducting Flux Qubit
Paauw, F.G.; Fedorov, A.; Harmans, C.J.P.M.; Mooij, J.E.
2009-01-01
We experimentally demonstrate the in situ tunability of the minimum energy splitting (gap) of a superconducting flux qubit by means of an additional flux loop. Pulses applied via a local control line allow us to tune the gap over a range of several GHz on a nanosecond time scale. The strong flux sen
Superconducting circuits for quantum information: an outlook.
Devoret, M H; Schoelkopf, R J
2013-03-08
The performance of superconducting qubits has improved by several orders of magnitude in the past decade. These circuits benefit from the robustness of superconductivity and the Josephson effect, and at present they have not encountered any hard physical limits. However, building an error-corrected information processor with many such qubits will require solving specific architecture problems that constitute a new field of research. For the first time, physicists will have to master quantum error correction to design and operate complex active systems that are dissipative in nature, yet remain coherent indefinitely. We offer a view on some directions for the field and speculate on its future.
Controllable injector for local flux entry into superconducting films
Energy Technology Data Exchange (ETDEWEB)
Carmo, D.; Colauto, F.; de Andrade, A. M. H.; Oliveira, A. A. M.; Ortiz, W. A.; Johansen, T. H.
2016-07-21
A superconducting flux injector (SFI) has been designed to allow for controlled injections of magnetic flux into a superconducting film from a predefined location along the edge. The SFI is activated by an external current pulse, here chosen to be 200 ms long, and it is demonstrated on films of Nb that the amount of injected flux is controlled by the pulse height. Examples of injections at two different temperatures where the flux enters by stimulated flux-flow and by triggered thermomagnetic avalanches are presented. The boundary between the two types of injection is determined and discussed. The SFI opens up for active use of phenomena which up to now have been considered hazardous for a safe operation of superconducting devices.
Macroscopic quantum oscillator based on a flux qubit
Energy Technology Data Exchange (ETDEWEB)
Singh, Mandip, E-mail: mandip@iisermohali.ac.in
2015-09-25
In this paper a macroscopic quantum oscillator is proposed, which consists of a flux-qubit in the form of a cantilever. The net magnetic flux threading through the flux-qubit and the mechanical degrees of freedom of the cantilever are naturally coupled. The coupling between the cantilever and the magnetic flux is controlled through an external magnetic field. The ground state of the flux-qubit-cantilever turns out to be an entangled quantum state, where the cantilever deflection and the magnetic flux are the entangled degrees of freedom. A variant, which is a special case of the flux-qubit-cantilever without a Josephson junction, is also discussed. - Highlights: • In this paper a flux-qubit-cantilever is proposed. • Coupling can be varied by an external magnetic field. • Ground state is a macroscopic entangled quantum state. • Ground state of the superconducting-loop-oscillator is a macroscopic quantum superposition. • Proposed scheme is based on a generalized quantum approach.
Dispersive Response of a Disordered Superconducting Quantum Metamaterial
Directory of Open Access Journals (Sweden)
Dmitriy S. Shapiro
2015-04-01
Full Text Available We consider a disordered quantum metamaterial formed by an array of superconducting flux qubits coupled to microwave photons in a cavity. We map the system on the Tavis-Cummings model accounting for the disorder in frequencies of the qubits. The complex transmittance is calculated with the parameters taken from state-of-the-art experiments. We demonstrate that photon phase shift measurements allow to distinguish individual resonances in the metamaterial with up to 100 qubits, in spite of the decoherence spectral width being remarkably larger than the effective coupling constant. Our simulations are in agreement with the results of the recently reported experiment.
rf superconducting quantum interference device metamaterials
Lazarides, N.; Tsironis, G. P.
2007-04-01
A rf superconducting quantum interference device (SQUID) array in an alternating magnetic field is investigated with respect to its effective magnetic permeability, within the effective medium approximation. This system acts as an inherently nonlinear magnetic metamaterial, leading to negative magnetic response, and thus negative permeability above the resonance frequency of the individual SQUIDs. Moreover, the permeability exhibits oscillatory behavior at low field intensities, allowing its tuning by a slight change of the intensity of the applied field.
Quasi-one-dimensional intermittent flux behavior in superconducting films
DEFF Research Database (Denmark)
Qviller, A. J.; Yurchenko, V. V.; Galperin, Y. M.
2012-01-01
. The intermittent behavior shows no threshold value in the applied field, in contrast to conventional flux jumping. The results strongly suggest that the quasi-one-dimensional flux jumps are of a different nature than the thermomagnetic dendritic (branching) avalanches that are commonly found in superconducting...
Hua, Ming; Tao, Ming-Jie; Deng, Fu-Guo
2016-02-24
We propose a quantum processor for the scalable quantum computation on microwave photons in distant one-dimensional superconducting resonators. It is composed of a common resonator R acting as a quantum bus and some distant resonators rj coupled to the bus in different positions assisted by superconducting quantum interferometer devices (SQUID), different from previous processors. R is coupled to one transmon qutrit, and the coupling strengths between rj and R can be fully tuned by the external flux through the SQUID. To show the processor can be used to achieve universal quantum computation effectively, we present a scheme to complete the high-fidelity quantum state transfer between two distant microwave-photon resonators and another one for the high-fidelity controlled-phase gate on them. By using the technique for catching and releasing the microwave photons from resonators, our processor may play an important role in quantum communication as well.
Controlling flux flow dissipation by changing flux pinning in superconducting films
Energy Technology Data Exchange (ETDEWEB)
Grimaldi, G.; Leo, A.; Nigro, A.; Pace, S. [CNR SPIN Salerno and Dipartimento di Fisica ' ' E. R. Caianiello' ' , Universita degli Studi di Salerno, via Ponte Don Melillo, 84084 Fisciano (Italy); Silhanek, A. V. [Department de Physique, Universite de Liege, B-4000 Sart Tilman (Belgium); INPAC-Institute for Nanoscale Physics and Chemistry, Nanoscale Superconductivity and Magnetism Group, K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Verellen, N.; Moshchalkov, V. V. [INPAC-Institute for Nanoscale Physics and Chemistry, Nanoscale Superconductivity and Magnetism Group, K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Milosevic, M. V. [Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen (Belgium); Casaburi, A.; Cristiano, R. [Istituto di Cibernetica ' ' E. Caianiello' ' , CNR, 80078 Pozzuoli (Italy)
2012-05-14
We study the flux flow state in superconducting materials characterized by rather strong intrinsic pinning, such as Nb, NbN, and nanostructured Al thin films, in which we drag the superconducting dissipative state into the normal state by current biasing. We modify the vortex pinning strength either by ion irradiation, by tuning the measuring temperature or by including artificial pinning centers. We measure critical flux flow voltages for all materials and the same effect is observed: switching to low flux flow dissipations at low fields for an intermediate pinning regime. This mechanism offers a way to additionally promote the stability of the superconducting state.
Quantum Computing Using Superconducting Qubits
2006-04-01
highlighted in the " Molecular Motors" first feature article of the November, 2002, Physics Today, page 38. http://www.physicstoday.org/vol-5 5/iss-I I...12-2003. the article was in http://www.mosac.com/ fisica /news/leggi.php?codice= 191. News coverage in French include the following three newspapers... molecular vibra- Josephson junction devices have been proposed and experi- tional mode [12], motional quantum states of a trapped - - mentally
Quantum device prospects of superconducting nanodiamond films
Mtsuko, D.; Churochkin, D.; Bhattacharyya, S.
2016-02-01
Nanostructured semiconducting carbon system, described by as a superlattice-like structure demonstrated its potential in switching device applications based on the quantum tunneling through the insulating carbon layer. This switching property can be enhanced further with the association of Josephson's tunneling between two superconducting carbon (diamond) grains separated by a very thin layer of carbon which holds the structure of the film firmly. The superconducting nanodiamond heterostructures form qubits which can lead to the development of quantum computers provided the effect of disorder present in these structure can be firmly understood. Presently we concentrate on electrical transport properties of heavily boron-doped nanocrystalline diamond films around the superconducting transition temperature measured as a function of magnetic fields and the applied bias current. Microstructure of these films is described by a two dimensional superlattice system which can also contain paramagnetic impurities. We report observation of anomalous negative Hall resistance in these films close to the superconductor-insulator-normal phase transition in the resistance versus temperature plots at low bias currents at zero and low magnetic field. The negative Hall effect is found to be suppressed as the bias current increase. Magnetoresistance study shows a distinct peak at zero field when measured in the low current regimes which suggest a superconductor-insulator-superconductor structure of films. Current vs. voltage characteristics show signature of π-Josephson like behaviour which can give rise to a characteristic frequency of several hundred of gigahertz. Signature of spin flipping also shows novel spintronic device applications.
Quantum memristor in a superconducting circuit
Salmilehto, Juha; Sanz, Mikel; di Ventra, Massimiliano; Solano, Enrique
Memristors, resistive elements that retain information of their past, have garnered interest due to their paradigm-changing potential in information processing and electronics. The emergent hysteretic behaviour allows for novel architectural applications and has recently been classically demonstrated in a simplified superconducting setup using the phase-dependent conductance in the tunnel-junction-microscopic model. In this contribution, we present a truly quantum model for a memristor constructed using established elements and techniques in superconducting nanoelectronics, and explore the parameters for feasible operation as well as refine the methods for quantifying the memory retention. In particular, the memristive behaviour is shown to arise from quasiparticle-induced tunneling in the full dissipative model and can be observed in the phase-driven tunneling current. The relevant hysteretic behaviour should be observable using current state-of-the-art measurements for detecting quasiparticle excitations. Our theoretical findings constitute the first quantum memristor in a superconducting circuit and act as the starting point for designing further circuit elements that have non-Markovian characteristics The authors acknowledge support from the CCQED EU project and the Finnish Cultural Foundation.
Quantum synchronization in disordered superconducting metamaterials
Fistul, M. V.
2017-03-01
I report a theoretical study of collective coherent quantum-mechanical oscillations in disordered superconducting quantum metamaterials (SQMs), i.e. artificial arrays of interacting qubits (two-levels system). An unavoidable disorder in qubits parameters results in a substantial spread of qubits frequencies, and in the absence of electromagnetic interaction between qubits these individual quantum-mechanical oscillations of single qubits manifest themselves by a large number of small resonant dips in the frequency dependent transmission of electromagnetic waves, |S21(ω)|2. We show that even a weak electromagnetic interaction between adjacent qubits can overcome the disorder and establish completely or partially synchronized quantum-mechanical dynamic state in the disordered SQM. In such a state a large amount of qubits displays the collective quantum mechanical oscillations, and this collective behavior manifests itself by a few giant resonant dips in the |S21(ω)|2 dependence. The size of a system r0 showing the collective (synchronized) quantum-mechanical behavior is determined in the one-dimensional SQMs as r0 ≃ a [K/δΔ]2, where K, δΔ, a are the effective energy of nearest-neighbor interaction, the spread of qubits energy splitting, and the distance between qubits, accordingly. We show that this phenomenon is mapped to the Anderson localization of spinon-type excitations arising in the SQM.
Quantum synchronization in disordered superconducting metamaterials
Fistul, M. V.
2017-01-01
I report a theoretical study of collective coherent quantum-mechanical oscillations in disordered superconducting quantum metamaterials (SQMs), i.e. artificial arrays of interacting qubits (two-levels system). An unavoidable disorder in qubits parameters results in a substantial spread of qubits frequencies, and in the absence of electromagnetic interaction between qubits these individual quantum-mechanical oscillations of single qubits manifest themselves by a large number of small resonant dips in the frequency dependent transmission of electromagnetic waves, |S21(ω)|2. We show that even a weak electromagnetic interaction between adjacent qubits can overcome the disorder and establish completely or partially synchronized quantum-mechanical dynamic state in the disordered SQM. In such a state a large amount of qubits displays the collective quantum mechanical oscillations, and this collective behavior manifests itself by a few giant resonant dips in the |S21(ω)|2 dependence. The size of a system r0 showing the collective (synchronized) quantum-mechanical behavior is determined in the one-dimensional SQMs as r0 ≃ a [K/δΔ]2, where K, δΔ, a are the effective energy of nearest-neighbor interaction, the spread of qubits energy splitting, and the distance between qubits, accordingly. We show that this phenomenon is mapped to the Anderson localization of spinon-type excitations arising in the SQM.
Nano-superconducting quantum interference devices with suspended junctions
Energy Technology Data Exchange (ETDEWEB)
Hazra, D.; Hasselbach, K. [Institut Néel, CNRS and Université Joseph Fourier, 25 Avenue des Martyrs, Grenoble (France); Kirtley, J. R. [Center for Probing the Nanoscale, Stanford University, Palo Alto, California 94305-4045 (United States)
2014-04-14
Nano-Superconducting Quantum Interference Devices (nano-SQUIDs) are usually fabricated from a single layer of either Nb or Al. We describe here a simple method for fabricating suspended nano-bridges in Nb/Al thin-film bilayers. We use these suspended bridges, which act as Josephson weak links, to fabricate nano-SQUIDs which show critical current oscillations at temperatures up to 1.5 K and magnetic flux densities up to over 20 mT. These nano-SQUIDs exhibit flux modulation depths intermediate between all-Al and all-Nb devices, with some of the desirable characteristics of both. The suspended geometry is attractive for magnetic single nanoparticle measurements.
Rabi model as a quantum coherent heat engine: From quantum biology to superconducting circuits
Altintas, Ferdi; Hardal, Ali Ü. C.; Müstecaplıoǧlu, Özgür E.
2015-02-01
We propose a multilevel quantum heat engine with a working medium described by a generalized Rabi model which consists of a two-level system coupled to a single-mode bosonic field. The model is constructed to be a continuum limit of a quantum biological description of light-harvesting complexes so that it can amplify quantum coherence by a mechanism which is a quantum analog of classical Huygens clocks. The engine operates in a quantum Otto cycle where the working medium is coupled to classical heat baths in the isochoric processes of the four-stroke cycle, while either the coupling strength or the resonance frequency is changed in the adiabatic stages. We found that such an engine can produce work with an efficiency close to the Carnot bound when it operates at low temperatures and in the ultrastrong-coupling regime. The interplay of the effects of quantum coherence and quantum correlations on the engine performance is discussed in terms of second-order coherence, quantum mutual information, and the logarithmic negativity of entanglement. We point out that the proposed quantum Otto engine can be implemented experimentally with modern circuit quantum electrodynamic systems where flux qubits can be coupled ultrastrongly to superconducting transmission-line resonators.
Optimal control of single flux quantum (SFQ) pulse sequences
Liebermann, Per; Wilhelm, Frank
Single flux quantum (SFQ) pulses are a natural candidate for on-chip control of superconducting qubits. High accuracy quantum gates are accessible with quantum optimal control methods. We apply trains of SFQ pulses to operate single qubit gates, under the constraint of fixed amplitude and duration of each pulse. Timing of the control pulses is optimized using genetic algorithms and simulated annealing, decreasing the average fidelity errorby several orders of magnitude. Furthermore we are able to reduce the gate time to the quantum speed limit. Leakage out of the qubit subspace as well as timing errors of the pulses are considered, exploring the robustness of our optimized sequence.This takes usone step further to a scalable quantum processor
Relativistic Quantum Teleportation with superconducting circuits
Friis, Nicolai; Truong, Kevin; Sabín, Carlos; Solano, Enrique; Johansson, Göran; Fuentes, Ivette
2012-01-01
We study the effects of relativistic motion on quantum teleportation and propose a realizable experiment where our results can be tested. We compute bounds on the optimal fidelity of teleportation when one of the observers undergoes non-uniform motion for a finite time. The upper bound to the optimal fidelity is degraded due to the observer's motion however, we discuss how this degradation can be corrected. These effects are observable for experimental parameters that are within reach of cutting-edge superconducting technology.
Magnetic Flux Dynamics in Horizontally Cooled Superconducting Cavities
Martinello, M; Grassellino, A; Crawford, A C; Melnychuk, O; Romanenko, A; Sergatkov, D A
2015-01-01
Previous studies on magnetic flux expulsion as a function of cooling details have been performed for superconducting niobium cavities with the cavity beam axis placed parallel respect to the helium cooling flow, and findings showed that for sufficient cooling thermogradients all magnetic flux could be expelled and very low residual resistance could be achieved. In this paper we investigate the flux trapping and its impact on radio frequency surface resistance when the resonators are positioned perpendicularly to the helium cooling flow, which is representative of how superconducting radio-frequency (SRF) cavities are cooled in an accelerator. We also extend the studies to different directions of applied magnetic field surrounding the resonator. Results show that in the cavity horizontal configuration there is a different impact of the various field components on the final surface resistance, and that several parameters have to be considered to understand flux dynamics. A newly discovered phenomenon of concent...
Optimal control and quantum simulations in superconducting quantum devices
Energy Technology Data Exchange (ETDEWEB)
Egger, Daniel J.
2014-10-31
Quantum optimal control theory is the science of steering quantum systems. In this thesis we show how to overcome the obstacles in implementing optimal control for superconducting quantum bits, a promising candidate for the creation of a quantum computer. Building such a device will require the tools of optimal control. We develop pulse shapes to solve a frequency crowding problem and create controlled-Z gates. A methodology is developed for the optimisation towards a target non-unitary process. We show how to tune-up control pulses for a generic quantum system in an automated way using a combination of open- and closed-loop optimal control. This will help scaling of quantum technologies since algorithms can calibrate control pulses far more efficiently than humans. Additionally we show how circuit QED can be brought to the novel regime of multi-mode ultrastrong coupling using a left-handed transmission line coupled to a right-handed one. We then propose to use this system as an analogue quantum simulator for the Spin-Boson model to show how dissipation arises in quantum systems.
Institute of Scientific and Technical Information of China (English)
Wu Yu-Lin; Deng Hui; Yu Hai-Feng; Xue Guang-Ming; Tian Ye; Li Jie; Chen Ying-Fei
2013-01-01
Besides serving as promising candidates for realizing quantum computing,superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested,giving rise to a vast field of intensive research work both theoretically and experimentally.In this paper we report our work on the fabrication of superconducting quantum circuits,starting from its building blocks:Al/AlOx/Al Josephson junctions.By using electron beam lithography patterning and shadow evaporation,we have fabricated aluminum Josephson junctions with a controllable critical current density (jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2.We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits.Furthermore,we have also fabricated superconducting quantum circuits such as superconducting flux qubits and charge-flux qubits.
Experiments on two-resonator circuit quantum electrodynamics. A superconducting quantum switch
Energy Technology Data Exchange (ETDEWEB)
Hoffmann, Elisabeth Christiane Maria
2013-05-29
The field of cavity quantum electrodynamics (QED) studies the interaction between light and matter on a fundamental level. In typical experiments individual natural atoms are interacting with individual photons trapped in three-dimensional cavities. Within the last decade the prospering new field of circuit QED has been developed. Here, the natural atoms are replaced by artificial solid state quantum circuits offering large dipole moments which are coupled to quasi-onedimensional cavities providing a small mode volume and hence a large vacuum field strength. In our experiments Josephson junction based superconducting quantum bits are coupled to superconducting microwave resonators. In circuit QED the number of parameters that can be varied is increased and regimes that are not accessible using natural atoms can be entered and investigated. Apart from design flexibility and tunability of system parameters a particular advantage of circuit QED is the scalability to larger system size enabled by well developed micro- and nanofabrication tools. When scaling up the resonator-qubit systems beyond a few coupled circuits, the rapidly increasing number of interacting subsystems requires an active control and directed transmission of quantum signals. This can, for example, be achieved by implementing switchable coupling between two microwave resonators. To this end, a superconducting flux qubit is used to realize a suitable coupling between two microwave resonators, all working in the Gigahertz regime. The resulting device is called quantum switch. The flux qubit mediates a second order tunable and switchable coupling between the resonators. Depending on the qubit state, this coupling can compensate for the direct geometric coupling of the two resonators. As the qubit may also be in a quantum superposition state, the switch itself can be ''quantum'': it can be a superposition of ''on'' and ''off''. This work
Simulation of the superconducting multiturn flux transformer integrated with a coplanar resonator
Yi, H. R.; Zhang, Y.; Klein, N.
2000-06-01
The analysis of the structure of a superconducting multiturn flux transformer integrated with a coplanar resonator for radio-frequency superconducting quantum interference devices is described. Electromagnetic simulations indicate that the loss is dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The simulated current distribution at its resonant frequency shows that the highest current density is distributed on the multiturn input coil. This current distribution leads to a very high loss when the loss tangent of the dielectric film is high. However, for the same loss tangent of the dielectric film, it is possible to get a reasonably high unloaded quality factor by providing a normal shunt for the multiturn input coil.
Odd-Parity Superconductivity and the Ferromagnetic Quantum Critical Point
Huxley, A. D.; Yates, S. J. C.; Lévy, F.; Sheikin, I.
2007-05-01
The study of the emergence of superconductivity close to quantum critical points affords a powerful means to identify the mechanism that drives the formation of unconventional superconductivity in heavy fermion materials. The recent discovery of superconducting states close to quantum critical points in ferromagnets UGe2 and URhGe is reviewed in this light. For URhGe we examine whether the predominant type of magnetic excitations involved are longitudinal excitations, hitherto considered theoretically to be the most promising candidate to mediate equal-spin-paired superconductivity.
Dielectric surface loss in superconducting resonators with flux-trapping holes
Chiaro, B.; Megrant, A.; Dunsworth, A.; Chen, Z.; Barends, R.; Campbell, B.; Chen, Y.; Fowler, A.; Hoi, I. C.; Jeffrey, E.; Kelly, J.; Mutus, J.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Martinis, John M.
2016-10-01
Surface distributions of two level system (TLS) defects and magnetic vortices are limiting dissipation sources in superconducting quantum circuits. Arrays of flux-trapping holes are commonly used to eliminate loss due to magnetic vortices, but may increase dielectric TLS loss. We find that dielectric TLS loss increases by approximately 25% for resonators with a hole array beginning 2 μ {{m}} from the resonator edge, while the dielectric loss added by holes further away was below measurement sensitivity. Other forms of loss were not affected by the holes. Additionally, we estimate the loss due to residual magnetic effects to be 9× {10}-10 {μ {{T}}}-1 for resonators patterned with flux-traps and operated in magnetic fields up to 5 μ {{T}}. This is orders of magnitude below the total loss of the best superconducting coplanar waveguide resonators.
SQUID detected NMR and NQR. Superconducting Quantum Interference Device.
Augustine, M P; TonThat, D M; Clarke, J
1998-03-01
The dc Superconducting QUantum Interference Device (SQUID) is a sensitive detector of magnetic flux, with a typical flux noise of the order 1 muphi0 Hz(-1/2) at liquid helium temperatures. Here phi0 = h/2e is the flux quantum. In our NMR or NQR spectrometer, a niobium wire coil wrapped around the sample is coupled to a thin film superconducting coil deposited on the SQUID to form a flux transformer. With this untuned input circuit the SQUID measures the flux, rather than the rate of change of flux, and thus retains its high sensitivity down to arbitrarily low frequencies. This feature is exploited in a cw spectrometer that monitors the change in the static magnetization of a sample induced by radio frequency irradiation. Examples of this technique are the detection of NQR in 27Al in sapphire and 11B in boron nitride, and a level crossing technique to enhance the signal of 14N in peptides. Research is now focused on a SQUID-based spectrometer for pulsed NQR and NMR, which has a bandwidth of 0-5 MHz. This spectrometer is used with spin-echo techniques to measure the NQR longitudinal and transverse relaxation times of 14N in NH4ClO4, 63+/-6 ms and 22+/-2 ms, respectively. With the aid of two-frequency pulses to excite the 359 kHz and 714 kHz resonances in ruby simultaneously, it is possible to obtain a two-dimensional NQR spectrum. As a third example, the pulsed spectrometer is used to study NMR spectrum of 129Xe after polariza-tion with optically pumped Rb. The NMR line can be detected at frequencies as low as 200 Hz. At fields below about 2 mT the longitudinal relaxation time saturates at about 2000 s. Two recent experiments in other laboratories have extended these pulsed NMR techniques to higher temperatures and smaller samples. In the first, images were obtained of mineral oil floating on water at room temperature. In the second, a SQUID configured as a thin film gradiometer was used to detect NMR in a 50 microm particle of 195Pt at 6 mT and 4.2 K.
Flux flow pinning and resistive behavior in superconducting networks
Energy Technology Data Exchange (ETDEWEB)
Teitel, S.
1990-10-01
We have studied the behavior of superconducting networks in terms of XY and Coulomb gas models. The dynamics of frustrated Josephson junction arrays has been simulated, with a view toward understanding the effects of vortex correlations on flux flow resistance. Randomness has been introduced, and its effects on the superconducting transition, and vortex mobility, have been studied. A three dimensional network has been simulated to study the effects of vortex line entanglement in high temperature superconductors. Preliminary calculations are in progress. The two dimensional classical Coulomb gas where charges map onto vortices in the superconducting network, has been simulated. The melting transitions of ordered charge (vortex) lattices have been studied, and we find clear evidence that these transitions do not have the critical behavior expected from standard symmetry analysis.
Energy Technology Data Exchange (ETDEWEB)
Nakanishi, Masakazu, E-mail: m.nakanishi@aist.go.jp [Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, AIST Central-3, 1-1, Umezono, Tsukuba, Ibaraki 305-8563 (Japan)
2014-10-15
Responses of a superconducting quantum interference device (SQUID) are periodically dependent on magnetic flux coupling to its superconducting ring and the period is a flux quantum (Φ{sub o} = h/2e, where h and e, respectively, express Planck's constant and elementary charge). Using this periodicity, we had proposed a digital to analog converter using a SQUID (SQUID DAC) of first generation with linear current output, interval of which corresponded to Φ{sub o}. Modification for increasing dynamic range by interpolating within each interval is reported. Linearity of the interpolation was also based on the quantum periodicity. A SQUID DAC with dynamic range of about 1.4 × 10{sup 7} was created as a demonstration.
Quantum information processing with superconducting circuits: a review
Wendin, G.
2017-10-01
During the last ten years, superconducting circuits have passed from being interesting physical devices to becoming contenders for near-future useful and scalable quantum information processing (QIP). Advanced quantum simulation experiments have been shown with up to nine qubits, while a demonstration of quantum supremacy with fifty qubits is anticipated in just a few years. Quantum supremacy means that the quantum system can no longer be simulated by the most powerful classical supercomputers. Integrated classical-quantum computing systems are already emerging that can be used for software development and experimentation, even via web interfaces. Therefore, the time is ripe for describing some of the recent development of superconducting devices, systems and applications. As such, the discussion of superconducting qubits and circuits is limited to devices that are proven useful for current or near future applications. Consequently, the centre of interest is the practical applications of QIP, such as computation and simulation in Physics and Chemistry.
Flux avalanches in Nb superconducting shifted strip arrays
Tsuchiya, Y.; Mawatari, Y.; Ibuka, J.; Tada, S.; Pyon, S.; Nagasawa, S.; Hidaka, M.; Maezawa, M.; Tamegai, T.
2013-09-01
Flux penetrations into three-dimensional Nb superconducting strip arrays, where two layers of strip arrays are stacked by shifting a half period, are studied using a magneto-optical imaging method. Flux avalanches are observed when the overlap between the top and bottom layers is large even if the width of each strip is well below the threshold value. In addition, anomalous linear avalanches perpendicular to the strip are observed in the shifted strip array when the overlap is very large and the thickness of the superconductor is greater than the penetration depth. We discuss possible origins for the flux avalanches, including linear ones, by considering flux penetration calculated by the Campbell method assuming the Bean model.
A strict experimental test of macroscopic realism in a superconducting flux qubit.
Knee, George C; Kakuyanagi, Kosuke; Yeh, Mao-Chuang; Matsuzaki, Yuichiro; Toida, Hiraku; Yamaguchi, Hiroshi; Saito, Shiro; Leggett, Anthony J; Munro, William J
2016-11-04
Macroscopic realism is the name for a class of modifications to quantum theory that allow macroscopic objects to be described in a measurement-independent manner, while largely preserving a fully quantum mechanical description of the microscopic world. Objective collapse theories are examples which aim to solve the quantum measurement problem through modified dynamical laws. Whether such theories describe nature, however, is not known. Here we describe and implement an experimental protocol capable of constraining theories of this class, that is more noise tolerant and conceptually transparent than the original Leggett-Garg test. We implement the protocol in a superconducting flux qubit, and rule out (by ∼84 s.d.) those theories which would deny coherent superpositions of 170 nA currents over a ∼10 ns timescale. Further, we address the 'clumsiness loophole' by determining classical disturbance with control experiments. Our results constitute strong evidence for the superposition of states of nontrivial macroscopic distinctness.
Orgiazzi, J.-L.; Deng, C.; Layden, D.; Marchildon, R.; Kitapli, F.; Shen, F.; Bal, M.; Ong, F. R.; Lupascu, A.
2016-03-01
We report experiments on superconducting flux qubits in a circuit quantum electrodynamics (cQED) setup. Two qubits, independently biased and controlled, are coupled to a coplanar waveguide resonator. Dispersive qubit state readout reaches a maximum contrast of 72%. We measure energy relaxation times at the symmetry point of 5 and 10 μ s , corresponding to 7 and 20 μ s when relaxation through the resonator due to Purcell effect is subtracted out, and levels of flux noise of 2.6 and 2.7 μ Φ0/√{Hz} at 1 Hz for the two qubits. We discuss the origin of decoherence in the measured devices. The strong coupling between the qubits and the cavity leads to a large, cavity-mediated, qubit-qubit coupling. This coupling, which is characterized spectroscopically, reaches 38 MHz. These results demonstrate the potential of cQED as a platform for fundamental investigations of decoherence and quantum dynamics of flux qubits.
Entanglement and Quantum Error Correction with Superconducting Qubits
Reed, Matthew
2015-03-01
Quantum information science seeks to take advantage of the properties of quantum mechanics to manipulate information in ways that are not otherwise possible. Quantum computation, for example, promises to solve certain problems in days that would take a conventional supercomputer the age of the universe to decipher. This power does not come without a cost however, as quantum bits are inherently more susceptible to errors than their classical counterparts. Fortunately, it is possible to redundantly encode information in several entangled qubits, making it robust to decoherence and control imprecision with quantum error correction. I studied one possible physical implementation for quantum computing, employing the ground and first excited quantum states of a superconducting electrical circuit as a quantum bit. These ``transmon'' qubits are dispersively coupled to a superconducting resonator used for readout, control, and qubit-qubit coupling in the cavity quantum electrodynamics (cQED) architecture. In this talk I will give an general introduction to quantum computation and the superconducting technology that seeks to achieve it before explaining some of the specific results reported in my thesis. One major component is that of the first realization of three-qubit quantum error correction in a solid state device, where we encode one logical quantum bit in three entangled physical qubits and detect and correct phase- or bit-flip errors using a three-qubit Toffoli gate. My thesis is available at arXiv:1311.6759.
Simulating Zeno physics by a quantum quench with superconducting circuits
Tong, Qing-Jun; An, Jun-Hong; Kwek, L. C.; Luo, Hong-Gang; Oh, C. H.
2014-06-01
Studying out-of-equilibrium physics in quantum systems under quantum quench is of vast experimental and theoretical interest. Using periodic quantum quenches, we present an experimentally accessible scheme to simulate the quantum Zeno and anti-Zeno effects in an open quantum system of a single superconducting qubit interacting with an array of transmission line resonators. The scheme is based on the following two observations: First, compared with conventional systems, the short-time nonexponential decay in our superconducting circuit system is readily observed; and second, a quench-off process mimics an ideal projective measurement when its time duration is sufficiently long. Our results show the active role of quantum quench in quantum simulation and control.
Superconducting quantum node for entanglement and storage of microwave radiation.
Flurin, E; Roch, N; Pillet, J D; Mallet, F; Huard, B
2015-03-06
Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage, and retrieval of an optimally shaped propagating microwave field, with an efficiency as high as 80%. We then demonstrate a second essential ability, which is the time-controlled generation of an entangled state distributed between the node and a microwave channel.
Superconducting Quantum Node for Entanglement and Storage of Microwave Radiation
Flurin, E.; Roch, N.; Pillet, J. D.; Mallet, F.; Huard, B.
2015-03-01
Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage, and retrieval of an optimally shaped propagating microwave field, with an efficiency as high as 80%. We then demonstrate a second essential ability, which is the time-controlled generation of an entangled state distributed between the node and a microwave channel.
Tunable Broadband Transparency of Macroscopic Quantum Superconducting Metamaterials
Directory of Open Access Journals (Sweden)
Daimeng Zhang
2015-12-01
Full Text Available Narrow-band invisibility in an otherwise opaque medium has been achieved by electromagnetically induced transparency (EIT in atomic systems. The quantum EIT behavior can be classically mimicked by specially engineered metamaterials via carefully controlled interference with a “dark mode.” However, the narrow transparency window limits the potential applications that require a tunable wideband transparent performance. Here, we present a macroscopic quantum superconducting metamaterial with manipulative self-induced broadband transparency due to a qualitatively novel nonlinear mechanism that is different from conventional EIT or its classical analogs. A near-complete disappearance of resonant absorption under a range of applied rf flux is observed experimentally and explained theoretically. The transparency comes from the intrinsic bistability of the meta-atoms and can be tuned on and off easily by altering rf and dc magnetic fields, temperature, and history. Hysteretic in situ 100% tunability of transparency paves the way for autocloaking metamaterials, intensity-dependent filters, and fast-tunable power limiters.
Institute of Scientific and Technical Information of China (English)
Xiao-Feng Pang
2008-01-01
The properties and rules of motion of superconductive electrons in steady and time-dependent non-equilibrium states of superconductors are studied by using the Ginzberg-Landau (GL) equations and nonlinear quantum theory. In the absence of external fields, the superconductive electrons move in the solitons with certain energy and velocity in a uniform system, The superconductive electron is still a soliton under action of an electromagnetic field, but its amplitude, phase and shape are changed. Thus we conclude that super- conductivity is a result of motion of soliton of superconductive electrons. Since soliton has the feature of motion for retaining its energy and form, thus a permanent current occurs in superconductor. From these solutions of GL equations under action of an electromagnetic field, we gain the structure of vortex lines-magnetic flux lines observed experimentally in type-II superconductors. In the time-dependent non- equilibrium states of superconductor, the motions of superconductive electrons exhibit still the soliton features, but the shape and amplitude have changed. In an invariant electric-field, it moves in a constant acceleration. In the medium with dissipation, the superconductive electron behaves still like a soliton, although its form, amplitude, and velocity are altered. Thus we have to convince that the superconductive electron is essentially a soliton in both non-equilibrium and equilibrium superconductors.
Integrated superconducting detectors on semiconductors for quantum optics applications
Kaniber, M.; Flassig, F.; Reithmaier, G.; Gross, R.; Finley, J. J.
2016-05-01
Semiconductor quantum photonic circuits can be used to efficiently generate, manipulate, route and exploit nonclassical states of light for distributed photon-based quantum information technologies. In this article, we review our recent achievements on the growth, nanofabrication and integration of high-quality, superconducting niobium nitride thin films on optically active, semiconducting GaAs substrates and their patterning to realize highly efficient and ultra-fast superconducting detectors on semiconductor nanomaterials containing quantum dots. Our state-of-the-art detectors reach external detection quantum efficiencies up to 20 % for ~4 nm thin films and single-photon timing resolutions <72 ps. We discuss the integration of such detectors into quantum dot-loaded, semiconductor ridge waveguides, resulting in the on-chip, time-resolved detection of quantum dot luminescence. Furthermore, a prototype quantum optical circuit is demonstrated that enabled the on-chip generation of resonance fluorescence from an individual InGaAs quantum dot, with a linewidth <15 μeV displaced by 1 mm from the superconducting detector on the very same semiconductor chip. Thus, all key components required for prototype quantum photonic circuits with sources, optical components and detectors on the same chip are reported.
A nanoCryotron comparator can connect single-flux quantum circuits to conventional electronics
Zhao, Qing-Yuan; Dane, Andrew E; Berggren, Karl K; Ortlepp, Thomas
2016-01-01
Integration with conventional electronics offers a straightforward and economical approach to upgrading existing superconducting technologies, such as scaling up superconducting detectors into large arrays and combining single flux quantum (SFQ) digital circuits with semiconductor logic and memories. However, direct output signals from superconducting devices (e.g., Josephson junctions) are usually not compatible with the input requirements of conventional devices (e.g., transistors). Here, we demonstrate the use of a single three-terminal superconducting-nanowire device, called the nanocryotron (nTron), as a digital comparator to combine SFQ circuits with mature semiconductor circuits such as complementary metal oxide semiconductor (CMOS) circuits. Since SFQ circuits can digitize output signals from general superconducting devices and CMOS circuits can interface existing CMOS-compatible electronics, our results demonstrate the feasibility of a general architecture that uses an nTron as an interface to realiz...
Changing the flux flow state in weak pinning superconducting films
Energy Technology Data Exchange (ETDEWEB)
Leo, A., E-mail: antoleo@sa.infn.it [Physics Department E.R. Caianiello, University of Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy); CNR-SPIN Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy); Grimaldi, G. [CNR-SPIN Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy); Nigro, A. [Physics Department E.R. Caianiello, University of Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy); CNR-SPIN Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy); Bruno, E.; Priolo, F. [Matis IMM-CNR and Physics-Astronomy Department, Catania University, CT 95123 (Italy); Pace, S. [Physics Department E.R. Caianiello, University of Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy); CNR-SPIN Salerno, Via Giovanni Paolo II, 132, Stecca 9, I-84084 Fisciano, SA (Italy)
2014-08-15
Highlights: • We analyzed the effect of light ion irradiation on weak pinning superconductors. • We found the light ion irradiation has a strong impact on current currying stability. • We compared the results to the ones of the case of moderate strong pinning materials. - Abstract: The current carrying dissipative state well above the critical current it is known to be related to the pinning properties of the material and to the microscopic mechanisms of vortex dynamics. Moreover, it has been demonstrated that in low temperature superconducting films exhibiting moderately strong pinning the light ion irradiation has the effect of changing the distribution of the pinning centers without changing their pinning strength and this results into an increase of current stability in the flux flow state. Here we present the results of light ion irradiation on weak pinning superconducting films focusing on the influence of pinning properties of the material in the flux flow state. We realize that the possibility to switch to low dissipations by changing weak pinning is not straightforward.
Contextuality without nonlocality in a superconducting quantum system
Jerger, Markus; Reshitnyk, Yarema; Oppliger, Markus; Potočnik, Anton; Mondal, Mintu; Wallraff, Andreas; Goodenough, Kenneth; Wehner, Stephanie; Juliusson, Kristinn; Langford, Nathan K.; Fedorov, Arkady
2016-10-01
Classical realism demands that system properties exist independently of whether they are measured, while noncontextuality demands that the results of measurements do not depend on what other measurements are performed in conjunction with them. The Bell-Kochen-Specker theorem states that noncontextual realism cannot reproduce the measurement statistics of a single three-level quantum system (qutrit). Noncontextual realistic models may thus be tested using a single qutrit without relying on the notion of quantum entanglement in contrast to Bell inequality tests. It is challenging to refute such models experimentally, since imperfections may introduce loopholes that enable a realist interpretation. Here we use a superconducting qutrit with deterministic, binary-outcome readouts to violate a noncontextuality inequality while addressing the detection, individual-existence and compatibility loopholes. This evidence of state-dependent contextuality also demonstrates the fitness of superconducting quantum circuits for fault-tolerant quantum computation in surface-code architectures, currently the most promising route to scalable quantum computing.
Hardware-Efficient and Fully Autonomous Quantum Error Correction in Superconducting Circuits
Kapit, Eliot
2016-04-01
Superconducting qubits are among the most promising platforms for building a quantum computer. However, individual qubit coherence times are not far past the scalability threshold for quantum error correction, meaning that millions of physical devices would be required to construct a useful quantum computer. Consequently, further increases in coherence time are very desirable. In this Letter, we blueprint a simple circuit consisting of two transmon qubits and two additional lossy qubits or resonators, which is passively protected against all single-qubit quantum error channels through a combination of continuous driving and engineered dissipation. Photon losses are rapidly corrected through two-photon drive fields implemented with driven superconducting quantum interference device couplings, and dephasing from random potential fluctuations is heavily suppressed by the drive fields used to implement the multiqubit Hamiltonian. Comparing our theoretical model to published noise estimates from recent experiments on flux and transmon qubits, we find that logical state coherence could be improved by a factor of 40 or more compared to the individual qubit T1 and T2 using this technique. We thus demonstrate that there is substantial headroom for improving the coherence of modern superconducting qubits with a fairly modest increase in device complexity.
Hardware-Efficient and Fully Autonomous Quantum Error Correction in Superconducting Circuits.
Kapit, Eliot
2016-04-15
Superconducting qubits are among the most promising platforms for building a quantum computer. However, individual qubit coherence times are not far past the scalability threshold for quantum error correction, meaning that millions of physical devices would be required to construct a useful quantum computer. Consequently, further increases in coherence time are very desirable. In this Letter, we blueprint a simple circuit consisting of two transmon qubits and two additional lossy qubits or resonators, which is passively protected against all single-qubit quantum error channels through a combination of continuous driving and engineered dissipation. Photon losses are rapidly corrected through two-photon drive fields implemented with driven superconducting quantum interference device couplings, and dephasing from random potential fluctuations is heavily suppressed by the drive fields used to implement the multiqubit Hamiltonian. Comparing our theoretical model to published noise estimates from recent experiments on flux and transmon qubits, we find that logical state coherence could be improved by a factor of 40 or more compared to the individual qubit T_{1} and T_{2} using this technique. We thus demonstrate that there is substantial headroom for improving the coherence of modern superconducting qubits with a fairly modest increase in device complexity.
Nano-patterned superconducting surface for high quantum efficiency cathode
Hannon, Fay; Musumeci, Pietro
2017-03-07
A method for providing a superconducting surface on a laser-driven niobium cathode in order to increase the effective quantum efficiency. The enhanced surface increases the effective quantum efficiency by improving the laser absorption of the surface and enhancing the local electric field. The surface preparation method makes feasible the construction of superconducting radio frequency injectors with niobium as the photocathode. An array of nano-structures are provided on a flat surface of niobium. The nano-structures are dimensionally tailored to interact with a laser of specific wavelength to thereby increase the electron yield of the surface.
Nano-patterned superconducting surface for high quantum efficiency cathode
Energy Technology Data Exchange (ETDEWEB)
Hannon, Fay; Musumeci, Pietro
2017-03-07
A method for providing a superconducting surface on a laser-driven niobium cathode in order to increase the effective quantum efficiency. The enhanced surface increases the effective quantum efficiency by improving the laser absorption of the surface and enhancing the local electric field. The surface preparation method makes feasible the construction of superconducting radio frequency injectors with niobium as the photocathode. An array of nano-structures are provided on a flat surface of niobium. The nano-structures are dimensionally tailored to interact with a laser of specific wavelength to thereby increase the electron yield of the surface.
The origins of macroscopic quantum coherence in high temperature superconductivity
Energy Technology Data Exchange (ETDEWEB)
Turner, Philip, E-mail: ph.turner@napier.ac.uk [Edinburgh Napier University, 10 Colinton Road, Edinburgh EH10 5DT (United Kingdom); Nottale, Laurent, E-mail: laurent.nottale@obspm.fr [CNRS, LUTH, Observatoire de Paris-Meudon, 5 Place Janssen, 92190 Meudon (France)
2015-08-15
Highlights: • We propose a new theoretical approach to superconductivity in p-type cuprates. • Electron pairing mechanisms in the superconducting and pseudogap phases are proposed. • A scale free network of dopants is key to macroscopic quantum coherence. - Abstract: A new, theoretical approach to macroscopic quantum coherence and superconductivity in the p-type (hole doped) cuprates is proposed. The theory includes mechanisms to account for e-pair coupling in the superconducting and pseudogap phases and their inter relations observed in these materials. Electron pair coupling in the superconducting phase is facilitated by local quantum potentials created by static dopants in a mechanism which explains experimentally observed optimal doping levels and the associated peak in critical temperature. By contrast, evidence suggests that electrons contributing to the pseudogap are predominantly coupled by fractal spin waves (fractons) induced by the fractal arrangement of dopants. On another level, the theory offers new insights into the emergence of a macroscopic quantum potential generated by a fractal distribution of dopants. This, in turn, leads to the emergence of coherent, macroscopic spin waves and a second associated macroscopic quantum potential, possibly supported by charge order. These quantum potentials play two key roles. The first involves the transition of an expected diffusive process (normally associated with Anderson localization) in fractal networks, into e-pair coherence. The second involves the facilitation of tunnelling between localized e-pairs. These combined effects lead to the merger of the super conducting and pseudo gap phases into a single coherent condensate at optimal doping. The underlying theory relating to the diffusion to quantum transition is supported by Coherent Random Lasing, which can be explained using an analogous approach. As a final step, an experimental program is outlined to validate the theory and suggests a new
The Quantum Socket: Wiring for Superconducting Qubits - Part 2
Bejanin, J. H.; McConkey, T. G.; Rinehart, J. R.; Bateman, J. D.; Earnest, C. T.; McRae, C. H.; Rohanizadegan, Y.; Shiri, D.; Mariantoni, M.; Penava, B.; Breul, P.; Royak, S.; Zapatka, M.; Fowler, A. G.
Quantum computing research has reached a level of maturity where quantum error correction (QEC) codes can be executed on linear arrays of superconducting quantum bits (qubits). A truly scalable quantum computing architecture, however, based on practical QEC algorithms, requires nearest neighbor interaction between qubits on a two-dimensional array. Such an arrangement is not possible with techniques that rely on wire bonding. To address this issue, we have developed the quantum socket, a device based on three-dimensional wires that enables the control of superconducting qubits on a two-dimensional grid. In this talk, we present experimental results characterizing this type of wiring. We will show that the quantum socket performs exceptionally well for the transmission and reflection of microwave signals up to 10 GHz, while minimizing crosstalk between adjacent wires. Under realistic conditions, we measured an S21 of -5 dB at 6 GHz and an average crosstalk of -60 dB. We also describe time domain reflectometry results and arbitrary pulse transmission tests, showing that the quantum socket can be used to control superconducting qubits.
Quantum chemistry and charge transport in biomolecules with superconducting circuits
García-Álvarez, L.; Las Heras, U.; Mezzacapo, A.; Sanz, M.; Solano, E.; Lamata, L.
2016-06-01
We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.
Quantum chemistry and charge transport in biomolecules with superconducting circuits
García-Álvarez, L.; Las Heras, U.; Mezzacapo, A.; Sanz, M.; Solano, E.; Lamata, L.
2016-01-01
We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects. PMID:27324814
Quantum chemistry and charge transport in biomolecules with superconducting circuits.
García-Álvarez, L; Las Heras, U; Mezzacapo, A; Sanz, M; Solano, E; Lamata, L
2016-06-21
We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.
Engineering Dissipation to Generate Entanglement Between Remote Superconducting Quantum Bits
Schwartz, Mollie Elisheva
Superconducting quantum circuits provide a promising avenue for scalable quantum computation and simulation. Their chief advantage is that, unlike physical atoms or electrons, these ''artificial atoms'' can be designed with nearly-arbitrarily large coupling to one another and to their electromagnetic environment. This strong coupling allows for fast quantum bit (qubit) operations, and for efficient readout. However, strong coupling comes at a price: a qubit that is strongly coupled to its environment is also strongly susceptible to losses and dissipation, as coherent information leaks from the quantum system under study into inaccessible ''bath'' modes. Extensive work in the field is dedicated to engineering away these losses to the extent possible, and to using error correction to undo the effects of losses that are unavoidable. This dissertation explores an alternate approach to dissipation: we study avenues by which dissipation itself can be used to generate, rather than destroy, quantum resources. We do so specifically in the context of quantum entanglement, one of the most important and most counter-intuitive aspects of quantum mechanics. Entanglement generation and stabilization is critical to most non-trivial implementations of quantum computing and quantum simulation, as it is the property that distinguishes a multi-qubit quantum system from a string of classical bits. The ability to harness dissipation to generate, purify, and stabilize entanglement is therefore highly desirable. We begin with an overview of quantum dissipation and measurement, followed by an introduction to entanglement and to the superconducting quantum information architecture. We then discuss three sets of experiments that highlight and explore the powerful uses of dissipation in quantum systems. First, we use an entangling measurement to probabilistically generate entanglement between two qubits separated by more than one meter of ordinary cable. This represents the first achievement
Stimulating Uncertainty: Amplifying the Quantum Vacuum with Superconducting Circuits
Nation, P D; Blencowe, M P; Nori, Franco
2011-01-01
The ability to generate particles from the quantum vacuum is one of the most pro- found consequences of Heisenberg's uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been limited to a few cases. Superconducting circuit devices, driven by the goal to achieve a viable quantum computer, may soon be able to realize the elusive verification of the dynamical Casimir effect and analogue Hawking radiation. This article describes several mechanisms for generating photons from the quantum vacuum and emphasizes their connection to the well-known parametric amplifier from quantum optics. Discussed in detail is the possible realization of each mechanism, or its analogue, in superconducting circuit systems. The ability to selectively engineer these circuit devices highlights the relationship between the various amplification mechanisms.
Colloquium: Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits
Nation, P. D.; Johansson, J. R.; Blencowe, M. P.; Nori, Franco
2012-01-01
The ability to generate particles from the quantum vacuum is one of the most profound consequences of Heisenberg’s uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been limited to a few cases. Superconducting circuit devices, driven by the goal to achieve a viable quantum computer, have been used in the experimental demonstration of the dynamical Casimir effect, and may soon be able to realize the elusive verification of analog Hawking radiation. This Colloquium article describes several mechanisms for generating photons from the quantum vacuum and emphasizes their connection to the well-known parametric amplifier from quantum optics. Discussed in detail is the possible realization of each mechanism, or its analog, in superconducting circuit systems. The ability to selectively engineer these circuit devices highlights the relationship between the various amplification mechanisms.
Gain-assisted optical bistability and multistability in superconducting phase quantum circuits
Amini Sabegh, Z.; Maleki, M. A.; Mahmoudi, M.
2017-02-01
We study the absorption and optical bistability (OB) behavior of the superconducting phase quantum circuits in the four-level cascade and closed-loop configurations. It is shown that the OB is established in both configurations and it can be controlled by the intensity and frequency of applied fluxes. It is also demonstrated that the gain-assisted OB is generated in both configurations and can switch to the gain-assisted optical multistability (OM) only by changing the relative phase of applied fluxes in closed-loop quantum system. It is worth noting that the several significant output fluxes with negligible inputs can be seen in bistable behavior of the closed-loop configuration due to the nonlinear processing.
Observing single quantum trajectories of a superconducting qubit
Murch, K W; Macklin, C; Siddiqi, I
2013-01-01
The length of time that a quantum system can exist in a superposition state is determined by how strongly it interacts with its environment. This interaction entangles the quantum state with the inherent fluctuations of the environment. If these fluctuations are not measured, the environment can be viewed as a source of noise, causing random evolution of the quantum system from an initially pure state into a statistical mixture-a process known as decoherence. However, by accurately measuring the environment in real time, the quantum system can be maintained in a pure state and its time evolution described by a quantum trajectory conditioned on the measurement outcome. We employ weak measurements to monitor a microwave cavity embedding a superconducting qubit and track the individual quantum trajectories of the system. In this architecture, the environment is dominated by the fluctuations of a single electromagnetic mode of the cavity. Using a near-quantum-limited parametric amplifier, we selectively measure e...
High sensitivity double relaxation oscillation superconducting quantum interference devices
Adelerhof, Derk Jan; Adelerhof, Derk Jan; Kawai, Jun; Uehara, Gen; Kado, Hisashi
1994-01-01
Double relaxation oscillationsuperconducting quantum interference devices(SQUIDs) (DROSs) have been fabricated with estimated relaxation frequencies up to 14 GHz. Both the intrinsic flux noise and the performance in a flux locked loop with direct voltage readout have been studied. In flux locked
A nanocryotron comparator can connect single-flux-quantum circuits to conventional electronics
Zhao, Qing-Yuan; McCaughan, Adam N.; Dane, Andrew E.; Berggren, Karl K.; Ortlepp, Thomas
2017-04-01
Integration with conventional electronics offers a straightforward and economical approach to upgrading existing superconducting technologies, such as scaling up superconducting detectors into large arrays and combining single flux quantum (SFQ) digital circuits with semiconductor logic gates and memories. However, direct output signals from superconducting devices (e.g., Josephson junctions) are usually not compatible with the input requirements of conventional devices (e.g., transistors). Here, we demonstrate the use of a single three-terminal superconducting-nanowire device, called the nanocryotron (nTron), as a digital comparator to combine SFQ circuits with mature semiconductor circuits such as complementary metal oxide semiconductor (CMOS) circuits. Since SFQ circuits can digitize output signals from general superconducting devices and CMOS circuits can interface existing CMOS-compatible electronics, our results demonstrate the feasibility of a general architecture that uses an nTron as an interface to realize a ‘super-hybrid’ system consisting of superconducting detectors, superconducting quantum electronics, CMOS logic gates and memories, and other conventional electronics.
Nonequilibrium Transport through a Spinful Quantum Dot with Superconducting Leads
DEFF Research Database (Denmark)
Andersen, Brian Møller; Flensberg, Karsten; Koerting, Verena
2011-01-01
We study the nonlinear cotunneling current through a spinful quantum dot contacted by two superconducting leads. Applying a general nonequilibrium Green function formalism to an effective Kondo model, we study the rich variation in the IV characteristics with varying asymmetry in the tunnel...
Controllable Quantum States Mesoscopic Superconductivity and Spintronics (MS+S2006)
Takayanagi, Hideaki; Nitta, Junsaku; Nakano, Hayato
2008-10-01
Mesoscopic effects in superconductors. Tunneling measurements of charge imbalance of non-equilibrium superconductors / R. Yagi. Influence of magnetic impurities on Josephson current in SNS junctions / T. Yokoyama. Nonlinear response and observable signatures of equilibrium entanglement / A. M. Zagoskin. Stimulated Raman adiabatic passage with a Cooper pair box / Giuseppe Falci. Crossed Andreev reflection-induced giant negative magnetoresistance / Francesco Giazotto -- Quantum modulation of superconducting junctions. Adiabatic pumping through a Josephson weak link / Fabio Taddei. Squeezing of superconducting qubits / Kazutomu Shiokawa. Detection of Berrys phases in flux qubits with coherent pulses / D. N. Zheng. Probing entanglement in the system of coupled Josephson qubits / A. S. Kiyko. Josephson junction with tunable damping using quasi-particle injection / Ryuta Yagi. Macroscopic quantum coherence in rf-SQUIDs / Alexey V. Ustinov. Bloch oscillations in a Josephson circuit / D. Esteve. Manipulation of magnetization in nonequilibrium superconducting nanostructures / F. Giazotto -- Superconducting qubits. Decoherence and Rabi oscillations in a qubit coupled to a quantum two-level system / Sahel Ashhab. Phase-coupled flux qubits: CNOT operation, controllable coupling and entanglement / Mun Dae Kim. Characteristics of a switchable superconducting flux transformer with a DC-SQUID / Yoshihiro Shimazu. Characterization of adiabatic noise in charge-based coherent nanodevices / E. Paladino -- Unconventional superconductors. Threshold temperatures of zero-bias conductance peak and zero-bias conductance dip in diffusive normal metal/superconductor junctions / Iduru Shigeta. Tunneling conductance in 2DEG/S junctions in the presence of Rashba spin-orbit coupling / T. Yokoyama. Theory of charge transport in diffusive ferromagnet/p-wave superconductor junctions / T. Yokoyama. Theory of enhanced proximity effect by the exchange field in FS bilayers / T. Yokoyama. Theory of
Optimal Qubit Control Using Single-Flux Quantum Pulses
Liebermann, Per J.; Wilhelm, Frank K.
2016-08-01
Single-flux quantum pulses are a natural candidate for on-chip control of superconducting qubits. We show that they can drive high-fidelity single-qubit rotations—even in leaky transmon qubits—if the pulse sequence is suitably optimized. We achieve this objective by showing that, for these restricted all-digital pulses, genetic algorithms can be made to converge to arbitrarily low error, verified up to a reduction in gate error by 2 orders of magnitude compared to an evenly spaced pulse train. Timing jitter of the pulses is taken into account, exploring the robustness of our optimized sequence. This approach takes us one step further towards on-chip qubit controls.
Resonator-assisted quantum bath engineering of a flux qubit
Zhang, Xian-Peng; Shen, Li-Tuo; Yin, Zhang-Qi; Wu, Huai-Zhi; Yang, Zhen-Biao
2015-01-01
We demonstrate quantum bath engineering for preparation of any orbital state with the controllable phase factor of a superconducting flux qubit assisted by a microwave coplanar waveguide resonator. We investigate the polarization efficiency of the arbitrary direction rotating on the Bloch sphere, and obtain an effective Rabi frequency by using the convergence condition of the Markovian master equation. The processes of polarization can be implemented effectively in a dissipative environment created by resonator photon loss when the spectrum of the microwave resonator matches with the specially tailored Rabi and resonant frequencies of the drive. Our calculations indicate that state-preparation fidelities in excess of 99% and the required time on the order of magnitude of a microsecond are in principle possible for experimentally reasonable sample parameters. Furthermore, our proposal could be applied to other systems with spin-based qubits.
Design infrastructure for Rapid Single Flux Quantum circuits
Toepfer, Hannes; Ortlepp, Thomas
2009-11-01
Cryoelectronic integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology are promising candidates for realizing systems exhibiting very high performance in combination with very low-power consumption. Like other superconductive logic circuits, they are characterized by a high switching speed. Their unique feature consists in the particular representation of binary information by means of short transient voltage pulses. The development of RSFQ circuits and systems requires a comprehensive design approach, supported by appropriate tools. Within the recent years, a dedicated design infrastructure has been developed in Europe in close association with a foundry for digital RSFQ integrated circuits. As a result, RSFQ technology has matured to such a level that engineering efforts enable the development of integrated circuits. In the contribution, the basic features of the RSFQ circuit design are addressed within the context of technical and infrastructural issues of implementation from a European perspective.
Atomic physics and quantum optics using superconducting circuits.
You, J Q; Nori, Franco
2011-06-29
Superconducting circuits based on Josephson junctions exhibit macroscopic quantum coherence and can behave like artificial atoms. Recent technological advances have made it possible to implement atomic-physics and quantum-optics experiments on a chip using these artificial atoms. This Review presents a brief overview of the progress achieved so far in this rapidly advancing field. We not only discuss phenomena analogous to those in atomic physics and quantum optics with natural atoms, but also highlight those not occurring in natural atoms. In addition, we summarize several prospective directions in this emerging interdisciplinary field.
Josephson directional amplifier for quantum measurement of superconducting circuits.
Abdo, Baleegh; Sliwa, Katrina; Shankar, S; Hatridge, Michael; Frunzio, Luigi; Schoelkopf, Robert; Devoret, Michel
2014-04-25
We realize a microwave quantum-limited amplifier that is directional and can therefore function without the front circulator needed in many quantum measurements. The amplification takes place in only one direction between the input and output ports. Directionality is achieved by multipump parametric amplification combined with wave interference. We have verified the device noise performances by using it to read out a superconducting qubit and observed quantum jumps. With an improved version of this device, the qubit and preamplifer could be integrated on the same chip.
Quantum magnonics: The magnon meets the superconducting qubit
Tabuchi, Yutaka; Ishino, Seiichiro; Noguchi, Atsushi; Ishikawa, Toyofumi; Yamazaki, Rekishu; Usami, Koji; Nakamura, Yasunobu
2016-08-01
The techniques of microwave quantum optics are applied to collective spin excitations in a macroscopic sphere of a ferromagnetic insulator. We demonstrate, in the single-magnon limit, strong coupling between a magnetostatic mode in the sphere and a microwave cavity mode. Moreover, we introduce a superconducting qubit in the cavity and couple the qubit with the magnon excitation via the virtual photon excitation. We observe the magnon-vacuum-induced Rabi splitting. The hybrid quantum system enables generation and characterization of non-classical quantum states of magnons. xml:lang="fr"
Semiconductor-inspired design principles for superconducting quantum computing.
Shim, Yun-Pil; Tahan, Charles
2016-03-17
Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit-based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits on the basis of variable super-semi junctions.
Semiconductor-inspired design principles for superconducting quantum computing
Shim, Yun-Pil; Tahan, Charles
2016-03-01
Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit-based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits on the basis of variable super-semi junctions.
Local imaging of magnetic flux in superconducting thin films
Energy Technology Data Exchange (ETDEWEB)
Shapoval, Tetyana
2010-01-26
Local studies of magnetic flux line (vortex) distribution in superconducting thin films and their pinning by natural and artificial defects have been performed using low-temperature magnetic force microscopy (LT-MFM). Taken a 100 nm thin NbN film as an example, the depinning of vortices from natural defects under the influence of the force that the MFM tip exerts on the individual vortex was visualized and the local pinning force was estimated. The good agreement of these results with global transport measurements demonstrates that MFM is a powerful and reliable method to probe the local variation of the pinning landscape. Furthermore, it was demonstrated that the presence of an ordered array of 1-{mu}m-sized ferromagnetic permalloy dots being in a magneticvortex state underneath the Nb film significantly influences the natural pinning landscape of the superconductor leading to commensurate pinning effects. This strong pinning exceeds the repulsive interaction between the superconducting vortices and allows vortex clusters to be located at each dot. Additionally, for industrially applicable YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films the main question discussed was the possibility of a direct correlation between vortices and artificial defects as well as vortex imaging on rough as-prepared thin films. Since the surface roughness (droplets, precipitates) causes a severe problem to the scanning MFM tip, a nanoscale wedge polishing technique that allows to overcome this problem was developed. Mounting the sample under a defined small angle results in a smooth surface and a monotonic thickness reduction of the film along the length of the sample. It provides a continuous insight from the film surface down to the substrate with surface sensitive scanning techniques. (orig.)
Quantum phase transition in ultra small doubly connected superconducting cylinders
Sternfeld, I.; Koret, R.; Shtrikman, H.; Tsukernik, A.; Karpovski, M.; Palevski, A.
2008-02-01
The kinetic energy of Cooper pairs, in doubly connected superconducting cylinders, is a function of the applied flux and the ratio between the diameter of the cylinder and the zero temperature coherence length d/ ξ(0). If d >ξ(0) the known Little-Parks oscillations are observed. On the other hand if d ξ(0), we observed the LP oscillations. In the Al cylinders we did not observe a transition to the superconducting state due to the proximity effect, resulted from an Au layer coating the Al. However, we did observe Altshuler-Aronov-Spivak (h/2e) oscillations in these cylinders.
Superconducting Switch for Fast On-Chip Routing of Quantum Microwave Fields
Pechal, M.; Besse, J.-C.; Mondal, M.; Oppliger, M.; Gasparinetti, S.; Wallraff, A.
2016-08-01
A switch capable of routing microwave signals at cryogenic temperatures is a desirable component for state-of-the-art experiments in many fields of applied physics, including but not limited to quantum-information processing, communication, and basic research in engineered quantum systems. Conventional mechanical switches provide low insertion loss but disturb operation of dilution cryostats and the associated experiments by heat dissipation. Switches based on semiconductors or microelectromechanical systems have a lower thermal budget but are not readily integrated with current superconducting circuits. Here we design and test an on-chip switch built by combining tunable transmission-line resonators with microwave beam splitters. The device is superconducting and as such dissipates a negligible amount of heat. It is compatible with current superconducting circuit fabrication techniques, operates with a bandwidth exceeding 100 MHz, is capable of handling photon fluxes on the order of 1 05 μ s-1 , equivalent to powers exceeding -90 dBm , and can be switched within approximately 6-8 ns. We successfully demonstrate operation of the device in the quantum regime by integrating it on a chip with a single-photon source and using it to route nonclassical itinerant microwave fields at the single-photon level.
High-Temperature Superconductivity
Tanaka, Shoji
2006-12-01
A general review on high-temperature superconductivity was made. After prehistoric view and the process of discovery were stated, the special features of high-temperature superconductors were explained from the materials side and the physical properties side. The present status on applications of high-temperature superconductors were explained on superconducting tapes, electric power cables, magnets for maglev trains, electric motors, superconducting quantum interference device (SQUID) and single flux quantum (SFQ) devices and circuits.
Enpuku, Keiji; Doi, Hideki; Tokita, Go; Maruo, Taku
1994-05-01
The effect of damping resistance on the voltage versus flux (V -Φ) relation of the high T c dc superconducting quantum interference device (SQUID) is studied experimentally. Dc SQUID using YBaCuO step-edge junction and damping resistance in parallel with SQUID inductance is fabricated. Measured values of modulation voltage in the V -Φ relation are compared with those of the conventional SQUID without damping resistance. It is shown that modulation voltage is much improved by using damping resistance. The obtained experimental results agree reasonably with theoretical predictions reported previously.
Architectural considerations in the design of a superconducting quantum annealing processor
Bunyk, P. I.; Hoskinson, E.; Johnson, M. W.; Tolkacheva, E.; Altomare, F.; Berkley, A. J.; Harris, R; Hilton, J. P.; Lanting, T.; Whittaker, J
2014-01-01
We have developed a quantum annealing processor, based on an array of tunably coupled rf-SQUID flux qubits, fabricated in a superconducting integrated circuit process [1]. Implementing this type of processor at a scale of 512 qubits and 1472 programmable inter-qubit couplers and operating at ~ 20 mK has required attention to a number of considerations that one may ignore at the smaller scale of a few dozen or so devices. Here we discuss some of these considerations, and the delicate balance n...
Quantum phase transition in ultra small doubly connected superconducting cylinders
Energy Technology Data Exchange (ETDEWEB)
Sternfeld, I. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)], E-mail: itayst@post.tau.ac.il; Koret, R. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel); Shtrikman, H. [Department of Condensed Matter, Weizmann Institute of Science, Rehovot 76100 (Israel); Tsukernik, A. [Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv 69978 (Israel); Karpovski, M.; Palevski, A. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)
2008-02-15
The kinetic energy of Cooper pairs, in doubly connected superconducting cylinders, is a function of the applied flux and the ratio between the diameter of the cylinder and the zero temperature coherence length d/{xi}(0). If d >{xi}(0) the known Little-Parks oscillations are observed. On the other hand if d <{xi}(0), the superconducting state is energetically not favored around odd multiples of half flux quanta even at T{approx}0, resulting in the so called destructive regime [Y. Liu, et al., Science 294 (2001) 2332]. We developed a novel technique to fabricate superconducting doubly connected nanocylinders with both diameter and thickness less than 100 nm, and performed magnetoresistance measurements on such Nb and Al cylinders. In the Nb cylinders, where d >{xi}(0), we observed the LP oscillations. In the Al cylinders we did not observe a transition to the superconducting state due to the proximity effect, resulted from an Au layer coating the Al. However, we did observe Altshuler-Aronov-Spivak (h/2e) oscillations in these cylinders.
Quantum acousto-optic transducer for superconducting qubits
Shumeiko, V S
2015-01-01
We propose theory for reversible quantum transducer connecting superconducting qubits and optical photons using acoustic waves in piezoelectrics. The proposed device consists of integrated acousto-optic resonator that utilizes stimulated Brillouin scattering for phonon-photon conversion, and piezoelectric e?ect for coupling of phonons to qubits. We evaluate the phonon-photon coupling rate, and show that the required power of optical pump as well as the other device parameters providing full and faithful quantum conversion are feasible for implementation with the state of the art integrated acousto-optics.
Superconducting Quantum Arrays for Wideband Antennas and Low Noise Amplifiers
Mukhanov, O.; Prokopemko, G.; Romanofsky, Robert R.
2014-01-01
Superconducting Quantum Iinetference Filters (SQIF) consist of a two-dimensional array of niobium Josephson Junctions formed into N loops of incommensurate area. This structure forms a magnetic field (B) to voltage transducer with an impulse like response at B0. In principle, the signal-to-noise ratio scales as the square root of N and the noise can be made arbitrarily small (i.e. The SQIF chips are expected to exhibit quantum limited noise performance). A gain of about 20 dB was recently demonstrated at 10 GHz.
Contextuality without nonlocality in a superconducting quantum system
Jerger, Markus; Reshitnyk, Yarema; Oppliger, Markus; Potočnik, Anton; Mondal, Mintu; Wallraff, Andreas; Goodenough, Kenneth; Wehner, Stephanie; Juliusson, Kristinn; Langford, Nathan K.; Fedorov, Arkady
2016-01-01
Classical realism demands that system properties exist independently of whether they are measured, while noncontextuality demands that the results of measurements do not depend on what other measurements are performed in conjunction with them. The Bell–Kochen–Specker theorem states that noncontextual realism cannot reproduce the measurement statistics of a single three-level quantum system (qutrit). Noncontextual realistic models may thus be tested using a single qutrit without relying on the notion of quantum entanglement in contrast to Bell inequality tests. It is challenging to refute such models experimentally, since imperfections may introduce loopholes that enable a realist interpretation. Here we use a superconducting qutrit with deterministic, binary-outcome readouts to violate a noncontextuality inequality while addressing the detection, individual-existence and compatibility loopholes. This evidence of state-dependent contextuality also demonstrates the fitness of superconducting quantum circuits for fault-tolerant quantum computation in surface-code architectures, currently the most promising route to scalable quantum computing. PMID:27698351
Emulating a mesoscopic system using superconducting quantum circuits
Chen, Yu; Barends, R.; Bochmann, J.; Campbell, B.; Chiaro, B.; Jeffrey, E.; Kelly, J.; Mariantoni, M.; Megrant, A.; Mutus, J.; Neill, C.; O'Malley, P.; Ohya, S.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Cleland, A. N.; Martinis, J. M.
2013-03-01
We demonstrate an emulation of a mesoscopic system using superconducting quantum circuits. Taking advantage of our ReZQu-architectured quantum processor, we controllably splitted a microwave photon and manipulated the splitted photons before they recombined for detection. In this way, we were able to simulate the weak localization effect in mesoscopic systems - a coherent backscattering process due to quantum interference. The influence of the phase coherence was investigated by tuning the coherence time of the quantum circuit, which in turn mimics the temperature effect on the weak localization process. At the end, we demonstrated an effect resembling universal conductance fluctuations, which arises from the frequency beating between different coherent backscattering processes. The universality of the observed fluctuation was shown as the independence of the fluctuation amplitude on detailed experimental conditions.
Realization and Modeling of Metamaterials Made of rf Superconducting Quantum-Interference Devices
Directory of Open Access Journals (Sweden)
M. Trepanier
2013-12-01
Full Text Available We have prepared meta-atoms based on radio-frequency superconducting quantum-interference devices (rf SQUIDs and examined their tunability with dc magnetic field, rf current, and temperature. rf SQUIDs are superconducting split-ring resonators in which the usual capacitance is supplemented with a Josephson junction, which introduces strong nonlinearity in the rf properties. We find excellent agreement between the data and a model that regards the Josephson junction as the resistively and capacitively shunted junction. A magnetic field tunability of 80 THz/G at 12 GHz is observed, a total tunability of 56% is achieved, and a unique electromagnetically induced transparency feature at intermediate excitation powers is demonstrated for the first time. An rf SQUID metamaterial is shown to have qualitatively the same behavior as a single rf SQUID with regard to dc flux and temperature tuning.
Vettoliere, A; Granata, C
2014-08-01
A fully integrated low noise superconducting quantum interference device (SQUID) in a magnetometer configuration is presented. An intrinsic high voltage responsivity as high as 500 μV/Φ0 has been obtained by introducing a resonance in the voltage - magnetic flux characteristic. This resonance is induced by an integrated superconducting coil surrounding the pick-up coil and connected to one end of the SQUID output. The SQUID magnetometer exhibits a spectral density of magnetic field noise as low as 3 fT/Hz(1/2). In order to verify the suitability of the magnetometer, measurements of bandwidth and slew rate have been performed and compared with those of the same device without the resonance and with additional positive feedback. Due to their good characteristics such devices can be employed in a large number of applications including biomagnetism.
Quantum phase-slips in superconducting AlO{sub x} nanowire arrays at microwave frequencies
Energy Technology Data Exchange (ETDEWEB)
Skacel, Sebastian T.; Pfirrmann, Marco; Voss, Jan N.; Muenzberg, Julian; Radtke, Lucas; Probst, Sebastian; Rotzinger, Hannes [Physikalisches Institut, Karlsruhe Institute of Technology, D-76131 Karlsruhe (Germany); Weides, Martin [Physikalisches Institut, Karlsruhe Institute of Technology, D-76131 Karlsruhe (Germany); Institute of Physics, Johannes Gutenberg University Mainz, D-55128 Mainz (Germany); Mooij, Hans E. [Physikalisches Institut, Karlsruhe Institute of Technology, D-76131 Karlsruhe (Germany); Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft (Netherlands); Ustinov, Alexey V. [Physikalisches Institut, Karlsruhe Institute of Technology, D-76131 Karlsruhe (Germany); Russian Quantum Center, 100 Novaya St., Skolkovo, Moscow region, 143025 (Russian Federation)
2015-07-01
Superconducting nanowires in the quantum phase slip (QPS) regime allow to study the flux and phase dynamics in duality to Josephson junction systems. However, due to the vanishing self-capacitance of the nanowires, the microwave response significantly differs. We experimentally study parallel arrays of nanowires which are embedded in a resonant circuit at GHz frequencies. The samples are probed at ultra-low microwave power and applied magnetic field at mK temperatures. The AlO{sub x} nanowires, with a sheet resistance in the kΩ range, are fabricated by sputter deposition of aluminium in a controlled oxygen atmosphere. The wires are defined with conventional electron beam lithography down to a width of approximately 15 nm. We present the fabrication of the nanowire arrays and measurement results for arrays coupled to superconducting microwave resonators.
Digitized adiabatic quantum computing with a superconducting circuit.
Barends, R; Shabani, A; Lamata, L; Kelly, J; Mezzacapo, A; Las Heras, U; Babbush, R; Fowler, A G; Campbell, B; Chen, Yu; Chen, Z; Chiaro, B; Dunsworth, A; Jeffrey, E; Lucero, E; Megrant, A; Mutus, J Y; Neeley, M; Neill, C; O'Malley, P J J; Quintana, C; Roushan, P; Sank, D; Vainsencher, A; Wenner, J; White, T C; Solano, E; Neven, H; Martinis, John M
2016-06-09
Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable.
Digitized adiabatic quantum computing with a superconducting circuit
Barends, R.; Shabani, A.; Lamata, L.; Kelly, J.; Mezzacapo, A.; Heras, U. Las; Babbush, R.; Fowler, A. G.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Lucero, E.; Megrant, A.; Mutus, J. Y.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Solano, E.; Neven, H.; Martinis, John M.
2016-06-01
Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable.
Sabegh, Z Amini; Maleki, M A; Mahmoudi, M
2015-01-01
We study the propagation and amplification of a microwave field in a four-level cascade quantum system which is realized in a superconducting phase quantum circuit. It is shown that by increasing the microwave pump tones feeding the system, the normal dispersion switches to the anomalous and the gain-assisted superluminal microwave propagation is obtained in this system. Moreover, it is demonstrated that the stimulated microwave field is generated via four-wave mixing without any inversion population in the energy levels of the system (amplification without inversion) and the group velocity of the generated pulse can be controlled by the external oscillating magnetic fluxes. We also show that in some special set of parameters, the absorption-free superluminal generated microwave propagation is obtained in superconducting phase quantum circuit system.
Spin analogs of superconductivity and integer quantum Hall effect in an array of spin chains
Hill, Daniel; Kim, Se Kwon; Tserkovnyak, Yaroslav
2017-05-01
Motivated by the successful idea of using weakly coupled quantum electronic wires to realize the quantum Hall effects and the quantum spin Hall effects, we theoretically study two systems composed of weakly coupled quantum spin chains within the mean-field approximations, which can exhibit spin analogs of superconductivity and the integer quantum Hall effect. First, a certain bilayer of two arrays of interacting spin chains is mapped, via the Jordan-Wigner transformation, to an attractive Hubbard model that exhibits fermionic superconductivity, which corresponds to spin superconductivity in the original spin Hamiltonian. Secondly, an array of spin-orbit-coupled spin chains in the presence of a suitable external magnetic field is transformed to an array of quantum wires that exhibits the integer quantum Hall effect, which translates into its spin analog in the spin Hamiltonian. The resultant spin superconductivity and spin integer quantum Hall effect can be characterized by their ability to transport spin without any resistance.
Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits
DEFF Research Database (Denmark)
Marcos, D.; Wubs, Martijn; Taylor, J.M.;
2010-01-01
We propose a method to achieve coherent coupling between nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the ma...
Estimating effects from trapped magnetic fluxes in superconducting magnetic levitation measurement
Institute of Scientific and Technical Information of China (English)
Masakazu Nakanishi
2008-01-01
Superconducting magnetic levitation measurement is one of the most promising approaches to define mass standard based on the fundamental physical constants. However, the present system has unknown factors causing error larger than 50 ppm. We examined the effects of magnetic fluxes trapped in the superconducting coil and the superconducting floating body. When fluxes were trapped in either coil or floating body, their effects were able to be cancelled by reversing polarities of current and magnetic field, as had been believed. However, fluxes trapped in both coil and body induced an attractive force between them and caused error. In order to reduce the fluxes, the coil and the floating body should be cooled in low magnetic field in magnetic and electromagnetic shields.
HiFi-MBQC High Fidelitiy Measurement-Based Quantum Computing using Superconducting Detectors
2016-04-04
computer. We exploit the conceptual framework of measurement - based quantum computation that enables a client to delegate a computation to a quantum...AFRL-AFOSR-UK-TR-2016-0006 HiFi-MBQC High Fidelitiy Measurement - Based Quantum Computing using Superconducting Detectors Philip Walther UNIVERSITT...HiFi-MBQC High Fidelitiy Measurement - Based Quantum Computing using Superconducting Detectors 5a. CONTRACT NUMBER FA8655-11-1-3004 5b. GRANT NUMBER
Induced Superconductivity in the Quantum Spin Hall Edge
Ren, Hechen; Hart, Sean; Wagner, Timo; Leubner, Philipp; Muehlbauer, Mathias; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; Yacoby, Amir
2014-03-01
Two-dimensional topological insulators have a gapped bulk and helical edge states, making it a quantum spin Hall insulator. Combining such edge states with superconductivity can be an excellent platform for observing and manipulating localized Majorana fermions. In the context of condensed matter, these are emergent electronic states that obey non-Abelian statistics and hence support fault-tolerant quantum computing. To realize such theoretical constructions, an essential step is to show these edge channels are capable of carrying coherent supercurrent. In our experiment, we fabricate Josephson junctions with HgTe/HgCdTe quantum wells, a two-dimensional material that becomes a quantum spin Hall insulator when the quantum well is thicker than 6.3 nm and the bulk density is depleted. In this regime, we observe supercurrents whose densities are confined to the edges of the junctions, with edge widths ranging from 180 nm to 408 nm. To verify the topological nature of these edges, we measure identical junctions with HgTe/HgCdTe quantum wells thinner than 6.3 nm and observe only uniform supercurrent density across the junctions. This research is supported by Microsoft Corporation Project Q, the NSF DMR-1206016, the DOE SCGF Program, the German Research Foundation, and EU ERC-AG program.
Quantum transport in coupled resonators enclosed synthetic magnetic flux
Jin, L.
2016-07-01
Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov-Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms.
Energy Technology Data Exchange (ETDEWEB)
Blencowe, M P [Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755 (United States); Armour, A D [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom)], E-mail: miles.p.blencowe@dartmouth.edu, E-mail: andrew.armour@nottingham.ac.uk
2008-09-15
We describe a possible implementation of the nanomechanical quantum superposition generation and detection scheme described in the preceding, companion paper (Armour A D and Blencowe M P 2008 New. J. Phys. 10 095004). The implementation is based on the circuit quantum electrodynamics (QED) set-up, with the addition of a mechanical degree of freedom formed out of a suspended, doubly-clamped segment of the superconducting loop of a dc SQUID located directly opposite the centre conductor of a coplanar waveguide (CPW). The relative merits of two SQUID based qubit realizations are addressed, in particular a capacitively coupled charge qubit and inductively coupled flux qubit. It is found that both realizations are equally promising, with comparable qubit-mechanical resonator mode as well as qubit-microwave resonator mode coupling strengths.
Superconducting Analogue of the Parafermion Fractional Quantum Hall States
Directory of Open Access Journals (Sweden)
Abolhassan Vaezi
2014-07-01
Full Text Available Read-Rezayi Z_{k} parafermion wave functions describe ν=2+(k/kM+2 fractional quantum Hall (FQH states. These states support non-Abelian excitations from which protected quantum gates can be designed. However, there is no experimental evidence for these non-Abelian anyons to date. In this paper, we study the ν=2/k FQH-superconductor heterostructure and find the superconducting analogue of the Z_{k} parafermion FQH state. Our main tool is the mapping of the FQH into coupled one-dimensional chains, each with a pair of counterpropagating modes. We show that by inducing intrachain pairing and charge preserving backscattering with identical couplings, the one-dimensional chains flow into gapless Z_{k} parafermions when k<4. By studying the effect of interchain coupling, we show that every parafermion mode becomes massive except for the two outermost ones. Thus, we achieve a fractional topological superconductor whose chiral edge state is described by a Z_{k} parafermion conformal field theory. For instance, we find that a ν=2/3 FQH in proximity to a superconductor produces a Z_{3} parafermion superconducting state. This state is topologically indistinguishable from the non-Abelian part of the ν=12/5 Read-Rezayi state. Both of these systems can host Fibonacci anyons capable of performing universal quantum computation through braiding operations.
Optimised quantum hacking of superconducting nanowire single-photon detectors
Tanner, Michael G.; Makarov, Vadim; Hadfield, Robert H.
2014-03-01
We explore bright-light control of superconducting nanowire single-photon detectors (SNSPDs) in the shunted configuration (a practical measure to avoid latching). In an experiment, we simulate an illumination pattern the SNSPD would receive in a typical quantum key distribution system under hacking attack. We show that it effectively blinds and controls the SNSPD. The transient blinding illumination lasts for a fraction of a microsecond and produces several deterministic fake clicks during this time. This attack does not lead to elevated timing jitter in the spoofed output pulse, and hence does not introduce significant errors. Five different SNSPD chip designs were tested. We consider possible countermeasures to this attack.
Simulating Quantum Chemical Dynamics with Improved Superconducting Qubits
Megrant, Anthony E.
A quantum computer will potentially solve far-reaching problems which are currently intractable on any classical computer. Many technological obstacles have prevented the realization of a quantum computer, the main obstacle being decoherence, which is the loss of quantum information. Decoherence arises from the undesired interaction between qubits and their environment. Isolated qubits have better coherence but are more difficult to control. Superconducting qubits are a promising platform since their macroscopic size allows for easy control and coupling to other qubits. While the coherence of superconducting qubits has substantially improved over the past two decades, further improvements in coherence are required. We have repeatedly and reliably increased the coherence times of superconducting qubits. Currently decoherence in these devices is dominated by coupling to material defects. These defects are present in the dielectrics used to fabricate these devices or introduced during fabrication. Using simpler resonators as a testbed, we individually isolate, characterize, and then improve each step of the more complicated fabrication of superconducting qubits. We increased the quality factor of resonators by a factor of four by first identifying the surfaces and interfaces as a major source of loss and then by optimizing the substrate preparation. Furthermore, we measure and subsequently mitigate additional defect loss, which is dependent on the position of ground plane holes used to limit the loss from magnetic vortices. Implementing these improvements led to an increase of our qubit coherence times by more than an order of magnitude. The progress made in coherence while maintaining a high degree of connectivity and controllability has been directly used in more complex circuits. One such device is a fully connected three qubit ring with both tunable qubit frequencies and adjustable qubit-qubit couplings. The considerable level of control allows us to generate the
Optimised quantum hacking of superconducting nanowire single-photon detectors
Tanner, Michael G; Hadfield, Robert H
2013-01-01
We explore optimised control of superconducting nanowire single-photon detectors (SNSPDs) through bright illumination. We consider the behaviour of the SNSPD in the shunted configuration (a practical measure to avoid latching) in long-running quantum key distribution experiments. We propose and demonstrate an effective bright-light attack on this realistic configuration, by applying transient blinding illumination lasting for a fraction of a microsecond and producing several deterministic fake clicks during this time. We show that this attack does not lead to elevated timing jitter in the spoofed output pulse, and is hence not introducing significant errors. Five different SNSPD chip designs were tested. We consider possible countermeasures to this attack.
Controlling group velocity in a superconductive quantum circuit
Institute of Scientific and Technical Information of China (English)
Qiu Tian-Hui; Yang Guo-Jian
2012-01-01
We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit (SQC) pumped by microwave fields,and the use of such a SQC function as an artificial A-type three-level atom.The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity,and the superluminal state is usually realized with a lower absorption.This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band.
Note on "Quantum superconducting criticality in graphene and topological insulators"
Roy, Bitan; Herbut, Igor F
2016-01-01
We correct our previous conclusion regarding the fate of a charged quantum critical point across the superconducting transition for two dimensional massless Dirac fermion. Within the leading order $\\epsilon$ expansion, we now find that the requisite number of four-component Dirac fermion flavors ($N_f$) for the continuous phase transition through a charged critical point is $N_f>18.2699$. For $N_f\\geq1/2$, the critical number of bosonic flavors for this transition is significantly reduced as compared to the value determined in the absence of the Dirac fermions in the theory.
Autonomously stabilized entanglement between two superconducting quantum bits.
Shankar, S; Hatridge, M; Leghtas, Z; Sliwa, K M; Narla, A; Vool, U; Girvin, S M; Frunzio, L; Mirrahimi, M; Devoret, M H
2013-12-19
Quantum error correction codes are designed to protect an arbitrary state of a multi-qubit register from decoherence-induced errors, but their implementation is an outstanding challenge in the development of large-scale quantum computers. The first step is to stabilize a non-equilibrium state of a simple quantum system, such as a quantum bit (qubit) or a cavity mode, in the presence of decoherence. This has recently been accomplished using measurement-based feedback schemes. The next step is to prepare and stabilize a state of a composite system. Here we demonstrate the stabilization of an entangled Bell state of a quantum register of two superconducting qubits for an arbitrary time. Our result is achieved using an autonomous feedback scheme that combines continuous drives along with a specifically engineered coupling between the two-qubit register and a dissipative reservoir. Similar autonomous feedback techniques have been used for qubit reset, single-qubit state stabilization, and the creation and stabilization of states of multipartite quantum systems. Unlike conventional, measurement-based schemes, the autonomous approach uses engineered dissipation to counteract decoherence, obviating the need for a complicated external feedback loop to correct errors. Instead, the feedback loop is built into the Hamiltonian such that the steady state of the system in the presence of drives and dissipation is a Bell state, an essential building block for quantum information processing. Such autonomous schemes, which are broadly applicable to a variety of physical systems, as demonstrated by the accompanying paper on trapped ion qubits, will be an essential tool for the implementation of quantum error correction.
Generation of Fock states in a superconducting quantum circuit.
Hofheinz, Max; Weig, E M; Ansmann, M; Bialczak, Radoslaw C; Lucero, Erik; Neeley, M; O'Connell, A D; Wang, H; Martinis, John M; Cleland, A N
2008-07-17
Spin systems and harmonic oscillators comprise two archetypes in quantum mechanics. The spin-1/2 system, with two quantum energy levels, is essentially the most nonlinear system found in nature, whereas the harmonic oscillator represents the most linear, with an infinite number of evenly spaced quantum levels. A significant difference between these systems is that a two-level spin can be prepared in an arbitrary quantum state using classical excitations, whereas classical excitations applied to an oscillator generate a coherent state, nearly indistinguishable from a classical state. Quantum behaviour in an oscillator is most obvious in Fock states, which are states with specific numbers of energy quanta, but such states are hard to create. Here we demonstrate the controlled generation of multi-photon Fock states in a solid-state system. We use a superconducting phase qubit, which is a close approximation to a two-level spin system, coupled to a microwave resonator, which acts as a harmonic oscillator, to prepare and analyse pure Fock states with up to six photons. We contrast the Fock states with coherent states generated using classical pulses applied directly to the resonator.
Macroscopic states induced in superconducting media by a transport current under flux creep
Romanovskii, V. R.
2016-08-01
The physical features of the formation of macroscopic states of superconducting composites consisting of a superconductor and a coating under flux creep are discussed. It is demonstrated that there exist characteristic electric field strengths depending on the properties of the superconductor, cooling conditions, and characteristics of the stabilizing coating, which affect the intensity of the E-I characteristics of the superconducting composites. Analysis shows that the measurements of the critical properties of superconductors can be accompanied by a nonuniform electric field distribution over the composite cross section and high stable superheating of the superconductor, which do not lead to superconductivity breaking.
Rabi model as a quantum coherent heat engine: From quantum biology to superconducting circuits
2014-01-01
PHYSICAL REVIEW A 91, 023816 (2015) Rabi model as a quantum coherent heat engine: From quantum biology to superconducting circuits Ferdi Altintas,1 Ali U¨ . C. Hardal,2 and O¨ zgu¨r E. Mu¨stecaplıog˘lu2,* 1Department of Physics, Abant Izzet Baysal University, Bolu, 14280, Turkey 2Department of Physics, Koc¸ University, Sarıyer, ˙Istanbul, 34450, Turkey (Received 10 November 2014; published 12 February 2015) We propose a multilevel quantum heat engine with a working medium de...
Mao, Ting; Yu, Yang
2010-01-01
We numerically investigated the quantum-classical transition in rf-superconducting quantum interference device (SQUID) systems coupled to a dissipative environment. It is found that chaos emerges and the degree of chaos, the maximal Lyapunov exponent lambda(m), exhibits nonmonotonic behavior as a function of the coupling strength D. By measuring the proximity of quantum and classical evolution with the uncertainty of dynamics, we show that the uncertainty is a monotonic function of lambda(m)/D. In addition, the scaling holds in SQUID systems to a relatively smaller variant Planck's over [symbol: see text], suggesting the universality for this scaling.
Driven superconducting proximity effect in interacting quantum dots
Energy Technology Data Exchange (ETDEWEB)
Moghaddam, Ali G.; Koenig, Juergen [Theoretische Physik, Univ. Duisburg-Essen, Duisburg (Germany); CeNIDE, Duisburg (Germany); Governale, Michele [School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140 (New Zealand)
2012-07-01
We show that strong superconducting correlations can be induced in an interacting quantum dot (QD) using fast oscillations in the effective coupling between the dot and superconducting leads which drive the dot out of equilibrium. This is in contrast with the well-known equilibrium state suppression of proximity effect in interacting QDs. In fact although interaction prohibits the superposition of empty (0) and doubly-occupied (d) states, fast coherent dynamics accompanied by the fast variations in the tunnel coupling can produce a nonequilibrium finite probability for such a superposition. Subsequently the superconducting correlations are established inside the QD when the energy difference between 0 and d states coincide with the frequency of driving oscillations. Simultaneously the nonequilibrium occupation probabilities of 0 and d states cause a pumping current flowing to the normal lead connected to the dot. Finally we demonstrate coherent oscillations in both dot charge and current by applying a pulsed oscillatory field to the coupling of dot and superconductor which show the possibility of coherent manipulation in the subspace of 0 and d states by changing the pulse duration.
Conclusive quantum steering with superconducting transition edge sensors
Smith, Devin H; de Almeida, Marcelo; Branciard, Cyril; Fedrizzi, Alessandro; Weinhold, Till J; Lita, Adriana; Calkins, Brice; Gerrits, Thomas; Nam, Sae Woo; White, Andrew G
2011-01-01
Quantum steering allows two parties to verify shared entanglement even if one measurement device is untrusted. A conclusive demonstration of steering through the violation of a steering inequality is of considerable fundamental interest and opens up applications in quantum communication. To date all experimental tests with single photon states have relied on post-selection, allowing untrusted devices to cheat by hiding unfavorable events in losses. Here we close this "detection loophole" by combining a highly efficient source of entangled photon pairs with superconducting transition edge sensors. We achieve an unprecedented $\\sim$62% conditional detection efficiency of entangled photons and violate a steering inequality with the minimal number of measurement settings by 48 standard deviations. Our results provide a clear path to practical applications of steering and to a photonic loophole-free Bell test.
Quantum search via superconducting quantum interference devices in a cavity
Institute of Scientific and Technical Information of China (English)
Lu Yan; Dong Ping; Xue Zheng-Yuan; Cao Zhuo-Liang
2007-01-01
We propose a scheme for implementing the Grover search algorithm with two superconducing quantum interference devices (SQUIDs) in a cavity. Our scheme only requires single resonant interaction of the SQUID-cavity system and the required interaction time is very short. The simplicity of the process and the reduction of the interaction time are important for restraining decoherence.
Numerical simulation on the flux avalanche behaviors of microstructured superconducting thin films
Jing, Ze; Yong, Huadong; Zhou, Youhe
2017-01-01
Controlling and suppressing the propagation of magnetic flux avalanches is an important issue for the application of type-II superconductors. The effects of engineered pinning centers (antidots) on the guidance of flux avalanche propagation paths in type-II superconducting thin films are numerically investigated by solving the coupled nonlinear Maxwell's equations and the thermal diffusion equations. The field dependence of critical current density is considered in the simulation in this paper. Dynamic propagations of the thermomagnetic avalanches within the superconducting films patterned with different arrangements of antidots (like random, periodic square, and conformal mapping arrays) are presented. We reveal that presence of the antidots significantly modifies the propagation paths of the avalanches. The flux avalanche patterns of the superconducting films change with the variation of the arrangements of antidots. The patterned antidots in the form of conformal mapping arrays within the superconducting film exhibit strong guidance to the thermomagnetic avalanches. In addition, introducing the antidots in the form of conformal mapping arrays into the superconducting film can effectively lower the magnetic flux jump sizes.
Development of a Cryostat to Characterize Nano-scale Superconducting Quantum Interference Devices
Longo, Mathew; Matheny, Matthew; Knudsen, Jasmine
2016-03-01
We have designed and constructed a low-noise vacuum cryostat to be used for the characterization of nano-scale superconducting quantum interference devices (SQUIDs). Such devices are very sensitive to magnetic fields and can measure changes in flux on the order of a single electron magnetic moment. As a part of the design process, we calculated the separation required between the cryogenic preamplifier and superconducting magnet, including a high-permeability magnetic shield, using a finite-element model of the apparatus. The cryostat comprises a vacuum cross at room temperature for filtered DC and shielded RF electrical connections, a thin-wall stainless steel support tube, a taper-sealed cryogenic vacuum can, and internal mechanical support and wiring for the nanoSQUID. The Dewar is modified with a room-temperature flange with a sliding seal for the cryostat. The flange supports the superconducting 3 Tesla magnet and thermometry wiring. Upon completion of the cryostat fabrication and Dewar modifications, operation of the nanoSQUIDs as transported from our collaborator's laboratory in Israel will be confirmed, as the lead forming the SQUID is sensitive to oxidation and the SQUIDs must be shipped in a vacuum container. After operation of the nanoSQUIDs is confirmed, the primary work of characterizing their high-speed properties will begin. This will include looking at the measurement of relaxation oscillations at high bandwidth in comparison to the theoretical predictions of the current model.
Multilayer MgB2 superconducting quantum interference filter magnetometers
Galan, Elias; Melbourne, Thomas; Davidson, Bruce A.; Xi, X. X.; Chen, Ke
2016-04-01
We report two types of all-MgB2 superconductive quantum interference filter (SQIF) magnetometers that can measure absolute magnetic fields with high sensitivity. In one configuration, the SQIFs were made of 20 multilayer nonplanar all-MgB2 superconducting quantum interference devices (SQUIDs) connected in parallel with loop areas ranging in size from 0.4 to 3.6 μm2. These devices are sensitive to magnetic fields parallel to the substrate and show a single antipeak from 3 to 16 K with a maximum transfer function of ˜16 V/T at 3 K and a field noise of ˜110 pT/Hz1/2 above 100 Hz at 10 K. In a second configuration, the SQIFs were made with 16 planar SQUIDs connected in parallel with loop areas ranging in size from 4 μm2 to 25 μm2 and are sensitive to the magnetic fields perpendicular to the substrate. The planar SQIF shows a single antipeak from 10 to 22 K with a maximum transfer function of 7800 V/T at 10 K and a field noise of ˜70 pT/Hz1/2 above 100 Hz at 20 K.
Flux Flow, Pinning, and Resistive Behavior in Superconducting Networks
Energy Technology Data Exchange (ETDEWEB)
Stephen Teitel
2005-05-03
Numerical simulators are used to study the behavior of interacting quantized vortices and vortex lines in superconducting networks, films, and three dimensional bulk samples. An emphasis is on the explanation of the phenomenological behavior of the ''high-Tc'' copper-oxide superconductors and related model systems.
Energy Technology Data Exchange (ETDEWEB)
Baba, Shoji, E-mail: baba@meso.t.u-tokyo.ac.jp; Sailer, Juergen [Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Deacon, Russell S. [Center for Emergent Matter Science (CEMS), RIKEN, Wako, Saitama 351-0198 (Japan); RIKEN Advanced Science Laboratory, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Oiwa, Akira [The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Shibata, Kenji [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Department of Electronics and Intelligent Systems, Tohoku Institute of Technology, Sendai 982-8577 (Japan); Hirakawa, Kazuhiko [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); JST CREST, 4-1-8 Hon-cho, Kawaguchi-shi, Saitama 332-0012 (Japan); Tarucha, Seigo [Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Center for Emergent Matter Science (CEMS), RIKEN, Wako, Saitama 351-0198 (Japan); INQIE, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan); QPEC, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku 113-8656 (Japan)
2015-11-30
We report conductance and supercurrent measurements for InAs single and parallel double quantum dot Josephson junctions contacted with Nb or NbTiN superconducting electrodes. Large superconducting gap energy, high critical field, and large switching current are observed, all reflecting the features of Nb-based electrodes. For the parallel double dots, we observe an enhanced supercurrent when both dots are on resonance, which may reflect split Cooper pair tunneling.
Nonlinearities in the quantum measurement process of superconducting qubits
Energy Technology Data Exchange (ETDEWEB)
Serban, Ioana
2008-05-15
The work described in this thesis focuses on the investigation of decoherence and measurement backaction, on the theoretical description of measurement schemes and their improvement. The study presented here is centered around quantum computing implementations using superconducting devices and most important, the Josephson effect. The measured system is invariantly a qubit, i. e. a two-level system. The objective is to study detectors with increasing nonlinearity, e. g. coupling of the qubit to the frequency a driven oscillator, or to the bifurcation amplifier, to determine the performance and backaction of the detector on the measured system and to investigate the importance of a strong qubit-detector coupling for the achievement of a quantum non-demolition type of detection. The first part gives a very basic introduction to quantum information, briefly reviews some of the most promising physical implementations of a quantum computer before focusing on the superconducting devices. The second part presents a series of studies of different qubit measurements, describing the backaction of the measurement onto the measured system and the internal dynamics of the detector. Methodology adapted from quantum optics and chemical physics (master equations, phase-space analysis etc.) combined with the representation of a complex environment yielded a tool capable of describing a nonlinear, non-Markovian environment, which couples arbitrarily strongly to the measured system. This is described in chapter 3. Chapter 4 focuses on the backaction on the qubit and presents novel insights into the qubit dephasing in the strong coupling regime. Chapter 5 uses basically the same system and technical tools to explore the potential of a fast, strong, indirect measurement, and determine how close such a detection would ideally come to the quantum non-demolition regime. Chapter 6 focuses on the internal dynamics of a strongly driven Josephson junction. The analytical results are based on
Quantum transport in coupled resonators enclosed synthetic magnetic flux
Energy Technology Data Exchange (ETDEWEB)
Jin, L., E-mail: jinliang@nankai.edu.cn
2016-07-15
Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov–Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms. -- Highlights: •The light transport is investigated through ring array of coupled resonators enclosed synthetic magnetic field. •Aharonov–Bohm ring interferometer of arbitrary configuration is investigated. •The half-integer magnetic flux quantum leads to destructive interference and transmission zeros for two-arm at equal length. •Complete transmission is available via tuning synthetic magnetic flux.
Institute of Scientific and Technical Information of China (English)
WU Tao; LIU Jian-She; LI Zheng
2006-01-01
@@ Superconducting flux qubits with three Josephson junctions are promising candidates for the building blocks of a quantum computer. We have applied the imaginary time evolution method to study the model of this qubit accurately by calculating its wavefunctions and eigenenergies. Because such qubits are manipulated with magnetic lux microwave pulses, they might be irradiated into non-computational states, which is called the leakage effect.By the evolution of the density matrix of the qubit under either hard-shaped π-pulse or Gaussian-shaped π-pulse to carry out quantum NOT operation, it has been demonstrated that the leakage effect for a flux qubit is very small even for hard-shaped microwave pulses while Gaussian-shaped pulses may suppress the leakage effect to a negligible level.
Energy Technology Data Exchange (ETDEWEB)
Reboiro, M., E-mail: reboiro@fisica.unlp.edu.ar [IFLP, CONICET-Department of Physics, University of La Plata, c.c. 67 1900, La Plata (Argentina); Civitarese, O., E-mail: osvaldo.civitarese@fisica.unlp.edu.ar [IFLP, CONICET-Department of Physics, University of La Plata, c.c. 67 1900, La Plata (Argentina); Ramírez, R. [IFLP, CONICET-Department of Mathematics, University of La Plata (Argentina)
2017-03-15
The degree of coherence in a hybrid system composed of superconducting flux-qubits and an electron ensemble is analysed. Both, the interactions among the electrons and among the superconducting flux-qubits are taken into account. The time evolution of the hybrid system is solved exactly, and discussed in terms of the reduced density matrix of each subsystem. It is seen that the inclusion of a line width, for the electrons and for the superconducting flux-qubits, influences the pattern of spin-squeezing and the coherence of the superconducting flux qubits. - Highlights: • The degree of coherence in a hybrid system, composed of superconducting flux qubits and an electron ensemble, is analysed. • The time evolution of the hybrid system is solved exactly and discussed in terms of the reduced density matrix of each subsystem. • It is shown that the initial state of the system evolves to a stationary squeezed state.
A superconducting microcalorimeter for low-flux detection of near-infrared single photons
Energy Technology Data Exchange (ETDEWEB)
Dreyling-Eschweiler, Jan
2014-07-15
This thesis covers the development and the characterization of a single photon detector based on a superconducting microcalorimeter. The detector development is motivated by the Any Light Particle Search II (ALPS II) experiment at DESY in Hamburg, which searches for weakly interacting sub-eV particles (WISPs). Therefore, a detection of low-fluxes of 1064 nm light is required. The work is divided in three analyses: the characterization of a milli-kelvin (mK) cryostat, the characterization of superconducting sensors for single photon detection, and the determination of dark count rates concerning 1064 nm signals. Firstly, an adiabatic demagnetization refrigerator (ADR) is characterized, which allows to reach mK-temperatures. During commissioning, the ADR cryostat is optimized and prepared to stably cool superconducting sensors at 80 mK±25 μK. It is found that sensors can be continuously operated for ∝20 h before recharging the system in <2 h. Furthermore, the adiabatic system reaches a chance of success of ∝80 % for a recharge without technical problems. Secondly, superconducting sensors are analyzed. The focus is on microcalorimetric transition-edge sensors (TESs) based on 20 nm Tungsten (W) films fabricated by the U.S. National Institute of Standards and Technology (NIST). NIST TESs have a near unity detection efficiency for 1064 nm light (literature value). The energy resolution for 1064 nm signals is measured to be <8 %. The exponential falling time of a photon pulse is 1.5 μs. Furthermore, by determining TES parameters, it is found that the linear TES theory describes measured photon pulses well. The TES response is read out by a superconducting quantum interference device (SQUID) fabricated by Physikalisch-Technische Bundesanstalt (PTB). The system bandwidth is measured to be 0.9 MHz. Finally, the operation in the ADR cryostat as well as the ALPS II laboratory is optimized. This setup forms the ALPS TES detector. Thirdly, the background is measured to
Flux rectification in the quantum XXZ chain.
Landi, Gabriel T; Novais, E; de Oliveira, Mário J; Karevski, Dragi
2014-10-01
Thermal rectification is the phenomenon by which the flux of heat depends on the direction of the flow. It has attracted much interest in recent years due to the possibility of devising thermal diodes. In this paper, we consider the rectification phenomenon in the quantum XXZ chain subject to an inhomogeneous field. The chain is driven out of equilibrium by the contact at its boundaries with two different reservoirs, leading to a constant flow of magnetization from one bath to the other. The nonunitary dynamics of this system, which is modeled by a Lindblad master equation, is treated exactly for small sizes and numerically for larger ones. The functional dependence of the rectification coefficient on the model parameters (anisotropy, field amplitude, and out of equilibrium driving strength) is investigated in full detail. Close to the XX point and at small inhomogeneity and low driving, we have found an explicit expression for the rectification coefficient that is valid at all system sizes. In particular, it shows that the phenomenon of rectification persists even in the thermodynamic limit. Finally, we prove that in the case of the XX chain, there is no rectification.
Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism
2016-06-09
AFRL-AFOSR-VA-TR-2016-0204 Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism Jose Rodriguez CALIFORNIA...TITLE AND SUBTITLE Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism 5a. CONTRACT NUMBER 5b. GRANT...SUBJECT TERMS quantum magnetism, HTS, superconductivity 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF
Quantum nondemolition measurements of a flux qubit coupled to a noisy detector
Institute of Scientific and Technical Information of China (English)
Jiang Wei; Yu Yang; Wei Lian-Fu
2011-01-01
We theoretically study the quantum nondemolition measurements of a flux qubit coupled to a noisy superconducting quantum interference device(SQUID).The obtained analytical results indicate that the measurement probability is frequency-dependent in a short time scale and has a close relationship with the measurement-induced dephasing.Furthermore,when the detuning between the driven and bare resonator equals the coupling strength,we can obtain the maximum measurement rate that is determined by the character of the noise in the SQUID.Finally,we analysed the mixed effect caused by coupling between the non-diagonal term and the external variable.It is found that the initial information of the qubit is destroyed due to quantum tunneling between the qubit states.
Superconducting nanowire single photon detectors for quantum information and communications
Wang, Zhen; Fujiwara, Mikio
2010-01-01
Superconducting nanowire single photon detectors (SNSPD or SSPD) are highly promising devices in the growing field of quantum information and communications technology. We have developed a practical SSPD system with our superconducting thin films and devices fabrication, optical coupling packaging, and cryogenic technology. The SSPD system consists of six-channel SSPD devices and a compact Gifford-McMahon (GM) cryocooler, and can operate continuously on 100 V ac power without the need for any cryogens. The SSPD devices were fabricated from high-quality niobium nitride (NbN) ultra-thin films that were epitaxially grown on single-crystal MgO substrates. The packaged SSPD devices were temperature stabilized to 2.96 K +/- 10 mK. The system detection efficiency for an SSPD device with an area of 20x20 $\\mu m^2$ was found to be 2.6% and 4.5% at wavelengths of 1550 and 1310 nm, respectively, at a dark count rate of 100 c/s, and a jitter of 100 ps full width at half maximum (FWHM). We also performed ultra-fast BB84 q...
Dynamical Lamb effect versus dissipation in superconducting quantum circuits
Zhukov, A. A.; Shapiro, D. S.; Pogosov, W. V.; Lozovik, Yu. E.
2016-06-01
Superconducting circuits provide a new platform for study of nonstationary cavity QED phenomena. An example of such a phenomenon is the dynamical Lamb effect, which is the parametric excitation of an atom due to nonadiabatic modulation of its Lamb shift. This effect was initially introduced for a natural atom in a varying cavity, while we suggest its realization in a superconducting qubit-cavity system with dynamically tunable coupling. In the present paper, we study the interplay between the dynamical Lamb effect and the energy dissipation, which is unavoidable in realistic systems. We find that despite naive expectations, this interplay can lead to unexpected dynamical regimes. One of the most striking results is that photon generation from vacuum can be strongly enhanced due to qubit relaxation, which opens another channel for such a process. We also show that dissipation in the cavity can increase the qubit excited-state population. Our results can be used for experimental observation and investigation of the dynamical Lamb effect and accompanying quantum effects.
Micron size superconducting quantum interference devices of lead (Pb)
Paul, Sagar; Biswas, Sourav; Gupta, Anjan K.
2017-02-01
Micron size superconducting quantum interference devices (μ-SQUID) of lead (Pb), for probing nano-magnetism, were fabricated and characterized. In order to get continuous Pb films with small grain size, Pb was thermally evaporated on a liquid nitrogen cooled Si substrate. Pb was sandwiched between two thin Cr layers for improved adhesion and protection. The SQUID pattern was made by e-beam lithography with Pb lift-off after deposition. The current-voltage characteristics of these devices show a critical current, which exhibits the expected SQUID oscillations with magnetic field, and two re-trapping currents. As a result these devices have hysteresis at low temperatures, which disappears just below the critical temperature.
Murrell, J K J
2001-01-01
previously unexplored regions of parameter space. We show that these calculations predict a range of previously unreported dynamical I-V characterises for SQUID rings in the strongly hysteretic regime. Finally, we present the successful realisation of a novel experimental technique that permits the weak link of a SQUID to be probed independently of the associated ring structure by mechanically opening and closing the ring. We demonstrate that this process can be completed during the same experimental run without the need for warming and re-cooling of the sample. This thesis is concerned with the investigation of the non-linear behaviour of a Superconducting Quantum Interference Device (SQUID) coupled to a RF tank circuit. We consider two regimes, one where the underlying SQUID behaviour is non-hysteretic with respect to an externally applied magnetic flux, and the other where hysteretic (dissipative) behaviour is observed. We show that, by following non-linearities induced in the tank circuit response, the un...
A unified theory of quantum Hall effect and high temperature superconductivity
Fujita, Shigeji; Suzuki, Akira
2014-03-01
The quantum Hall effect (QHE) and high temperature superconductivity (HTSC) have remarkable common features. They occur only in two-dimensional (2D) solids. The critical temperature Tc of some HTSC exceeds 160K while the room temperature QHE is observed in graphene. The cause of both QHE and HTSC is the phonon exchange attraction. We develop a theoretical model for the QHE in terms of the composite bosons (fermions), each containing an electron and an odd (even) number of fluxons (magnetic flux quanta). The composite particles (boson, fermion) are bound by the phonon exchange attraction. If the Bose-Einstein condensation (BEC) of the composite (c)- bosons occurs, then the system exhibits zero resistivity and the associated Hall conductivity plateau. The Hall conductivity is calculated rigorously without averaging. The mystery of the fractional charge carried by the c-bosons is resolved in our model.
Fiber-coupled NbN superconducting single-photon detectors for quantum correlation measurements
Slysz, W.; Wegrzecki, M.; Bar, J.; Grabiec, P.; Gorska, M.; Reiger, E.; Dorenbos, S.; Zwiller, V.; Milostnaya, I.; Minaeva, O.
2007-01-01
We have fabricated fiber-coupled superconducting single-photon detectors (SSPDs), designed for quantum-correlationtype experiments. The SSPDs are nanostructured (~100-nm wide and 4-nm thick) NbN superconducting meandering stripes, operated in the 2 to 4.2 K temperature range, and known for ultrafast
Bosonic Operator Realization of Hamiltonian for a Superconducting Quantum Interference Device
Institute of Scientific and Technical Information of China (English)
FAN Hong-Yi
2004-01-01
Based on the appropriate bosonic phase operator diagonalized in the entangled state representation we construct the Hamiltonian operator model for a superconducting quantum interference device. The current operator and voltage operator equations are derived.
Wei, Tzu-Chieh; Goldbart, Paul M.
2008-06-01
As a function of the magnetic flux threading the object, the Little-Parks oscillation in the critical temperature of a large-radius, thin-walled superconducting ring or hollow cylinder has a period given by h/2e , due to the binding of electrons into Cooper pairs. On the other hand, the single-electron Aharonov-Bohm oscillation in the resistance or persistent current for a clean (i.e., ballistic) normal-state system, having the same topological structure, has a period given by h/e . A basic question is whether the Little-Parks oscillation changes its character, as the radius of the superconducting structure becomes smaller, and if it is even comparable to the zero-temperature coherence length. We supplement a physical argument that the h/e oscillations should also be exhibited with a microscopic analysis of this regime, formulated in terms of the Gor’kov approach to BCS theory. We see that, as the radius of the ring is made smaller, an oscillation in the critical temperature of period h/e emerges in addition to the usual Little-Parks h/2e -period oscillation. We argue that, in the clean limit, there is a superconductor-normal transition at nonzero flux as the ring radius becomes sufficiently small and that the transition can be either continuous or discontinuous, depending on the radius and the external flux. In the dirty limit, we argue that the transition is rendered continuous, which results in continuous quantum phase transitions tuned by flux and radius.
Phase-controlled coherent population trapping in superconducting quantum circuits
Institute of Scientific and Technical Information of China (English)
程广玲; 王一平; 陈爱喜
2015-01-01
We investigate the influences of the-applied-field phases and amplitudes on the coherent population trapping behavior in superconducting quantum circuits. Based on the interactions of the microwave fields with a single∆-type three-level fluxonium qubit, the coherent population trapping could be obtainable and it is very sensitive to the relative phase and amplitudes of the applied fields. When the relative phase is tuned to 0 orπ, the maximal atomic coherence is present and coherent population trapping occurs. While for the choice ofπ/2, the atomic coherence becomes weak. Meanwhile, for the fixed relative phaseπ/2, the value of coherence would decrease with the increase of Rabi frequency of the external field coupled with two lower levels. The responsible physical mechanism is quantum interference induced by the control fields, which is indicated in the dressed-state representation. The microwave coherent phenomenon is present in our scheme, which will have potential applications in optical communication and nonlinear optics in solid-state devices.
Superconducting resonators as beam splitters for linear-optics quantum computation.
Chirolli, Luca; Burkard, Guido; Kumar, Shwetank; Divincenzo, David P
2010-06-11
We propose and analyze a technique for producing a beam-splitting quantum gate between two modes of a ring-resonator superconducting cavity. The cavity has two integrated superconducting quantum interference devices (SQUIDs) that are modulated by applying an external magnetic field. The gate is accomplished by applying a radio frequency pulse to one of the SQUIDs at the difference of the two mode frequencies. Departures from perfect beam splitting only arise from corrections to the rotating wave approximation; an exact calculation gives a fidelity of >0.9992. Our construction completes the toolkit for linear-optics quantum computing in circuit quantum electrodynamics.
Cavity-assisted dynamical quantum phase transition in superconducting quantum simulators
Tian, Lin
Coupling a quantum many-body system to a cavity can create bifurcation points in the phase diagram, where the many-body system switches between different phases. Here I will discuss the dynamical quantum phase transitions at the bifurcation points of a one-dimensional transverse field Ising model coupled to a cavity. The Ising model can be emulated with various types of superconducting qubits connected in a chain. With a time-dependent Bogoliubov method, we show that an infinitesimal quench of the driving field can cause gradual evolution of the transverse field on the Ising spins to pass through the quantum critical point. Our calculation shows that the cavity-induced nonlinearity plays an important role in the dynamics of this system. Quasiparticles can be excited in the Ising chain during this process, which results in the deviation of the system from its adiabatic ground state. This work is supported by the National Science Foundation under Award Number 0956064.
Institute of Scientific and Technical Information of China (English)
ZHAN Zhi-Ming
2008-01-01
We put forward a simple scheme for one-step realization of a two-qubit SWAP gate with SQUIDs (super-conducting quantum-interference devices) in cavity QED via Raman transition. In this scheme, the cavity field is only virtually excited and thus the cavity decay is suppressed. The SWAP gate is realized by using only two lower flux states of the SQUID system and the excited state would not be excited. Therefore, the effect of decoherence caused from the levels of the SQUID system is possibly minimized. The scheme can also be used to implement the SWAP gate with atoms.
Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid.
Yu, Deshui; Valado, María Martínez; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer
2016-12-06
Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa.
Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid
Yu, Deshui; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer
2016-01-01
Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa.
Rapid single-flux-quantum circuits for low noise mK operation
Intiso, Samuel; Pekola, Jukka; Savin, Alexander; Devyatov, Ygor; Kidiyarova-Shevchenko, Anna
2006-05-01
Rapid single-flux-quantum (RSFQ) technology has been proposed as control electronics for superconducting quantum bits because of the material and working temperature compatibility. In this work, we consider practical aspects of RSFQ circuit design for low noise low power operation. At the working temperature of 20 mK and operational frequency of 2 GHz, dissipated power per junction is reduced to 25 pW by using 6 µA critical current junctions available at the Hypres and VTT low Jc fabrication process. To limit phonon temperature to 30 mK, a maximum of 40 junctions can be placed on a 5 mm × 5 mm chip. Electron temperature in resistive shunts of Josephson junctions is minimized by use of cooling fins, giving minimum electron temperatures of about 150 mK for the Hypres process and 70 mK for the VTT process.
Superconducting flux pump for high-temperature superconductor insert coils of NMR magnets
Jeong, S.; Lee, H.; Iwasa, Y.
2002-05-01
This paper describes a prototype flux pump recently operated at the MIT Francis Bitter Magnet Laboratory. The results of the prototype flux pump will be used in the development of a full-scale flux pump that will be coupled to a high-temperature superconductor (HTS) insert coil of a high-field NMR magnet. Such an HTS insert is unlikely to operate in persistent mode because of the conductor's low index (n). The flux pump can compensate for field decay in the HTS insert coil and make the insert operate effectively in persistent mode. The flux pump, comprised essentially of a transformer and two switches, all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A prototype flux pump has been designed, fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the range of microamperes has been measured in the magnet after each pumping action. The superconducting prototype flux pump is made of Nb3Sn tape. The pump is placed in a gaseous environment above the liquid helium level to keep its heat dissipation from directly discharged in the liquid; the effluent helium vapor maintains the thermal stability of the flux pump. [This paper is also published in Advances in Cryogenic Engineering Volume 47A, AIP Conference Proceedings Volume 613, pp. 441-448.
Poole, Charles P; Farach, Horacio A
1995-01-01
Superconductivity covers the nature of the phenomenon of superconductivity. The book discusses the fundamental principles of superconductivity; the essential features of the superconducting state-the phenomena of zero resistance and perfect diamagnetism; and the properties of the various classes of superconductors, including the organics, the buckministerfullerenes, and the precursors to the cuprates. The text also describes superconductivity from the viewpoint of thermodynamics and provides expressions for the free energy; the Ginzburg-Landau and BCS theories; and the structures of the high
Low-noise nano superconducting quantum interference device operating in Tesla magnetic fields.
Schwarz, Tobias; Nagel, Joachim; Wölbing, Roman; Kemmler, Matthias; Kleiner, Reinhold; Koelle, Dieter
2013-01-22
Superconductivity in the cuprate YBa(2)Cu(3)O(7) (YBCO) persists up to huge magnetic fields (B) up to several tens of Teslas, and sensitive direct current (dc) superconducting quantum interference devices (SQUIDs) can be realized in epitaxially grown YBCO films by using grain boundary Josephson junctions (GBJs). Here we present the realization of high-quality YBCO nanoSQUIDs, patterned by focused ion beam milling. We demonstrate low-noise performance of such a SQUID up to B = 1 T applied parallel to the plane of the SQUID loop at the temperature T = 4.2 K. The GBJs are shunted by a thin Au layer to provide nonhysteretic current voltage characteristics, and the SQUID incorporates a 90 nm wide constriction which is used for on-chip modulation of the magnetic flux through the SQUID loop. The white flux noise of the device increases only slightly from 1.3 μΦ(0)/(Hz)(1/2) at B = 0 to 2.3 μΦ(0)/(Hz))(1/2) at 1 T. Assuming that a point-like magnetic particle with magnetization in the plane of the SQUID loop is placed directly on top of the constriction and taking into account the geometry of the SQUID, we calculate a spin sensitivity S(μ)(1/2) = 62 μ(B)/(Hz))(1/2) at B = 0 and 110 μ(B)/(Hz))(1/2) at 1 T. The demonstration of low noise of such a SQUID in Tesla fields is a decisive step toward utilizing the full potential of ultrasensitive nanoSQUIDs for direct measurements of magnetic hysteresis curves of magnetic nanoparticles and molecular magnets.
Design and market considerations for axial flux superconducting electric machine design
Ainslie, M. D.; George, A.; Shaw, R.; Dawson, L.; Winfield, A.; Steketee, M.; Stockley, S.
2014-05-01
In this paper, the authors investigate a number of design and market considerations for an axial flux superconducting electric machine design that uses high temperature superconductors. The axial flux machine design is assumed to utilise high temperature superconductors in both wire (stator winding) and bulk (rotor field) forms, to operate over a temperature range of 65-77 K, and to have a power output in the range from 10s of kW up to 1 MW (typical for axial flux machines), with approximately 2-3 T as the peak trapped field in the bulk superconductors. The authors firstly investigate the applicability of this type of machine as a generator in small- and medium-sized wind turbines, including the current and forecasted market and pricing for conventional turbines. Next, a study is also carried out on the machine's applicability as an in-wheel hub motor for electric vehicles. Some recommendations for future applications are made based on the outcome of these two studies. Finally, the cost of YBCO-based superconducting (2G HTS) wire is analysed with respect to competing wire technologies and compared with current conventional material costs and current wire costs for both 1G and 2G HTS are still too great to be economically feasible for such superconducting devices.
Hriscu, A.M.; Nazarov, Y.V.
2013-01-01
We propose a way to achieve quantum synchronization of two canonically conjugated variables. For this, we employ a superconducting device where the synchronization of Josephson and Bloch oscillations results in the quantization of transresistance similar to that in the (fractional) quantum Hall effe
Flux Pinning in Superconducting Niobium-Titanium Alloys
McKinnell, James Charles
1990-01-01
By studying Nb-Ti alloys from Nb44wt%Ti to Nb62wt%Ti the low field (2T) current density has been raised from 6500A/mm^2 (4.2^ circK) with standard Nb46.5wt%Ti to 7400A/mm ^2 with Nb58wt%Ti. When standard processing sequences were used, the alloys containing more than 46.5wt%Ti exhibited non-uniform microstructures following a precipitation heat treatment and the hardness rose from 200 DPN to over 300 DPN. By increasing the cold work prior to heat treatment the non-uniform precipitation was avoided. The amount of cold work needed prior to heat treatment to suppress non-uniform precipitation increased as the Ti content of the alloy increased. The volume fraction of precipitate produced during a given heat treatment also increased as the Ti content of the alloy increased. As the Ti content increased, the peak in the reduced pinning force curve shifted from b = 0.5 to b = 0.25. In order to determine whether the change in the flux pinning properties was due to the change in microstructure or due to enhanced Delta H_{c} pinning as the Ti content was increased, a set of wires with similar microstructures was developed. Their flux pinning behavior showed that the higher Ti alloys have pinning force curves which peak at progressively lower reduced fields. Thus Delta H_{c} pinning becomes the dominant pinning mechanism as the Ti content is increased.
Towards Quantum Simulation of Chemical Dynamics with Prethreshold Superconducting Qubits
Stancil, P C; Cook, A; Sornborger, A T; Geller, M R
2016-01-01
The single excitation subspace (SES) method for universal quantum simulation is investigated for a number of diatomic molecular collision complexes. Assuming a system of $n$ tunably-coupled, and fully-connected superconducting qubits, computations are performed in the $n$-dimensional SES which maps directly to an $n$-channel collision problem within a diabatic molecular wave function representation. Here we outline the approach on a classical computer to solve the time-dependent Schr\\"odinger equation in an $n$-dimensional molecular basis - the so-called semiclassical molecular-orbital close-coupling (SCMOCC) method - and extend the treatment beyond the straight-line, constant-velocity approximation which is restricted to large kinetic energies ($\\gtrsim 0.1$ keV/u). We explore various multichannel potential averaging schemes and an Ehrenfest symmetrization approach to allow for the application of the SCMOCC method to much lower collision energies (approaching 1 eV/u). In addition, a computational efficiency ...
Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point
Lederer, Samuel; Schattner, Yoni; Berg, Erez; Kivelson, Steven A.
2017-05-01
Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin mn>1mn>mn>2mn>12 itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting TcTc enclosing the nematic quantum critical point. For temperatures above TcTc, we see strikingly non-Fermi liquid behavior, including a “nodal-antinodal dichotomy” reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with “bad metal” phenomenology.
Nori, Franco
2012-02-01
This talk will present an overview of some of our recent results on atomic physics and quantum optics using superconducting circuits. Particular emphasis will be given to photons interacting with qubits, interferometry, the Dynamical Casimir effect, and also studying Majorana fermions using superconducting circuits.[4pt] References available online at our web site:[0pt] J.Q. You, Z.D. Wang, W. Zhang, F. Nori, Manipulating and probing Majorana fermions using superconducting circuits, (2011). Arxiv. J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in a superconducting coplanar waveguide, Phys. Rev. Lett. 103, 147003 (2009). [0pt] J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in superconducting microwave circuits, Phys. Rev. A 82, 052509 (2010). [0pt] C.M. Wilson, G. Johansson, A. Pourkabirian, J.R. Johansson, T. Duty, F. Nori, P. Delsing, Observation of the Dynamical Casimir Effect in a superconducting circuit. Nature, in press (Nov. 2011). P.D. Nation, J.R. Johansson, M.P. Blencowe, F. Nori, Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits, Rev. Mod. Phys., in press (2011). [0pt] J.Q. You, F. Nori, Atomic physics and quantum optics using superconducting circuits, Nature 474, 589 (2011). [0pt] S.N. Shevchenko, S. Ashhab, F. Nori, Landau-Zener-Stuckelberg interferometry, Phys. Reports 492, 1 (2010). [0pt] I. Buluta, S. Ashhab, F. Nori. Natural and artificial atoms for quantum computation, Reports on Progress in Physics 74, 104401 (2011). [0pt] I.Buluta, F. Nori, Quantum Simulators, Science 326, 108 (2009). [0pt] L.F. Wei, K. Maruyama, X.B. Wang, J.Q. You, F. Nori, Testing quantum contextuality with macroscopic superconducting circuits, Phys. Rev. B 81, 174513 (2010). [0pt] J.Q. You, X.-F. Shi, X. Hu, F. Nori, Quantum emulation of a spin system with topologically protected ground states using superconducting quantum circuit, Phys. Rev. A 81, 063823 (2010).
Energy Technology Data Exchange (ETDEWEB)
Ella, Lior, E-mail: lior.ella@weizmann.ac.il; Yuvaraj, D.; Suchoi, Oren; Shtempluk, Oleg; Buks, Eyal [Faculty of Electrical Engineering, Technion, Haifa 32000 (Israel)
2015-01-07
We present a study of the controllable nonlinear dynamics of a micromechanical beam coupled to a dc-SQUID (superconducting quantum interference device). The coupling between these systems places the modes of the beam in a highly nonlinear potential, whose shape can be altered by varying the bias current and applied flux of the SQUID. We detect the position of the beam by placing it in an optical cavity, which sets free the SQUID to be used solely for actuation. This enables us to probe the previously unexplored full parameter space of this device. We measure the frequency response of the beam and find that it displays a Duffing oscillator behavior which is periodic in the applied magnetic flux. To account for this, we develop a model based on the standard theory for SQUID dynamics. In addition, with the aim of understanding if the device can reach nonlinearity at the single phonon level, we use this model to show that the responsivity of the current circulating in the SQUID to the position of the beam can become divergent, with its magnitude limited only by noise. This suggests a direction for the generation of macroscopically distinguishable superposition states of the beam.
Millar, A J
2002-01-01
This thesis is concerned with the development of Superconducting Quantum Interference Device (SQUID) gradiometers based on the high temperature superconductor YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (YBCO). A step-edge Josephson junction fabrication process was developed to produce sufficiently steep (>60 deg) step-edges such that junctions exhibited RSJ-like current-voltage characteristics. The mean I sub C R sub N product of a sample of twenty step-edge junctions was 130 mu V. Step-edge dc SQUIDs with inductances between 67pH and 114pH were fabricated. Generally the SQUIDs had an intrinsic white flux noise in the 10-30 mu PHI sub 0 /sq root Hz range, with the best device, a 70pH SQUID, exhibiting a white flux noise of 5 mu PHI sub 0 /sq root Hz. Different first-order SQUID gradiometer designs were fabricated from single layers of YBCO. Two single-layer gradiometer (SLG) designs were fabricated on 10x10mm sup 2 substrates. The best balance and lowest gradient sensitivity measured for these devices were 1/3...
Distributed quantum computation with superconducting qubit via LC circuit using dressed states
Institute of Scientific and Technical Information of China (English)
Wu Chao; Fang Mao-Fa; Xiao Xing; Li Yan-Ling; Cao Shuai
2011-01-01
A scheme is proposed where two superconducting qubits driven by a classical field interacting separately with two distant LC circuits connected by another LC circuit through mutual inductance, are used for implementing quantum gates. By using dressed states, quantum state transfer and quantum entangling gate can be implemented. With the help of the time-dependent electromagnetic field, any two dressed qubits can be selectively coupled to the data bus (the last LC circuit), then quantum state can be transferred from one dressed qubit to another and multi-mode entangled state can also be formed. As a result, the promising perspectives for quantum information processing of mesoscopic superconducting qubits are obtained and the distributed and scalable quantum computation can be implemented in this scheme.
Fermion-fermion scattering in quantum field theory with superconducting circuits.
García-Álvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
2015-02-20
We propose an analog-digital quantum simulation of fermion-fermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexity-simulating-complexity concept should become a leading paradigm in any effort towards scalable quantum simulations.
Institute of Scientific and Technical Information of China (English)
SONG Ke-Hui; ZHOU Zheng-Wei; GUO Guang-Can
2006-01-01
We present a scheme to realize geometric phase-shift gate for two superconducting quantum interference device (SQUID) qubits coupled to a single-mode microwave field. The geometric phase-shift gate operation is performed transitions during the gate operation. Thus, the docoherence due to energy spontaneous emission based on the levels of SQUIDs are suppressed. The gate is insensitive to the cavity decay throughout the operation since the cavity mode is displaced along a circle in the phase space, acquiring a phase conditional upon the two lower flux states of the SQUID qubits, and the cavity mode is still in the original vacuum state. Based on the SQUID qubits interacting with the cavity mode, our proposed approach may open promising prospects for quantum logic in SQUID-system.
A novel protection layer of superconducting microwave circuits toward a hybrid quantum system
Lee, Jongmin
2014-01-01
We propose a novel multilayer structure based on Bragg layers that can protect a superconducting microwave resonator from photons and blackbody radiation and have little effect on its quality factor. We also discuss a hybrid quantum system exploiting a superconducting microwave circuit and a two-color evanescent field atom trap, where surface-scattered photons and absorption-induced broadband blackbody radiation might deteriorate the system.
Quantum interference in heterogeneous superconducting-photonic circuits on a silicon chip
Schuck, Carsten; Fan, Linran; Ma, Xiao-Song; Poot, Menno; Tang, Hong X
2015-01-01
Quantum information processing holds great promise for communicating and computing data efficiently. However, scaling current photonic implementation approaches to larger system size remains an outstanding challenge for realizing disruptive quantum technology. Two main ingredients of quantum information processors are quantum interference and single-photon detectors. Here we develop a hybrid superconducting-photonic circuit system to show how these elements can be combined in a scalable fashion on a silicon chip. We demonstrate the suitability of this approach for integrated quantum optics by interfering and detecting photon pairs directly on the chip with waveguide-coupled single-photon detectors. Using a directional coupler implemented with silicon nitride nanophotonic waveguides, we observe 97% interference visibility when measuring photon statistics with two monolithically integrated superconducting single photon detectors. The photonic circuit and detector fabrication processes are compatible with standa...
Universal holonomic quantum gates in decoherence-free subspace on superconducting circuits
Xue, Zheng-Yuan; Zhou, Jian; Wang, Z. D.
2015-08-01
To implement a set of universal quantum logic gates based on non-Abelian geometric phases, it is conventional wisdom that quantum systems beyond two levels are required, which is extremely difficult to fulfill for superconducting qubits and appears to be a main reason why only single-qubit gates were implemented in a recent experiment [A. A. Abdumalikov, Jr. et al., Nature (London) 496, 482 (2013), 10.1038/nature12010]. Here we propose to realize nonadiabatic holonomic quantum computation in decoherence-free subspace on circuit QED, where one can use only the two levels in transmon qubits, a usual interaction, and a minimal resource for the decoherence-free subspace encoding. In particular, our scheme not only overcomes the difficulties encountered in previous studies but also can still achieve considerably large effective coupling strength, such that high-fidelity quantum gates can be achieved. Therefore, the present scheme makes realizing robust holonomic quantum computation with superconducting circuits very promising.
Comment on 'Realism and quantum flux tunneling'
Leggett, A. J.; Garg, Anupam
1987-01-01
A reply is presented to Ballentine's (1987) critique of the Legett and Garg (1985) experiment to discriminate between the experimental predictions of quantum mechanics (QM) and those of a class of macrorealistic theories. Legett and Garg uphold their earlier conclusions on the basis of the fact that the present critique refers to an experiment which was not in fact proposed. It is stressed that the original work involved an analysis according to macrorealism, while the calculations of Ballentine only demonstrate the internal consistency of the formalism of QM when applied to three consecutive actually performed experiments.
Thomas, D B
1974-01-01
A short general review is presented of the progress made in applied superconductivity as a result of work performed in connection with the high-energy physics program in Europe. The phenomenon of superconductivity and properties of superconductors of Types I and II are outlined. The main body of the paper deals with the development of niobium-titanium superconducting magnets and of radio-frequency superconducting cavities and accelerating structures. Examples of applications in and for high-energy physics experiments are given, including the large superconducting magnet for the Big European Bubble Chamber, prototype synchrotron magnets for the Super Proton Synchrotron, superconducting d.c. beam line magnets, and superconducting RF cavities for use in various laboratories. (0 refs).
Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED
Institute of Scientific and Technical Information of China (English)
CHEN Chang-Yong
2012-01-01
We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.
Mostame, Sarah; Tsomokos, Dimitris I; Aspuru-Guzik, Alán
2011-01-01
In the initial stage of photosynthesis, light-harvested energy is transferred with remarkably high efficiency to a reaction center, with the vibrational environment assisting the transport mechanism. It is of great interest to mimic this process with present-day technologies. Here we propose an analog quantum simulator of open system dynamics, where noise engineering of the environment has a central role. In particular, we propose the use of superconducting qubits for the simulation of exciton transport in the Fenna-Matthew-Olson protein, a prototypical photosynthetic complex. Our method allows for a single-molecule implementation and the investigation of energy transfer pathways as well as non-Markovian and spatiotemporal noise-correlation effects.
Mostame, Sarah; Rebentrost, Patrick; Eisfeld, Alexander; Kerman, Andrew J.; Tsomokos, Dimitris I.; Aspuru-Guzik, Alan
2012-02-01
In the initial stage of photosynthesis, light-harvested energy is transferred with remarkably high efficiency to a reaction center, with the vibrational environment assisting the transport mechanism. It is of great interest to mimic this process with present-day technologies. Here we propose an analog quantum simulator of open system dynamics, where noise engineering of the environment has a central role. In particular, we propose the use of superconducting qubits for the simulation of exciton transport in the Fenna-Matthew-Olson protein, a prototypical photosynthetic complex. Our method allows for a single-molecule implementation and the investigation of energy transfer pathways as well as non-Markovian and spatiotemporal noise-correlation effects.
Superconducting quantum circuits at the surface code threshold for fault tolerance.
Barends, R; Kelly, J; Megrant, A; Veitia, A; Sank, D; Jeffrey, E; White, T C; Mutus, J; Fowler, A G; Campbell, B; Chen, Y; Chen, Z; Chiaro, B; Dunsworth, A; Neill, C; O'Malley, P; Roushan, P; Vainsencher, A; Wenner, J; Korotkov, A N; Cleland, A N; Martinis, John M
2014-04-24
A quantum computer can solve hard problems, such as prime factoring, database searching and quantum simulation, at the cost of needing to protect fragile quantum states from error. Quantum error correction provides this protection by distributing a logical state among many physical quantum bits (qubits) by means of quantum entanglement. Superconductivity is a useful phenomenon in this regard, because it allows the construction of large quantum circuits and is compatible with microfabrication. For superconducting qubits, the surface code approach to quantum computing is a natural choice for error correction, because it uses only nearest-neighbour coupling and rapidly cycled entangling gates. The gate fidelity requirements are modest: the per-step fidelity threshold is only about 99 per cent. Here we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92 per cent and a two-qubit gate fidelity of up to 99.4 per cent. This places Josephson quantum computing at the fault-tolerance threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger-Horne-Zeilinger state using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.
Jing, Ze; Yong, Huadong; Zhou, Youhe
2016-10-01
In this paper, the anisotropic flux avalanche processes in thin square-shaped type-II superconducting films are numerically investigated by solving the coupled nonlinear Maxwell’s equations and the thermal diffusion equations. Influences of the non-uniformities and intrinsic critical current density anisotropies originate from the manufacturing process are considered in the simulation. In addition, we also studied the effect of the extrinsic anisotropy induced by the in-plane magnetic field. The results demonstrate that the non-uniformities and anisotropies of the critical current density play significant roles in the flux avalanche process of the thin film superconductors. Slight anisotropy (either intrinsic or extrinsic) can dramatically change the propagation direction of avalanches in the superconducting film, which is consistent with the experimental results. Simulations on the thin square-shaped isotropic superconducting films show that the threshold magnetic field for the flux avalanches increases with the angle between the applied field and the superconducting film-plane. In addition, the flux avalanche patterns change with the angular variation of the in-plane component of external magnetic field. When the in-plane magnetic field component is along the diagonal lines of the superconducting square, symmetric flux avalanche penetration patterns occur to the film.
Realignment of the flux-line lattice by a change in the symmetry of superconductivity in UPt3
Huxley, Andrew; Rodière, Pierre; Paul, Donald M. K.; van Dijk, Niels; Cubitt, Robert; Flouquet, Jacques
2000-07-01
In 1957, Abrikosov described how quanta of magnetic flux enter the interior of a bulk type II superconductor. It was subsequently predicted that, in an isotropic superconductor, the repulsive forces between the flux lines would cause them to order in two dimensions, forming a hexagonal lattice. Flux-line lattices with different geometry can also be found in conventional (type II) superconductors; however, the ideal hexagonal lattice structure should always occur when the magnetic field is applied along a hexagonal crystal direction. Here we report measurements of the orientation of the flux-line lattice in the heavy-fermion superconductor UPt3, for this special case. As the temperature is increased, the hexagonal lattice, which is initially aligned along the crystal symmetry directions, realigns itself with the anisotropic superconducting gap. The superconductivity in UPt3 is unusual (even compared to unconventional oxide superconductors) because the superconducting gap has a lower rotational symmetry than the crystal structure. This special feature enables our data to demonstrate clearly the link between the microscopic symmetry of the superconductivity and the mesoscopic physics of the flux-line lattice. Moreover, our observations provide a stringent test of the theoretical description of the unconventional superconductivity in UPt3.
Simulation of electronic structure Hamiltonians in a superconducting quantum computer architecture
Energy Technology Data Exchange (ETDEWEB)
Kaicher, Michael; Wilhelm, Frank K. [Theoretical Physics, Saarland University, 66123 Saarbruecken (Germany); Love, Peter J. [Department of Physics, Haverford College, Haverford, Pennsylvania 19041 (United States)
2015-07-01
Quantum chemistry has become one of the most promising applications within the field of quantum computation. Simulating the electronic structure Hamiltonian (ESH) in the Bravyi-Kitaev (BK)-Basis to compute the ground state energies of atoms/molecules reduces the number of qubit operations needed to simulate a single fermionic operation to O(log(n)) as compared to O(n) in the Jordan-Wigner-Transformation. In this work we will present the details of the BK-Transformation, show an example of implementation in a superconducting quantum computer architecture and compare it to the most recent quantum chemistry algorithms suggesting a constant overhead.
1989-07-01
SUPERCONDUCTIVITY HIGH-POWER APPLICATIONS Electric power generation/transmission Energy storage Acoustic projectors Weapon launchers Catapult Ship propulsion • • • Stabilized...temperature superconductive shields could be substantially enhanced by use of high-Tc materials. 27 28 NRAC SUPERCONDUCTIVITY SHIP PROPULSION APPLICATIONS...motor shown in the photograph. As a next step in the evolution of electric-drive ship propulsion technology, DTRC has proposed to scale up the design
Supersymmetric quantum mechanics of the flux tube
Belitsky, A V
2016-01-01
The Operator Product Expansion approach to scattering amplitudes in maximally supersymmetric gauge theory operates in terms of pentagon transitions for excitations propagating on a color flux tube. These obey a set of axioms which allow to determine them to all orders in 't Hooft coupling and confront against explicit calculations. One of the simplifying features of the formalism is the factorizability of multiparticle transitions in terms of single-particle ones. In this paper we extend an earlier consideration of a sector populated by one kind of excitations to the case of a system with fermionic as well as bosonic degrees of freedom to address the origin of the factorization. While the purely bosonic case was analyzed within an integrable noncompact open-spin chain model, the current case is solved in the framework of a supersymmetric sl(2|1) magnet. We find the eigenfunctions for the multiparticle system making use of the R-matrix approach. Constructing resulting pentagon transitions, we prove their facto...
Supersymmetric quantum mechanics of the flux tube
Belitsky, A. V.
2016-12-01
The Operator Product Expansion approach to scattering amplitudes in maximally supersymmetric gauge theory operates in terms of pentagon transitions for excitations propagating on a color flux tube. These obey a set of axioms which allow one to determine them to all orders in 't Hooft coupling and confront against explicit calculations. One of the simplifying features of the formalism is the factorizability of multiparticle transitions in terms of single-particle ones. In this paper we extend an earlier consideration of a sector populated by one kind of excitations to the case of a system with fermionic as well as bosonic degrees of freedom to address the origin of the factorization. While the purely bosonic case was analyzed within an integrable noncompact open-spin chain model, the current case is solved in the framework of a supersymmetric sl (2 | 1) magnet. We find the eigenfunctions for the multiparticle system making use of the R-matrix approach. Constructing resulting pentagon transitions, we prove their factorized form. The discussion corresponds to leading order of perturbation theory.
Universal transport signatures of topological superconductivity in quantum spin Hall architectures
Lee, Shu-Ping; Aasen, David; Karzig, Torsten; Alicea, Jason
2015-03-01
Interfacing s-wave superconductors with quantum spin Hall systems provides a promising route to ``engineered'' topological superconductivity. Given exciting recent progress on the fabrication side, identifying experiments that definitively expose the topological superconducting phase (and clearly distinguish it from a trivial state) raises an increasingly important problem. With this goal in mind we use renormalization group methods to extract universal transport characteristics of superconductor/quantum spin Hall heterostructures where the native edge states serve as a lead. Interestingly, arbitrarily weak interactions induce qualitative changes in the behavior relative to the free-fermion limit, leading to a sharp dichotomy in conductance for the trivial (narrow superconductor) and topological (wide superconductor) cases. Furthermore, we find that strong interactions can in principle induce power-law-localized ``parafermion'' excitations at a superconductor/quantum spin Hall junction. NSF Grant DMR-1341822. (2) Institute for Quantum Information and Matter, an NSF physics frontier center with support from the Moore Foundation.
Jerger, Markus; Macha, Pascal; Hamann, Andrés Rosario; Reshitnyk, Yarema; Juliusson, Kristinn; Fedorov, Arkady
2016-07-01
Binary-outcome measurements allow one to determine whether a multilevel quantum system is in a certain state while preserving quantum coherence between all orthogonal states. In this paper, we explore different regimes of the dispersive readout of a three-level superconducting quantum system coupled to a microwave cavity in order to implement binary-outcome measurements. By designing identical cavity-frequency shifts for the first and second excited states of the system, we realize strong projective binary-outcome measurements onto its ground state with a fidelity of 94.3%. Complemented with standard microwave control and low-noise parametric amplification, this scheme enables the quantum nondemolition detection of leakage errors and can be used to create sets of compatible measurements to reveal the contextual nature of superconducting circuits.
Detection of bacteria in suspension using a superconducting Quantum interference device
Energy Technology Data Exchange (ETDEWEB)
Grossman, H.L.; Myers, W.R.; Vreeland, V.J.; Alper, J.D.; Bertozzi, C.R.; Clarke, J.
2003-06-09
We demonstrate a technique for detecting magnetically-labeled Listeria monocytogenes and for measuring the binding rate between antibody-linked magnetic particles and bacteria. This assay, which is both sensitive and straightforward to perform, can quantify specific bacteria in a sample without the need to immobilize the bacteria or wash away unbound magnetic particles. In the measurement, we add 50 nm diameter superparamagnetic particles, coated with antibodies, to a liquid sample containing L. monocytogenes. We apply a pulsed magnetic field to align the magnetic dipole moments and use a high transition temperature Superconducting Quantum Interference Device (SQUID), an extremely sensitive detector of magnetic flux, to measure the magnetic relaxation signal when the field is turned off. Unbound particles randomize direction by Brownian rotation too quickly to be detected. In contrast, particles bound to L. monocytogenes are effectively immobilized and relax in about 1 s by rotation of the internal dipole moment. This Neel relaxation process is detected by the SQUID. The measurements indicate a detection limit of (5.6 {+-} 1.1) x 10{sup 6} L. monocytogenes for a 20 {micro}L sample volume. If the sample volume were reduced to 1 nL, we estimate that the detection limit could be improved to 230 {+-} 40 L. monocytogenes cells. Time-resolved measurements yield the binding rate between the particles and bacteria.
Detection of bacteria in suspension using a superconducting Quantum interference device
Energy Technology Data Exchange (ETDEWEB)
Grossman, H.L.; Myers, W.R.; Vreeland, V.J.; Alper, J.D.; Bertozzi, C.R.; Clarke, J.
2003-06-09
We demonstrate a technique for detecting magnetically-labeled Listeria monocytogenes and for measuring the binding rate between antibody-linked magnetic particles and bacteria. This assay, which is both sensitive and straightforward to perform, can quantify specific bacteria in a sample without the need to immobilize the bacteria or wash away unbound magnetic particles. In the measurement, we add 50 nm diameter superparamagnetic particles, coated with antibodies, to a liquid sample containing L. monocytogenes. We apply a pulsed magnetic field to align the magnetic dipole moments and use a high transition temperature Superconducting Quantum Interference Device (SQUID), an extremely sensitive detector of magnetic flux, to measure the magnetic relaxation signal when the field is turned off. Unbound particles randomize direction by Brownian rotation too quickly to be detected. In contrast, particles bound to L. monocytogenes are effectively immobilized and relax in about 1 s by rotation of the internal dipole moment. This Neel relaxation process is detected by the SQUID. The measurements indicate a detection limit of (5.6 {+-} 1.1) x 10{sup 6} L. monocytogenes for a 20 {micro}L sample volume. If the sample volume were reduced to 1 nL, we estimate that the detection limit could be improved to 230 {+-} 40 L. monocytogenes cells. Time-resolved measurements yield the binding rate between the particles and bacteria.
Operation of a superconducting nanowire quantum interference device with mesoscopic leads
Pekker, David; Bezryadin, Alexey; Hopkins, David S.; Goldbart, Paul M.
2005-09-01
A theory describing the operation of a superconducting nanowire quantum interference device (NQUID) is presented. The device consists of a pair of thin-film superconducting leads connected by a pair of topologically parallel ultranarrow superconducting wires. It exhibits intrinsic electrical resistance, due to thermally activated dissipative fluctuations of the superconducting order parameter. Attention is given to the dependence of this resistance on the strength of an externally applied magnetic field aligned perpendicular to the leads, for lead dimensions such that there is essentially complete and uniform penetration of the leads by the magnetic field. This regime, in which at least one of the lead dimensions—length or width—lies between the superconducting coherence and penetration lengths, is referred to as the mesoscopic regime. The magnetic field causes a pronounced oscillation of the device resistance, with a period not dominated by the Aharonov-Bohm effect through the area enclosed by the wires and the film edges but, rather, in terms of the geometry of the leads, in contrast to the well-known Little-Parks resistance of thin-walled superconducting cylinders. A detailed theory, encompassing this phenomenology quantitatively, is developed through extensions, to the setting of parallel superconducting wires, of the Ivanchenko-Zil’berman-Ambegaokar-Halperin theory of intrinsic resistive fluctuations in a current-biased Josephson junction and the Langer-Ambegaokar-McCumber-Halperin theory of intrinsic resistive fluctuations in a superconducting wire. In particular, it is demonstrated that via the resistance of the NQUID, the wires act as a probe of spatial variations in the superconducting order parameter along the perimeter of each lead: in essence, a superconducting phase gradiometer.
Coplanar waveguide flux qubit suitable for quantum annealing
Quintana, Chris; Chen, Yu; Sank, D.; Kafri, D.; Megrant, A.; White, T. C.; Shabani, A.; Barends, R.; Campbell, B.; Chen, Z.; Chiaro, B.; Dunsworth, A.; Fowler, A.; Jeffrey, E.; Kelly, J.; Lucero, E.; Mutus, J. Y.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Vainsencher, A.; Wenner, J.; Martinis, J. M.
We introduce the ''fluxmon'' flux qubit, designed with the goal of practical quantum annealing. The qubit's capacitance and linear inductance are provided by a coplanar waveguide on a low loss substrate, minimizing dielectric dissipation and in principle allowing for GHz-scale inter-qubit coupling in a highly connected tunable architecture. Utilizing a dispersive microwave readout scheme, we characterize single-qubit noise and dissipation, and present a simple tunable inter-qubit coupler. We discuss tradeoffs between coherence and coupling in a quantum annealing architecture. This work was supported by Google Inc. and by the NSF GRFP.
Giant flux jumps through a thin superconducting Nb film in a vortex free region
Energy Technology Data Exchange (ETDEWEB)
Tsindlekht, M.I., E-mail: mtsindl@vms.huji.ac.il [The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Genkin, V.M.; Felner, I.; Zeides, F.; Katz, N. [The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Gazi, Š.; Chromik, Š. [The Institute of Electrical Engineering SAS, Dúbravská cesta 9, 84104 Bratislava (Slovakia)
2016-10-15
Highlights: Giant magnetic flux jumps into thin-walled cylinder were measured using peak up coil method in a swept magnetic field. Magnetic moment jumps were observed in magnetic fields lower and above Hc1. - Abstract: We measure the dynamics of magnetic field penetration into thin-walled superconducting niobium cylinders. It is shown that magnetic field penetrates through the wall of a cylinder in a series of giant jumps with amplitude 1 - 2 mT and duration of less than a microsecond in a wide range of magnetic fields, including the vortex free region. Surprisingly, the jumps take place when the total current in the wall, not the current density, exceeds a critical value. In addition, there are small jumps and/or smooth penetration, but their contribution reaches only ≃ 20 % of the total penetrating flux. The number of jumps decreases with increased temperature. Thermomagnetic instabilities cannot explain the experimental observations.
Institute of Scientific and Technical Information of China (English)
ZHAN Zhi-Ming
2009-01-01
In this paper, a theoretical scheme is proposed to implement the Deutsch-Jozsa algorithm with SQUIDs (superconducting quantum-interference devices) in cavity via Raman transition. The scheme only requires a quantized cavity field and classical microwave pulses. In this scheme, no transfer of quantum information between the SQUIDs and the cavity is required, the cavity field is only virtually excited and thus the cavity decay is suppressed.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
We propose a scheme for generating a maximally entangled state of two three-level superconducting quantum interference devices (SQUIDs) by using a quantized cavity field and classical microwave pluses in cavity. In this scheme, no quantum information will be transferred from the SQUIDs to the cavity since the cavity field is only virtually excited. Thus, the cavity decay is suppressed during the entanglement generation.
Magnetic and superconducting quantum critical points of heavy-fermion systems
Energy Technology Data Exchange (ETDEWEB)
Demuer, A.; Sheikin, I.; Braithwaite, D. E-mail: dbraithwaite@cea.fr; Faak, B.; Huxley, A.; Raymond, S.; Flouquet, J
2001-05-01
Two examples of heavy-fermion systems are presented : CePd{sub 2}Si{sub 2}, an antiferromagnet with a quantum critical point at P{sub C}=28 kbar and UGe{sub 2} an itinerant ferromagnet which transits in a paramagnetic phase above P{sub C}=16 kbar. In CePd{sub 2}Si{sub 2} the superconductivity domain is centered on P{sub C}. Special attention was given to the superconducting and magnetic anomalies at their superconducting and Neel temperatures. In UGe{sub 2} superconductivity appears in 9 kbar at a temperature T{sub S}, more than two orders of magnitude lower than the Curie temperature; furthermore, it occurs only on the magnetic border (P
Magnetic and superconducting quantum critical points of heavy-fermion systems
Demuer, A.; Sheikin, I.; Braithwaite, D.; Fåk, B.; Huxley, A.; Raymond, S.; Flouquet, J.
2001-05-01
Two examples of heavy-fermion systems are presented : CePd 2Si 2, an antiferromagnet with a quantum critical point at PC=28 kbar and UGe 2 an itinerant ferromagnet which transits in a paramagnetic phase above PC=16 kbar. In CePd 2Si 2 the superconductivity domain is centered on PC. Special attention was given to the superconducting and magnetic anomalies at their superconducting and Néel temperatures. In UGe 2 superconductivity appears in 9 kbar at a temperature TS, more than two orders of magnitude lower than the Curie temperature; furthermore, it occurs only on the magnetic border ( P< PC). Another characteristic temperature TX is detected by resistivity; the zigzag uranium chain of the lattice may favor a supplementary nesting in the majority spin band.
2015-01-01
On Tuesday, 25 August, J. Georg Bednorz (Nobel prize in physics 1987, IBM Research Zurich) and Louis Taillefer (physicist and professor at the University of Sherbrooke, Canada, and at the Canadian Institute for Advanced Research) will give a conference on the fascinating theme of superconductivity. "Superconductivity: theory and practical challenges of a quantum phenonemon" Uni Dufour Tuesday, 25 August at 7 p.m. This conference is organized by the Faculty of science of the University of Geneva, as part of the International Congress Materials and Mechanisms of Superconductivity (M2S - 2015). Discovered more than 100 years ago, superconductivity remains one of the most fascinating manifestations of the laws of physics, observable only at low temperatures. This phenomenon, which allows the transport of electricity without any loss of energy, leads to various technological applications, for example in magnetically levitated vehicles, in MRI and in ...
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.
Dong, J K; Zhou, S Y; Guan, T Y; Zhang, H; Dai, Y F; Qiu, X; Wang, X F; He, Y; Chen, X H; Li, S Y
2010-02-26
The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.
TonThat, Dinh M.; Clarke, John
1996-08-01
A spectrometer based on a dc superconducting quantum interference device (SQUID) has been developed for the direct detection of nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR) at frequencies up to 5 MHz. The sample is coupled to the input coil of the niobium-based SQUID via a nonresonant superconducting circuit. The flux locked loop involves the direct offset integration technique with additional positive feedback in which the output of the SQUID is coupled directly to a low-noise preamplifier. Precession of the nuclear quadrupole spins is induced by a magnetic field pulse with the feedback circuit disabled; subsequently, flux locked operation is restored and the SQUID amplifies the signal produced by the nuclear free induction signal. The spectrometer has been used to detect 27Al NQR signals in ruby (Al2O3[Cr3+]) at 359 and 714 kHz.
Note: A hand-held high-Tc superconducting quantum interference device operating without shielding.
He, D F
2011-02-01
By improving the compensation circuit, a hand-held high-Tc rf superconducting quantum interference devices (SQUID) system was developed. It could operate well when moving in unshielded environment. To check the operation, it was used to do eddy-current testing by hand moving the SQUID, and the artificial defect under 6 mm aluminum plate could be successfully detected in shielded environment.
Local anharmonic vibrations strong correlations and superconductivity : a quantum simulation study
Frick, M.; Linden, W. von der; Morgenstern, I.; Raedt, H. de
1990-01-01
We investigate the importance of local anharmonic vibrations of the bridging oxygen in the copper oxide high-Tc materials in the context of superconductivity. For the numerical simulation we employ the projector quantum Monte Carlo method to study the ground state properties of the coupled electron-
Generation of Entangled States of Multiple Superconducting Quantum Interference Devices in Cavity
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
We propose a scheme for generating the maximally entangled states of many superconducting quantum interference devices (SQUIDs) by using a quantized cavity field and classicalmicrowave pulses in cavity. In the scheme,the maximally entangled states can be generated without requiring the measurement and individual addressing of the SQUIDs.
Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.
Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q
2016-09-01
Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.
Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions
Weng, Z. F.; Smidman, M.; Jiao, L.; Lu, Xin; Yuan, H. Q.
2016-09-01
Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.
Rao, S. M.; Loo, B. H.; Wang, N. P.; Kelley, R. J.
1991-04-01
Growth of completely flux-separated YBa2Cu3O6 + δ (referred to as 123 phase) crystals using a novel technique is described. The technique employs a modification of the seed pulling method commonly used in crystal growth. The crystals are grown in the temperature range of 960-1000°C using a BaCuO2 flux. A 123 flux ratio of 1:5 is maintained. Photographs of the crystals and photomicrograph of the surfaces are presented to show complete flux-separation of the crystals measuring 6 mm × 3 mm × 1 mm. The Raman spectra recorded on the as-grown crystals show that they are in the tetragonal phase. Magnetic susceptibility measurements on crystals annealed in an oxygen atmosphere show a superconducting transition starting at 71 K. The present technique offers a possibility of growing large, completely flux-separated crystals of 123 for superconductivity research.
Superconducting detector dynamics studied by quantum pump-probe spectroscopy
Heeres, R.W.; Zwiller, V.
2012-01-01
We explore the dynamics of superconducting single-photon detectors (SSPDs) on the picosecond time-scale using a correlated photon-pair source based on spontaneous parametric downconversion (SPDC), corresponding to a pump-probe experiment at the single-photon level. We show that the detector can oper
Demonstrating quantum speed-up in a superconducting two-qubit processor
Dewes, A; Ong, F R; Schmitt, V; Milman, P; Bertet, P; Vion, D; Esteve, D
2011-01-01
We operate a superconducting quantum processor consisting of two tunable transmon qubits coupled by a swapping interaction, and equipped with non destructive single-shot readout of the two qubits. With this processor, we run the Grover search algorithm among four objects and find that the correct answer is retrieved after a single run with a success probability between 0.52 and 0.67, significantly larger than the 0.25 achieved with a classical algorithm. This constitutes a proof-of-concept for the quantum speed-up of electrical quantum processors.
Hybrid quantum circuit with a superconducting qubit coupled to an electron spin ensemble
Energy Technology Data Exchange (ETDEWEB)
Kubo, Yuimaru; Grezes, Cecile; Vion, Denis; Esteve, Daniel; Bertet, Patrice [Quantronics Group, SPEC (CNRS URA 2464), CEA-Saclay, 91191 Gif-sur-Yvette (France); Diniz, Igor; Auffeves, Alexia [Institut Neel, CNRS, BP 166, 38042 Grenoble (France); Isoya, Jun-ichi [Research Center for Knowledge Communities, University of Tsukuba, 305-8550 Tsukuba (Japan); Jacques, Vincent; Dreau, Anais; Roch, Jean-Francois [LPQM (CNRS, UMR 8537), Ecole Normale Superieure de Cachan, 94235 Cachan (France)
2013-07-01
We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy (NV) centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare arbitrary superpositions of the qubit states that we store into collective excitations of the spin ensemble and retrieve back into the qubit. We also report a new method for detecting the magnetic resonance of electronic spins at low temperature with a qubit using the hybrid quantum circuit, as well as our recent progress on spin echo experiments.
Quantum tricritical fluctuations driving mass enhancement and reentrant superconductivity in URhGe
Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Kambe, S.; Hattori, T.; Araki, S.
2016-02-01
The field-induced reentrant superconductivity (RSC) discovered near a quantum critical point (QCP) in a ferromagnetic superconductor URhGe highlights the close interplay between superconductivity and magnetism. While the origin of the RSC is broadly thought to be associated with quantum critical fluctuations, their exact nature had not been well identified. Here we review our recent 59Co NMR study in a single crystal of URh0.9Co0.1Ge. Our measurements of the NMR spin-spin relaxation reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced QCP at HR ≈ 13 T. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum wing-critical points. We show that these tricritical fluctuations enhance the effective mass of the conduction electrons and, further, drive the RSC near the HR.
Ketterson, John B
2008-01-01
Conceived as the definitive reference in a classic and important field of modern physics, this extensive and comprehensive handbook systematically reviews the basic physics, theory and recent advances in the field of superconductivity. Leading researchers, including Nobel laureates, describe the state-of-the-art in conventional and unconventional superconductors at a particularly opportune time, as new experimental techniques and field-theoretical methods have emerged. In addition to full-coverage of novel materials and underlying mechanisms, the handbook reflects continued intense research into electron-phone based superconductivity. Considerable attention is devoted to high-Tc superconductivity, novel superconductivity, including triplet pairing in the ruthenates, novel superconductors, such as heavy-Fermion metals and organic materials, and also granular superconductors. What’s more, several contributions address superconductors with impurities and nanostructured superconductors. Important new results on...
Ma, Mingwei; Yuan, Dongna; Wu, Yue; Zhou, Huaxue; Dong, Xiaoli; Zhou, Fang
2014-12-01
A flux-free solution to the growth of large and composition homogeneous superconducting FeSe crystal is reported for the first time, which is based on the traveling-solvent floating-zone technique. The size of the crystal samples prepared by this approach is up to 15 × 6 × 2 mm3, being far bigger than previously reported in all dimensions, and the main phase of the crystals is of a single preferred orientation along the tetragonal (101) plane. X-ray diffraction analysis identifies the main phase to be the superconducting tetragonal β-FeSe. The superconducting transition temperature (TC) is determined to be 9.4 K by AC magnetic susceptibility and electronic transport measurements. A nearly perfect diamagnetic shielding of -97% is observed, indicating a bulk superconductivity in the crystal sample.
From quantum matter to high-temperature superconductivity in copper oxides.
Keimer, B; Kivelson, S A; Norman, M R; Uchida, S; Zaanen, J
2015-02-12
The discovery of high-temperature superconductivity in the copper oxides in 1986 triggered a huge amount of innovative scientific inquiry. In the almost three decades since, much has been learned about the novel forms of quantum matter that are exhibited in these strongly correlated electron systems. A qualitative understanding of the nature of the superconducting state itself has been achieved. However, unresolved issues include the astonishing complexity of the phase diagram, the unprecedented prominence of various forms of collective fluctuations, and the simplicity and insensitivity to material details of the 'normal' state at elevated temperatures.
Quintana, C. M.; Megrant, A.; Chen, Z.; Dunsworth, A.; Chiaro, B.; Barends, R.; Campbell, B.; Chen, Yu; Hoi, I.-C.; Jeffrey, E.; Kelly, J.; Mutus, J. Y.; O'Malley, P. J. J.; Neill, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Cleland, A. N.; Martinis, John M.
2014-08-01
Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.
Energy Technology Data Exchange (ETDEWEB)
Quintana, C. M.; Megrant, A.; Chen, Z.; Dunsworth, A.; Chiaro, B.; Barends, R.; Campbell, B.; Chen, Yu; Hoi, I.-C.; Jeffrey, E.; Kelly, J.; Mutus, J. Y.; O' Malley, P. J. J.; Neill, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Cleland, A. N. [Department of Physics, University of California, Santa Barbara, California 93106 (United States); and others
2014-08-11
Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.
Energy Technology Data Exchange (ETDEWEB)
Ranzani, Leonardo [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); University of Colorado at Boulder, Boulder, Colorado 80309 (United States); Spietz, Lafe; Aumentado, Jose [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States)
2013-07-08
In this work, we characterize the 2-port scattering parameters of a superconducting quantum interference device amplifier at {approx}20 mK over several gigahertz of bandwidth. The measurement reference plane is positioned on a 6.25 {Omega} microstrip line situated directly at the input and output of the device by means of a thru-reflect-line cryogenic calibration procedure. From the scattering parameters, we derive the device available power gain, isolation, and input impedance over the 2-8 GHz range. This measurement methodology provides a path towards designing wide-band matching circuits for low impedance superconducting amplifiers operating at dilution refrigerator temperatures.
Design and market considerations for axial flux superconducting electric machine design
Ainslie, Mark D; Shaw, Robert; Dawson, Lewis; Winfield, Andy; Steketee, Marina; Stockley, Simon
2013-01-01
In this paper, the authors investigate a number of design and market considerations for an axial flux superconducting electric machine design that uses high temperature superconductors. This work was carried out as part of the University of Cambridge's Centre for Entrepreneurial Learning ETECH Project programme, designed to accelerate entrepreneurship and diffusion of innovations based on early stage and potentially disruptive technologies from the University. The axial flux machine design is assumed to utilise high temperature superconductors in both wire (stator winding) and bulk (rotor field) forms, to operate over a temperature range of 65-77 K, and to have a power output in the range from 10s of kW up to 1 MW (typical for axial flux machines), with approximately 2-3 T as the peak trapped field in the bulk superconductors. The authors firstly investigate the applicability of this type of machine as a generator in small- and medium-sized wind turbines, including the current and forecasted market and pricin...
Flux formulation of loop quantum gravity: Classical framework
Dittrich, Bianca
2014-01-01
We recently introduced a new representation for loop quantum gravity, which is based on the BF vacuum and is in this sense much nearer to the spirit of spin foam dynamics. In the present paper we lay out the classical framework underlying this new formulation. The central objects in our construction are the so-called integrated fluxes, which are defined as the integral of the electric field variable over surfaces of codimension one, and related in turn to Wilson surface operators. These integrated flux observables will play an important role in the coarse graining of states in loop quantum gravity, and can be used to encode in this context the notion of curvature-induced torsion. We furthermore define a continuum phase space as the modified projective limit of a family of discrete phase spaces based on triangulations. This continuum phase space yields a continuum (holonomy-flux) algebra of observables. We show that the corresponding Poisson algebra is closed by computing the Poisson brackets between the integ...
Quantum and wave dynamical chaos in superconducting microwave billiards
Energy Technology Data Exchange (ETDEWEB)
Dietz, B., E-mail: dietz@ikp.tu-darmstadt.de; Richter, A., E-mail: richter@ikp.tu-darmstadt.de [Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt (Germany)
2015-09-15
Experiments with superconducting microwave cavities have been performed in our laboratory for more than two decades. The purpose of the present article is to recapitulate some of the highlights achieved. We briefly review (i) results obtained with flat, cylindrical microwave resonators, so-called microwave billiards, concerning the universal fluctuation properties of the eigenvalues of classically chaotic systems with no, a threefold and a broken symmetry; (ii) summarize our findings concerning the wave-dynamical chaos in three-dimensional microwave cavities; (iii) present a new approach for the understanding of the phenomenon of dynamical tunneling which was developed on the basis of experiments that were performed recently with unprecedented precision, and finally, (iv) give an insight into an ongoing project, where we investigate universal properties of (artificial) graphene with superconducting microwave photonic crystals that are enclosed in a microwave resonator, i.e., so-called Dirac billiards.
Energy Technology Data Exchange (ETDEWEB)
Dhavale Ashavai, Pashupati Dhakal, Anatolii A Polyanskii, Gianluigi Ciovati
2012-04-01
We present the results of from DC magnetization and penetration depth measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities. The surface treatment consisted of electropolishing and low temperature baking as they are typically applied to SRF cavities. The magnetization data were fitted using a modified critical state model. The critical current density Jc and pinning force Fp are calculated from the magnetization data and their temperature dependence and field dependence are presented. The LG samples have lower critical current density and pinning force density compared to FG samples which implies a lower flux trapping efficiency. This effect may explain the lower values of residual resistance often observed in LG cavities than FG cavities.
A ferroelectric quantum phase transition inside the superconducting dome of Sr1-xCaxTiO3-δ
Rischau, Carl Willem; Lin, Xiao; Grams, Christoph P.; Finck, Dennis; Harms, Steffen; Engelmayer, Johannes; Lorenz, Thomas; Gallais, Yann; Fauqué, Benoît; Hemberger, Joachim; Behnia, Kamran
2017-07-01
SrTiO3, a quantum paraelectric, becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms. It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium. The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity. Here, we show that in Sr1-xCaxTiO3-δ (0.002 content, a quantum phase transition destroys the ferroelectric order. We detect an upturn in the normal-state scattering and a significant modification of the superconducting dome in the vicinity of this quantum phase transition. The enhancement of the superconducting transition temperature with calcium substitution documents the role played by ferroelectric vicinity in the precocious emergence of superconductivity in this system, restricting possible theoretical scenarios for pairing.
Digital-analog quantum simulation of generalized Dicke models with superconducting circuits
Lamata, Lucas
2017-01-01
We propose a digital-analog quantum simulation of generalized Dicke models with superconducting circuits, including Fermi- Bose condensates, biased and pulsed Dicke models, for all regimes of light-matter coupling. We encode these classes of problems in a set of superconducting qubits coupled with a bosonic mode implemented by a transmission line resonator. Via digital-analog techniques, an efficient quantum simulation can be performed in state-of-the-art circuit quantum electrodynamics platforms, by suitable decomposition into analog qubit-bosonic blocks and collective single-qubit pulses through digital steps. Moreover, just a single global analog block would be needed during the whole protocol in most of the cases, superimposed with fast periodic pulses to rotate and detune the qubits. Therefore, a large number of digital steps may be attained with this approach, providing a reduced digital error. Additionally, the number of gates per digital step does not grow with the number of qubits, rendering the simulation efficient. This strategy paves the way for the scalable digital-analog quantum simulation of many-body dynamics involving bosonic modes and spin degrees of freedom with superconducting circuits. PMID:28256559
Digital-analog quantum simulation of generalized Dicke models with superconducting circuits
Lamata, Lucas
2017-03-01
We propose a digital-analog quantum simulation of generalized Dicke models with superconducting circuits, including Fermi- Bose condensates, biased and pulsed Dicke models, for all regimes of light-matter coupling. We encode these classes of problems in a set of superconducting qubits coupled with a bosonic mode implemented by a transmission line resonator. Via digital-analog techniques, an efficient quantum simulation can be performed in state-of-the-art circuit quantum electrodynamics platforms, by suitable decomposition into analog qubit-bosonic blocks and collective single-qubit pulses through digital steps. Moreover, just a single global analog block would be needed during the whole protocol in most of the cases, superimposed with fast periodic pulses to rotate and detune the qubits. Therefore, a large number of digital steps may be attained with this approach, providing a reduced digital error. Additionally, the number of gates per digital step does not grow with the number of qubits, rendering the simulation efficient. This strategy paves the way for the scalable digital-analog quantum simulation of many-body dynamics involving bosonic modes and spin degrees of freedom with superconducting circuits.
Superconductivity around quantum critical point in P-doped iron arsenides
Energy Technology Data Exchange (ETDEWEB)
Cao Guanghan, E-mail: ghcao@zju.edu.c [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Jiang Shuai; Wang Cao; Li Yuke; Ren Zhi; Tao Qian; Dai Jianhui; Xu Zhuan [Department of Physics, Zhejiang University, Hangzhou 310027 (China)
2010-12-15
We demonstrate that, by the P/As substitution-without doping of charge carriers-in a FeAs-layer-based parent compound, superconductivity can be universally introduced. The maximum superconducting critical temperature (T{sub c}) of BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2} achieves 30 K. The P doping in LnFeAsO system (Ln = La and Sm) produces superconductivity below 11 K. The normal-state resistivity obeys linear temperature dependence and the normal-state Hall coefficient shows strong temperature dependence. These non-Fermi liquid behaviors suggest magnetic quantum criticality. The maximum T{sub c} values in different systems correlates strongly with the diagonal bondangle of Fe-As-Fe, implying the important role of the next-nearest-neighbor magnetic exchange coupling in iron pnictide superconductors.
Li, Hao; Liu, Jianshe; Zhang, Yingshan; Cai, Han; Li, Gang; Liu, Qichun; Han, Siyuan; Chen, Wei
2017-03-01
A negative-inductance superconducting quantum interference device (nSQUID) is an adiabatic superconducting logic device with high energy efficiency, and therefore a promising building block for large-scale low-power superconducting computing. However, the principle of the nSQUID is not that straightforward and an nSQUID driven by voltage is vulnerable to common mode noise. We investigate a single nSQUID driven by current instead of voltage, and clarify the principle of the adiabatic transition of the current-driven nSQUID between different states. The basic logic operations of the current-driven nSQUID with proper parameters are simulated by WRspice. The corresponding circuit is fabricated with a 100 A cm‑2 Nb-based lift-off process, and the experimental results at low temperature confirm the basic logic operations as a gated buffer.
Energy Technology Data Exchange (ETDEWEB)
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob, E-mail: ihahn@caltech.edu [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
2014-09-15
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.
Eom, Byeong Ho; Penanen, Konstantin; Hahn, Inseob
2014-09-01
Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.
Chancellor, N.; Zohren, S.; Warburton, P. A.
2017-06-01
Quantum annealing provides a way of solving optimization problems by encoding them as Ising spin models which are implemented using physical qubits. The solution of the optimization problem then corresponds to the ground state of the system. Quantum tunneling is harnessed to enable the system to move to the ground state in a potentially high non-convex energy landscape. A major difficulty in encoding optimization problems in physical quantum annealing devices is the fact that many real world optimization problems require interactions of higher connectivity, as well as multi-body terms beyond the limitations of the physical hardware. In this work we address the question of how to implement multi-body interactions using hardware which natively only provides two-body interactions. The main result is an efficient circuit design of such multi-body terms using superconducting flux qubits in which effective N-body interactions are implemented using N ancilla qubits and only two inductive couplers. It is then shown how this circuit can be used as the unit cell of a scalable architecture by applying it to a recently proposed embedding technique for constructing an architecture of logical qubits with arbitrary connectivity using physical qubits which have nearest-neighbor four-body interactions. It is further shown that this design is robust to non-linear effects in the coupling loops, as well as mismatches in some of the circuit parameters.
Chen, Lei; Wang, Hao; Liu, Xiaoyu; Wu, Long; Wang, Zhen
2016-12-14
A superconducting quantum interference device (SQUID) miniaturized into the nanoscale is promising in the inductive detection of a single electron spin. A nano-SQUID with a strong spin coupling coefficient, a low flux noise, and a wide working magnetic field range is highly desired in a single spin resonance measurement. Nano-SQUIDs with Dayem bridge junctions excel in a high working field range and in the direct coupling from spins to the bridge. However, the common planar structure of nano-SQUIDs is known for problems such as a shallow flux modulation depth and a troublesome hysteresis in current-voltage curves. Here, we developed a fabrication process for creating three-dimensional (3-D) niobium (Nb) nano-SQUIDs with nanobridge junctions that can be tuned independently. Characterization of the device shows up to 45.9% modulation depth with a reversible current-voltage curve. Owning to the large modulation depth, the measured flux noise is as low as 0.34 μΦ0/Hz(1/2). The working field range of the SQUID is greater than 0.5 T parallel to the SQUID plane. We believe that 3-D Nb nano-SQUIDs provide a promising step toward effective single-spin inductive detection.
Low-noise dc superconducting quantum interference devices for gravity wave detection
Jin, Insik
I have designed, built and tested a low noise dc Superconducting QUantum Interference Device (SQUID) system which is intended primarily for use in a 50 mK omnidirectional gravity wave antenna. The SQUID system has three SQUIDs on a single chip: one SQUID is the sensor, another SQUID is the main readout, and the last is a spare readout. For good impedance matching between the sensor SQUID and the input circuit, I use a thin-film transformer. This thin-film transformer gives an input inductance of about 1 muH, which is good for many applications. A SQUID system in a gravity wave antenna must operate continuously for at least 6 months with high reliability. To meet these requirements, I fabricated dc SQUID chips from Nb-Al/AlOsbx-Nb trilayers. I tested the SQUID chips in a liquid helium bath and a dilution refrigerator in the temperature range of 4.2 K to 90 mK. I have designed and tested an eddy-current damping filter as a distributed microwave filter to damp out microwave resonances in strip-line input coils coupled to SQUIDs. The filter chip consists of a Au/Cu-dot array. The filter chip was coupled to the SQUID using a flip-chip arrangement on the SQUID chip. I found that the filter reduced noise bumps and removed distortion from the current-voltage curves. To flux-lock the SQUID system, I developed 2-stage SQUID feedback loops. I investigated two cascade SQUID systems in which I feed the feedback signal into the sensor SQUID and couple the ac modulation signal to the readout SQUID. I found that the noise spectrum with 2-SQUID feedback operation recovers the noise spectrum of the sensor SQUID with about 9% higher noise.
Tournet, J.; Gosselink, D.; Miao, G.-X.; Jaikissoon, M.; Langenberg, D.; McConkey, T. G.; Mariantoni, M.; Wasilewski, Z. R.
2016-06-01
The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)-(2× 4) reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)-(4× 4) reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.
Poole, Charles P; Creswick, Richard J; Prozorov, Ruslan
2014-01-01
Superconductivity, Third Edition is an encyclopedic treatment of all aspects of the subject, from classic materials to fullerenes. Emphasis is on balanced coverage, with a comprehensive reference list and significant graphics from all areas of the published literature. Widely used theoretical approaches are explained in detail. Topics of special interest include high temperature superconductors, spectroscopy, critical states, transport properties, and tunneling. This book covers the whole field of superconductivity from both the theoretical and the experimental point of view. This third edition features extensive revisions throughout, and new chapters on second critical field and iron based superconductors.
Y1Ba2Cu3O(7-delta) thin film dc SQUIDs (superconducting quantum interference device)
Racah, Daniel
1991-03-01
Direct current superconducting quantum interferometers (SQUIDs) based on HTSC thin films have been measured and characterized. The thin films used were of different quality: (1) Granular films on Sapphire substrates, prepared either by e-gun evaporation, by laser ablation or by MOCVD (metal oxide chemical vapor deposition), (2) Epitaxial films on MgO substrates. Modulations of the voltage on the SQUIDs as a function of the applied flux have been observed in a wide range of temperatures. The nature of the modulation was found to be strongly dependent on the morphology of the film and on its critical current. The SQUIDs based on granular films were relatively noisy, hysteretic and with a complicated V-phi shape. Those devices based on low quality (lowIc) granular films could be measured only at low temperatures (much lower than 77 K). While those of higher quality (granular films with high Ic) could be measured near to the superconductive transition. The SQUID based on high quality epitaxial film was measured near Tc and showed an anomalous, time dependent behavior.
Quantum phase transition in a multiconnected superconducting Jaynes-Cummings lattice
Seo, Kangjun; Tian, Lin
2015-05-01
The connectivity and tunability of superconducting qubits and resonators provide us with an appealing platform to study the many-body physics of microwave excitations. Here we present a multiconnected Jaynes-Cummings lattice model which is symmetric with respect to the nonlocal qubit-resonator couplings. Our calculation shows that this model exhibits a Mott insulator-superfluid-Mott insulator phase transition at commensurate fillings, featured by symmetric quantum critical points. Phase diagrams in the grand canonical ensemble are also derived, which confirm the incompressibility of the Mott insulator phase. Different from a general-purposed quantum computer, it only requires two operations to demonstrate this phase transition: the preparation and the detection of commensurate many-body ground state. We discuss the realization of these operations in a superconducting circuit.
Testing Elementary Cycles Formulation of Quantum Mechanics in Carbon Nanotubes and Superconductivity
Dolce, Donatello
2016-01-01
Elementary Cycles are intrinsic periodic phenomena, classical in the essence, whose classical relativistic dynamics reproduce the complete coherence (perfect recurrences) typically associated to the pure quantum behaviours of elementary particles. They can be regarded as effective representations of 't Hooft Cellular Automata. By means of Elementary Cycles physics we obtain a consistent, intuitive, novel derivation of the peculiar quantum dynamics of electrons in Carbon Nanotubes, as well as of Superconductivity fundamental phenomenology. In particular we derive, from classical arguments, the essential electronic properties of graphene systems, such as energy bands and density of states. Similarly, in the second part of the paper, we derive the Superconductivity fundamental phenomenology in terms of simple geometrical considerations, directly from the Elementary Cycles dynamics rather than from empirical aspects and effective quantities connected to the microscopical characteristics of materials as in the sta...
Superconductivity near a Quantum-Critical Point: The Special Role of the First Matsubara Frequency.
Wang, Yuxuan; Abanov, Artem; Altshuler, Boris L; Yuzbashyan, Emil A; Chubukov, Andrey V
2016-10-07
Near a quantum-critical point in a metal strong fermion-fermion interaction mediated by a soft collective boson gives rise to incoherent, non-Fermi liquid behavior. It also often gives rise to superconductivity which masks the non-Fermi liquid behavior. We analyze the interplay between the tendency to pairing and fermionic incoherence for a set of quantum-critical models with effective dynamical interaction between low-energy fermions. We argue that superconducting T_{c} is nonzero even for strong incoherence and/or weak interaction due to the fact that the self-energy from dynamic critical fluctuations vanishes for the two lowest fermionic Matsubara frequencies ω_{m}=±πT. We obtain the analytic formula for T_{c}, which reproduces well earlier numerical results for the electron-phonon model at vanishing Debye frequency.
Kubo, Takayuki
2016-01-01
During the cool-down of a superconducting accelerating cavity, a magnetic flux is trapped as quantized vortices, which yield additional dissipation and contribute to the residual resistance. Recently, cooling down with a large spatial temperature gradient attracts much attention for successful reductions of trapped vortices. The purpose of the present paper is to propose a model to explain the observed efficient flux expulsions and the role of spatial temperature gradient during the cool-down of cavity. In the vicinity of a region with a temperature close to the critical temperature Tc,the critical fields are strongly suppressed and can be smaller than the ambient magnetic field. A region with a lower critical field smaller than the ambient field is in the vortex state. As a material is cooled down, a region with a temperature close Tc associating the vortex state domain sweeps and passes through the material. In this process, vortices contained in the vortex state domain are trapped by pinning centers that r...
Fujii, Toshiyuki; Matsuo, Shigemasa; Hatakenaka, Noriyuki
2009-01-01
We propose a fluxon-controlled quantum computer incorporated with three-qubit quantum error correction using special gate operations, i.e., joint-phase and SWAP gate operations, inherent in capacitively coupled superconducting flux qubits. The proposed quantum computer acts exactly like a knitting machine at home.
Quantum computing in decoherence-free subspaces with superconducting charge qubits
Energy Technology Data Exchange (ETDEWEB)
Feng Zhibo [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China); Institute for Condensed Matter Physics, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510631 (China); Zhang Xinding [Institute for Condensed Matter Physics, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510631 (China)], E-mail: xdzhang2000@gmail.com
2007-12-10
Taking into account the main noises in superconducting charge qubits (SCQs), we propose a feasible scheme to realize quantum computing (QC) in a specially-designed decoherence-free subspace (DFS). In our scheme two physical qubits are connected with a common inductance to form a strong coupling subsystem, which acts as a logical qubit. Benefiting from the well-designed DFS, our scheme is helpful to suppress certain decoherence effects.
Lévy, F.; Sheikin, I.; Huxley, A.
2007-07-01
When a pure material is tuned to the point where a continuous phase-transition line is crossed at zero temperature, known as a quantum critical point (QCP), completely new correlated quantum ordered states can form. These phases include exotic forms of superconductivity. However, as superconductivity is generally suppressed by a magnetic field, the formation of superconductivity ought not to be possible at extremely high field. Here, we report that as we tune the ferromagnet, URhGe, towards a QCP by applying a component of magnetic field in the material's easy magnetic plane, superconductivity survives in progressively higher fields applied simultaneously along the material's magnetic hard axis. Thus, although superconductivity never occurs above a temperature of 0.5K, we find that it can survive in extremely high magnetic fields, exceeding 28T.
Energy Technology Data Exchange (ETDEWEB)
Levy, F.; Huxley, A. [CEA, SPSMS, DRFMC, F-38054 Grenoble, (France); Levy, F.; Sheikin, I. [CNRS, GHMFL, F-38042 Grenoble, (France); Huxley, A. [Univ Edinburgh, Scottish Univ Phys Alliance, Sch Phys, Edinburgh EH9 3JZ, Midlothian, (United Kingdom)
2007-07-01
When a pure material is tuned to the point where a continuous phase-transition line is crossed at zero temperature, known as a quantum critical point (QCP), completely new correlated quantum ordered states can form. These phases include exotic forms of superconductivity. However, as superconductivity is generally suppressed by a magnetic field, the formation of superconductivity ought not to be possible at extremely high field. Here, we report that as we tune the ferromagnet, URhGe, towards a QCP by applying a component of magnetic field in the material's easy magnetic plane, superconductivity survives in progressively higher fields applied simultaneously along the material's magnetic hard axis. Thus, although superconductivity never occurs above a temperature of 0.5 K, we find that it can survive in extremely high magnetic fields, exceeding 28 T. (authors)
Encoding quantum information in a stabilized manifold of a superconducting cavity
Touzard, S.; Leghtas, Z.; Mundhada, S. O.; Axline, C.; Reagor, M.; Chou, K.; Blumoff, J.; Sliwa, K. M.; Shankar, S.; Frunzio, L.; Schoelkopf, R. J.; Mirrahimi, M.; Devoret, M. H.
In a superconducting Josephson circuit architecture, we activate a multi-photon process between two modes by applying microwave drives at specific frequencies. This creates a pairwise exchange of photons between a high-Q cavity and the environment. The resulting open dynamical system develops a two-dimensional quasi-energy ground state manifold. Can we encode, protect and manipulate quantum information in this manifold? We experimentally investigate the convergence and escape rates in and out of this confined subspace. Finally, using quantum Zeno dynamics, we aim to perform gates which maintain the state in the protected manifold at all times. Work supported by: ARO, ONR, AFOSR and YINQE.
Coupling InSb quantum dots to a superconducting microwave resonator
Cassidy, Maja; Kammhuber, Jakob; Car, Diana; Plissard, Sebastien; Bakkers, Erik; Dicarlo, Leo; Kouwenhoven, Leo
2014-03-01
We present measurements of a superconducting half-wave resonator coupled to two InSb nanowire quantum dots. Precise nanowire alignment at the electric field antinodes at opposite ends of the microwave cavity allows for a maximal electric field along the wire axis, without compromising the intrinsic quality factor of the cavity. This architecture may be useful for reaching the strong coupling limit between a single spin and a microwave photon, paving the way to on-chip coupling of single spins for quantum information processing.
Energy Technology Data Exchange (ETDEWEB)
Andraka, Bohdan [Univ. of Florida, Gainesville, FL (United States)
2015-05-14
The main goal of this program was to explore the possibility of novel states and behaviors in Pr-based system exhibiting quantum critical behavior, PrOs₄Sb₁₂. Upon small changes of external parameter, such as magnetic field, physical properties of PrOs₄Sb₁₂ are drastically altered from those corresponding to a superconductor, to heavy fermion, to field-induced ordered phase with primary quadrupolar order parameter. All these states are highly unconventional and not understood in terms of current theories thus offer an opportunity to expand our knowledge and understanding of condensed matter. At the same time, these novel states and behaviors are subjects to intense international controversies. In particular, two superconducting phases with different transition temperatures were observed in some samples and not observed in others leading to speculations that sample defects might be partially responsible for these exotic behaviors. This work clearly established that crystal disorder is important consideration, but contrary to current consensus this disorder suppresses exotic behavior. Superconducting properties imply unconventional inhomogeneous state that emerges from unconventional homogeneous normal state. Comprehensive structural investigations demonstrated that upper superconducting transition is intrinsic, bulk, and unconventional. The high quality of in-house synthesized single crystals was indirectly confirmed by de Haas-van Alphen quantum oscillation measurements. These measurements, for the first time ever reported, spanned several different phases, offering unprecedented possibility of studying quantum oscillations across phase boundaries.
Institute of Scientific and Technical Information of China (English)
崔珊; 何兰坡; 洪晓晨; 朱相德; Cedomir Petrovic; 李世燕
2016-01-01
It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk supercon-ductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3−x Sex near x≈0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3−x Sex single crystals (x=0.044 and 0.051) down to 80 mK. For both samples, the residual linear termκ0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence ofκ0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3−x Sex , which indicates conventional superconductivity despite of the existence of a CDW QCP.
Controllable coherent population transfers in superconducting qubits for quantum computing.
Wei, L F; Johansson, J R; Cen, L X; Ashhab, S; Nori, Franco
2008-03-21
We propose an approach to coherently transfer populations between selected quantum states in one- and two-qubit systems by using controllable Stark-chirped rapid adiabatic passages. These evolution-time insensitive transfers, assisted by easily implementable single-qubit phase-shift operations, could serve as elementary logic gates for quantum computing. Specifically, this proposal could be conveniently demonstrated with existing Josephson phase qubits. Our proposal can find an immediate application in the readout of these qubits. Indeed, the broken parity symmetries of the bound states in these artificial atoms provide an efficient approach to design the required adiabatic pulses.
Geng, J.; Matsuda, K.; Fu, L.; Fagnard, J.-F.; Zhang, H.; Zhang, X.; Shen, B.; Dong, Q.; Baghdadi, M.; Coombs, T. A.
2016-03-01
Superconducting flux pumps are the kind of devices which can generate direct current into superconducting circuit using external magnetic field. The key point is how to induce a dc voltage across the superconducting load by ac fields. Giaever (1966 IEEE Spectr. 3 117) pointed out flux motion in superconductors will induce a dc voltage, and demonstrated a rectifier model which depended on breaking superconductivity. van de Klundert et al (1981 Cryogenics 21 195, 267) in their review(s) described various configurations for flux pumps all of which relied on inducing the normal state in at least part of the superconductor. In this letter, following their work, we reveal that a variation in the resistivity of type II superconductors is sufficient to induce a dc voltage in flux pumps and it is not necessary to break superconductivity. This variation in resistivity is due to the fact that flux flow is influenced by current density, field intensity, and field rate of change. We propose a general circuit analogy for travelling wave flux pumps, and provide a mathematical analysis to explain the dc voltage. Several existing superconducting flux pumps which rely on the use of a travelling magnetic wave can be explained using the analysis enclosed. This work can also throw light on the design and optimization of flux pumps.
Superconducting single-photon detectors for integrated quantum optics
Energy Technology Data Exchange (ETDEWEB)
Kahl, Oliver
2016-01-29
This thesis reports on the implementation and characterization of a fully integrated single-photon detector. Several detector circuits are realized and it is shown that the detectors exhibit supreme detection performance over a wide optical spectrum. The detectors' scalability is showcased by the parallel operation of multiple detectors within a single integrated circuit. These demonstrations are essential for future developments in integrated quantum optics.
A twofold quantum delayed-choice experiment in a superconducting circuit.
Liu, Ke; Xu, Yuan; Wang, Weiting; Zheng, Shi-Biao; Roy, Tanay; Kundu, Suman; Chand, Madhavi; Ranadive, Arpit; Vijay, Rajamani; Song, Yipu; Duan, Luming; Sun, Luyan
2017-05-01
Wave-particle complementarity lies at the heart of quantum mechanics. To illustrate this mysterious feature, Wheeler proposed the delayed-choice experiment, where a quantum system manifests the wave- or particle-like attribute, depending on the experimental arrangement, which is made after the system has entered the interferometer. In recent quantum delayed-choice experiments, these two complementary behaviors were simultaneously observed with a quantum interferometer in a superposition of being closed and open. We suggest and implement a conceptually different quantum delayed-choice experiment by introducing a which-path detector (WPD) that can simultaneously record and neglect the system's path information, but where the interferometer itself is classical. Our experiment is realized with a superconducting circuit, where a cavity acts as the WPD for an interfering qubit. Using this setup, we implement the first twofold delayed-choice experiment, which demonstrates that the system's behavior depends not only on the measuring device's configuration that can be chosen even after the system has been detected but also on whether we a posteriori erase or mark the which-path information, the latter of which cannot be revealed by previous quantum delayed-choice experiments. Our results represent the first demonstration of both counterintuitive features with the same experimental setup, significantly extending the concept of quantum delayed-choice experiment.
Understanding and enhancing superconductivity in FeSe/SrTiO3 by quantum size effects
Murta, Bruno; García-García, Antonio M.
2016-11-01
Superconductivity in one-atom-layer iron selenide (FeSe) on a strontium titanate (STO) substrate is enhanced by almost an order of magnitude with respect to bulk FeSe. There is recent experimental evidence suggesting that this enhancement persists in FeSe/STO nanoislands. More specifically, for sizes L ˜10 nm, the superconducting gap is a highly nonmonotonic function of L with peaks well above the bulk gap value. This is the expected behavior only for weakly-coupled metallic superconductors such as Al or Sn. Here we develop a theoretical formalism to describe these experiments based on three ingredients: Eliashberg theory of superconductivity in the weak coupling limit, pairing dominated by forward scattering, and periodic orbit theory to model spectral fluctuations. We obtain an explicit analytical expression for the size dependence of the gap that describes quantitatively the experimental results with no free parameters. This is a strong suggestion that superconductivity in FeSe/STO is mediated by STO phonons. We propose that, since FeSe/STO is still a weakly coupled superconductor, quantum size effects can be used to further enhance the bulk critical temperature in this interface.
Energy Technology Data Exchange (ETDEWEB)
Zhou, Jian, E-mail: jzhou2@vcu.edu, E-mail: pjena@vcu.edu; Jena, Puru, E-mail: jzhou2@vcu.edu, E-mail: pjena@vcu.edu [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Zhang, Shunhong [Center for Applied Physics and Technology, College of Engineering, Peking University, Beijing 100871 (China); Wang, Qian [Center for Applied Physics and Technology, College of Engineering, Peking University, Beijing 100871 (China); Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284 (United States)
2016-06-20
Motivated by the growth of superconducting atomic hexagonal Ga layers on GaN surface we have calculated the electronic properties of Hf intercalated honeycomb Ga layers using first-principles theory. In contrast to the hexagonal Ga layers where substrate is necessary for their stability, we find the above structure to be dynamically stable in its freestanding form with small formation energy. In particular, six Dirac cones composed of Hf-d{sub xy}/d{sub x2-y2} orbitals are observed in the first Brillouin zone, slightly below the Fermi energy. Spin-orbit coupling opens a large band gap of 177 meV on these Dirac cones. By calculating its mirror Chern number, we demonstrate that this band gap is topologically nontrivial and protected by mirror symmetry. Such mirror symmetry protected band gaps are rare in hexagonal lattice. A large topological crystalline quantum spin Hall conductance σ{sub SH} ∼ −4 e{sup 2}/h is also revealed. Moreover, electron-phonon coupling calculations reveal that this material is superconducting with a transition temperature T{sub c} = 2.4 K, mainly contributed by Ga out-of-plane vibrations. Our results provide a route toward manipulating quantum spin Hall and superconducting behaviors in a single material which helps to realize Majorana fermions and topological superconductors.
Quantum computation with prethreshold superconducting qubits: Single-excitation subspace approach
Galiautdinov, Andrei
2011-01-01
We describe an alternative approach to quantum computation that is ideally suited for today's sub-threshold-fidelity qubits, and which can be applied to a family of hardware models that includes superconducting qubits with tunable coupling. In this approach, the computation on an n-qubit processor is carried out in the n-dimensional single-excitation subspace (SES) of the full 2^n-dimensional Hilbert space. Because any real Hamiltonian can be directly generated in the SES [E. J. Pritchett et al., arXiv:1008.0701], high-dimensional unitary operations can be carried out in a single step, bypassing the need to decompose into single- and two-qubit gates. Although technically nonscalable and unsuitable for applications (including Shor's) requiring enormous Hilbert spaces, this approach would make practical a first-generation quantum computer capable of achieving significant quantum speedup.
Superconducting quantum criticality of topological surface states at three loops
Zerf, Nikolai; Maciejko, Joseph
2016-01-01
The semimetal-superconductor quantum phase transition on the two-dimensional (2D) surface of a 3D topological insulator is conjectured to exhibit an emergent $\\mathcal{N}=2$ supersymmetry, based on a renormalization group (RG) analysis at one-loop order in the $\\epsilon$ expansion. We provide additional support for this conjecture by performing a three-loop RG analysis and showing that the supersymmetric fixed point found at this order survives the extrapolation to 2D. We compute critical exponents to order $\\epsilon^3$, obtaining the more accurate value $\
Superconducting quantum criticality of topological surface states at three loops
Zerf, Nikolai; Lin, Chien-Hung; Maciejko, Joseph
2016-11-01
The semimetal-superconductor quantum phase transition on the two-dimensional (2D) surface of a 3D topological insulator is conjectured to exhibit an emergent N =2 supersymmetry, based on a one-loop renormalization group (RG) analysis in the ɛ expansion. We provide additional support for this conjecture by performing a three-loop RG analysis and showing that the supersymmetric fixed point found at this order survives the extrapolation to 2D. We compute critical exponents to order ɛ3, obtaining the more accurate value ν ≈0.985 for the correlation length exponent and confirming that the fermion and boson anomalous dimensions remain unchanged beyond one loop, as expected from non-renormalization theorems in supersymmetric theories. We further couple the system to a dynamical U(1) gauge field, and argue that the transition becomes fluctuation-induced first order in an appropriate type-I regime. We discuss implications of this result for quantum phase transitions between certain symmetry-preserving correlated surface states of 3D topological insulators.
External driving synchronization in a superconducting quantum interference device based oscillator
Zhao, Jie; Zhao, Peng; Yu, Haifeng; Yu, Yang
2016-11-01
We propose an external driving, self-sustained oscillator based on superconducting resonators. The dynamics of the self-sustained oscillator can be described by a Duffing-van der Pol like equation. Under external driving, the self-sustained oscillator presents synchronization phenomena. We analytically and numerically investigate the synchronization regions, and the results show that the synchronization bandwidth can be quickly adjusted in situ by the external weak magnetic field in sub-nano seconds. Moreover, the system can re-stabilize in about 10 ns with a certain sudden change of driving frequency or the critical current of the superconducting quantum interference device (SQUID). These advantages allow the potential applications of self-sustained oscillators in timing reference, microwave communication and electromagnetic sensing.
Quantum oscillations in antiferromagnetic CaFe(2)As(2) on the brink of superconductivity.
Harrison, N; McDonald, R D; Mielke, C H; Bauer, E D; Ronning, F; Thompson, J D
2009-08-12
We report quantum oscillation measurements on CaFe(2)As(2) under strong magnetic fields-recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05% of the paramagnetic Brillouin zone volume-consistent with Fermi surface reconstruction caused by antiferromagnetism. On comparing several alkaline earth AFe(2)As(2) antiferromagnets (with A = Ca, Sr and Ba), the dependences of the Fermi surface cross-sectional area F(α) and the effective mass m(α)(*) of the primary observed pocket on the antiferromagnetic/structural transition temperature T(s) are both found to be consistent with the case for quasiparticles in a conventional spin-density wave model. These findings suggest that the recently proposed strain-enhanced superconductivity in these materials occurs within a broadly conventional spin-density wave phase.
Capture cavity cryomodule for quantum beam experiment at KEK superconducting RF test facility
Tsuchiya, K.; Hara, K.; Hayano, H.; Kako, E.; Kojima, Y.; Kondo, Y.; Nakai, H.; Noguchi, S.; Ohuchi, N.; Terashima, A.; Horikoshi, A.; Semba, T.
2014-01-01
A capture cavity cryomodule was fabricated and used in a beam line for quantum beam experiments at the Superconducting RF Test Facility (STF) of the High Energy Accelerator Research Organization in Japan. The cryomodule is about 4 m long and contains two nine-cell cavities. The cross section is almost the same as that of the STF cryomodules that were fabricated to develop superconducting RF cavities for the International Linear Collider. An attempt was made to reduce the large deflection of the helium gas return pipe (GRP) that was observed in the STF cryomodules during cool-down and warm-up. This paper briefly describes the structure and cryogenic performance of the captures cavity cryomodule, and also reports the measured displacement of the GRP and the cavity-containing helium vessels during regular operation.
Capture cavity cryomodule for quantum beam experiment at KEK superconducting RF test facility
Energy Technology Data Exchange (ETDEWEB)
Tsuchiya, K.; Hara, K.; Hayano, H.; Kako, E.; Kojima, Y.; Kondo, Y.; Nakai, H.; Noguchi, S.; Ohuchi, N.; Terashima, A. [High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan); Horikoshi, A.; Semba, T. [Hitachi, Ltd., Hitachi Works, Hitachi, Ibaraki 317-8511 (Japan)
2014-01-29
A capture cavity cryomodule was fabricated and used in a beam line for quantum beam experiments at the Superconducting RF Test Facility (STF) of the High Energy Accelerator Research Organization in Japan. The cryomodule is about 4 m long and contains two nine-cell cavities. The cross section is almost the same as that of the STF cryomodules that were fabricated to develop superconducting RF cavities for the International Linear Collider. An attempt was made to reduce the large deflection of the helium gas return pipe (GRP) that was observed in the STF cryomodules during cool-down and warm-up. This paper briefly describes the structure and cryogenic performance of the captures cavity cryomodule, and also reports the measured displacement of the GRP and the cavity-containing helium vessels during regular operation.
Demonstration of two-qubit algorithms with a superconducting quantum processor.
DiCarlo, L; Chow, J M; Gambetta, J M; Bishop, Lev S; Johnson, B R; Schuster, D I; Majer, J; Blais, A; Frunzio, L; Girvin, S M; Schoelkopf, R J
2009-07-09
Quantum computers, which harness the superposition and entanglement of physical states, could outperform their classical counterparts in solving problems with technological impact-such as factoring large numbers and searching databases. A quantum processor executes algorithms by applying a programmable sequence of gates to an initialized register of qubits, which coherently evolves into a final state containing the result of the computation. Building a quantum processor is challenging because of the need to meet simultaneously requirements that are in conflict: state preparation, long coherence times, universal gate operations and qubit readout. Processors based on a few qubits have been demonstrated using nuclear magnetic resonance, cold ion trap and optical systems, but a solid-state realization has remained an outstanding challenge. Here we demonstrate a two-qubit superconducting processor and the implementation of the Grover search and Deutsch-Jozsa quantum algorithms. We use a two-qubit interaction, tunable in strength by two orders of magnitude on nanosecond timescales, which is mediated by a cavity bus in a circuit quantum electrodynamics architecture. This interaction allows the generation of highly entangled states with concurrence up to 94 per cent. Although this processor constitutes an important step in quantum computing with integrated circuits, continuing efforts to increase qubit coherence times, gate performance and register size will be required to fulfil the promise of a scalable technology.
Quantum Criticality Beneath the Superconducting Dome in β-YbAlB4
Tomita, T.; Kuga, K.; Uwatoko, Y.; Nakatsuji, S.
2016-02-01
Yb-based heavy fermion superconductor β-YbAlB4 at 0 K and 0 T at ambient pressure is located near the quantum critical point with strong mixed valiancy. In this type of Yb electron system, we expect that the magnetic order connected to the quantum critical point derives from the applied pressure. We built a pressure-temperature phase diagram for β-YbAlB4 by measuring the electrical resistivity of high quality single crystal at temperatures down to 40 mK under an applied pressure. A strange metal region appeared, showing non-Fermi liquid ρab α T1.5 behavior, which is stable with applied pressure up to 0.4 GPa, even when below the superconducting dome excluded by a magnetic field of 0.1 T. By increasing of pressure above 2.5 GPa, a magnetic order is first generated. Such ambient quantum criticality/superconductivity is unconventional and is detached from the magnetic order.
Villegas, Javier E.
2009-03-01
Superconducting/Ferromagnetic (S/F) hybrids exhibit a plethora of induced effects and novel physical properties, due to the interplay between the competing S and F orders. We will show a few examples of those, in a series of experiments on a simple hybrid system: a S thin film with an array of F nanodots. Changing the array geometry, the nanodots size or their magnetic-state allows to investigate a large variety of physical phenomena. We will focus on two of them: flux pinning effects and stray-magnetic-field induced manipulation of superconductivity. We will firstly consider geometry induced effects; in particular, we will compare the pinning properties of periodic, quasiperiodic, and fractal arrays [1]. Secondly, we will discuss the effects induced by particular nanodot magnetic-states. We will show experiments on the interaction between flux quanta and nanodot magnetic vortices, which can be used to obtain switchable flux pinning potentials [2]. Finally, we will describe an experiment in which the magnetic reversal events of the nanodot magnetic vortices are imprinted into the transport properties of a superconducting thin film [3]. This yields a very unusual hysteretic magnetoresistance. This effect is induced by the stray magnetic fields from the nanodots, which drive the superconducting-to-normal transition of the hybrid depending on the magnetic history. [4pt] [1] J.E. Villegas et al., Phys. Rev. Lett. 97, 027002 (2006). [0pt] [2] J.E. Villegas et al., Phys. Rev. B 77, 134510 (2008). [0pt] [3] J.E. Villegas et al., Phys. Rev. Lett. 99, 227001 (2007).
A hybrid superconducting quantum dot acting as an efficient charge and spin Seebeck diode
Hwang, Sun-Yong; Sánchez, David; López, Rosa
2016-09-01
We propose a highly efficient thermoelectric diode device built from the coupling of a quantum dot with a normal or ferromagnetic electrode and a superconducting reservoir. The current shows a strongly nonlinear behavior in the forward direction (positive thermal gradients) while it almost vanishes in the backward direction (negative thermal gradients). Our discussion is supported by a gauge-invariant current-conserving transport theory accounting for electron-electron interactions inside the dot. We find that the diode behavior is greatly tuned with external gate potentials, Zeeman splittings or lead magnetizations. Our results are thus relevant for the search of novel thermoelectric devices with enhanced functionalities.
Transition between different quantum states in a mesoscopic system: The superconducting ring
Energy Technology Data Exchange (ETDEWEB)
Horane, E.M. [Instituto Balseiro, Universidad Nacional de Cuyo and Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina); Castro, J.I. [Departamento Fisico-Quimica, Facultad Filosofia Humanidades y Artes, Universidad Nacional de San Juan, San Juan (Argentina); Buscaglia, G.C.; Lopez, A. [Instituto Balseiro, and Centro Atomico Bariloche, Universidad Nacional de Cuyo and Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina)
1996-04-01
We investigate the thermodynamic properties of a superconducting ring, both analytically and numerically, relying upon the Ginzburg-Landau theory. We find that modulated solutions for the order parameter play a role in describing the thermodynamic transitions between consecutive modes of uniform order parameter, associated with different quantum numbers. Exact expressions for these solutions are given in terms of elliptic functions. We identify the family of energy extrema which, being saddle points of the energy in the functional space of the distributions of the order parameter, represent the energy barrier to be overcome for transitions between different solutions. {copyright} {ital 1996 The American Physical Society.}
Institute of Scientific and Technical Information of China (English)
WANG Yi-Min; ZHOU Yan-Li; LIANG Lin-Mei; LI Cheng-Zu
2009-01-01
We propose a feasible scheme to achieve universal quantum gate operations in decoherence-free subspace with superconducting charge qubits placed in a microwave cavity.Single-logic-qubit gates can be realized with cavity assisted interaction, which possesses the advantages of unconventional geometric gate operation.The two-logic-qubit controlled-phase gate between subsystems can be constructed with the help of a variable electrostatic transformer, The collective decoherence can be successfully avoided in our well-designed system.Moreover, GHZ state for logical qubits can also be easily produced in this system.
Quantum dynamics of a microwave driven superconducting phase qubit coupled to a two-level system
Sun, Guozhu; Wen, Xueda; Mao, Bo; Zhou, Zhongyuan; Yu, Yang; Wu, Peiheng; Han, Siyuan
2010-10-01
We present an analytical and comprehensive description of the quantum dynamics of a microwave resonantly driven superconducting phase qubit coupled to a microscopic two-level system (TLS), covering a wide range of the external microwave field strength. Our model predicts several interesting phenomena in such an ac driven four-level bipartite system including anomalous Rabi oscillations, high-contrast beatings of Rabi oscillations, and extraordinary two-photon transitions. Our experimental results in a coupled qubit-TLS system agree quantitatively very well with the predictions of the theoretical model.
InSb nanowire double quantum dots coupled to a superconducting microwave cavity
Wang, R.; Deacon, R. S.; Car, D.; Bakkers, E. P. A. M.; Ishibashi, K.
2016-05-01
By employing a micrometer precision mechanical transfer technique, we embed individual InSb nanowires into a superconducting coplanar waveguide resonator. We investigate the characteristics of a double quantum dot formed in an InSb nanowire interacting with a single mode microwave field. The charge stability diagram can be obtained from the amplitude and phase response of the resonator independently from the dc transport measurement. As the charge transits between dot-dot, or dot-lead, the change of resonator transmission is compared and the charge-cavity coupling strength is extracted to be in the magnitude of several MHz.
InSb nanowire double quantum dots coupled to a superconducting microwave cavity
Energy Technology Data Exchange (ETDEWEB)
Wang, R. [Advanced Device Laboratory, RIKEN, Wako, Saitama 351-0198 (Japan); Deacon, R. S., E-mail: russell@riken.jp; Ishibashi, K. [Advanced Device Laboratory, RIKEN, Wako, Saitama 351-0198 (Japan); Center for Emergent Matter Science (CEMS), RIKEN, Wako, Saitama 351-0198 (Japan); Car, D. [Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands); Bakkers, E. P. A. M. [Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands); Kavli Institute, Quantum Transport Group, Delft University of Technology, 2628 CJ Delft (Netherlands)
2016-05-16
By employing a micrometer precision mechanical transfer technique, we embed individual InSb nanowires into a superconducting coplanar waveguide resonator. We investigate the characteristics of a double quantum dot formed in an InSb nanowire interacting with a single mode microwave field. The charge stability diagram can be obtained from the amplitude and phase response of the resonator independently from the dc transport measurement. As the charge transits between dot-dot, or dot-lead, the change of resonator transmission is compared and the charge-cavity coupling strength is extracted to be in the magnitude of several MHz.
Fluxon-controlled quantum computer
Fujii, Toshiyuki; Matsuo, Shigemasa; Hatakenaka, Noriyuki
2016-11-01
We propose a fluxon-controlled quantum computer incorporated with three-qubit quantum error correction using special gate operations, i.e. joint-phase and SWAP gate operations, inherent in capacitively coupled superconducting flux qubits. The proposed quantum computer acts exactly like a knitting machine at home.
Fully superconducting rectifiers and fluxpumps Part 1: Realized methods for pumping flux
Klundert, van de L.J.M.; Kate, ten H.H.J.
1981-01-01
The magnetic and electrical properties of superconductors were a challenge for many inventors and designers to use superconducting materials in the construction of fully superconducting voltage and current sources commonly called fluxpumps. In the past twenty years a large variety of mechanically or
Energy Technology Data Exchange (ETDEWEB)
Oz, E.; Myers, C. E.; Edwards, M. R.; Berlinger, B.; Brooks, A.; Cohen, S. A.
2011-01-05
The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-Β plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (τfc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (τfc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.
Superconducting single electron transistor for charge sensing in Si/SiGe-based quantum dots
Yang, Zhen
Si-based quantum devices, including Si/SiGe quantum dots (QD), are promising candidates for spin-based quantum bits (quits), which are a potential platform for quantum information processing. Meanwhile, qubit readout remains a challenging task related to semiconductor-based quantum computation. This thesis describes two readout devices for Si/SiGe QDs and the techniques for developing them from a traditional single electron transistor (SET). By embedding an SET in a tank circuit and operating it in the radio-frequency (RF) regime, a superconducting RF-SET has quick response as well as ultra high charge sensitivity and can be an excellent charge sensor for the QDs. We demonstrate such RF-SETs for QDs in a Si/SiGe heterostructure. Characterization of the SET in magnetic fields is studied for future exploration of advanced techniques such as spin detection and spin state manipulation. By replacing the tank circuit with a high-quality-factor microwave cavity, the embedded SET will be operated in the supercurrent regime as a single Cooper pair transistor (CPT) to further increase the charge sensitivity and reduce any dissipation. The operating principle and implementation of the cavity-embedded CPT (cCPT) will be introduced.
Zhang, Zhedong
2015-01-01
We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the energy and charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in th...
Charge Kondo effect in negative-U quantum dots with superconducting electrodes
Fang, Tie-Feng; Guo, Ai-Min; Lu, Han-Tao; Luo, Hong-Gang; Sun, Qing-Feng
2017-08-01
Recent experimental realization of superconducting quantum dot devices with intradot attraction U [Nature (London) 521, 196 (2015), 10.1038/nature14398; Phys. Rev. X 6, 041042 (2016), 10.1103/PhysRevX.6.041042] offers unique opportunities to study the charge Kondo effect in a superconducting environment. In such devices pseudospin flips are caused by two tunneling processes. One is the cotunneling of normal electrons which generates near-gap Kondo resonances in the single-electron spectral density. This negative-U charge Kondo effect is more robust than the conventional spin Kondo effect against the suppression by the superconductivity. The other tunneling is the mean-field Cooper-pair tunneling which produces a zero-energy bound state in the pair spectral density. Interesting crossover physics from the strongly-correlated Kondo screening to the mean-field polarization of local pseudospin is demonstrated. Due to the interplay of these two tunnelings, the supercurrent is suppressed for intermediate couplings, but it can increase to the unitary limits both in the strong and weak coupling regimes. We obtain the magnetic field-dependent supercurrent which is consistent with the key experimental findings.
Kang, Yi-Hao; Chen, Ye-Hong; Shi, Zhi-Cheng; Song, Jie; Xia, Yan
2016-11-01
In this paper, we propose a protocol to prepare W states with superconducting quantum interference devices by using dressed states. Through choosing a set of dressed states suitably, the protocol can be used to accelerate the adiabatic passages while additional couplings are unnecessary. Moreover, we can optimize the evolution of the system with the restraint to the populations of the intermediate states by choosing suitable control parameters. Numerical simulations show that the protocol is robust against the parameter variations and decoherence mechanisms. Furthermore, the protocol is faster and more robust against the dephasing compared with that by the adiabatic passages. As for the Rabi frequencies of pulses designed by the method, they can be expressed by the linear superpositions of Gaussian functions, which does not increase difficulty in the experiments. In addition, the protocol could be controlled and manipulated easily in experiments with a circuit quantum electrodynamics system.
Demonstration of Johnson noise thermometry with all-superconducting quantum voltage noise source
Energy Technology Data Exchange (ETDEWEB)
Yamada, Takahiro, E-mail: yamada-takahiro@aist.go.jp; Urano, Chiharu; Maezawa, Masaaki [National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)
2016-01-25
We present a Johnson noise thermometry (JNT) system based on an integrated quantum voltage noise source (IQVNS) that has been fully implemented using superconducting circuit technology. To enable precise measurement of Boltzmann's constant, an IQVNS chip was designed to produce intrinsically calculable pseudo-white noise to calibrate the JNT system. On-chip real-time generation of pseudo-random codes via simple circuits produced pseudo-voltage noise with a harmonic tone interval of less than 1 Hz, which was one order of magnitude finer than the harmonic tone interval of conventional quantum voltage noise sources. We estimated a value for Boltzmann's constant experimentally by performing JNT measurements at the temperature of the triple point of water using the IQVNS chip.
Man'ko, M. A.; Man'ko, V. I.
2016-03-01
We show that the density-matrix states of noncomposite qudit systems satisfy entropic and information relations like the subadditivity condition, strong subadditivity condition, and Araki-Lieb inequality, which characterize hidden quantum correlations of observables associated with these indivisible systems. We derive these relations employing a specific map of the entropic inequalities known for density matrices of multiqudit systems to the inequalities for density matrices of single-qudit systems. We present the obtained relations in the form of mathematical inequalities for arbitrary Hermitian N × N-matrices. We consider examples of superconducting qubits and qudits. We discuss the hidden correlations in single- qudit states as a new resource for quantum technologies analogous to the known resource in correlations associated with the entanglement in multiqudit systems.
Otto refrigerator based on a superconducting qubit: Classical and quantum performance
Karimi, B.; Pekola, J. P.
2016-11-01
We analyze a quantum Otto refrigerator based on a superconducting qubit coupled to two L C resonators, each including a resistor acting as a reservoir. We find various operation regimes: nearly adiabatic (low driving frequency), ideal Otto cycle (intermediate frequency), and nonadiabatic coherent regime (high frequency). In the nearly adiabatic regime, the cooling power is quadratic in frequency, and we find a substantially enhanced coefficient of performance ɛ , as compared to that of an ideal Otto cycle. Quantum coherent effects lead invariably to a decrease in both cooling power and ɛ as compared to purely classical dynamics. In the nonadiabatic regime we observe strong coherent oscillations of the cooling power as a function of frequency. We investigate various driving wave forms: Compared to the standard sinusoidal drive, a truncated trapezoidal drive with optimized rise and dwell times yields higher cooling power and efficiency.
Vakaryuk, Victor
2008-10-17
A universal mechanism of restoration of minimal hc/e periodicity in the response of small superconducting rings or cylinders to the magnetic flux is proposed. The mechanism is based on the dependence of the Cooper pair's internal energy on its motion as a whole and does not rely on the presence of quasiparticles in the system. The thermal equilibrium hc/2e periodicity is broken by an offset of the transition between different current-carrying states. The magnitude of the offset is calculated for an s-wave superconducting cylinder of radius R in the limit R>xi_{0}, where xi_{0} is the BCS coherence length and turns out to be exponentially small. A possible enhancement of the effect for nodal superconductors is suggested. Similar conclusions should also apply to the response of charged or neutral superfluids to rotation.
Cai, Ang; Pixley, Jedediah; Si, Qimiao
Heavy fermion metals represent a canonical system to study superconductivity driven by quantum criticality. We are particularly motivated by the properties of CeRhIn5, which shows the characteristic features of a Kondo destruction quantum critical point (QCP) in its normal state, and has one of the highest Tc's among the heavy fermion superconductors. As a first step to study this problem within a cluster-EDMFT approach, we analyze a four-site Anderson impurity model with the antiferromagnetic spin component of the cluster coupled to a sub-Ohmic bosonic bath. We find a QCP that belongs to the same universality class as the single-site Bose-Fermi Anderson model. Together with previous work on a two-site model, our result suggests that the Kondo destruction QCP is robust as cluster size increases. More importantly, we are able to calculate the d-wave pairing susceptibility, which we find to be enhanced near the QCP. Using this model as the effective cluster model of the periodic Anderson model, we are also able to study the superconducting pairing near the Kondo-destruction QCP of the lattice model; preliminary results will be presented.
Nori, Franco
2008-03-01
Superconducting (SC) circuits can behave like atoms making transitions between a few energy levels. Such circuits can test quantum mechanics at macroscopic scales and be used to conduct atomic-physics experiments on a silicon chip. This talk overviews a few of our theoretical studies on SC circuits and quantum information processing (QIP) including: SC qubits for single photon generation and for lasing; controllable couplings among qubits; how to increase the coherence time of qubits using a capacitor in parallel to one of the qubit junctions; hybrid circuits involving both charge and flux qubits; testing Bell's inequality in SC circuits; generation of GHZ states; quantum tomography in SC circuits; preparation of macroscopic quantum superposition states of a cavity field via coupling to a SC qubit; generation of nonclassical photon states using a SC qubit in a microcavity; scalable quantum computing with SC qubits; and information processing with SC qubits in a microwave field. Controllable couplings between qubits can be achieved either directly or indirectly. This can be done with and without coupler circuits, and with and without data-buses like EM fields in cavities (e.g., we will describe both the variable-frequency magnetic flux approach and also a generalized double-resonance approach that we introduced). It is also possible to ``turn a quantum bug into a feature'' by using microscopic defects as qubits, and the macroscopic junction as a controller of it. We have also studied ways to implement radically different approaches to QIP by using ``cluster states'' in SC circuits. For a general overview of this field, see, J.Q. You and F. Nori, Phys. Today 58 (11), 42 (2005)
Quantum transport through two series Aharonov-Bohm interferometers with zero total magnetic flux
Institute of Scientific and Technical Information of China (English)
Wang Jian-Ming; Wang Rui; Zhang Yong-Ping; Liang Jiu-Qing
2007-01-01
With the help of nonequilibrium Green's function technique, the electronic transport through series AharonovBohm (AB) interferometers is investigated. We obtain the AB interference pattern of the transition probability characterized by the algebraic sum φ and the difference θ of two magnetic fluxes, and particularly a general rule of AB oscillation period depending on the ratio of integer quantum numbers of the fluxes. A parity effect is observed, showing the asymmetric AB oscillations with respect to the even and odd quantum numbers of the total flux in antiparallel AB interferometers. It is also shown that the AB flux can shift the Fano resonance peaks of the transmission spectrum.
A scheme to implement the Deutsch-Josza algorithm on a superconducting charge-qubit quantum computer
Institute of Scientific and Technical Information of China (English)
HUO Wenyi; LONG Guilu
2006-01-01
We have studied the implementation of the Deutsch-Josza quantum algorithm in a superconducting charge-qubit quantum computer. Different from previous studies, we have used the inductance coupled system of You et al. The detailed pulse sequences have been designed for the four possible functions in a 2-qubit system. The result is generalized to an arbitrary n-qubit system. This scheme will be useful for practical implementation of the algorithm.
Directory of Open Access Journals (Sweden)
Jeong Ryeol Choi
2015-01-01
Full Text Available An adiabatic invariant, which is a conserved quantity, is useful for studying quantum and classical properties of dynamical systems. Adiabatic invariants for time-dependent superconducting qubit-oscillator systems and resonators are investigated using the Liouville-von Neumann equation. At first, we derive an invariant for a simple superconducting qubit-oscillator through the introduction of its reduced Hamiltonian. Afterwards, an adiabatic invariant for a nanomechanical resonator linearly interfaced with a superconducting circuit, via a coupling with a time-dependent strength, is evaluated using the technique of unitary transformation. The accuracy of conservation for such invariant quantities is represented in detail. Based on the results of our developments in this paper, perturbation theory is applicable to the research of quantum characteristics of more complicated qubit systems that are described by a time-dependent Hamiltonian involving nonlinear terms.
Superconductivity versus quantum criticality: what can we learn from heavy fermions?
Steglich, F; Arndt, J; Friedemann, S; Krellner, C; Tokiwa, Y; Westerkamp, T; Brando, M; Gegenwart, P; Geibel, C; Wirth, S; Stockert, O
2010-04-28
Two quantum critical point (QCP) scenarios are being discussed for different classes of antiferromagnetic (AF) heavy-fermion (HF) systems. In the itinerant one, where AF order is of the spin-density wave (SDW) type, the heavy 'composite' charge carriers keep their integrity at the QCP. The second one implies a breakdown of the Kondo effect and a disintegration of the composite fermions at the AF QCP. We discuss two isostructural compounds as exemplary materials for these two different scenarios: CeCu(2)Si(2) exhibits a three-dimensional (3D) SDW QCP and superconductivity, presumably mediated by SDW fluctuations, as strongly suggested by recent inelastic neutron scattering experiments. In Y bRh(2)Si(2), the AF QCP is found to coincide with a Kondo-destroying one. However, in the latter compound these two QCPs can be detached by varying the average unit-cell volume, e.g. through the application of chemical pressure, as realized by partial substitution of either Ir or Co for Rh. A comparison of CeCu(2)Si(2) and Y bRh(2)Si(2) indicates that the apparent differences in quantum critical behaviour go along with disparate behaviour concerning the (non-) existence of superconductivity (SC). No sign of SC could be detected in Y bRh(2)Si(2) down to mK temperatures. A potential correlation between the specific nature of the QCP and the occurrence of SC, however, requires detailed studies on further quantum critical HF superconductors, e.g. on β-Y bAlB(4), UBe(13), CeCoIn(5) and CeRhIn(5).
Energy Technology Data Exchange (ETDEWEB)
Martinello, Martina [Illinois Inst. of Technology, Chicago, IL (United States)
2016-12-01
Accelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators. Superconducting accelerating cavities are made out of niobium and operate at the liquid helium temperature. Even if superconducting, these resonating structures have some RF driven surface resistance that causes power dissipation. In order to decrease as much as possible the power losses, the cavity quality factor must be increased by decreasing the surface resistance. In this dissertation, the RF surface resistance is analyzed for a large variety of cavities made with different state-of-the-art surface treatments, with the goal of finding the surface treatment capable to return the highest Q-factor values in a cryomodule-like environment. This study analyzes not only the superconducting properties described by the BCS surface resistance, which is the contribution that takes into account dissipation due to quasi-particle excitations, but also the increasing of the surface resistance due to trapped flux. When cavities are cooled down below their critical temperature inside a cryomodule, there is always some remnant magnetic field that may be trapped increasing the global RF surface resistance. This thesis also analyzes how the fraction of external magnetic field, which is actually trapped in the cavity during the cooldown, can be minimized. This study is performed on an elliptical single-cell horizontally cooled cavity, resembling the geometry of cavities cooled in accelerator cryomodules. The horizontal cooldown study reveals that, as in case of the vertical cooldown, when the cooling is performed fast, large thermal gradients are created along the cavity helping magnetic flux expulsion. However, for this geometry the complete magnetic flux expulsion from the cavity equator is more difficult to achieve. This becomes even more challenging in presence of orthogonal magnetic field, that is easily trapped on top of the cavity equator
Institute of Scientific and Technical Information of China (English)
ZHENG An-Shou; LIU Ji-Bing; XIANG Dong; LIU Cui-Lan; YUAN Hong
2007-01-01
An alternative approach is proposed to realize an n-qubit Toffoli gate with superconducting quantum-interference devices (SQUIDs) in cavity quantum electrodynamics (QED). In the proposal, we represent two logical gates of a qubit with the two lowest levels of a SQUID while a higher-energy intermediate level of each SQUID is utilized for the gate manipulation. During the operating process, because the cavity field is always in vacuum state, the requirement on the cavity is greatly loosened and there is no transfer of quantum information between the cavity and SQUIDs.
Modern aspects of Josephson dynamics and superconductivity electronics
Askerzade, Iman; Cantürk, Mehmet
2017-01-01
In this book new experimental investigations of properties of Josephson junctions and systems are explored with the help of recent developments in superconductivity. The theory of the Josephson effect is presented taking into account the influence of multiband and anisotropy effects in new superconducting compounds. Anharmonicity effects in current-phase relation on Josephson junctions dynamics are discussed. Recent studies in analogue and digital superconductivity electronics are presented. Topics of special interest include resistive single flux quantum logic in digital electronics. Application of Josephson junctions in quantum computing as superconducting quantum bits are analyzed. Particular attention is given to understanding chaotic behaviour of Josephson junctions and systems. The book is written for graduate students and researchers in the field of applied superconductivity.
Energy Technology Data Exchange (ETDEWEB)
Armour, A D [School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD (United Kingdom); Blencowe, M P [Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755 (United States)], E-mail: andrew.armour@nottingham.ac.uk, E-mail: miles.p.blencowe@dartmouth.edu
2008-09-15
We propose a scheme in which the quantum coherence of a nanomechanical resonator can be probed using a superconducting qubit. We consider a mechanical resonator coupled capacitively to a Cooper pair box and assume that the superconducting qubit is tuned to the degeneracy point so that its coherence time is maximized and the electro-mechanical coupling can be approximated by a dispersive Hamiltonian. When the qubit is prepared in a superposition of states, this drives the mechanical resonator progressively into a superposition which in turn leads to apparent decoherence of the qubit. Applying a suitable control pulse to the qubit allows its population to be inverted resulting in a reversal of the resonator dynamics. However, the resonator's interactions with its environment mean that the dynamics is not completely reversible. We show that this irreversibility is largely due to the decoherence of the mechanical resonator and can be inferred from appropriate measurements on the qubit alone. Using estimates for the parameters involved based on a specific realization of the system, we show that it should be possible to carry out this scheme with existing device technology.
An ultra-sensitive and wideband magnetometer based on a superconducting quantum interference device
Storm, Jan-Hendrik; Hömmen, Peter; Drung, Dietmar; Körber, Rainer
2017-02-01
The magnetic field noise in superconducting quantum interference devices (SQUIDs) used for biomagnetic research such as magnetoencephalography or ultra-low-field nuclear magnetic resonance is usually limited by instrumental dewar noise. We constructed a wideband, ultra-low noise system with a 45 mm diameter superconducting pick-up coil inductively coupled to a current sensor SQUID. Thermal noise in the liquid helium dewar is minimized by using aluminized polyester fabric as superinsulation and aluminum oxide strips as heat shields. With a magnetometer pick-up coil in the center of the Berlin magnetically shielded room 2 (BMSR2), a noise level of around 150 aT Hz-1/2 is achieved in the white noise regime between about 20 kHz and the system bandwidth of about 2.5 MHz. At lower frequencies, the resolution is limited by magnetic field noise arising from the walls of the shielded room. Modeling the BMSR2 as a closed cube with continuous μ-metal walls, we can quantitatively reproduce its measured field noise.
Energy Technology Data Exchange (ETDEWEB)
Vinante, A., E-mail: anvinante@fbk.eu; Falferi, P. [Istituto di Fotonica e Nanotecnologie, CNR - Fondazione Bruno Kessler, I-38123 Povo, Trento (Italy); Mezzena, R. [Dipartimento di Fisica, Università di Trento, I-38123 Povo, Trento (Italy)
2014-10-15
Superconducting Quantum Interference Device (SQUID) microsusceptometers have been widely used to study magnetic properties of materials at microscale. As intrinsically balanced devices, they could also be exploited for direct SQUID-detection of nuclear magnetic resonance (NMR) from micron sized samples, or for SQUID readout of mechanically detected NMR from submicron sized samples. Here, we demonstrate a double balancing technique that enables achievement of very low residual imbalance of a SQUID microsusceptometer over a wide bandwidth. In particular, we can generate ac magnetic fields within the SQUID loop as large as 1 mT, for frequencies ranging from dc up to a few MHz. As an application, we demonstrate direct detection of NMR from {sup 1}H spins in a glycerol droplet placed directly on top of the 20 μm SQUID loops.
Energy Technology Data Exchange (ETDEWEB)
Krauss, R.H. Jr.; Flynn, E.; Ruminer, P. [and others
1997-10-01
This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This project has supported the collaborative development with Sandia National Laboratories (SNL) and the University of New Mexico (UNM) of two critical components for a hand-held low-field magnetic sensor based on superconducting quantum interference device (SQUID) sensor technology. The two components are a digital signal processing (DSP) algorithm for background noise rejection and a small hand-held dewar cooled by a cryocooler. A hand-held sensor has been designed and fabricated for detection of extremely weak magnetic fields in unshielded environments. The sensor is capable of measuring weak magnetic fields in unshielded environments and has multiple applications. We have chosen to pursue battlefield medicine as the highest probability near-term application because of stated needs of several agencies.
Optical transmission modules for multi-channel superconducting quantum interference device readouts
Energy Technology Data Exchange (ETDEWEB)
Kim, Jin-Mok, E-mail: jmkim@kriss.re.kr; Kwon, Hyukchan; Yu, Kwon-kyu; Lee, Yong-Ho; Kim, Kiwoong [Brain Cognition Measurement Center, Korea Research Institute of Standards and Science, Daejeon 305-600 (Korea, Republic of)
2013-12-15
We developed an optical transmission module consisting of 16-channel analog-to-digital converter (ADC), digital-noise filter, and one-line serial transmitter, which transferred Superconducting Quantum Interference Device (SQUID) readout data to a computer by a single optical cable. A 16-channel ADC sent out SQUID readouts data with 32-bit serial data of 8-bit channel and 24-bit voltage data at a sample rate of 1.5 kSample/s. A digital-noise filter suppressed digital noises generated by digital clocks to obtain SQUID modulation as large as possible. One-line serial transmitter reformed 32-bit serial data to the modulated data that contained data and clock, and sent them through a single optical cable. When the optical transmission modules were applied to 152-channel SQUID magnetoencephalography system, this system maintained a field noise level of 3 fT/√Hz @ 100 Hz.
Song, Wan-Lu; Yang, Wan-Li; Yin, Zhang-Qi; Chen, Chang-Yong; Feng, Mang
2016-09-01
We explore controllable quantum dynamics of a hybrid system, which consists of an array of mutually coupled superconducting resonators (SRs) with each containing a nitrogen-vacancy center spin ensemble (NVE) in the presence of inhomogeneous broadening. We focus on a three-site model, which compared with the two-site case, shows more complicated and richer dynamical behavior, and displays a series of damped oscillations under various experimental situations, reflecting the intricate balance and competition between the NVE-SR collective coupling and the adjacent-site photon hopping. Particularly, we find that the inhomogeneous broadening of the spin ensemble can suppress the population transfer between the SR and the local NVE. In this context, although the inhomogeneous broadening of the spin ensemble diminishes entanglement among the NVEs, optimal entanglement, characterized by averaging the lower bound of concurrence, could be achieved through accurately adjusting the tunable parameters.
Analog approaches to quantum computation using highly-controllable superconducting qubits
Neill, C.; Roushan, P.; Barends, R.; Campbell, B.; Chen, Y.; Chen, Z.; Chiaro, B.; Dunsworth, A.; Fowler, A.; Jeffrey, E.; Kelly, J.; Lucero, E.; Megrant, A.; Mutus, J.; Neeley, M.; O'Malley, P.; Quintana, C.; Sank, D.; Wenner, J.; White, T.; Martinis, J.
The first generation of quantum hardware that outperforms classical computers will likely be analog in nature. In an effort to realize such a platform, we have built a one-dimensional chain of 9 superconducting gmon qubits. This device provides individual time-dependent control over all nearest-neighbor couplings and local fields (X, Y, Z) in the multi-qubit Hamiltonian. In this talk, I will focus on open problems in non-equilibrium statistical mechanics where dynamical properties become impossible to compute for only a few 10s of qubits. In particular, I will review device performance and the scaling of analog errors with system size. By studying how errors scale during practical applications, we aim to predict if otherwise-intractable computations could be carried out with 30 to 40 qubits.
Optical transmission modules for multi-channel superconducting quantum interference device readouts
Kim, Jin-Mok; Kwon, Hyukchan; Yu, Kwon-kyu; Lee, Yong-Ho; Kim, Kiwoong
2013-12-01
We developed an optical transmission module consisting of 16-channel analog-to-digital converter (ADC), digital-noise filter, and one-line serial transmitter, which transferred Superconducting Quantum Interference Device (SQUID) readout data to a computer by a single optical cable. A 16-channel ADC sent out SQUID readouts data with 32-bit serial data of 8-bit channel and 24-bit voltage data at a sample rate of 1.5 kSample/s. A digital-noise filter suppressed digital noises generated by digital clocks to obtain SQUID modulation as large as possible. One-line serial transmitter reformed 32-bit serial data to the modulated data that contained data and clock, and sent them through a single optical cable. When the optical transmission modules were applied to 152-channel SQUID magnetoencephalography system, this system maintained a field noise level of 3 fT/√Hz @ 100 Hz.
Srinivasan, S J; Hoffman, A J; Gambetta, J M; Houck, A A
2011-02-25
We introduce a new type of superconducting charge qubit that has a V-shaped energy spectrum and uses quantum interference to provide independently tunable qubit energy and coherent coupling to a superconducting cavity. Dynamic access to the strong coupling regime is demonstrated by tuning the coupling strength from less than 200 kHz to greater than 40 MHz. This tunable coupling can be used to protect the qubit from cavity-induced relaxation and avoid unwanted qubit-qubit interactions in a multiqubit system.
Droste, Stephanie; Governale, Michele
2016-04-01
We study the finite-time full counting statistics for subgap transport through a single-level quantum dot tunnel-coupled to one normal and one superconducting lead. In particular, we determine the factorial and the ordinary cumulants both for finite times and in the long-time limit. We find that the factorial cumulants violate the sign criterion, indicating a non-binomial distribution, even in absence of Coulomb repulsion due to the presence of superconducting correlations. At short times the cumulants exhibit oscillations which are a signature of the coherent transfer of Cooper pairs between the dot and the superconductor.
Superconducting qubit-resonator-atom hybrid system
Yu, Deshui; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer
2017-09-01
We propose a hybrid quantum system where an LC resonator inductively interacts with a flux qubit and is capacitively coupled to a Rydberg atom. Varying the external magnetic flux bias controls the flux qubit flipping and the flux qubit-resonator interface. The atomic spectrum is tuned via an electrostatic field, manipulating the qubit-state transition of atom and the atom-resonator coupling. Different types of entanglement of superconducting, photonic and atomic qubits can be prepared via simply tuning the flux bias and electrostatic field, leading to the implementation of three-qubit Toffoli logic gate.
Energy Technology Data Exchange (ETDEWEB)
Sano, K., E-mail: sano-kyosuke-cw@ynu.jp [Department Electrical and Computer Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501 (Japan); Muramatsu, Y.; Yamanashi, Y.; Yoshikawa, N. [Department Electrical and Computer Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501 (Japan); Zen, N.; Ohkubo, M. [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba 305-8568 (Japan)
2014-09-15
Highlights: • We proposed single-flux-quantum (SFQ) time-to-digital converters (TDCs) for TOF-MS. • SFQ TDC can measure time intervals between multiple signals with high-resolution. • SFQ TDC can directly convert the time intervals into binary data. • We designed two types of SFQ TDCs to reduce the jitter. • The jitter is reduced to less than 100 ps. - Abstract: We have been developing a high-resolution superconducting time-of-flight mass spectrometry (TOF-MS) system, which utilizes a superconducting strip ion detector (SSID) and a single-flux-quantum (SFQ) time-to-digital converter (TDC). The SFQ TDC can measure time intervals between multiple input signals and directly convert them into binary data. In our previous study, 24-bit SFQ TDC with a 3 × 24-bit First-In First-Out (FIFO) buffer was designed and implemented using the AIST Nb standard process 2 (STP2), whose time resolution and dynamic range are 100 ps and 1.6 ms, respectively. In this study we reduce the jitter of the TDC by using two different approaches: one uses an on-chip clock generator with an on-chip low-pass filter for reducing the noise in the bias current, and the other uses a low-jitter external clock source at room temperature. We confirmed that the jitter is reduced to less than 100 ps in the latter approach.
Memory Effect in Upper Bound of Heat Flux Induced by Quantum Fluctuations
Koide, T
2016-01-01
We develop a model of quantum open systems as a quantum Brownian motion coupled to a classical heat bath by introducing a mathematical definition of operator differentials. We then define a heat operator by extending the stochastic energetics and show that this operator satisfies properties corresponding to the first and second laws in thermodynamics. We further find that the upper bound of the heat flux depends on the memory effect induced by quantum fluctuations and hence the maximum extractable work can be qualitatively modified in quantum thermodynamics.
Takeuchi, Naoki; Suzuki, Hideo; Yoshikawa, Nobuyuki
2017-05-01
Adiabatic quantum-flux-parametron (AQFP) is an energy-efficient superconductor logic. The advantage of AQFP is that the switching energy can be reduced by lowering operation frequencies or by increasing the quality factors of Josephson junctions, while keeping the energy barrier height much larger than thermal energy. In other words, both low energy dissipation and low bit error rates (BERs) can be achieved. In this paper, we report the first measurement results of the low BERs of AQFP logic. We used a superconductor voltage driver with a stack of dc superconducting-quantum-interference-devices to amplify the logic signals of AQFP gates into mV-range voltage signals for the BER measurement. Our measurement results showed 3.3 dB and 2.6 dB operation margins, in which BERs were less than 10-20, for 1 Gbps and 2 Gbps data rates, respectively. While the observed BERs were very low, the estimated switching energy for the 1-Gbps operation was only 2 zJ or 30kBT, where kB is the Boltzmann's constant and T is the temperature. Unlike conventional non-adiabatic logic, BERs are not directly associated with switching energy in AQFP.
CaFeAs2: A staggered intercalation of quantum spin Hall and high-temperature superconductivity
Wu, Xianxin; Qin, Shengshan; Liang, Yi; Le, Congcong; Fan, Heng; Hu, Jiangping
2015-02-01
We predict that CaFeAs2, a newly discovered iron-based high-temperature (Tc) superconductor, is a staggered intercalation compound that integrates topological quantum spin Hall (QSH) and superconductivity (SC). CaFeAs2 has a structure with staggered CaAs and FeAs layers. While the FeAs layers are known to be responsible for high Tc superconductivity, we show that with spin orbital coupling each CaAs layer is a Z2 topologically nontrivial two-dimensional QSH insulator and the bulk is a three-dimensional weak topological insulator. In the superconducting state, the edge states in the CaAs layer are natural one-dimensional topological superconductors. The staggered intercalation of QSH and SC provides us a unique opportunity to realize and explore physics, such as Majorana modes and Majorana fermion chains.
Energy Technology Data Exchange (ETDEWEB)
Bose, Sangita; Galande, Charudatta; Chockalingam, S P; Raychaudhuri, Pratap; Ayyub, Pushan [Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Mumbai 400005 (India); Banerjee, Rajarshi [Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203-5310 (United States)], E-mail: Sangita.Bose@fkf.mpg.de, E-mail: pratap@tifr.res.in, E-mail: pushan@tifr.res.in
2009-05-20
The superconducting transition temperature (T{sub C}) in nanostructured Pb decreases from 7.24 to 6.4 K as the particle size is reduced from 65 to 7 nm, below which superconductivity is lost rather abruptly. In contrast, there is a large enhancement in the upper critical field (H{sub C2}) in the same size regime. We explore the origin of the unusual robustness of T{sub C} over such a large particle size range in nanostructured Pb by measuring the temperature dependence of the superconducting energy gap in planar tunnel junctions of Al/Al{sub 2}O{sub 3}/nano-Pb. We show that below 22 nm, the electron-phonon coupling strength increases monotonically with decreasing particle size, and almost exactly compensates for the quantum size effect, which is expected to suppress T{sub C}.
Energy Technology Data Exchange (ETDEWEB)
Kawasaki, S; Tabuchi, T; Zheng Guoqing [Department of Physics, Okayama University, Okayama 700-8530 (Japan); Wang, X F; Chen, X H [Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2010-05-15
{sup 75}As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe{sub 2}As{sub 2} under pressure. At P = 4.7 and 10.8 kbar, the temperature dependencies of nuclear-spin-lattice relaxation rate (1/T{sub 1}) measured in the tetragonal phase show no coherence peak just below T{sub c}(P) and decrease with decreasing temperature. The superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point under pressures in the range 4.7 kbar {<=} P {<=} 10.8 kbar. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.
Sato, Taku J.; Okuyama, Daisuke; Kimura, Hideo
2016-12-01
A tiny adiabatic-demagnetization refrigerator (T-ADR) has been developed for a commercial superconducting quantum interference device magnetometer [Magnetic Property Measurement System (MPMS) from Quantum Design]. The whole T-ADR system is fit in a cylindrical space of diameter 8.5 mm and length 250 mm, and can be inserted into the narrow sample tube of MPMS. A sorption pump is self-contained in T-ADR, and hence no complex gas handling system is necessary. With the single crystalline Gd3Ga5O12 garnet (˜2 g) used as a magnetic refrigerant, the routinely achievable lowest temperature is ˜0.56 K. The lower detection limit for a magnetization anomaly is ˜1 × 10-7 emu, estimated from fluctuation of the measured magnetization. The background level is ˜5 × 10-5 emu below 2 K at H = 100 Oe, which is largely attributable to a contaminating paramagnetic signal from the magnetic refrigerant.
Sato, Taku J; Okuyama, Daisuke; Kimura, Hideo
2016-12-01
A tiny adiabatic-demagnetization refrigerator (T-ADR) has been developed for a commercial superconducting quantum interference device magnetometer [Magnetic Property Measurement System (MPMS) from Quantum Design]. The whole T-ADR system is fit in a cylindrical space of diameter 8.5 mm and length 250 mm, and can be inserted into the narrow sample tube of MPMS. A sorption pump is self-contained in T-ADR, and hence no complex gas handling system is necessary. With the single crystalline Gd3Ga5O12 garnet (∼2 g) used as a magnetic refrigerant, the routinely achievable lowest temperature is ∼0.56 K. The lower detection limit for a magnetization anomaly is ∼1 × 10(-7) emu, estimated from fluctuation of the measured magnetization. The background level is ∼5 × 10(-5) emu below 2 K at H = 100 Oe, which is largely attributable to a contaminating paramagnetic signal from the magnetic refrigerant.
Readout of a superconducting qubit. A problem of quantum escape processes for driven systems
Energy Technology Data Exchange (ETDEWEB)
Verso, Alvise
2010-10-27
We started this work with a description of two devices that were recently developed in the context of quantum information processing. These devices are used as read-out for superconducting quantum bits based on Josephson junctions. The classical description has to be extended to the quantum regime. As the main result we calculate the leading order corrections in {Dirac_h} on the escape rate. We took into account a standard metastable potential with a static energy barrier and showed how to derive an extension of the classical diffusion equation. We did this within a systematic semiclassical formalism starting from a quantum mechanical master equation. This master equation contains an extra term for the loss of population due to tunneling through the barrier and, in contrast to previous approaches, finite barrier transmission which also affects the transition probabilities between the states. The escape rate is obtained from the stationary non-equilibrium solution of the diffusion equation. The quantum corrections on the escape rate are captured by two factors, the first one describes zero-point fluctuations in the well, while the second one describes the impact of finite barrier transmission close to the top. Interestingly, for weak friction there exists a temperature range, where the latter one can actually prevail and lead to a reduction of the escape compared to the classical situation due to finite reflection from the barrier even for energies above the barrier. Only for lower temperatures does the quantum result exceed the classical one. The approach can not strictly be used for the Duffing oscillator because of the time dependent term in its Hamiltonian. But it is possible to move in a frame rotating with a frequency equal to the response frequency of the Duffing oscillator in order to obtain a time-independent Hamiltonian. Therefore a system plus reservoir model was applied to consistently derive in the weak coupling limit the master equation for the reduced
Quantum Transport in a Biphenyl Molecule: Effects of Magnetic Flux
Maiti, Santanu K.
2009-01-01
Electron transport properties of a biphenyl molecule are studied based on the Green's function formalism. The molecule is sandwiched between two metallic electrodes, where each benzene ring is threaded by a magnetic flux $\\phi$. The results are focused on the effects of the molecule to electrode coupling strength and the magnetic flux $\\phi$. Our numerical study shows that, for a fixed molecular coupling, the current amplitude across the bridge can be {\\em regulated} significantly just by tun...
Extending the lifetime of a quantum bit with error correction in superconducting circuits
Ofek, Nissim; Petrenko, Andrei; Heeres, Reinier; Reinhold, Philip; Leghtas, Zaki; Vlastakis, Brian; Liu, Yehan; Frunzio, Luigi; Girvin, S. M.; Jiang, L.; Mirrahimi, Mazyar; Devoret, M. H.; Schoelkopf, R. J.
2016-08-01
Quantum error correction (QEC) can overcome the errors experienced by qubits and is therefore an essential component of a future quantum computer. To implement QEC, a qubit is redundantly encoded in a higher-dimensional space using quantum states with carefully tailored symmetry properties. Projective measurements of these parity-type observables provide error syndrome information, with which errors can be corrected via simple operations. The ‘break-even’ point of QEC—at which the lifetime of a qubit exceeds the lifetime of the constituents of the system—has so far remained out of reach. Although previous works have demonstrated elements of QEC, they primarily illustrate the signatures or scaling properties of QEC codes rather than test the capacity of the system to preserve a qubit over time. Here we demonstrate a QEC system that reaches the break-even point by suppressing the natural errors due to energy loss for a qubit logically encoded in superpositions of Schrödinger-cat states of a superconducting resonator. We implement a full QEC protocol by using real-time feedback to encode, monitor naturally occurring errors, decode and correct. As measured by full process tomography, without any post-selection, the corrected qubit lifetime is 320 microseconds, which is longer than the lifetime of any of the parts of the system: 20 times longer than the lifetime of the transmon, about 2.2 times longer than the lifetime of an uncorrected logical encoding and about 1.1 longer than the lifetime of the best physical qubit (the |0>f and |1>f Fock states of the resonator). Our results illustrate the benefit of using hardware-efficient qubit encodings rather than traditional QEC schemes. Furthermore, they advance the field of experimental error correction from confirming basic concepts to exploring the metrics that drive system performance and the challenges in realizing a fault-tolerant system.
Extending the lifetime of a quantum bit with error correction in superconducting circuits.
Ofek, Nissim; Petrenko, Andrei; Heeres, Reinier; Reinhold, Philip; Leghtas, Zaki; Vlastakis, Brian; Liu, Yehan; Frunzio, Luigi; Girvin, S M; Jiang, L; Mirrahimi, Mazyar; Devoret, M H; Schoelkopf, R J
2016-08-25
Quantum error correction (QEC) can overcome the errors experienced by qubits and is therefore an essential component of a future quantum computer. To implement QEC, a qubit is redundantly encoded in a higher-dimensional space using quantum states with carefully tailored symmetry properties. Projective measurements of these parity-type observables provide error syndrome information, with which errors can be corrected via simple operations. The 'break-even' point of QEC--at which the lifetime of a qubit exceeds the lifetime of the constituents of the system--has so far remained out of reach. Although previous works have demonstrated elements of QEC, they primarily illustrate the signatures or scaling properties of QEC codes rather than test the capacity of the system to preserve a qubit over time. Here we demonstrate a QEC system that reaches the break-even point by suppressing the natural errors due to energy loss for a qubit logically encoded in superpositions of Schrödinger-cat states of a superconducting resonator. We implement a full QEC protocol by using real-time feedback to encode, monitor naturally occurring errors, decode and correct. As measured by full process tomography, without any post-selection, the corrected qubit lifetime is 320 microseconds, which is longer than the lifetime of any of the parts of the system: 20 times longer than the lifetime of the transmon, about 2.2 times longer than the lifetime of an uncorrected logical encoding and about 1.1 longer than the lifetime of the best physical qubit (the |0〉f and |1〉f Fock states of the resonator). Our results illustrate the benefit of using hardware-efficient qubit encodings rather than traditional QEC schemes. Furthermore, they advance the field of experimental error correction from confirming basic concepts to exploring the metrics that drive system performance and the challenges in realizing a fault-tolerant system.
Fu, Lin; Matsuda, Koichi; Lecrevisse, Thibault; Iwasa, Yukikazu; Coombs, Tim
2016-04-01
This letter presents a flux pumping method and the results gained when it was used to magnetize a range of different YBCO coils. The pumping device consists of an iron magnetic circuit with eight copper coils which apply a traveling magnetic field to the superconductor. The copper poles are arranged vertically with an air gap length of 1 mm and the iron cores are made of laminated electric steel plates to minimize eddy-current losses. We have used this arrangement to investigate the best possible pumping result when parameters such as frequency, amplitude and waveform are varied. We have successfully pumped current into the superconducting coil up to a value of 90% of I c and achieved a resultant magnetic field of 1.5 T.
Quantum state engineering with flux-biased Josephson phase qubits by rapid adiabatic passages
Nie, W.; Huang, J. S.; Shi, X.; Wei, L. F.
2010-09-01
In this article, the scheme of quantum computing based on the Stark-chirped rapid adiabatic passage (SCRAP) technique [L. F. Wei, J. R. Johansson, L. X. Cen, S. Ashhab, and F. Nori, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.100.113601 100, 113601 (2008)] is extensively applied to implement quantum state manipulations in flux-biased Josephson phase qubits. The broken-parity symmetries of bound states in flux-biased Josephson junctions are utilized to conveniently generate the desirable Stark shifts. Then, assisted by various transition pulses, universal quantum logic gates as well as arbitrary quantum state preparations can be implemented. Compared with the usual π-pulse operations widely used in experiments, the adiabatic population passages proposed here are insensitive to the details of the applied pulses and thus the desirable population transfers can be satisfyingly implemented. The experimental feasibility of the proposal is also discussed.
Nano Superconducting Quantum Interference device: A powerful tool for nanoscale investigations
Energy Technology Data Exchange (ETDEWEB)
Granata, Carmine, E-mail: carmine.granata@cnr.it; Vettoliere, Antonio
2016-02-19
The magnetic sensing at nanoscale level is a promising and interesting research topic of nanoscience. Indeed, magnetic imaging is a powerful tool for probing biological, chemical and physical systems. The study of small spin cluster, like magnetic molecules and nanoparticles, single electron, cold atom clouds, is one of the most stimulating challenges of applied and basic research of the next years. In particular, the magnetic nanoparticle investigation plays a fundamental role for the modern material science and its relative technological applications like ferrofluids, magnetic refrigeration and biomedical applications, including drug delivery, hyper-thermia cancer treatment and magnetic resonance imaging contrast-agent. Actually, one of the most ambitious goals of the high sensitivity magnetometry is the detection of elementary magnetic moment or spin. In this framework, several efforts have been devoted to the development of a high sensitivity magnetic nanosensor pushing sensing capability to the individual spin level. Among the different magnetic sensors, Superconducting QUantum Interference Devices (SQUIDs) exhibit an ultra high sensitivity and are widely employed in numerous applications. Basically, a SQUID consists of a superconducting ring (sensitive area) interrupted by two Josephson junctions. In the recent years, it has been proved that the magnetic response of nano-objects can be effectively measured by using a SQUID with a very small sensitive area (nanoSQUID). In fact, the sensor noise, expressed in terms of the elementary magnetic moment (spin or Bohr magneton), is linearly dependent on the SQUID loop side length. For this reason, SQUIDs have been progressively miniaturized in order to improve the sensitivity up to few spin per unit of bandwidth. With respect to other techniques, nanoSQUIDs offer the advantage of direct measurement of magnetization changes in small spin systems. In this review, we focus on nanoSQUIDs and its applications. In
Nano Superconducting Quantum Interference device: A powerful tool for nanoscale investigations
Granata, Carmine; Vettoliere, Antonio
2016-02-01
The magnetic sensing at nanoscale level is a promising and interesting research topic of nanoscience. Indeed, magnetic imaging is a powerful tool for probing biological, chemical and physical systems. The study of small spin cluster, like magnetic molecules and nanoparticles, single electron, cold atom clouds, is one of the most stimulating challenges of applied and basic research of the next years. In particular, the magnetic nanoparticle investigation plays a fundamental role for the modern material science and its relative technological applications like ferrofluids, magnetic refrigeration and biomedical applications, including drug delivery, hyper-thermia cancer treatment and magnetic resonance imaging contrast-agent. Actually, one of the most ambitious goals of the high sensitivity magnetometry is the detection of elementary magnetic moment or spin. In this framework, several efforts have been devoted to the development of a high sensitivity magnetic nanosensor pushing sensing capability to the individual spin level. Among the different magnetic sensors, Superconducting QUantum Interference Devices (SQUIDs) exhibit an ultra high sensitivity and are widely employed in numerous applications. Basically, a SQUID consists of a superconducting ring (sensitive area) interrupted by two Josephson junctions. In the recent years, it has been proved that the magnetic response of nano-objects can be effectively measured by using a SQUID with a very small sensitive area (nanoSQUID). In fact, the sensor noise, expressed in terms of the elementary magnetic moment (spin or Bohr magneton), is linearly dependent on the SQUID loop side length. For this reason, SQUIDs have been progressively miniaturized in order to improve the sensitivity up to few spin per unit of bandwidth. With respect to other techniques, nanoSQUIDs offer the advantage of direct measurement of magnetization changes in small spin systems. In this review, we focus on nanoSQUIDs and its applications. In
Wang, H L; Yu, X Z; Wang, S L; Chen, L; Zhao, J H
2013-08-01
We have developed a sample rod which makes the conventional superconducting quantum interference device magnetometer capable of performing magnetization and electrical transport measurements simultaneously. The sample holder attached to the end of a 140 cm long sample rod is a nonmagnetic drinking straw or a 1.5 mm wide silicon strip with small magnetic background signal. Ferromagnetic semiconductor (Ga,Mn)As films are used to test the new sample rod, and the results are in good agreement with previous report.
Effects of intergrain and intragrain currents on flux profile in granular superconducting ceramics
Godelaine, P. A.; Ausloos, M.
1990-11-01
We present generalizations of Bean critical state model to take into account granular effects as in high critical temperature superconductor ceramics. Both intragrain and intergrain critical current effect are discussed as they modify the "flux profile" determined by AC susceptibility measurements. We also examine the effect of Josephson weak links on the flux profile. We show how to obtain these electrical currents from the data together with the "granular fraction" and the flux penetration depth. Data on Bi 0.85Pb 0.15SrCa 1.2Cu 2O 6 sample is shown to be fitted to our theoretical expressions.
Brisbois, J.; Adami, O.-A.; Avila, J. I.; Motta, M.; Ortiz, W. A.; Nguyen, N. D.; Vanderbemden, P.; Vanderheyden, B.; Kramer, R. B. G.; Silhanek, A. V.
2016-02-01
We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n . In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities.
Nanofabrication for On-Chip Optical Levitation, Atom-Trapping, and Superconducting Quantum Circuits
Norte, Richard Alexander
a final value of Qm = 5.8(1.1) x 105, representing more than an order of magnitude improvement over the conventional limits of SiO2 for a pendulum geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems. We then give a detailed overview of the techniques used to produce high-aspect-ratio nanostructures with applications in a wide range of quantum optics experiments. The ability to fabricate such nanodevices with high precision opens the door to a vast array of experiments which integrate macroscopic optical setups with lithographically engineered nanodevices. Coupled with atom-trapping experiments in the Kimble Lab, we use these techniques to realize a new waveguide chip designed to address ultra-cold atoms along lithographically patterned nanobeams which have large atom-photon coupling and near 4pi Steradian optical access for cooling and trapping atoms. We describe a fully integrated and scalable design where cold atoms are spatially overlapped with the nanostring cavities in order to observe a resonant optical depth of d0 ≈ 0.15. The nanodevice illuminates new possibilities for integrating atoms into photonic circuits and engineering quantum states of atoms and light on a microscopic scale. We then describe our work with superconducting microwave resonators coupled to a phononic cavity towards the goal of building an integrated device for quantum-limited microwave-to-optical wavelength conversion. We give an overview of our characterizations of several types of substrates for fabricating a low-loss high-frequency electromechanical system. We describe our electromechanical system fabricated on a SiN membrane which consists of a 12 GHz superconducting LC resonator coupled capacitively to the high frequency localized modes of a phononic nanobeam. Using our suspended membrane geometry we isolate our system from substrates with significant loss tangents
Wen, Hai-hu; Ziemann, Paul; Radovan, Henri A.; Herzog, Thomas
1998-09-01
By using a superconducting quantum interference device (SQUID), the temporal relaxation of the magnetization was determined for ring-shaped Tl 2Ba 2CaCu 2O 8 thin films at various temperatures between 10 K and 80 K in magnetic fields ranging from 2 mT to 0.3 T. Based on these data, a detailed analysis has been performed related to the following methods or models: (1) Fitting the data to the thermally activated flux motion and collective pinning model; (2) Applying the Generalized Inversion Scheme to extract the temperature dependence of the unrelaxed critical current density jc( T) and pinning potential Uc( T); (3) Testing a modified Maley's method to obtain the current dependent activation energy for flux motion; (4) 2D vortex glass scaling. It is found that, for low fields (2 mT, 10 mT, 40 mT) the experimental data can be described by an elastic flux motion, most probably due to 3D single vortex creep. At higher fields (0.1 T, 0.2 T, 0.3 T), the observed behavior can be interpreted in terms of plastic flux motion which is probably governed by dislocation mediated flux creep. These high field data can also be consistently described by the 2D vortex glass scaling with scaling parameters ν2D, T0 and p being consistent with those derived from corresponding transport measurement. Also, results are presented demonstrating the importance of optimizing the scan length of the sample in a moving sample SQUID magnetometer to avoid artifacts.
Gonnella, Dan; Kaufman, John; Liepe, Matthias
2016-02-01
Future particle accelerators such as the SLAC "Linac Coherent Light Source-II" (LCLS-II) and the proposed Cornell Energy Recovery Linac require hundreds of superconducting radio-frequency (SRF) niobium cavities operating in continuous wave mode. In order to achieve economic feasibility of projects such as these, the cavities must achieve a very high intrinsic quality factor (Q0) to keep cryogenic losses within feasible limits. To reach these high Q0's in the case of LCLS-II, nitrogen-doping of niobium cavities has been selected as the cavity preparation technique. When dealing with Q0's greater than 1 × 1010, the effects of ambient magnetic field on Q0 become significant. Here, we show that the sensitivity to RF losses from trapped magnetic field in a cavity's walls is strongly dependent on the cavity preparation. Specifically, standard electropolished and 120 °C baked cavities show a sensitivity of residual resistance from trapped magnetic flux of ˜0.6 and ˜0.8 nΩ/mG trapped, respectively, while nitrogen-doped cavities show a higher sensitivity of residual resistance from trapped magnetic flux of ˜1 to 5 nΩ/mG trapped. We show that this difference in sensitivities is directly related to the mean free path of the RF surface layer of the niobium: shorter mean free paths lead to less sensitivity of residual resistance to trapped magnetic flux in the dirty limit (ℓ ≪ ξ0), while longer mean free paths lead to lower sensitivity of residual resistance to trapped magnetic flux in the clean limit (ℓ ≫ ξ0). These experimental results are also shown to have good agreement with recent theoretical predictions for pinned vortex lines oscillating in RF fields.
100 years of superconductivity
Rogalla, Horst
2011-01-01
Even a hundred years after its discovery, superconductivity continues to bring us new surprises, from superconducting magnets used in MRI to quantum detectors in electronics. 100 Years of Superconductivity presents a comprehensive collection of topics on nearly all the subdisciplines of superconductivity. Tracing the historical developments in superconductivity, the book includes contributions from many pioneers who are responsible for important steps forward in the field.The text first discusses interesting stories of the discovery and gradual progress of theory and experimentation. Emphasizi
Sung, Z.-H.; Wang, M.; Polyanskii, A. A.; Santosh, C.; Balachandran, S.; Compton, C.; Larbalestier, D. C.; Bieler, T. R.; Lee, P. J.
2017-05-01
This study shows that low angle grain boundaries (LAGBs) can be created by small 5% strains in high purity (residual resistivity ratio ≥ 200) superconducting radio frequency (SRF)-grade single crystalline niobium (Nb) and that these boundaries act as hydrogen traps as indicated by the distribution of niobium hydrides (Nb1-xHx). Nb1-xHx is detrimental to SRF Nb cavities due to its normal conducting properties at cavity operating temperatures. By designing a single crystal tensile sample extracted from a large grain (>5 cm) Nb ingot slice for preferred slip on one slip plane, LAGBs and dense dislocation boundaries developed. With chemical surface treatments following standard SRF cavity fabrication practice, Nb1-xHx phases were densely precipitated at the LAGBs upon cryogenic cooling (8-10 K/min). Micro-crystallographic analysis confirmed heterogeneous hydride precipitation, which included significant hydrogen atom accumulation in LAGBs. Magneto-optical imaging analysis showed that these sites can then act as sites for both premature flux penetration and eventually flux trapping. However, this hydrogen related degradation at LAGBs did not completely disappear even after an 800 °C/2 h anneal typically used for hydrogen removal in SRF Nb cavities. These findings suggest that hydride precipitation at an LAGB is facilitated by a non-equilibrium concentration of vacancy-hydrogen (H) complexes aided by mechanical deformation and the hydride phase interferes with the recovery process under 800 °C annealing.
DEFF Research Database (Denmark)
Il'ichev, E. V.; Andreev, A. V.; Jacobsen, Claus Schelde
1993-01-01
Experimental results on some radio-frequency superconducting quantum interference device (rf-SQUID) signal properties are presented. The quantum interferometer was made of ceramic YBa2Cu3O7−x and was due to a low critical current operated in the inductance or nonhysteretic mode. With bias current...
Upper critical field and quantum oscillations in tetragonal superconducting FeS
Terashima, Taichi; Kikugawa, Naoki; Lin, Hai; Zhu, Xiyu; Wen, Hai-Hu; Nomoto, Takuya; Suzuki, Katsuhiro; Ikeda, Hiroaki; Uji, Shinya
2016-09-01
The magnetoresistance and magnetic torque of FeS are measured in magnetic fields B of up to 18 T down to a temperature of 0.03 K. The superconducting transition temperature is found to be Tc=4.1 K , and the anisotropy ratio of the upper critical field Bc 2 at Tc is estimated from the initial slopes to be Γ (Tc)=6.9 . Bc 2(0 ) is estimated to be 2.2 and 0.36 T for B ∥a b and c , respectively. Quantum oscillations are observed in both the resistance and torque. Two frequencies F =0.15 and 0.20 kT are resolved and assigned to a quasi-two-dimensional Fermi surface cylinder. The carrier density and Sommerfeld coefficient associated with this cylinder are estimated to be 5.8 ×10-3 carriers/Fe and 0.48 mJ /(K2mol ) , respectively. Other Fermi surface pockets still remain to be found. Band-structure calculations are performed and compared to the experimental results.
Parasitic effects in superconducting quantum interference device-based radiation comb generators
Energy Technology Data Exchange (ETDEWEB)
Bosisio, R., E-mail: riccardo.bosisio@nano.cnr.it [SPIN-CNR, Via Dodecaneso 33, 16146 Genova (Italy); NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy); Giazotto, F., E-mail: giazotto@sns.it [NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy); Solinas, P., E-mail: paolo.solinas@spin.cnr.it [SPIN-CNR, Via Dodecaneso 33, 16146 Genova (Italy)
2015-12-07
We study several parasitic effects on the implementation of a Josephson radiation comb generator based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. This system can be used as a radiation generator similarly to what is done in optics and metrology, and allows one to generate up to several hundreds of harmonics of the driving frequency. First we take into account how the assumption of a finite loop geometrical inductance and junction capacitance in each SQUID may alter the operation of the devices. Then, we estimate the effect of imperfections in the fabrication of an array of SQUIDs, which is an unavoidable source of errors in practical situations. We show that the role of the junction capacitance is, in general, negligible, whereas the geometrical inductance has a beneficial effect on the performance of the device. The errors on the areas and junction resistance asymmetries may deteriorate the performance, but their effect can be limited to a large extent by a suitable choice of fabrication parameters.
Mathew, R.; Kumar, A.; Eckel, S.; Jendrzejewski, F.; Campbell, G. K.; Edwards, Mark; Tiesinga, E.
2015-09-01
We present theoretical and experimental analysis of an interferometric measurement of the in situ phase drop across and current flow through a rotating barrier in a toroidal Bose-Einstein condensate (BEC). This experiment is the atomic analog of the rf-superconducting quantum interference device (SQUID). The phase drop is extracted from a spiral-shaped density profile created by the spatial interference of the expanding toroidal BEC and a reference BEC after release from all trapping potentials. We characterize the interferometer when it contains a single particle, which is initially in a coherent superposition of a torus and reference state, as well as when it contains a many-body state in the mean-field approximation. The single-particle picture is sufficient to explain the origin of the spirals, to relate the phase-drop across the barrier to the geometry of a spiral, and to bound the expansion times for which the in situ phase can be accurately determined. Mean-field estimates and numerical simulations show that the interatomic interactions shorten the expansion time scales compared to the single-particle case. Finally, we compare the mean-field simulations with our experimental data and confirm that the interferometer indeed accurately measures the in situ phase drop.
Cibella, S.; Beck, M.; Carelli, P.; Castellano, M. G.; Chiarello, F.; Faist, J.; Leoni, R.; Ortolani, M.; Sabbatini, L.; Scalari, G.; Torrioli, G.; Turcinkova, D.
2012-06-01
We make use of a niobium film to produce a micrometric vacuum-bridge superconducting bolometer responding to THz frequency. The bolometer works anywhere in the temperature range 2-7 K, which can be easily reached in helium bath cryostats or closed-cycle cryocoolers. In this work the bolometer is mounted on a pulse tube refrigerator and operated to measure the equivalent noise power (NEP) and the response to fast (μs) terahertz pulses. The NEP above 100 Hz equals that measured in a liquid helium cryostat showing that potential drawbacks related to the use of a pulse tube refrigerator (like mechanical and thermal oscillations, electromagnetic interference, noise) are irrelevant. At low frequency, instead, the pulse tube expansion-compression cycles originate lines at 1 Hz and harmonics in the noise spectrum. The bolometer was illuminated with THz single pulses coming either from a Quantum Cascade Laser operating at liquid nitrogen temperature or from a frequency-multiplied electronic oscillator. The response of the bolometer to the single pulses show that the device can track signals with a rise time as fast as about 450 ns.
Energy Technology Data Exchange (ETDEWEB)
Pretzell, Alf
2012-07-01
This doctoral thesis was aimed at establishing a set-up with high-temperature superconductor (HTS) radio-frequency (rf) superconducting quantum interference device (SQUID) technology for the detection of magnetic nanoparticles and in particular for testing applications of magnetic nanoparticle immunoassays. It was part of the EU-project ''Biodiagnostics'' running from 2005 to 2008. The method of magnetic binding assays was developed as an alternative to other methods of concentration determination like enzyme linked immunosorbent assay (ELISA), or fluorescent immunoassay. The ELISA has sensitivities down to analyte-concentrations of pg/ml. Multiple incubation and washing steps have to be performed for these techniques, the analyte has to diffuse to the site of binding. The magnetic assay uses magnetic nanoparticles as markers for the substance to be detected. It is being explored by current research and shows similar sensitivity compared to ELISA but in contrast - does not need any washing and can be read out directly after binding - can be applied in solution with opaque media, e.g. blood or muddy water - additionally allows magnetic separation or concentration - in combination with small magnetoresistive or Hall sensors, allows detection of only a few particles or even single beads. For medical or environmental samples, maybe opaque and containing a multitude of substances, it would be advantageous to devise an instrument, which allows to be read out quickly and with high sensitivity. Due to the mentioned items the magnetic assay might be a possibility here.
Graf zu Eulenburg, A
1999-01-01
the best balance and gradient sensitivity at 1kHz were 3x10 sup - sup 3 and 222fT/(cm sq root Hz))) respectively. The measured spatial response to a current carrying wire was in good agreement with a theoretical model. A significant performance improvement was obtained with the development of a single layer gradiometer with 13mm baseline, fabricated on 30x10mm sup 2 bicrystals. For such a device, the gradient sensitivity at 1kHz was 50fT/(cm sq root Hz)) and the gradiometer was used successfully for unshielded magnetocardiography. A parasitic effective area compensation scheme was employed with two neighbouring SQUIDs coupled in an opposite sense to the same gradiometer loop. This improved the balance from the intrinsic value of 10 sup - sup 3 to 3x10 sup - sup 5. This thesis describes several aspects of the development of gradiometers using high temperature Superconducting Quantum Interference Devices (SQUID). The pulsed laser deposition of thin films of YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (YBCO) on Sr...
Quantum critical point for stripe order: An organizing principle of cuprate superconductivity
Energy Technology Data Exchange (ETDEWEB)
Doiron-Leyraud, Nicolas [Departement de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Canada Canadian Institute for Advanced Research, Toronto (Canada); Taillefer, Louis, E-mail: Louis.Taillefer@USherbrooke.ca [Departement de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Canada Canadian Institute for Advanced Research, Toronto (Canada)
2012-11-01
A spin density-wave quantum critical point (QCP) is the central organizing principle of organic, iron-pnictide, heavy-fermion and electron-doped cuprate superconductors. It accounts for the superconducting T{sub c} dome, the non-Fermi-liquid resistivity, and the Fermi-surface reconstruction. Outside the magnetically ordered phase above the QCP, scattering and pairing decrease in parallel as the system moves away from the QCP. Here we argue that a similar scenario, based on a stripe-order QCP, is a central organizing principle of hole-doped cuprate superconductors. Key properties of La{sub 1.8-x}Eu{sub 0.2}Sr{sub x}CuO{sub 4}, La{sub 1.6-x}Nd{sub 0.4}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub y} are naturally unified, including stripe order itself, its QCP, Fermi-surface reconstruction, the linear-T resistivity, and the nematic character of the pseudogap phase.
Connor, C.; Chang, J.; Pines, A.
1990-12-01
We report the application of our dc SQUID (superconducting quantum interference device) spectrometer [C. Connor, J. Chang, and A. Pines, Rev. Sci. Instrum. 61, 1059(1990)] to nuclear quadrupole resonance (NQR) studies of aluminum-27, and boron-11 in crystalline and glassy solids. Our results give e2qQ/h=2.38 MHz and η=0.0 for α-Al2O3 at 4.2 K. For the natural mineral petalite (LiAlSi4O10), we obtain e2qQ/h=4.56 MHz and η=0.47. The quadrupole resonance frequency is 1467 kHz in boron nitride, and in the vicinity of 1300 kHz for various borates in the B2O3ṡxH2O system. The distribution of boron environments in a B2O3 glass gives rise to a linewidth of about 80 kHz in the SQUID detected resonance.
Microwave testing of high-Tc based direct current to a single flux quantum converter
DEFF Research Database (Denmark)
Kaplunenko, V. K.; Fischer, Gerd Michael; Ivanov, Z. G.
1994-01-01
Design, simulation, and experimental investigations of a direct current to a single flux quantum converter loaded with a Josephson transmission line and driven by an external 70 GHz microwave oscillator are reported. The test circuit includes nine YBaCuO Josephson junctions aligned on the grain b...
Optimizing the architecture of SFQ-RDP (Single Flux Quantum- Reconfigurable Datapath)
Mehdipour, Farhad; Honda, Hiroaki; Kataoka, Hiroshi; Inoue, Koji; Murakami, Kazuaki
2009-01-01
A large-scale reconfigurable data-path (LSRDP) processor based on single-flux quantum circuits is designed to overcome the issues originating from the CMOS technology. The LSRDP micro-architecture design procedure and its outcome will be presented in this paper.
Nikulov, A V
2009-01-01
Superconducting loop interrupted by one or three Josephson junctions is considered in many publications as a possible quantum bit, flux qubit, which can be used for creation of quantum computer. But the assumption on superposition of two macroscopically distinct quantum states of superconducting loop contradict to the fundamental law of angular momentum conservation and the universally recognized quantum formalism. Numerous publications devoted to the flux qubit testify to an inadequate interpretation by many authors of paradoxical nature of superposition principle and the subject of quantum description.
Energy Technology Data Exchange (ETDEWEB)
Konoplev, Ivan [Univ. of Oxford (United Kingdom). JAI, Dept. of Physics; Ainsworth, Robert [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Burt, Graeme [Lancaster Univ. (United Kingdom). Cockcroft Inst.; Seryi, Andrei [Univ. of Oxford (United Kingdom). JAI, Dept. of Physics
2016-06-01
The conventional ERLs have limited peak beam current because increasing the beam charge and repetition rate leads to appearance of the beam break-up instabilities. At this stage the highest current, from the SRF ERL, is around 300 mA. A single-turn (the beam will be transported through the accelerating section, interaction point and deceleration section of the AERL only once) Asymmetric Energy Recovery LINAC (AERL) is proposed. The RF cells in different sections of the cavity are tuned in such a way that only operating mode is uniform inside all of the cells. The AERL will drive the electron beams with typical energies of 10 - 30 MeV and peak currents above 1 A, enabling the generation of high flux UV/X-rays and high power coherent THz radiation. We aim to build a copper prototype of the RF cavity for a compact AERL to study its EM properties. The final goal is to build AERL based on the superconducting RF cavity. Preliminary design for AERL's cavity has been developed and will be presented. The results of numerical and analytical models and the next steps toward the AERL operation will also be discussed.
Energy Technology Data Exchange (ETDEWEB)
Konoplev, Ivan [JAI, UK; Ainsworth, Robert [Fermilab; Burt, Graeme [Lancaster U.; Seryi, Andrei [JAI, UK
2016-06-01
The conventional ERLs have limited peak beam current because increasing the beam charge and repetition rate leads to appearance of the beam break-up instabilities. At this stage the highest current, from the SRF ERL, is around 300 mA. A single turn (the beam will be transported through the accelerating section, interaction point and deceleration section of the AERL only once) Asymmetric Energy Recovery LINAC (AERL) is proposed. The RF cells in different sections of the cavity are tuned in such a way that only operating mode is uniform inside all of the cells. The AERL will drive the electron beams with typical energies of 10 - 30 MeV and peak currents above 1 A, enabling the generation of high flux UV/X-rays and high power coherent THz radiation. We aim to build a copper prototype of the RF cavity for a compact AERL to study its EM properties. The final goal is to build AERL based on the superconducting RF cavity. Preliminary design for AERL's cavity has been developed and will be presented. The results of numerical and analytical models and the next steps toward the AERL operation will also be discussed.
Flux quantum tunneling effect and its influence on the experimental critical current density
Institute of Scientific and Technical Information of China (English)
闻海虎; 赵忠贤; GriessenR.
1995-01-01
By using magnetic sweeping method, the temperature and magnetic field dependencies of the experimental current density and the normalized relaxation rate have been obtained. The true critical current density corresponding to the zero activation energy has been carried out based on the collective-pinning and the thermally-activated flux motion models, and therefore the influences of the quantum tunneling effect and the thermal activation effect on the experimental critical current density are distinguished. It is found that, with temperature lower than 10 K, the relaxation rate will not drop to zero when T approaches zero K because of the occurrence of the flux quantum tunneling. This additional flux motion further reduces the experimental critical current density j making it saturated with lowering temperature.
Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, Fang-Cheng; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A
2017-03-06
A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor bismuth tellurohalide BiTeI with giant Rashba spin splitting. In this work, evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted topological quantum phase transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr, while resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that superconductivity may develop from the multivalley semiconductor phase. The superconducting transition temperature, Tc , increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. The results demonstrate that BiTeX (X = I, Br) compounds with nontrivial topology of electronic states display new ground states upon compression.
Takagi, Naofumi; Murakami, Kazuaki; Fujimaki, Akira; Yoshikawa, Nobuyuki; Inoue, Koji; Honda, Hiroaki
We propose a desk-side supercomputer with large-scale reconfigurable data-paths (LSRDPs) using superconducting rapid single-flux-quantum (RSFQ) circuits. It has several sets of computing unit which consists of a general-purpose microprocessor, an LSRDP and a memory. An LSRDP consists of a lot of, e. g., a few thousand, floating-point units (FPUs) and operand routing networks (ORNs) which connect the FPUs. We reconfigure the LSRDP to fit a computation, i. e., a group of floating-point operations, which appears in a ‘for’ loop of numerical programs by setting the route in ORNs before the execution of the loop. We propose to implement the LSRDPs by RSFQ circuits. The processors and the memories can be implemented by semiconductor technology. We expect that a 10 TFLOPS supercomputer, as well as a refrigerating engine, will be housed in a desk-side rack, using a near-future RSFQ process technology, such as 0.35μm process.
Energy Technology Data Exchange (ETDEWEB)
Myers, Whittier Ryan [Univ. of California, Berkeley, CA (United States)
2006-01-01
This dissertation describes magnetic resonance imaging (MRI) of protons performed in a precession field of 132 μT. In order to increase the signal-to-noise ratio (SNR), a pulsed 40-300 mT magnetic field prepolarizes the sample spins and an untuned second-order superconducting gradiometer coupled to a low transition temperature superconducting quantum interference device (SQUID) detects the subsequent 5.6-kHz spin precession. Imaging sequences including multiple echoes and partial Fourier reconstruction are developed. Calculating the SNR of prepolarized SQUID-detected MRI shows that three-dimensional Fourier imaging yields higher SNR than slice-selection imaging. An experimentally demonstrated field-cycling pulse sequence and post-processing algorithm mitigate image artifacts caused by concomitant gradients in low-field MRI. The magnetic field noise of SQUID untuned detection is compared to the noise of SQUID tuned detection, conventional Faraday detection, and the Nyquist noise generated by conducting biological samples. A second-generation microtesla MRI system employing a low-noise SQUID is constructed to increase SNR. A 2.4-m cubic, eddy-current shield with 6-mm thick aluminum walls encloses the experiment to attenuate external noise. The measured noise is 0.75 fT Hz^{-1/2} referred to the bottom gradiometer loop. Solenoids wound from 30-strand braided wire to decrease Nyquist noise and cooled by either liquid nitrogen or water polarize the spins. Copper wire coils wound on wooden supports produce the imaging magnetic fields and field gradients. Water phantom images with 0.8 x 0.8 x 10 mm^{3} resolution have a SNR of 6. Three-dimensional 1.6 x 1.9 x 14 mm^{3} images of bell peppers and 3 x 3 x 26 mm^{3} in vivo images of the human arm are presented. Since contrast based on the transverse spin relaxation rate (T_{1}) is enhanced at low magnetic fields, microtesla MRI could potentially be used for tumor imaging. The
Energy Technology Data Exchange (ETDEWEB)
Wang, W.T., E-mail: wtwang@swjtu.edu.cn [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Southwest Jiaotong University, Mail Stop 165, Chengdu, Sichuan 610031 (China); Pu, M.H.; Lei, M.; Zhang, H.; Wang, Z. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Southwest Jiaotong University, Mail Stop 165, Chengdu, Sichuan 610031 (China); Zhang, H. [Department of Physics, Peking University, Beijing 100871 (China); Cheng, C.H. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Southwest Jiaotong University, Mail Stop 165, Chengdu, Sichuan 610031 (China); Superconductivity Research Group, School of Materials Science and Engineering, University of New South Wale, Sydney, 2052 NSW (Australia); Zhao, Y., E-mail: yzhao@swjtu.edu.cn [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Southwest Jiaotong University, Mail Stop 165, Chengdu, Sichuan 610031 (China); Superconductivity Research Group, School of Materials Science and Engineering, University of New South Wale, Sydney, 2052 NSW (Australia)
2013-10-15
Highlights: • Pure and Co-doped YBCO films were prepared by newly-developed chemical method. • The doped films have much denser and smoother surface microstructures. • Significantly enhanced fux-pinning properties have been obtained for dilute Co-doped flm. -- Abstract: Pure and cobalt-doped superconducting YBa{sub 2}Cu{sub 3}O{sub 7−z} (YBCO) films were prepared on (0 0 l) LaAlO{sub 3} substrate by a newly developed polymer-assisted metal organic deposition method. The cobalt-doped YBCO films display much denser and smoother surface microstructures and the superconducting transition temperature T{sub c} spans a small range of 1.7 K with the doping levels. Significantly enhanced flux-pinning properties have been obtained for dilute cobalt-doped film. This may be attributed to the good grain connections and the effective flux pinning centers introduced by cobalt doping.
Energy Technology Data Exchange (ETDEWEB)
Chen, Lei, E-mail: stclchen1982@163.com [School of Electrical Engineering, Wuhan University, Wuhan 430072 (China); Zheng, Feng; Deng, Changhong; Li, Shichun; Li, Miao; Liu, Hui [School of Electrical Engineering, Wuhan University, Wuhan 430072 (China); Zhu, Lin [Department of Electrical Engineering and Computer Science, University of Tennessee, Knoxville 37996 (United States); Guo, Fang [Department of Substation, Guang Dong Electric Power Design Institute, Guangzhou 510663 (China)
2015-11-15
Highlights: • A modified flux-coupling type SFCL is suggested to enhance the transient performance of a micro-grid. • The SFCL’s main contribution is to improve the micro-grid’s fault ride-through capability. • The SFCL also can make the micro-grid carry out a smooth transition between its grid-connected and islanded modes. • The simulations show that the SFCL can availably strengthen the micro-grid’s voltage and frequency stability. - Abstract: Concerning the application and development of a micro-grid system which is designed to accommodate high penetration of intermittent renewable resources, one of the main issues is related to an increase in the fault-current level. It is crucial to ensure the micro-grid’s operational stability and service reliability when a fault occurs in the main network. In this paper, our research group suggests a modified flux-coupling type superconducting fault current limiter (SFCL) to enhance the transient performance of a typical micro-grid system. The SFCL is installed at the point of common coupling (PCC) between the main network and the micro-grid, and it is expected to actively improve the micro-grid’s fault ride-through capability. And for some specific faults, the micro-grid should disconnect from the main network, and the SFCL’s contribution is to make the micro-grid carry out a smooth transition between its grid-connected and islanded modes. Related theory derivation, technical discussion and simulation analysis are performed. From the demonstrated results, applying the SFCL can effectively limit the fault current, maintain the power balance, and enhance the voltage and frequency stability of the micro-grid.
Chen, Lei; Zheng, Feng; Deng, Changhong; Li, Shichun; Li, Miao; Liu, Hui; Zhu, Lin; Guo, Fang
2015-11-01
Concerning the application and development of a micro-grid system which is designed to accommodate high penetration of intermittent renewable resources, one of the main issues is related to an increase in the fault-current level. It is crucial to ensure the micro-grid's operational stability and service reliability when a fault occurs in the main network. In this paper, our research group suggests a modified flux-coupling type superconducting fault current limiter (SFCL) to enhance the transient performance of a typical micro-grid system. The SFCL is installed at the point of common coupling (PCC) between the main network and the micro-grid, and it is expected to actively improve the micro-grid's fault ride-through capability. And for some specific faults, the micro-grid should disconnect from the main network, and the SFCL's contribution is to make the micro-grid carry out a smooth transition between its grid-connected and islanded modes. Related theory derivation, technical discussion and simulation analysis are performed. From the demonstrated results, applying the SFCL can effectively limit the fault current, maintain the power balance, and enhance the voltage and frequency stability of the micro-grid.
Tuckerman, David B.; Hamilton, Michael C.; Reilly, David J.; Bai, Rujun; Hernandez, George A.; Hornibrook, John M.; Sellers, John A.; Ellis, Charles D.
2016-08-01
We describe progress and initial results achieved towards the goal of developing integrated multi-conductor arrays of shielded controlled-impedance flexible superconducting transmission lines with ultra-miniature cross sections and wide bandwidths (dc to >10 GHz) over meter-scale lengths. Intended primarily for use in future scaled-up quantum computing systems, such flexible thin-film niobium/polyimide ribbon cables could provide a physically compact and ultra-low thermal conductance alternative to the rapidly increasing number of discrete coaxial cables that are currently used by quantum computing experimentalists to transmit signals between the several low-temperature stages (from ˜4 K down to ˜20 mK) of a dilution refrigerator. We have concluded that these structures are technically feasible to fabricate, and so far they have exhibited acceptable thermo-mechanical reliability. S-parameter results are presented for individual 2-metal layer Nb microstrip structures having 50 Ω characteristic impedance; lengths ranging from 50 to 550 mm were successfully fabricated. Solderable pads at the end terminations allowed testing using conventional rf connectors. Weakly coupled open-circuit microstrip resonators provided a sensitive measure of the overall transmission line loss as a function of frequency, temperature, and power. Two common microelectronic-grade polyimide dielectrics, one conventional and the other photo-definable (PI-2611 and HD-4100, respectively) were compared. Our most striking result, not previously reported to our knowledge, was that the dielectric loss tangents of both polyimides, over frequencies from 1 to 20 GHz, are remarkably low at deep cryogenic temperatures, typically 100× smaller than corresponding room temperature values. This enables fairly long-distance (meter-scale) transmission of microwave signals without excessive attenuation, and also permits usefully high rf power levels to be transmitted without creating excessive dielectric
A note on the Poisson bracket of 2d smeared fluxes in loop quantum gravity
Cattaneo, Alberto S
2016-01-01
We show that the non-Abelian nature of geometric fluxes---the corner-stone in the definition of quantum geometry in the framework of loop quantum gravity (LQG)---follows directly form the continuum canonical commutations relations of gravity in connection variables and the validity of the Gauss law. The present treatment simplifies previous formulations and thus identifies more clearly the root of the discreteness of geometric operators in LQG. Our statement generalizes to arbitrary gauge theories and relies only on the validity of the Gauss law.
Magnetic flux periodicities and finite momentum pairing in unconventional superconductors
Energy Technology Data Exchange (ETDEWEB)
Loder, Florian
2009-12-22
This work contains a thorough study of the magnetic flux periodicity of loops of conventional and unconventional, especially d-wave, superconductors. Although already in 1961, several independent works showed that the flux period of a conventional superconducting loop is the superconducting flux quantum hc/2e, this question has never been investigated deeply for unconventional superconductors. And indeed, we show here that d-wave superconducting loops show a basic flux period of the normal flux quantum hc/e, a property originating from the nodal quasi-particle states. This doubling of the flux periodicity is best visible in the persistent current circulating in the loop, and it affects other properties of the superconductor such as the periodicity of d-wave Josephson junctions. In the second part of this work, the theory of electron pairing with finite center-of-mass momentum, necessary for the description of superconducting loops, is extended to systems in zero magnetic field. We show that even in the field free case, an unconventional pairing symmetry can lead to a superconducting ground state with finite-momentum electron pairs. Such a state has an inhomogeneous charge density and therefore is a basis for the description of coexistence of superconductivity and stripe order. (orig.)
Shen, Shengchun; Xing, Ying; Wang, Pengjie; Liu, Haiwen; Fu, Hailong; Zhang, Yangwei; He, Lin; Xie, X. C.; Lin, Xi; Nie, Jiacai; Wang, Jian
2016-10-01
Diverse phenomena emerge at the interface between band insulators LaAl O3 and SrTi O3 , such as superconductivity and ferromagnetism, showing an opportunity for potential applications as well as contributing to fundamental research interests. Here, we report the superconductor-metal transition driven by a perpendicular magnetic field in superconducting two-dimensional electron gas formed at the LaAl O3/SrTi O3(110 ) interface, which offers an appealing platform for quantum phase transition from a superconductor to a weakly localized metal. Interestingly, when approaching the quantum critical point, the dynamic critical exponent is not a constant but a diverging value, which is direct evidence of a quantum Griffiths singularity arising from quenched disorder at ultralow temperatures. Furthermore, the hysteretic property of magnetoresistance is observed at the LaAl O3/SrTi O3(110 ) interface, which suggests the potential coexistence of superconductivity and ferromagnetism.
Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G.; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, F. C.; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A.
2016-01-01
A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor BiTeI with giant Rashba spin splitting. In this work, the evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr while the resist...
Yang, S. Y.; Chieh, J. J.; Wang, W. C.; Yu, C. Y.; Hing, N. S.; Horng, H. E.; Hong, Chin-Yih; Yang, H. C.; Chang, C. F.; Lin, H. Y.
2011-03-01
In this work, we investigate the feasibility of detecting quantitatively DNA molecules utilizing the technology named after the immunomagnetic reduction (IMR) assay. Magnetic nanoparticles dispersed in a phosphate buffer saline solution were bio-functionalized with probing single-strand DNA. A superconducting quantum interference device (SQUID) ac magnetosusceptometer was employed to detect IMR signals related to the concentration of the target DNA. The results reveal that use of IMR assay had merits such as a high convenience level, e.g. wash-free processes and high sensitivity, down to pM, for DNA detection.
Öisjöen, F.; Schneiderman, J. F.; Figueras, G. A.; Chukharkin, M. L.; Kalabukhov, A.; Hedström, A.; Elam, M.; Winkler, D.
2012-03-01
We have performed single- and two-channel high transition temperature (high-Tc) superconducting quantum interference device (SQUID) magnetoencephalography (MEG) recordings of spontaneous brain activity in two healthy human subjects. We demonstrate modulation of two well-known brain rhythms: the occipital alpha rhythm and the mu rhythm found in the motor cortex. We further show that despite higher noise-levels compared to their low-Tc counterparts, high-Tc SQUIDs can be used to detect and record physiologically relevant brain rhythms with comparable signal-to-noise ratios. These results indicate the utility of high-Tc technology in MEG recordings of a broader range of brain activity.
Energy Technology Data Exchange (ETDEWEB)
Walker, M.E.; Nakane, H.; Cochran, A.; Weston, R.G.; Klein, U.; Pegrum, C.M.; Donaldson, G.B. [Department of Physics and Applied Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)
1997-07-01
Novel nondestructive evaluation measurements made using niobium dc superconducting quantum interference devices with integrated asymmetric first-order gradiometers are described. Comparative theoretical and experimental studies of their spatial response have been described, and it is shown that the gradiometric response makes operation possible in an unshielded and electromagnetically noisy environment. As a demonstration of their capabilities, subsurface defects in a multilayer aluminum structure have been located and mapped using induced eddy currents at 70 Hz, with no magnetic shielding around the specimen or cryostat. {copyright} {ital 1997 American Institute of Physics.}
Fan, N. Q.; Clarke, John
1991-06-01
A sensitive spectrometer, based on a dc superconducting quantum interference device, for the direct detection of low-frequency pulsed nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR), is described. The frequency response extends from about 10 to 200 kHz, and the recovery time after the magnetic pulse is removed is typically 50 μs. As examples, NMR spectra are shown from Pt and Cu metal powders in a magnetic field of 6 mT, and NQR spectra are shown from 2D in a tunneling methyl group and 14N in NH4ClO4.
Jia, Dongming; Manz, Jörn; Paulus, Beate; Pohl, Vincent; Tremblay, Jean Christophe; Yang, Yonggang
2017-01-01
We design four linearly x- and y-polarized as well as circularly right (+) and left (-) polarized, resonant π / 2 -laser pulses that prepare the model benzene molecule in four different degenerate superposition states. These consist of equal (0.5) populations of the electronic ground state S0 (1A1g) plus one of four degenerate excited states, all of them accessible by dipole-allowed transitions. Specifically, for the molecule aligned in the xy-plane, these excited states include different complex-valued linear combinations of the 1E1u,x and 1E1u,y degenerate states. As a consequence, the laser pulses induce four different types of periodic adiabatic attosecond (as) charge migrations (AACM) in benzene, all with the same period, 504 as, but with four different types of angular fluxes. One of the characteristic differences of these fluxes are the two angles for zero fluxes, which appear as the instantaneous angular positions of the "source" and "sink" of two equivalent, or nearly equivalent branches of the fluxes which flow in pincer-type patterns from one molecular site (the "source") to the opposite one (the "sink"). These angles of zero fluxes are either fixed at the positions of two opposite carbon nuclei in the yz-symmetry plane, or at the centers of two opposite carbon-carbon bonds in the xz-symmetry plane, or the angles of zero fluxes rotate in angular forward (+) or backward (-) directions, respectively. As a resume, our quantum model simulations demonstrate quantum control of the electronic fluxes during AACM in degenerate superposition states, in the attosecond time domain, with the laser polarization as the key knob for control.
DEFF Research Database (Denmark)
Bukh, K. R.; Jacobsen, Claus Schelde; Hansen, Jørn Bindslev
2000-01-01
The characteristics of the magnetic flux noise in high temperature superconducting thin-films of yttrium-barium-copper-oxide (YBa2Cu3O7) in the vicinity of artificial grain boundaries have been studied by means of a low critical temperature superconducting quantum interference device (SQUID...
Spontaneous fluxoid formation in superconducting loops
DEFF Research Database (Denmark)
Monaco, R.; Mygind, Jesper; Rivers, R.
2009-01-01
a scaling relation on the quenching time τQ, as one would expect if the transition took place as fast as causality permits. However, the observed Zurek-Kibble scaling exponent σ=0.62±0.15 is two times larger than anticipated for large loops. Assuming Gaussian winding number densities we show......We report on the experimental verification of the Zurek-Kibble scenario in an isolated superconducting ring over a wide parameter range. The probability of creating a single flux quantum spontaneously during the fast normal-superconducting phase transition of a wide Nb loop clearly follows...
Gerdel, Katharina; Spielmann, Felix M.; Hammerle, Albin; Wohlfahrt, Georg
2016-04-01
Carbonyl sulfide (COS) is the most abundant sulfur containing trace gas present in the troposphere at concentrations of around 500 ppt. Recent interest in COS by the ecosystem-physiological community has been sparked by the fact that COS co-diffuses into plant leaves pretty much the same way as carbon dioxide (CO2) does, but in contrast to CO2, COS is not known to be emitted by plants. Thus uptake of COS by vegetation has the potential to be used as a tracer for canopy gross photosynthesis, which cannot be measured directly, however represents a key term in the global carbon cycle. Since a few years, quantum cascade laser absorption spectrometers (QCLAS) are commercially available with the precision, sensitivity and time response suitable for eddy covariance (EC) flux measurements. While there exist a handful of published reports on EC flux measurements in the recent literature, no rigorous investigation of the applicability of QCLAS for EC COS flux measurements has been carried out so far, nor have been EC processing and QA/QC steps developed for carbon dioxide and water vapor flux measurements within FLUXNET been assessed for COS. The aim of this study is to close this knowledge gap, to discuss critical steps in the post-processing chain of COS EC flux measurements and to devise best-practice guidelines for COS EC flux data processing. To this end we collected EC COS (and CO2, H2O and CO) flux measurements above a temperate mountain grassland in Austria over the vegetation period 2015 with a commercially available QCLAS. We discuss various aspects of EC data post-processing, in particular issues with the time-lag estimation between sonic anemometer and QCLAS signals and QCLAS time series detrending, as well as QA/QC, in particular flux detection limits, random flux uncertainty, the interaction of various processing steps with common EC QA/QC filters (e.g. detrending and stationarity tests), u*-filtering, etc.
Quintana, C. M.; Chen, Yu; Sank, D.; Petukhov, A. G.; White, T. C.; Kafri, Dvir; Chiaro, B.; Megrant, A.; Barends, R.; Campbell, B.; Chen, Z.; Dunsworth, A.; Fowler, A. G.; Graff, R.; Jeffrey, E.; Kelly, J.; Lucero, E.; Mutus, J. Y.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Shabani, A.; Smelyanskiy, V. N.; Vainsencher, A.; Wenner, J.; Neven, H.; Martinis, John M.
2017-02-01
By analyzing the dissipative dynamics of a tunable gap flux qubit, we extract both sides of its two-sided environmental flux noise spectral density over a range of frequencies around 2 kBT /h ≈1 GHz , allowing for the observation of a classical-quantum crossover. Below the crossover point, the symmetric noise component follows a 1 /f power law that matches the magnitude of the 1 /f noise near 1 Hz. The antisymmetric component displays a 1 /T dependence below 100 mK, providing dynamical evidence for a paramagnetic environment. Extrapolating the two-sided spectrum predicts the linewidth and reorganization energy of incoherent resonant tunneling between flux qubit wells.
Flux-driven quantum phase transitions in two-leg Kitaev ladder topological superconductor systems
Wang, H. Q.; Shao, L. B.; Pan, Y. M.; Shen, R.; Sheng, L.; Xing, D. Y.
2016-12-01
We investigate a two-leg ladder topological superconductor system consisting of two parallel Kitaev chains with interchain coupling. It is found that either uniform or staggered fluxes threading through the ladder holes may change the ladder system from the BDI class in the Altland-Zirnbauer (AZ) classification to the D class. After explicitly calculating the topological Z and/or Z2 indices and from the evolution of Majorana zero energy states (MZES), we obtain the flux-dependent phase diagrams, and find that quantum phase transitions between topologically distinct phases characterized by different number of MZES may happen by simply tuning the flux, which could be realized experimentally in ultracold systems.
Tateiwa, Naoyuki; Haga, Yoshinori; Fisk, Zachary; Ōnuki, Yoshichika
2011-05-01
A miniature opposed-anvil high-pressure cell has been developed for magnetic measurement in a commercial superconducting quantum interference device magnetometer. Non-magnetic anvils made of composite ceramic material were used to generate high-pressure with a Cu-Be gasket. We have examined anvils with different culet sizes (1.8, 1.6, 1.4, 1.2, 1.0, 0.8, and 0.6 mm). The pressure generated at low temperature was determined by the pressure dependence of the superconducting transition of lead (Pb). The maximum pressure P(max) depends on the culet size of the anvil: the values of P(max) are 2.4 and 7.6 GPa for 1.8 and 0.6 mm culet anvils, respectively. We revealed that the composite ceramic anvil has potential to generate high-pressure above 5 GPa. The background magnetization of the Cu-Be gasket is generally two orders of magnitude smaller than the Ni-Cr-Al gasket for the indenter cell. The present cell can be used not only with ferromagnetic and superconducting materials with large magnetization but also with antiferromagnetic compounds with smaller magnetization. The production cost of the present pressure cell is about one tenth of that of a diamond anvil cell. The anvil alignment mechanism is not necessary in the present pressure cell because of the strong fracture toughness (6.5 MPa m(1∕2)) of the composite ceramic anvil. The simplified pressure cell is easy-to-use for researchers who are not familiar with high-pressure technology. Representative results on the magnetization of superconducting MgB(2) and antiferromagnet CePd(5)Al(2) are reported.
Superconducting qubits can be coupled and addressed as trapped ions
Liu, Y. X.; Wei, L. F.; Johansson, J. R.; Tsai, J. S.; Nori, F.
2009-03-01
Exploiting the intrinsic nonlinearity of superconducting Josephson junctions, we propose a scalable circuit with superconducting qubits (SCQs) which is very similar to the successful one now being used for trapped ions. The SCQs are coupled to the ``vibrational'' mode provided by a superconducting LC circuit or its equivalent (e.g., a superconducting quantum interference device). Both single-qubit rotations and qubit-LC-circuit couplings and/or decouplings can be controlled by the frequencies of the time-dependent magnetic fluxes. The circuit is scalable since the qubit-qubit interactions, mediated by the LC circuit, can be selectively performed, and the information transfer can be realized in a controllable way. [4pt] Y.X. Liu, L.F. Wei, J.R. Johansson, J.S. Tsai, F. Nori, Superconducting qubits can be coupled and addressed as trapped ions, Phys. Rev. B 76, 144518 (2007). URL: http://link.aps.org/abstract/PRB/v76/e144518
Energy Technology Data Exchange (ETDEWEB)
Zhang, Z. D. [Department of Physics and Astronomy, SUNY Stony Brook, New York 11794 (United States); Wang, J. [Department of Physics and Astronomy, SUNY Stony Brook, New York 11794 (United States); Department of Chemistry, SUNY Stony Brook, New York 11794 (United States); State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022 (China)
2014-06-28
We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the energy and charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Populations of states give the probabilities of individual states and therefore quantify the population landscape. Both curl flux and coherence depend on steady state population landscape. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in the regime of small tunneling while reduced by the coherence in the regime of large tunneling, due to the non-monotonic relationship between the coherence and tunneling. This is in contrast to the previously found linear relationship. For the systems coupled to bosonic (photonic and phononic) reservoirs the flux is significantly promoted at large voltage while for fermionic (electronic) reservoirs the flux reaches a saturation after a significant enhancement at large voltage due to the Pauli exclusion principle. In view of the system as a quantum heat engine, we studied the non-equilibrium thermodynamics and established the analytical connections of curl quantum flux to the transport quantities such as energy (charge) transfer efficiency, chemical reaction efficiency, energy
Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K
2015-11-13
The family of the superconducting quasiskutterudites (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) features a structural quantum critical point at x(c)=0.9, around which a dome-shaped variation of the superconducting transition temperature T(c) is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x(c), which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2Δ/k(B)T(c) and ΔC/γT(c) beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.
Modeling flux noise in SQUIDs due to hyperfine interactions.
Wu, Jiansheng; Yu, Clare C
2012-06-15
Recent experiments implicate spins on the surface of metals as the source of flux noise in superconducting quantum interference devices and indicate that these spins are able to relax without conserving total magnetization. We present a model of 1/f flux noise in which electron spins on the surface of metals can relax via hyperfine interactions. Our results indicate that flux noise would be significantly reduced in superconducting materials where the most abundant isotopes do not have nuclear moments, such as zinc and lead.
Quantum Bayesian rule for weak measurements of qubits in superconducting circuit QED
Wang, Peiyue; Qin, Lupei; Li, Xin-Qi
2014-01-01
Compared with the quantum trajectory equation, the quantum Bayesian approach has the advantage of being more efficient to infer quantum state under monitoring, based on the integrated output of measurement. For weak measurement of qubits in circuit quantum electrodynamics(cQED), properly accounting for the measurement backaction effects within the Bayesian framework is an important problem of current interest.Elegant work towards this task was carried out by Korotkov in "bad-cavity" and weak-...
Lin, S.; Zhang, G.; Li, C.; Song, Z.
2016-08-01
We study the tight-binding model for a graphene tube with perimeter N threaded by a magnetic field. We show exactly that this model has different nontrivial topological phases as the flux changes. The winding number, as an indicator of topological quantum phase transition (QPT) fixes at N/3 if N/3 equals to its integer part [N/3], otherwise it jumps between [N/3] and [N/3] + 1 periodically as the flux varies a flux quantum. For an open tube with zigzag boundary condition, exact edge states are obtained. There exist two perfect midgap edge states, in which the particle is completely located at the boundary, even for a tube with finite length. The threading flux can be employed to control the quantum states: transferring the perfect edge state from one end to the other, or generating maximal entanglement between them.
Quantum magnetic flux lines, BPS vortex zero modes, and one-loop string tension shifts
Alonso-Izquierdo, A.; Mateos Guilarte, J.; de la Torre Mayado, M.
2016-08-01
Spectral heat kernel/zeta function regularization procedures are employed in this paper to control the divergences arising from vacuum fluctuations of Bogomolnyi-Prasad-Sommerfield vortices in the Abelian Higgs model. Zero modes of vortex fluctuations are the source of difficulties appearing when the standard Gilkey-de Witt expansion is the tool used in the calculations of one-loop shifts of vortex masses and string tensions. A modified GdW expansion is developed to diminish the impact of the infrared divergences due to the vortex zero modes of fluctuation. With this new technique at our disposal we compute the one-loop vortex mass shifts in the planar AHM and the quantum corrections to the string tension of the magnetic flux tubes living in three dimensions. In both cases it is observed that weak repulsive forces surge between these classically noninteracting topological defects caused by vacuum quantum fluctuations.
On quantum magnetic flux lines, BPS vortex zero modes, and one-loop string tension shifts
Alonso-Izquierdo, A; Mayado, M de la Torre
2016-01-01
Spectral heat kernel/zeta function regularization procedures are employed in this paper to control the divergences arising from vacuum fluctuations of Bogomolnyi-Prasad-Sommerfield vortices in the Abelian Higgs model. Zero modes of vortex fluctuations are the source of difficulties appearing when the standard Gilkey-de Witt expansion is performed. A modified GdW expansion is developed to diminish the impact of the infrared divergences due to the vortex zero modes. With this new technique at our disposal we compute the one-loop vortex mass shift in the planar AHM and the quantum corrections to the string tension of the magnetic flux tubes living in three dimensions. In both cases it is observed that weak repulsive forces surge between these classically non interacting topological defects caused by vacuum quantum fluctuations.
Flux Quantum Oscillations in GaAs/InAs Core/shell Nanowires
Grützmacher, D.; Gül, Ö.; Demarina, N.; Lepsa, M.; Hardtdegen, H.; Rieger, T.; Haas, F.; Sladek, K.; Blömers, Ch.; Lüth, H.; Schäpers, Th.
2013-05-01
Phase-based quantum devices are promising for future fast and low-power consumption nanoelectronics since electron interference might be used for the switching function. A robust operation of these devices necessitates nanoscale dimensions. The epitaxial growth of III/V nanowires opens unique possibilities for the realization of low dimensional structures by employing radial and axial heterostructures within the nanowire. Here we discuss the growth of GaAs/InAs core/shell nanowires as well as their magneto-transport properties. The InAs shell forms a tube shaped electron gas with coherent circular states. Magneto transport measurements with a magnetic field parallel to the axis of the nanowire exhibit oscillations in the conductivity with a periodicity of 1/Φ with Φ being the magnetic flux. It is shown that the oscillations can be explained by the number of coherent quantum states participating in the transport.
Nonclassical correlations in superconducting circuits
Energy Technology Data Exchange (ETDEWEB)
Migliore, Rosanna [Dipartimento di Scienze Fisiche ed Astronomiche, Universita di Palermo (Italy); CNR-INFM, UdR CNISM di Palermo, Palermo (Italy); Scala, Matteo [Dipartimento di Scienze Fisiche ed Astronomiche, Universita di Palermo (Italy); Departamento de Optica, Facultad de Fisica, Universidad Complutense, Madrid (Spain); Guccione, Marina; Sanchez-Soto, Luis L. [Dipartimento di Scienze Fisiche ed Astronomiche, Universita di Palermo (Italy); Messina, Antonino [Departamento de Optica, Facultad de Fisica, Universidad Complutense, Madrid (Spain)
2009-05-15
A key step on the road map to solid-state quantum information processing (and to a deeper understanding of many counterintuitive aspects of quantum mechanics) is the generation and manipulation of nonclassical correlations between different quantum systems. Within this framework, we analyze the possibility of generating maximally entangled states in a system of two superconducting flux qubits, as well as the effectof their own environments on the entanglement dynamics. The analysis reported here confirms that the phenomena of sudden birth and sudden death of the entanglement do not depend on the particular measure of the entanglement adopted (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Quantum Dynamics of Nonlinear Cavity Systems
Nation, Paul D.
2010-01-01
We investigate the quantum dynamics of three different configurations of nonlinear cavity systems. To begin, we carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector comprised of a SQUID with a mechanically compliant loop segment. The SQUID is approximated by a nonlinear current-dependent inductor, inducing a flux tunable nonlinear Duffing term in the cavity equation of motion. Expressions are derived for the detector signal ...
Holmqvist, C.; Belzig, W.; Fogelström, M.
2012-08-01
The supercurrent through a quantum point contact coupled to a nanomagnet strongly depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic model to calculate the transport properties of a junction coupled to a spin whose dynamics is modeled as Larmor precession brought about by an external magnetic field and find that the dynamics affects the charge and spin currents by inducing transitions between the continuum states outside the superconducting gap region and the Andreev levels. This redistribution of the quasiparticles leads to a nonequilibrium population of the Andreev levels and an enhancement of the supercurrent which is visible as a modified current-phase relation as well as a nonmonotonous critical current as function of temperature. The nonmonotonous behavior is accompanied by a corresponding change in spin-transfer torques acting on the precessing spin and leads to the possibility of using temperature as a means to tune the back-action on the spin.
Energy Technology Data Exchange (ETDEWEB)
Mizukami, A.; Nishiura, H.; Sakuta, K.; Kobayashi, T
2003-10-15
Magnetocardiographic (MCG) measurement in unshielded environment for practical use requires to suppress the environmental magnetic noise. We have designed the high critical temperature superconducting quantum interference device (High-T{sub c} SQUID) magnetometer with feedforward active noise control (ANC) system to suppress the environmental magnetic noise. The compensatory system consisted of two SQUID magnetometers, a digital signal processor (DSP) and the coil wound around the input magnetometer. The DSP calculated the output data to minimize the environmental noise from the input and reference date and then the coil generated the magnetic field to cancel the environmental noise. This method achieved the effective noise attenuation below 100 Hz about 40 dB. MCG measurement in unshielded environment was also performed.
Jeannic, H Le; Cavaillès, A; Marsili, F; Shaw, M D; Huang, K; Morin, O; Nam, S W; Laurat, J
2016-01-01
We report on high-efficiency superconducting nanowire single-photon detectors based on amorphous WSi and optimized at 1064 nm. At an operating temperature of 1.8 K, we demonstrated a 93% system detection efficiency at this wavelength with a dark noise of a few counts per second. Combined with cavity-enhanced spontaneous parametric down-conversion, this fiber-coupled detector enabled us to generate narrowband single photons with a heralding efficiency greater than 90% and a high spectral brightness of $0.6\\times10^4$ photons/(s$\\cdot$mW$\\cdot$MHz). Beyond single-photon generation at large rate, such high-efficiency detectors open the path to efficient multiple-photon heralding and complex quantum state engineering.
Institute of Scientific and Technical Information of China (English)
Shi Zhen-Gang; Chen Xiong-Wen; Zhu Xi-Xiang; Song Ke-Hui
2009-01-01
This paper proposes a simple scheme for realizing one-qubit and two-qubit quantum gates as well as multiqubit entanglement based on dc-SQUID charge qubits through the control of their coupling to a ID transmission line resonator (TLR). The TLR behaves effectively as a quantum data-bus mode of a harmonic oscillator, which has several practical advantages including strong coupling strength, reproducibility, immunity to 1// noise, and suppressed spontaneous emission. In this protocol, the data-bus does not need to stay adiabatically in its ground state, which results in not only fast quantum operation, but also high-fidelity quantum information processing. Also, it elaborates the transfer process with the 1D transmission line.
Deterministic phase slips in mesoscopic superconducting rings
Petković, I.; Lollo, A.; Glazman, L. I.; Harris, J. G. E.
2016-11-01
The properties of one-dimensional superconductors are strongly influenced by topological fluctuations of the order parameter, known as phase slips, which cause the decay of persistent current in superconducting rings and the appearance of resistance in superconducting wires. Despite extensive work, quantitative studies of phase slips have been limited by uncertainty regarding the order parameter's free-energy landscape. Here we show detailed agreement between measurements of the persistent current in isolated flux-biased rings and Ginzburg-Landau theory over a wide range of temperature, magnetic field and ring size; this agreement provides a quantitative picture of the free-energy landscape. We also demonstrate that phase slips occur deterministically as the barrier separating two competing order parameter configurations vanishes. These results will enable studies of quantum and thermal phase slips in a well-characterized system and will provide access to outstanding questions regarding the nature of one-dimensional superconductivity.
Energy Technology Data Exchange (ETDEWEB)
Du, Renjun
2015-10-30
Bilayer graphene (BLG) p-n junctions made of hBN-BLG-hBN (hexagonal boron nitride) heterostructures enable ballistic transport over long distances. We investigate Fabry-Perot interferences, and detect that the bilayer-like anti-Klein tunneling transits into single-layer-like Klein tunneling when tuning the Fermi level towards the band edges. Furthermore, the proximity-induced superconductivity has been studied in these devices with Al leads.
Falaye, Babatunde James; Silva-Ortigoza, Ramón; Dong, Shi-Hai
2016-01-01
This study presents the confinement influences of Aharonov-Bohm-flux (AB-flux), electric and magnetic fields directed along $z$-axis and encircled by quantum plasmas, on the hydrogen atom. The all-inclusive effects result to a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that, the combined effect of the fields is stronger than solitary effect and consequently, there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for hydrogen atom in quantum plasmas, strong electric field and weak magnetic field are required, where AB-flux field can be used as a regulator. The application of perturbation technique utilized in this paper is not restricted to plasma physics, it can also be applied in molecular physics.
Nie, W; Shi, X; Wei, L F
2010-01-01
In this paper, the scheme of quantum computing based on Stark chirped rapid adiabatic passage (SCRAP) technique [L. F. Wei et al., Phys. Rev. Lett. 100, 113601 (2008)] is extensively applied to implement the quantum-state manipulations in the flux-biased Josephson phase qubits. The broken-parity symmetries of bound states in flux-biased Josephson junctions are utilized to conveniently generate the desirable Stark-shifts. Then, assisted by various transition pulses universal quantum logic gates as well as arbitrary quantum-state preparations could be implemented. Compared with the usual PI-pulses operations widely used in the experiments, the adiabatic population passage proposed here is insensitive the details of the applied pulses and thus the desirable population transfers could be satisfyingly implemented. The experimental feasibility of the proposal is also discussed.
Wu, Jin-Lei; Song, Chong; Xu, Jing; Yu, Lin; Ji, Xin; Zhang, Shou
2016-09-01
An efficient scheme is proposed for generating n-qubit Greenberger-Horne-Zeilinger states of n superconducting qubits separated by (n-1) coplanar waveguide resonators capacitively via adiabatic passage with the help of quantum Zeno dynamics in one step. In the scheme, it is not necessary to precisely control the time of the whole operation and the Rabi frequencies of classical fields because of the introduction of adiabatic passage. The numerical simulations for three-qubit Greenberger-Horne-Zeilinger state show that the scheme is insensitive to the dissipation of the resonators and the energy relaxation of the superconducting qubits. The three-qubit Greenberger-Horne-Zeilinger state can be deterministically generated with comparatively high fidelity in the current experimental conditions, though the scheme is somewhat sensitive to the dephasing of superconducting qubits.
SUPERCONDUCTING PHOTOCATHODES.
Energy Technology Data Exchange (ETDEWEB)
SMEDLEY, J.; RAO, T.; WARREN, J.; SEKUTOWICZ, LANGNER, J.; STRZYZEWSKI, P.; LEFFERS, R.; LIPSKI, A.
2005-10-09
We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.
Josephson ϕ0-junction in nanowire quantum dots
Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S. R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.
2016-06-01
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.
Holonomic quantum computation with superconducting charge-phase qubits in a cavity
Energy Technology Data Exchange (ETDEWEB)
Feng Zhibo [National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093 (China) and Institute for Condensed Matter Physics, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510631 (China)], E-mail: zbfeng010@163.com; Zhang Xinding [Institute for Condensed Matter Physics, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510631 (China)
2008-03-03
We theoretically propose a feasible scheme to realize holonomic quantum computation with charge-phase qubits placed in a microwave cavity. By appropriately adjusting the controllable parameters, each charge-phase qubit is set as an effective four-level subsystem, based on which a universal set of holonomic quantum gates can be realized. Further analysis shows that our system is robust to the first-order fluctuation of the gate charges, and the intrinsic leakages between energy levels can be ignored.
Energy Technology Data Exchange (ETDEWEB)
Fan, Non Q. (San Diego, CA); Clarke, John (Berkeley, CA)
1993-01-01
A spectrometer for measuring the nuclear quadrupole resonance spectra or the zero-field nuclear magnetic resonance spectra generated by a sample is disclosed. The spectrometer uses an amplifier having a dc SQUID operating in a flux-locked loop for generating an amplified output as a function of the intensity of the signal generated by the sample. The flux-locked loop circuit includes an integrator. The amplifier also includes means for preventing the integrator from being driven into saturation. As a result, the time for the flux-locked loop to recover from the excitation pulses generated by the spectrometer is reduced.
Energy Technology Data Exchange (ETDEWEB)
Fan, N.Q.; Clarke, J.
1993-10-19
A spectrometer for measuring the nuclear quadrupole resonance spectra or the zero-field nuclear magnetic resonance spectra generated by a sample is disclosed. The spectrometer uses an amplifier having a dc SQUID operating in a flux-locked loop for generating an amplified output as a function of the intensity of the signal generated by the sample. The flux-locked loop circuit includes an integrator. The amplifier also includes means for preventing the integrator from being driven into saturation. As a result, the time for the flux-locked loop to recover from the excitation pulses generated by the spectrometer is reduced. 7 figures.
Nonlinear optics quantum computing with circuit QED.
Adhikari, Prabin; Hafezi, Mohammad; Taylor, J M
2013-02-08
One approach to quantum information processing is to use photons as quantum bits and rely on linear optical elements for most operations. However, some optical nonlinearity is necessary to enable universal quantum computing. Here, we suggest a circuit-QED approach to nonlinear optics quantum computing in the microwave regime, including a deterministic two-photon phase gate. Our specific example uses a hybrid quantum system comprising a LC resonator coupled to a superconducting flux qubit to implement a nonlinear coupling. Compared to the self-Kerr nonlinearity, we find that our approach has improved tolerance to noise in the qubit while maintaining fast operation.
Quantum Criticality and Superconductivity in SmFe1-xCoxAsO
Kaneko, H.; Yun, Y.; Shumsun, N.; Savinkov, A.; Suzuki, H.; Li, Y. K.; Tao, Q.; Cao, G. H.; Xu, Z. A.
2012-12-01
One of the iron pnictide superconductors, SmFe1-xCoxAsO shows a domelike TC curve against Co concentration x. The parent compound SmFeAsO shows the crystal structure transition and antiferromagnetic spin density wave (SDW) ordering. With increasing x, the structural transition temperature TD and SDW ordering temperature TN decrease and reach 0 K at the critical concentration xC. It is not so clear that the critical concentrations for TD and for TN coincident to each other or not. In our present report, we investigated the structural transition by the low temperature x-ray diffraction and the SDW ordering and the superconducting transition by measuring the magnetization using the SQUID magnetometer, MPMS We determined the phase diagram of TD, TN and the superconductive transition temperature TC against the Co concentration x near the xC precisely. We found that the maximum of TC in domelike shape locates near the xC, suggesting the QCP.
All-high-Tc superconductor rapid-single-flux-quantum circuit operating at ˜30 K
Shokhor, S.; Nadgorny, B.; Gurvitch, M.; Semenov, V.; Polyakov, Yu.; Likharev, K.; Hou, S. Y.; Phillips, Julia M.
1995-11-01
We have implemented a simple circuit of the rapid single-flux-quantum (RSFQ) logic family using a single-layer YBa2Cu3O7-x thin-film structure with 14 in-plane Josephson junctions formed by direct electron beam writing. The circuit includes two dc/SFQ converters, two Josephson transmission lines, a complete RS SFQ flip-flop, and an SFQ/dc converter (readout SQUID). Low-frequency testing has shown that the dc-current-biased circuit operates correctly and reliably at T˜30 K, a few degrees below the effective critical temperature of the junctions. Prospects for a further increase of the operation temperature and implementation of more complex RSFQ circuits are discussed in brief.
Bose-Hubbard models with staggered flux: Quantum phases, collective excitation, and tricriticality
Yao, Juan; Zhang, Shizhong
2014-08-01
We study the quantum phases of a Bose-Hubbard model with staggered magnetic flux in two dimensions, as was realized recently [M. Aidelsburger, M. Atala, M. Lohse, J. T. Barreiro, B. Paredes, and I. Bloch, Phys. Rev. Lett. 107, 255301 (2011), 10.1103/PhysRevLett.107.255301]. Within mean-field theory, we show how the structure of the condensates evolves from the weak- to the strong-coupling limit, exhibiting a tricritical point at the Mott-superfluid transition. Nontrivial topological structures (Dirac points) in the quasiparticle (hole) excitations in the Mott state are found within random phase approximation and we discuss how interaction modifies their structures. The excitation gap in the Mott state closes at different k points when approaching the superfluid states, which is consistent with the findings of mean-field theory.
High-speed rapid single-flux-quantum (RSFQ) Batcher-banyan switching core
Zinoviev, Dmitry Y.
1996-11-01
We have carried out a paper feasibility study of the implementation of most common packet switching cores (crossbar, Batcher-banyan, time-division shared bus, and token ring) using the superconductor rapid single flux quantum (RSFQ) digital technology. According to our estimates, the best performance-to-complexity ratio may be obtained for the Batcher-banyan network. For example, a 128 by 128 switching core with self-routing (but without address translation, contention resolution, and broadcast features), consisting of about 180,000 Josephson junctions with the internal clock frequency of 60 GHz could handle a workload of 7.5 Tbps. This core could fit on a single 1 cm by 1 cm chip and dissipate as low as 45 mW. The estimated parameters are achievable using a simple 1.5-micrometer niobium- trilayer technology.
Design of a datapath for single-flux-quantum microprocessors with multiple ALUs
Tanaka, M.; Kondo, T.; Kawamoto, T.; Kamiya, Y.; Fujiwara, K.; Yamanashi, Y.; Akimoto, A.; Fujimaki, A.; Yoshikawa, N.; Terai, H.; Yorozu, S.
2005-10-01
We have demonstrated the components of datapath toward single-flux-quantum microprocessors based on our new architecture called the forwarding architecture. In the forwarding architecture, we improve the performance by utilizing multiple ALUs to conceal the inefficiency of bit-serial processing. The key components of the datapath are a register file and cascaded ALUs. We have designed the register file to hold four bit-serial data with two read ports and one write port. In each ALU, we have implemented six functionalities: addition, subtraction, logical AND, OR and Exclusive OR operations, and comparison with zero. We have tested the register file and the ALU using high-speed on-chip testing, and confirmed the correct operations up to 18 GHz and 23 GHz, respectively.
40-GHz operation of a single-flux-quantum (SFQ) 4 × 4 switch scheduler
Kameda, Y.; Yorozu, S.; Hashimoto, Y.; Terai, H.; Fujimaki, A.; Yoshikawa, N.
2006-10-01
We designed a single-flux-quantum (SFQ) scheduler for a 4 × 4 network switch. It receives requests serially and arbitrates them. Fair scheduling is achieved by using a round-robin priority pointer at each output port. The pointer is updated so that the input port that was granted permission has the lowest priority in the next scheduling cycle. We divided the scheduler into sub-blocks, which were separately designed. The sub-blocks, which have asynchronous interfaces, were then connected with passive transmission lines. Ladder-type on-chip clock generators were included in the circuit for high-speed operation. Using logic simulation, we verified the scheduler test circuit. The scheduler test circuit was composed of about 3000 Josephson junctions. We tested the scheduler circuit at high speed and confirmed correct operations at over 40 GHz.
Quantum Bayesian rule for weak measurements of qubits in superconducting circuit QED
Wang, Peiyue; Qin, Lupei; Li, Xin-Qi
2014-12-01
Compared with the quantum trajectory equation (QTE), the quantum Bayesian approach has the advantage of being more efficient to infer a quantum state under monitoring, based on the integrated output of measurements. For weak measurement of qubits in circuit quantum electrodynamics (cQED), properly accounting for the measurement backaction effects within the Bayesian framework is an important problem of current interest. Elegant work towards this task was carried out by Korotkov in ‘bad-cavity’ and weak-response limits (Korotkov 2011 Quantum Bayesian approach to circuit QED measurement (arXiv:1111.4016)). In the present work, based on insights from the cavity-field states (dynamics) and the help of an effective QTE, we generalize the results of Korotkov to more general system parameters. The obtained Bayesian rule is in full agreement with Korotkov's result in limiting cases and as well holds satisfactory accuracy in non-limiting cases in comparison with the QTE simulations. We expect the proposed Bayesian rule to be useful for future cQED measurement and control experiments.
Energy Technology Data Exchange (ETDEWEB)
Bubanja, Vladimir, E-mail: vladimir.bubanja@callaghaninnovation.govt.nz
2015-06-15
We present schemes for quantum teleportation and entanglement swapping of electronic spin states in hybrid superconductor–normal-metal systems. The proposed schemes employ subgap transport whereby the lowest order processes involve Cooper pair-electron and double Cooper-pair cotunneling in quantum teleportation and entanglement swapping protocols, respectively. The competition between elastic cotunneling and Cooper-pair splitting results in the success probability of 25% in both cases. Described implementations of these protocols are within reach of present-day experimental techniques.
Search for half-flux-quantum Little-Parks oscillations in mesoscopic rings of Sr2RuO4
Cai, Xinxin; Zakrzewski, Brian; Ying, Yiqun; Fobes, David; Liu, Tijiang; Mao, Zhiqiang; Liu, Ying
2015-03-01
Recent cantilever magnetometry measurements on micron-sized, doubly-connected crystals of Sr2RuO4 have indicated that a half-flux-quantum state may be present in this material. To provide independent evidence for the presence of this new topological object by electrical transport measurements and examine its stability, we carried out Little-Parks (L-P) oscillation measurements, which trace out the phase boundary of a system, on mesoscopic rings of Sr2RuO4. Sr2RuO4 rings were fabricated using a combination of mechanical exfoliation of Sr2RuO4 single crystals, photolithography, and focused ion beam techniques. Without an in-plane magnetic field, large-amplitude resistance oscillations of a full-flux quantum were found as ramping the out-of-plane field. When the in-plane field and the measurement current were sufficiently large, a pronounced second set of resistance peaks was observed in one sample, supporting the existence of half-flux-quantum states. Preparation and measurements on more samples have been carried out and the most recent measurements suggest that the half-flux-quantum states, if indeed present, are likely to be metastable. This work is supported by DOE under Grant DE-FG02-04ER46159.
Diestler, D J
2012-03-22
The Born-Oppenheimer (BO) description of electronically adiabatic molecular processes predicts a vanishing electronic flux density (j(e)), =1/2∫dR[Δ(b) (x;R) - Δ(a) (x;R)] even though the electrons certainly move in response to the movement of the nuclei. This article, the first of a pair, proposes a quantum-mechanical "coupled-channels" (CC) theory that allows the approximate extraction of j(e) from the electronically adiabatic BO wave function . The CC theory is detailed for H(2)(+), in which case j(e) can be resolved into components associated with two channels α (=a,b), each of which corresponds to the "collision" of an "internal" atom α (proton a or b plus electron) with the other nucleus β (proton b or a). The dynamical role of the electron, which accommodates itself instantaneously to the motion of the nuclei, is submerged in effective electronic probability (population) densities, Δ(α), associated with each channel (α). The Δ(α) densities are determined by the (time-independent) BO electronic energy eigenfunction, which depends parametrically on the configuration of the nuclei, the motion of which is governed by the usual BO nuclear Schrödinger equation. Intuitively appealing formal expressions for the electronic flux density are derived for H(2)(+).
Multi-photon dressing of an anharmonic superconducting many-level quantum circuit
Energy Technology Data Exchange (ETDEWEB)
Braumueller, Jochen; Cramer, Joel; Schloer, Steffen; Rotzinger, Hannes; Radtke, Lucas; Lukashenko, Alexander; Yang, Ping; Skacel, Sebastian; Probst, Sebastian; Weides, Martin [Karlsruhe Institute of Technology (KIT), Physikalisches Institut, 76131 Karlsruhe (Germany); Marthaler, Michael; Guo, Lingzhen [Karlsruhe Institute of Technology (KIT), Institut fuer Theoretische Festkoerperphysik, 76131 Karlsruhe (Germany); Ustinov, Alexey V. [Karlsruhe Institute of Technology (KIT), Physikalisches Institut, 76131 Karlsruhe (Germany); National University of Science and Technology MISIS, Moscow 119049 (Russian Federation)
2015-07-01
We report on the investigation of a superconducting anharmonic multi-level circuit that is coupled to a harmonic readout resonator. We observe multi-photon transitions via virtual energy levels of our system up to the fifth excited state. The back-action of these higher-order excitations on our readout device is analyzed quantitatively and demonstrated to be in accordance with theoretical expectation. By applying a strong microwave drive we achieve multi-photon dressing of our system which is dynamically coupled by a weak probe tone. The emerging higher-order Rabi sidebands and associated Autler-Townes splittings involving up to five levels of the investigated anharmonic circuit are observed. Experimental results are in good agreement with master equation simulations.
Epitaxial Al2O3 capacitors for low microwave loss superconducting quantum circuits
Directory of Open Access Journals (Sweden)
K.-H. Cho
2013-10-01
Full Text Available We have characterized the microwave loss of high-Q parallel plate capacitors fabricated from thin-film Al/Al2O3/Re heterostructures on (0001 Al2O3 substrates. The superconductor-insulator-superconductor trilayers were grown in situ in a hybrid deposition system: the epitaxial Re base and polycrystalline Al counterelectrode layers were grown by sputtering, while the epitaxial Al2O3 layer was grown by pulsed laser deposition. Structural analysis indicates a highly crystalline epitaxial Al2O3 layer and sharp interfaces. The measured intrinsic (low-power, low-temperature quality factor of the resonators is as high as 3 × 104. These results indicate that low-loss grown Al2O3 is an attractive candidate dielectric for high-fidelity superconducting qubit circuits.
Superconductive imaging surface magnetometer
Overton, Jr., William C.; van Hulsteyn, David B.; Flynn, Edward R.
1991-01-01
An improved pick-up coil system for use with Superconducting Quantum Interference Device gradiometers and magnetometers involving the use of superconducting plates near conventional pick-up coil arrangements to provide imaging of nearby dipole sources and to deflect environmental magnetic noise away from the pick-up coils. This allows the practice of gradiometry and magnetometry in magnetically unshielded environments. One embodiment uses a hemispherically shaped superconducting plate with interior pick-up coils, allowing brain wave measurements to be made on human patients. another embodiment using flat superconducting plates could be used in non-destructive evaluation of materials.
Reduction of Decoherence in the Flux Qubit
2014-12-08
110.147002 J. Aumentado, K. W. Murch, L. Friedland, I. Siddiqi, R. Vijay, I. Barth, O. Naaman. Quantum fluctuations in the chirped pendulum , Nature...from the reversal of spins on the upper and lower surfaces of the superconducting films. Flux noise has a spectral density that scales as 1/f...fα noise via spin reversals with a broad range of time constants. The temperature dependent exponent α(T) approaches unity as the temperature is
Xiao, Y. M.; Keiser, G. M.
1991-01-01
A magnetic field trapped in a superconducting sphere was examined at temperatures from 4.6 K to 5.5 K. The sphere was the rotor of a precision gyroscope and was made of fused quartz and coated with a sputtered niobium film. The rotor diameter was 3.8 cm. The film thickness was 2.5 microns. The tests were carried out at an ambient magnetic field of about 1 mG. Unexpected instability of the trapped field was observed. The experimental results and possible explanations are presented.
Reproducible Operating Margins on a 72800-Device Digital Superconducting Chip (Open Access)
2015-10-28
Reproducible operating margins on a 72800- device digital superconducting chip Quentin P Herr, Joshua Osborne, Micah J A Stoutimore, Harold Hearne...super- conducting-quantum-interference- device circuits [6–8] and even more directly using magnetic imaging [9]. For larger, digital circuits, flux...design and test of reciprocal quantum logic shift-register yield vehicles consisting of up to 72 800 Josephson junction devices per die, the largest
Tateiwa, Naoyuki; Haga, Yoshinori; Matsuda, Tatsuma D; Fisk, Zachary
2012-05-01
A miniature ceramic anvil high pressure cell (mCAC) was earlier designed by us for magnetic measurements at pressures up to 7.6 GPa in a commercial superconducting quantum interference magnetometer [N. Tateiwa et al., Rev. Sci. Instrum. 82, 053906 (2011)]. Here, we describe methods to generate pressures above 10 GPa in the mCAC. The efficiency of the pressure generation is sharply improved when the Cu-Be gasket is sufficiently preindented. The maximum pressure for the 0.6 mm culet anvils is 12.6 GPa when the Cu-Be gasket is preindented from the initial thickness of 300-60 μm. The 0.5 mm culet anvils were also tested with a rhenium gasket. The maximum pressure attainable in the mCAC is about 13 GPa. The present cell was used to study YbCu(2)Si(2) which shows a pressure induced transition from the non-magnetic to magnetic phases at 8 GPa. We confirm a ferromagnetic transition from the dc magnetization measurement at high pressure. The mCAC can detect the ferromagnetic ordered state whose spontaneous magnetic moment is smaller than 1 μ(B) per unit cell. The high sensitivity for magnetic measurements in the mCAC may result from the simplicity of cell structure. The present study shows the availability of the mCAC for precise magnetic measurements at pressures above 10 GPa.
Dong, Bing; Ding, G. H.; Lei, X. L.
2017-01-01
We present a theoretical investigation for the full counting statistics of the Andreev tunneling through a quantum dot (QD) embedded between superconducting (SC) and normal leads in the presence of a strong on-site electron-phonon interaction using nonequilibrium Green function method. For this purpose, we generalize the dressed tunneling approximation (DTA) recently developed in dealing with inelastic tunneling in a normal QD system to the Andreev transport issue. This method takes account of vibrational effect in evaluation of electronic tunneling self energy in comparison with other simple approaches and meanwhile allows us to derive an explicit analytical formula for the cumulant generating function at the subgap region. We then analyze the interplay of polaronic and SC proximity effects on the Andreev reflection spectrum, current-voltage characteristics, and current fluctuations of the hybrid system. Our main findings include: (1) no phonon side peaks in the linear Andreev conductance; (2) a negative differential conductance stemming from the suppressed Andreev reflection spectrum; (3) a novel inelastic resonant peak in the differential conductance due to phonon assisted Andreev reflection; (4) enhancement or suppression of shot noise for the symmetric or asymmetric tunnel-coupling system, respectively.
Advances in quantum control of three-level superconducting circuit architectures
Energy Technology Data Exchange (ETDEWEB)
Falci, G.; Paladino, E. [Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); CNR-IMM UOS Universita (MATIS), Consiglio Nazionale delle Ricerche, Catania (Italy); INFN, Sezione di Catania (Italy); Di Stefano, P.G. [Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen' s University Belfast(United Kingdom); Ridolfo, A.; D' Arrigo, A. [Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); Paraoanu, G.S. [Low Temperature Laboratory, Department of Applied Physics, Aalto University School of Science (Finland)
2017-06-15
Advanced control in Lambda (Λ) scheme of a solid state architecture of artificial atoms and quantized modes would allow the translation to the solid-state realm of a whole class of phenomena from quantum optics, thus exploiting new physics emerging in larger integrated quantum networks and for stronger couplings. However control solid-state devices has constraints coming from selection rules, due to symmetries which on the other hand yield protection from decoherence, and from design issues, for instance that coupling to microwave cavities is not directly switchable. We present two new schemes for the Λ-STIRAP control problem with the constraint of one or two classical driving fields being always-on. We show how these protocols are converted to apply to circuit-QED architectures. We finally illustrate an application to coherent spectroscopy of the so called ultrastrong atom-cavity coupling regime. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Development of a NbN Deposition Process for Superconducting Quantum Sensors
Glowacka, D M; Withington, S; Muhammad, H; Yassin, G; Tan, B K
2014-01-01
We have carried out a detailed programme to explore the superconducting characteristics of reactive DC-magnetron sputtered NbN. The basic principle is to ignite a plasma using argon, and then to introduce a small additional nitrogen flow to achieve the nitridation of a Nb target. Subsequent sputtering leads to the deposition of NbN onto the host substrate. The characteristics of a sputtered film depend on a number of parameters: argon pressure, nitrogen flow rate and time-evolution profile, substrate material, etc. Crucially, the hysteresis in the target voltage as a function of the nitrogen flow can be used to provide a highly effective monitor of nitrogen consumption during the reactive process. By studying these dependencies we have been able to achieve highly reproducible film characteristics on sapphire, silicon dioxide on silicon, and silicon nitride on silicon. Intrinsic film stress was minimised by optimising the argon pressure, giving NbN films having Tc = 14.65 K. In the paper, we report characteris...
Development of a NbN Deposition Process for Superconducting Quantum Sensors
Glowacka, D M; Withington, S; Muhammad, H; Yassin, G
2014-01-01
We have carried out a detailed programme to explore the superconducting characteristics of reactive DC-magnetron sputtered NbN. The basic principle is to ignite a plasma using argon, and then to introduce a small additional nitrogen flow to achieve the nitridation of a Nb target. Subsequent sputtering leads to the deposition of NbN onto the host substrate. The characteristics of a sputtered film depend on a number of parameters: argon pressure, nitrogen flow rate and time-evolution profile, substrate material, etc. Crucially, the hysteresis in the target voltage as a function of the nitrogen flow can be used to provide a highly effective monitor of nitrogen consumption during the reactive process. By studying these dependencies we have been able to achieve highly reproducible film characteristics on sapphire, silicon dioxide on silicon, and silicon nitride on silicon. Intrinsic film stress was minimised by optimising the argon pressure, giving NbN films having Tc = 14.65 K. In the paper, we report characteris...
Varma, Chandra M.
2016-08-01
The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum \\mathbf{q} , measured from the ordering vector, and of the frequency ω and the temperature T which scale as \\tanh (ω /2T) at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy \\propto \\text{max}(ω,T) for all momenta, a resistivity \\propto T , a T\\ln T contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle-particle vertex in the d-wave channel is the same as the irreducible
Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Kambe, S.; Araki, S.
2015-05-01
Our measurements of the Co 59 NMR spin-spin relaxation in URh0.9Co0.1Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at HR≈13 T , around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We map out the strength of spin fluctuations in the (Hb,Hc ) plane of magnetic field components and show that critical fluctuations develop in the same limited region near the field HR as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum critical end points.
Flux Pinning Properties and Magnetic Relaxation of Superconducting SmFe0.9Co0.1AsO
Zhuang, J. C.; Sun, Y.; Ding, Y.; Yuan, F. F.; Liu, J. T.; Shi, Z. X.; Li, X. W.
2012-12-01
Magnetic Co ion doped SmFeAsO polycrystal was synthesized via solid-state reaction. Resistivity, SEM and magnetic hysteresis loops (MHLs) were measured to investigate magnetic properties of the sample. Critical current densities as well as the flux pinning forces densities were estimated from MHLs. This paper reports for the first time the research of superconducting MHLs as well as magnetic relaxation properties of SmFe0.9Co0.1AsO. Results suggest that: (i) A tail effect in the resistivity measurement together with the rapid decrease in critical current densities at low fields shows the evidence for granularity of the sample; (ii) The asymmetry of the MHLs may be caused by the Bean-Livingstone (BL) surface pinning or granular nature, and none of theoretical models are suitable to the scaling behaviors of flux pinning forces densities; (iii) The anomalous tendency of the temperature dependence of magnetic relaxation rate as well as the effective pinning energy were observed, which may be attributed to the competition between the bulk pinning and the BL surface pinning.
DEFF Research Database (Denmark)
Eskildsen, M.R.; Abrahamsen, A.B.; Kogan, V.G.;
2001-01-01
We have investigated the temperature dependence of the H parallel to c flux line lattice structural phase transition from square to hexagonal symmetry, in the tetragonal superconductor LuNi2B2C (T-c = 16.6 K). At temperatures below 10 K the transition onset field, H-2(T), is only weakly temperature...... dependent. Above 10 K, H-2(T) rises sharply, bending away from the upper critical field. This contradicts theoretical predictions of H-2(T) merging with the upper critical field and suggests that just below the H-c2(T) curve the flux line lattice might be hexagonal....
Quantum-limited detection of millimeter waves using superconducting tunnel junctions
Energy Technology Data Exchange (ETDEWEB)
Mears, C.A.
1991-09-01
The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus_minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker`s theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.
Quantum-limited detection of millimeter waves using superconducting tunnel junctions
Energy Technology Data Exchange (ETDEWEB)
Mears, C.A.
1991-09-01
The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker's theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.
Preliminary design of the advanced quantum beam source
Energy Technology Data Exchange (ETDEWEB)
Lee, Byung Cheol; Lee, Jong Min; Jeong, Young Uk; Cho, Sung Oh; Yoo, Jae Gwon; Park, Seong Hee
2000-07-01
The preliminary design of the advanced quantum beam source based on a superconducting electron accelerator is presented. The advanced quantum beams include: high power free electron lasers, monochromatic X-rays and {gamma}-rays, high-power medium-energy electrons, high-flux pulsed neutrons, and high-flux monochromatic slow positron beam. The AQBS system is being re-designed, assuming that the SPS superconducting RF cavities used for LEP at CERN will revived as a main accelerator of the AQBS system at KAERI, after the decommissioning of LEP at the end of 2000. Technical issues of using the SPS superconducting RF cavities for the AQBS project are discussed in this report. The advanced quantum beams will be used for advanced researches in science and industries.
DEFF Research Database (Denmark)
Yurchenko, V.V.; Qviller, A.J.; Mozhaev, P.B.
2010-01-01
directions of the current flow we determine the anisotropy parameter of the in-plane current, as well as its field and temperature dependences. The artificially introduced defects also have a dramatic effect on the dynamics of the flux propagation: for 10 degrees
Design of a pipelined 8-bit-serial single-flux-quantum microprocessor with multiple ALUs
Energy Technology Data Exchange (ETDEWEB)
Tanaka, M [Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Kawamoto, T [Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yamanashi, Y [Yokohama National University, 79-5 Tokiwa-dai, Hodogaya-ku, Yokohama 240-8501 (Japan); Kamiya, Y [Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Akimoto, A [Yokohama National University, 79-5 Tokiwa-dai, Hodogaya-ku, Yokohama 240-8501 (Japan); Fujiwara, K [Yokohama National University, 79-5 Tokiwa-dai, Hodogaya-ku, Yokohama 240-8501 (Japan); Fujimaki, A [Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yoshikawa, N [Yokohama National University, 79-5 Tokiwa-dai, Hodogaya-ku, Yokohama 240-8501 (Japan); Terai, H [National Institute of Information and Communications Technology, 588-2 Iwaoka, Nishi-ku, Kobe 651-2492 (Japan); Yorozu, S [International Superconductivity Technology Center/Superconductivity Research Laboratory, 34 Miyukigaoka, Tsukuba 305-8501 (Japan)
2006-05-15
We have designed a pipelined 8-bit-serial single-flux-quantum microprocessor with multiple ALUs, called CORE1 {beta}. In the CORE1 {beta}, two ALUs connected in cascade enable us to perform two calculations on serial data using a register-to-register instruction, to enhance the peak performance. In addition, we have introduced pipelining to boost the performance. Although the pipelining is a difficult technique that requires a complex design in the datapath, we have implemented a simplified pipeline with seven stages by using two techniques. One is the separation of clock signals for pipelining and bit processing, and the other is the introduction of new buffers driven by independent clock signals for reading and writing flexibly in order to ease the difficulty in timing design between the register file and the ALUs. According to the logic simulation, the peak performance of the designed microprocessor is estimated to be 1500 million operations per second with a power consumption of 3.3 mW. We have fabricated the CORE1 {beta} chip by using the NEC 2.5 kA cm{sup -2} niobium standard process, and confirmed the correct operations of several instructions using high-speed clocks.
Design of a pipelined 8-bit-serial single-flux-quantum microprocessor with multiple ALUs
Tanaka, M.; Kawamoto, T.; Yamanashi, Y.; Kamiya, Y.; Akimoto, A.; Fujiwara, K.; Fujimaki, A.; Yoshikawa, N.; Terai, H.; Yorozu, S.
2006-05-01
We have designed a pipelined 8-bit-serial single-flux-quantum microprocessor with multiple ALUs, called CORE1 β. In the CORE1 β, two ALUs connected in cascade enable us to perform two calculations on serial data using a register-to-register instruction, to enhance the peak performance. In addition, we have introduced pipelining to boost the performance. Although the pipelining is a difficult technique that requires a complex design in the datapath, we have implemented a simplified pipeline with seven stages by using two techniques. One is the separation of clock signals for pipelining and bit processing, and the other is the introduction of new buffers driven by independent clock signals for reading and writing flexibly in order to ease the difficulty in timing design between the register file and the ALUs. According to the logic simulation, the peak performance of the designed microprocessor is estimated to be 1500 million operations per second with a power consumption of 3.3 mW. We have fabricated the CORE1 β chip by using the NEC 2.5 kA cm-2 niobium standard process, and confirmed the correct operations of several instructions using high-speed clocks.
Entangled States in a Single-Qubit Structure with SQUID Coupled with a Super-conducting Resonator
Institute of Scientific and Technical Information of China (English)
SONG Jian-Wen; LIANG Bao-Long; HAI Wen-Hua; WANG Ji-Suo; ZHONG Hong-Hua; MENG Xiang-Guo; LUO Xiao-Bing
2008-01-01
In this paper, the number-phase quantization scheme of the mesoscopic circuit, which consists of a single-qubit structure with superconducting quantum interference device coupled with a super-conducting resonator, is given. By introducing a unitary matrix and by means of spectral decomposition, the Hamiltonian operator of the system is exactly formulated in compact forms in spin-1/2 notation. The eigenvalues and the eigenstates of the system are investigated. It is found that using this system the entangled states can not only be prepared, but also be manipulated by tuning the magnetic flux through the super-conducting loop.
Energy Technology Data Exchange (ETDEWEB)
Asai, Hidehiro, E-mail: hd-asai@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ota, Yukihiro [CCSE, Japan Atomic Energy Agency, Kashiwa, Chiba 277-8587 (Japan); Kawabata, Shiro [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Nori, Franco [CEMS, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 (United States)
2014-09-15
Highlights: • We study MQT in Josephson junctions composed of multi-gap superconductors. • We derive a formula of the MQT escape rate for multiple phase differences. • We investigate the effect of inter-band phase fluctuation on MQT. • The MQT escape rate is significantly enhanced by the inter-band phase fluctuation. - Abstract: We theoretically investigate macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multi-gap superconductor. In such Josephson junctions, phase differences for each tunneling channel are defined, and the fluctuation of the relative phase differences appear which is referred to as Josephson–Leggett’s mode. We take into account the effect of the fluctuation in the tunneling process and calculate the MQT escape rate for various junction parameters. We show that the fluctuation of relative phase differences drastically enhances the escape rate.
Quantum criticality of D-wave quasiparticles and superconducting phase fluctuations.
Vafek, Oskar; Tesanović, Zlatko
2003-12-05
We present finite temperature (T) extension of the (2+1)-dimensional QED (QED3) theory of under-doped cuprates. The theory describes nodal quasiparticles whose interactions with quantum proliferated hc/2e vortex-antivortex pairs are represented by an emergent U(1) gauge field. Finite T introduces a scale beyond which the spatial fluctuations of vorticity are suppressed. As a result, the spin susceptibility of the pseudogap state is bounded by T2 at low T and crosses over to approximately T at higher T, while the low-T specific heat scales as T2, reflecting the thermodynamics of QED3. The Wilson ratio vanishes as T-->0; the pseudogap state is a "thermal (semi)metal" but a "spin-charge dielectric." This non-Fermi liquid behavior originates from two general principles: spin correlations induced by "gauge" interactions of quasiparticles and fluctuating vortices and the "relativistic" scaling of the T=0 fixed point.
Spin-orbit Josephson ϕ0-junction in nanowire quantum dots
Szombati, Daniel; Nadj-Perge, Stevan; Car, Diana; Bakkers, Erik; Kouwenhoven, Leo
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads and it is strictly zero when ϕ vanishes, due to the chiral and time reversal symmetry of the Cooper pair tunneling process. Only if these underlying symmetries are broken the supercurrent for ϕ = 0 may be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0. Here, for the first time, we report such Josephson ϕ0-junction. Our realization is based on a nanowire quantum dot. We use a quantum interferometer device in order to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results have possible far reaching implications for superconducting flux and phase defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.
Diestler, D J; Kenfack, A; Manz, J; Paulus, B
2012-03-22
This article presents the results of the first quantum simulations of the electronic flux density (j(e)) by the "coupled-channels" (CC) theory, the fundamentals of which are presented in the previous article [Diestler, D. J. J. Phys. Chem. A 2012, DOI: 10.1021/jp207843z]. The principal advantage of the CC scheme is that it employs exclusively standard methods of quantum chemistry and quantum dynamics within the framework of the Born-Oppenheimer approximation (BOA). The CC theory goes beyond the BOA in that it yields a nonzero j(e) for electronically adiabatic processes, in contradistinction to the BOA itself, which always gives j(e) = 0. The CC is applied to oriented H(2)(+) vibrating in the electronic ground state ((2)Σ(g)(+)), for which the nuclear and electronic flux densities evolve on a common time scale of about 22 fs per vibrational period. The system is chosen as a touchstone for the CC theory, because it is the only one for which highly accurate flux densities have been calculated numerically without invoking the BOA [Barth et al, Chem. Phys. Lett. 2009, 481, 118]. Good agreement between CC and accurate results supports the CC approach, another advantage of which is that it allows a transparent interpretation of the temporal and spatial properties of j(e).
Wu, C. C.; Hong, B. F.; Wu, B. H.; Yang, S. Y.; Horng, H. E.; Yang, H. C.; Tseng, W. Y. Isaac; Tseng, W. K.; Liu, Y. B.; Lin, L. C.; Lu, L. S.; Lee, Y. H.
2007-01-01
In this work, the authors used a superconducting quantum interference device (SQUID) magnetocardiography (MCG) system consisted of 64-channel low-transition-temperature SQUID gradiometers to detect the MCG signals of hepercholesterolemic rabbits. In addition, the MCG signals were recorded before and after the injection of magnetic nanoparticles into the rabbits' ear veins to investigate the effects of magnetic nanoparticles on the MCG signals. These MCG data were compared to those of normal rabbits to reveal the feasibility for early detection of the electromagnetic changes induced by hypercholesterolemia using MCG with the assistance of magnetic nanoparticle injection.
Yang, Chui-Ping; Han, Siyuan
2004-12-01
A scheme is proposed for generating Greenberger-Horne-Zeilinger (GHZ) entangled states of multiple superconducting quantum-interference device (SQUID) qubits by the use of a microwave cavity. The scheme operates essentially by creating a single photon through an auxiliary SQUID built in the cavity and performing a joint multiqubit phase shift with assistance of the cavity photon. It is shown that entanglement can be generated using this method, deterministic and independent of the number of SQUID qubits. In addition, we show that the present method can be applied to preparing many atoms in a GHZ entangled state, with tolerance to energy relaxation during the operation.
Zheng, An-Shou; Cheng, Yong-Jin; Liu, Ji-Bing; Li, Tie-Ping
We propose an alternative scheme to prepare the Greenberg-Horne-Zeilinger (GHZ) state and realize a SWAP gate by using Superconducting Quantum-interference devices (SQUIDs) coupled to a cavity. The present scheme, based on the adiabatic evolution of dark state, constitutes a decoherence-free method in the sense that spontaneous emission and cavity damping are avoided. Besides, the standard GHZ state can be directly obtained without measurement or any auxiliary SQUIDs and the construction of the SWAP gate does not require a composition of elementary gates from a universal set. Thus the procedure is simplified and decoherence is greatly suppressed.
Solving a quantum chemistry equations and high-temperature superconductivity problems
Liverts, E Z
2000-01-01
The conventional technique for solving the equation of quantum chemistry (of solids) is unusually extended to the structures possessing certain symmetries. The extension proposed gives a chance to find unoccupied electronic states located lower than the Fermi level of the ground state of a specific system. Such states can be treated as 'spectral holes'. Application of this technique, in particular, when calculating the electronic structure of the HTSC-compound YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (0<= delta<=1) results in the following. For all versions of the examined charge distributions over a crystal lattice, spectral holes of high spatial localization are found. The 'spatial spectral holes' are mainly located at the p sub y -orbitals of the apex oxygens. These orbitals overlap and form linear chains which are parallel too but do not coincide with the known Cu(1)-O chains which disappear when delta is close tio 1. One can suppose that these linear chains of the overlapping hole states from a su...
Nonstationary Superconductivity: Quantum Dissipation and Time-Dependent Ginzburg-Landau Equation
Directory of Open Access Journals (Sweden)
Anatoly A. Barybin
2011-01-01
Full Text Available Transport equations of the macroscopic superfluid dynamics are revised on the basis of a combination of the conventional (stationary Ginzburg-Landau equation and Schrödinger's equation for the macroscopic wave function (often called the order parameter by using the well-known Madelung-Feynman approach to representation of the quantum-mechanical equations in hydrodynamic form. Such an approach has given (a three different contributions to the resulting chemical potential for the superfluid component, (b a general hydrodynamic equation of superfluid motion, (c the continuity equation for superfluid flow with a relaxation term involving the phenomenological parameters GL and GL, (d a new version of the time-dependent Ginzburg-Landau equation for the modulus of the order parameter which takes into account dissipation effects and reflects the charge conservation property for the superfluid component. The conventional Ginzburg-Landau equation also follows from our continuity equation as a particular case of stationarity. All the results obtained are mutually consistent within the scope of the chosen phenomenological description and, being model-neutral, applicable to both the low-c and high-c superconductors.
Weston, Joseph; Waintal, Xavier
2016-04-01
We report on a "source-sink" algorithm which allows one to calculate time-resolved physical quantities from a general nanoelectronic quantum system (described by an arbitrary time-dependent quadratic Hamiltonian) connected to infinite electrodes. Although mathematically equivalent to the nonequilibrium Green's function formalism, the approach is based on the scattering wave functions of the system. It amounts to solving a set of generalized Schrödinger equations that include an additional "source" term (coming from the time-dependent perturbation) and an absorbing "sink" term (the electrodes). The algorithm execution time scales linearly with both system size and simulation time, allowing one to simulate large systems (currently around 106 degrees of freedom) and/or large times (currently around 105 times the smallest time scale of the system). As an application we calculate the current-voltage characteristics of a Josephson junction for both short and long junctions, and recover the multiple Andreev reflection physics. We also discuss two intrinsically time-dependent situations: the relaxation time of a Josephson junction after a quench of the voltage bias, and the propagation of voltage pulses through a Josephson junction. In the case of a ballistic, long Josephson junction, we predict that a fast voltage pulse creates an oscillatory current whose frequency is controlled by the Thouless energy of the normal part. A similar effect is found for short junctions; a voltage pulse produces an oscillating current which, in the absence of electromagnetic environment, does not relax.
Paul, Ganesh C.; Saha, Arijit
2017-01-01
We theoretically investigate the phenomena of adiabatic quantum charge pumping through a normal-insulator-superconductor-insulator-normal (NISIN) setup of silicene within the scattering matrix formalism. Assuming a thin barrier limit, we consider the strength of the two barriers (χ1 and χ2) as the two pumping parameters in the adiabatic regime. Within this geometry, we obtain crossed Andreev reflection (CAR) with probability unity in the χ1-χ2 plane without concomitant transmission or elastic co-tunneling. Tunability of the band gap at the Dirac point by applying an external electric field perpendicular to the silicene sheet and variation of the chemical potential at the normal silicene region, open up the possibility of achieving either a perfect CAR or transmission process through our setup. This resonant behavior is periodic with the barrier strengths. We analyze the behavior of the pumped charge through the NISIN structure as a function of the pumping strength and angles of the incident electrons. We show that large (Q ˜2 e ) pumped charge can be obtained through our geometry when the pumping contour encloses either the CAR or transmission resonance in the pumping parameter space. We discuss possible experimental feasibility of our theoretical predictions.
Flux qubit to a transmission line
Energy Technology Data Exchange (ETDEWEB)
Haeberlein, Max; Baust, Alexander; Zhong, Ling; Gross, Rudolf [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Physik-Department, TU Muenchen, Garching (Germany); Nanosystems Initiative Munich (NIM), Muenchen (Germany); Anderson, Gustav; Wang, Lujun; Eder, Peter; Fischer, Michael; Goetz, Jan; Xie, Edwar; Schwarz, Manuel; Wulschner, Karl Friedrich; Deppe, Frank; Fedorov, Kirill; Huebl, Hans; Menzel, Edwin [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Physik-Department, TU Muenchen, Garching (Germany); Marx, Achim [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany)
2015-07-01
Within the last decade, superconducting qubits coupled to microwave resonators have been extensively studied within the framework of quantum electrodynamics. Ultimately, quantum computing seems within reach in such architectures. However, error correction schemes are necessary to achieve the required fidelity in multi-qubit operations, drastically increasing the number of qubits involved. In this work, we couple a flux qubit to a transmission line where it interacts with itinerant microwave photons granting access to all-optical quantum computing. In this approach, travelling photons generate entanglement between two waveguides, containing the qubit information. In this presentation, we show experimental data on flux qubits coupled to transmission lines. Furthermore, we will discuss entanglement generation between two separate paths.
Superconductive combinational logic circuit using magnetically coupled SQUID array
Energy Technology Data Exchange (ETDEWEB)
Yamanashi, Y., E-mail: yamanasi@ynu.ac.j [Interdisciplinary Research Center, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501 (Japan); Umeda, K.; Sai, K. [Department of Electrical and Computer Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501 (Japan)
2010-11-01
In this paper, we propose the development of superconductive combinational logic circuits. One of the difficulties in designing superconductive single-flux-quantum (SFQ) digital circuits can be attributed to the fundamental nature of the SFQ circuits, in which all logic gates have latching functions and are based on sequential logic. The design of ultralow-power superconductive digital circuits can be facilitated by the development of superconductive combinational logic circuits in which the output is a function of only the present input. This is because superconductive combinational logic circuits do not require determination of the timing adjustment and clocking scheme. Moreover, semiconductor design tools can be used to design digital circuits because CMOS logic gates are based on combinational logic. The proposed superconductive combinational logic circuits comprise a magnetically coupled SQUID array. By adjusting the circuit parameters and coupling strengths between neighboring SQUIDs, fundamental combinational logic gates, including the AND, OR, and NOT gates, can be built. We have verified the accuracy of the operations of the fundamental logic gates by analog circuit simulations.
Javerzac-Galy, C.; Plekhanov, K.; Bernier, N. R.; Toth, L. D.; Feofanov, A. K.; Kippenberg, T. J.
2016-11-01
We propose a device architecture capable of direct quantum coherent electro-optical conversion of microwave-to-optical photons. The hybrid system consists of a planar superconducting microwave circuit coupled to an integrated whispering-gallery-mode microresonator made from an electro-optical material. We show that by exploiting the large vacuum electric field of the planar microwave resonator, electro-optical (vacuum) coupling strengths g0 as large as ˜2 π O (10 -100 ) kHz are achievable with currently available technology—a more than 3 orders of magnitude improvement over prior designs and realizations. Operating at millikelvin temperatures, such a converter would enable high-efficiency conversion of microwave-to-optical photons. We analyze the added noise and show that maximum quantum coherent conversion efficiency is achieved for a multiphoton cooperativity of unity which can be reached with optical power as low as O (1 ) mW.
Imprinting superconducting vortex footsteps in a magnetic layer.
Brisbois, Jérémy; Motta, Maycon; Avila, Jonathan I; Shaw, Gorky; Devillers, Thibaut; Dempsey, Nora M; Veerapandian, Savita K P; Colson, Pierre; Vanderheyden, Benoît; Vanderbemden, Philippe; Ortiz, Wilson A; Nguyen, Ngoc Duy; Kramer, Roman B G; Silhanek, Alejandro V
2016-06-06
Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories.
Superconductivity in doped insulators
Energy Technology Data Exchange (ETDEWEB)
Emery, V.J. [Brookhaven National Lab., Upton, NY (United States); Kivelson, S.A. [California Univ., Los Angeles, CA (United States). Dept. of Physics
1995-12-31
It is shown that many synthetic metals, including high temperature superconductors are ``bad metals``, with such a poor conductivity that the usual meanfield theory of superconductivity breaks down because of anomalously large classical and quantum fluctuations of the phase of the superconducting order parameter. It is argued that the supression of a first order phase transition (phase separation) by the long-range Coulomb interaction leads to high temperature superconductivity accompanied by static or dynamical charge inhomogeneIty. Evidence in support of this picture for high temperature superconductors is described.
Thermally activated flux flow in FeSe0.5Te0.5 superconducting single crystal
Hamad, R. M.; Kayed, T. S.; Kunwar, S.; Ziq, Kh A.
2017-07-01
The current-voltage (J-E) isotherms of single crystal FeSe0.5Te0.5 sample have been measured at several temperatures near the transition temperature (Tc) and under applied magnetic fields (H). A power law (E ˜ Jβ ) has been used to fit the data and evaluate the activation energy Uo (T) using β = Uo/kBT. At low current density (J > Jc vortex flux flow (FF) behavior is expected. The effects of applied magnetic field on FF and TAFF also been investigated. We found that Uo(FF) was reduced with by about an order of magnitude in magnetic fields as low as ˜1.5 Tesla-the reduction in Uo(TAFF) is even faster than in Uo(FF)-hence reflecting the low pinning nature (defects, vacancies etc.) of FeSe0.5Te0.5 superconductor.
Yu, T.; Wu, M. W.
2016-11-01
We investigate the quasiparticle spin relaxation with superconducting-velocity-tunable state in GaAs (100) quantum wells in proximity to an s -wave superconductor. We first present the influence of the supercurrent on the quasiparticle state in GaAs (100) quantum wells, which can be tuned by the superconducting velocity. Rich features such as the suppressed Cooper pairings, large quasiparticle density and nonmonotonically tunable momentum current can be realized by varying the superconducting velocity. In the degenerate regime, the quasiparticle Fermi surface is composed by two arcs, referred to as Fermi arcs, which are contributed by the electron- and holelike branches. The D'yakonov-Perel' spin relaxation is then explored, and intriguing physics is revealed when the Fermi arc emerges. Specifically, when the order parameter tends to zero, it is found that the branch-mixing scattering is forbidden in the quasielectron band. When the condensation process associated with the annihilation of the quasielectron and quasihole is slow, this indicates that the electron- and holelike Fermi arcs in the quasielectron band are independent. The open structure of the Fermi arc leads to the nonzero angular average of the effective magnetic field due to the spin-orbit coupling, which acts as an effective Zeeman field. This Zeeman field leads to spin oscillations even in the strong-scattering regime. Moreover, in the strong-scattering regime, we show that the open structure of the Fermi arc also leads to the insensitiveness of the spin relaxation to the momentum scattering, in contrast to the conventional motional narrowing situation. Nevertheless, with a finite order parameter, the branch-mixing scattering can be triggered, opening the interbranch spin relaxation channel, which is dominant in the strong-scattering regime. In contrast to the situation with an extremely small order parameter, due to the interbranch channel, the spin oscillations vanish and the spin relaxation
Optical Manipulation of Single Flux Quanta
Veshchunov, I S; Mironov, S V; Godin, A G; Trebbia, J -B; Buzdin, A I; Tamarat, Ph; Lounis, B
2016-01-01
Magnetic field can penetrate into type-II superconductors in the form of Abrikosov vortices, which are magnetic flux tubes surrounded by circulating supercurrents often trapped at defects referred to as pinning sites. Although the average properties of the vortex matter can be tuned with magnetic fields, temperature or electric currents, handling of individual vortices remains challenging and has been demonstrated only with sophisticated magnetic force, superconducting quantum interference device or strain-induced scanning local probe microscopies. Here, we introduce a far-field optical method based on local heating of the superconductor with a focused laser beam to realize a fast, precise and non-invasive manipulation of individual Abrikosov vortices, in the same way as with optical tweezers. This simple approach provides the perfect basis for sculpting the magnetic flux profile in superconducting devices like a vortex lens or a vortex cleaner, without resorting to static pinning or ratchet effects. Since a ...
Chen, Hsin-Hsien; Huang, Kai-Wen; Yang, Hong-Chang; Horng, Herng-Er; Liao, Shu-Hsien
2013-08-01
This study presents an optimization of the detection coil of high-Tc superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) in microtesla fields for discriminating a minimum amount of liver tumor in rats by characterizing the longitudinal relaxation rate, T1-1, of tested samples. The detection coil, which was coupled to the SQUID through a flux transformer, was optimized by varying the copper wires' winding turns and diameters. When comparing the measured NMR signals, we found that the simulated NMR signal agrees with simulated signals. When discriminating liver tumors in rats, the averaged longitudinal relaxation rate was observed to be T1-1 = 3.3 s-1 for cancerous liver tissue and T1-1 = 6.6 s-1 for normal liver tissue. The results suggest that it can be used to successfully discriminate cancerous liver tissue from normal liver tissues in rats. The minimum amount of samples that can be detected is 0.2 g for liver tumor and 0.4 g for normal liver tissue in 100 μT fields. The specimen was not damaged; it can be used for other pathological analyses. The proposed method provides more possibilities for examining undersized specimens.
Memory effect in the upper bound of the heat flux induced by quantum fluctuations
Koide, T.
2016-10-01
Thermodynamic behaviors in a quantum Brownian motion coupled to a classical heat bath is studied. We then define a heat operator by generalizing the stochastic energetics and show the energy balance (first law) and the upper bound of the expectation value of the heat operator (second law). We further find that this upper bound depends on the memory effect induced by quantum fluctuations and hence the maximum extractable work can be qualitatively modified in quantum thermodynamics.
Tuning an rf-SQUID flux qubit system's potential with magnetic flux bias
Institute of Scientific and Technical Information of China (English)
Hua Tao; Xu Wei-Wei; Shi Jian-Xin; An De-Yue; Sun Guo-Zhu; Yu Yang; Wu Pei-Heng
2012-01-01
At an extremely low temperature of 20 mK,we measured the loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID.By adjusting the magnetic flux applied to the rf-SQUID loop (φf) and the small dc-SQUID (φcjjf),respectively,the potential shape of the system can be fully controlled in situ.Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed,from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.
Newhouse, Vernon L
1975-01-01
Applied Superconductivity, Volume II, is part of a two-volume series on applied superconductivity. The first volume dealt with electronic applications and radiation detection, and contains a chapter on liquid helium refrigeration. The present volume discusses magnets, electromechanical applications, accelerators, and microwave and rf devices. The book opens with a chapter on high-field superconducting magnets, covering applications and magnet design. Subsequent chapters discuss superconductive machinery such as superconductive bearings and motors; rf superconducting devices; and future prospec
Brümmer, Christian; Lyshede, Bjarne; Lempio, Dirk; Delorme, Jean-Pierre; Rüffer, Jeremy J.; Fuß, Roland; Moffat, Antje M.; Hurkuck, Miriam; Ibrom, Andreas; Ambus, Per; Flessa, Heinz; Kutsch, Werner L.
2017-03-01
Recent advances in laser spectrometry offer new opportunities to investigate the soil-atmosphere exchange of nitrous oxide. During two field campaigns conducted at a grassland site and a willow field, we tested the performance of a quantum cascade laser (QCL) connected to a newly developed automated chamber system against a conventional gas chromatography (GC) approach using the same chambers plus an automated gas sampling unit with septum capped vials and subsequent laboratory GC analysis. Through its high precision and time resolution, data of the QCL system were used for quantifying the commonly observed nonlinearity in concentration changes during chamber deployment, making the calculation of exchange fluxes more accurate by the application of exponential models. As expected, the curvature values in the concentration increase was higher during long (60 min) chamber closure times and under high-flux conditions (FN2O > 150 µg N m-2 h-1) than those values that were found when chambers were closed for only 10 min and/or when fluxes were in a typical range of 2 to 50 µg N m-2 h-1. Extremely low standard errors of fluxes, i.e., from ˜ 0.2 to 1.7 % of the flux value, were observed regardless of linear or exponential flux calculation when using QCL data. Thus, we recommend reducing chamber closure times to a maximum of 10 min when a fast-response analyzer is available and this type of chamber system is used to keep soil disturbance low and conditions around the chamber plot as natural as possible. Further, applying linear regression to a 3 min data window with rejecting the first 2 min after closure and a sampling time of every 5 s proved to be sufficient for robust flux determination while ensuring that standard errors of N2O fluxes were still on a relatively low level. Despite low signal-to-noise ratios, GC was still found to be a useful method to determine the mean the soil-atmosphere exchange of N2O on longer timescales during specific campaigns. Intriguingly
Quantum QED Flux Tubes in 2+1 and 3+1 Dimensions
Graham, N; Quandt, M; Schröder, O; Weigel, H
2004-01-01
We compute energies and energy densities of static electromagnetic flux tubes in three and four spacetime dimensions. Our non-perturbative calculation uses scattering data from the potential induced by the flux tube. The calculation is exact to one-loop order and imposes standard perturbative renormalization conditions. We embed the flux tube in a configuration with zero total flux so that we can fully apply standard results from scattering theory. We find that upon choosing the same on-shell renormalization conditions, the functional dependence of the energy and energy density on the parameters of the flux tube is very similar for three and four spacetime dimensions. We compare our exact results to those obtained from the derivative and perturbation expansion approximations, and find good agreement for appropriate parameters of the flux tube, in contrast to previous claims in the literature.
Institute of Scientific and Technical Information of China (English)
吴韬; 何娟; 倪致祥
2009-01-01
本文提出了一个基于SQUIDs和腔场的大失谐相互作用传送量子信息的方案,此方案可以直接地、百分之百地实现量子信息的传送.该方案中腔场和SQUIDs系统之间没有量子信息的传递,腔场只是虚激发,这样对腔的品质因子的要求大大的降低了.同时也可以在SQUIDs之间建立传送量子信息的量子网络.%We propose a scheme for transferring Quantum information via superconducting quantum interference device (SQUID) qubits and cavity field interaction with a large detuning.In the scheme,no quantum information is transferred between the SQUIDs and the cavities,the cavity-fields are only virtually excited,thus the requirement on the quality factor of the cavities is greatly relaxed.In addition,in the scheme the quantum information can be directly transferred with a successful probability of 100% in a simple manner.And meanwhile we can establish a network for transferring quantum information between SQUID qubits.
Strong Coupling of a Quantum Oscillator to a Flux Qubit at Its Symmetry Point
Fedorov, A.; Feofanov, A.K.; Macha, P.; Forn-Díaz, P.; Harmans, C.J.P.M.; Mooij, J.E.
2010-01-01
A flux qubit biased at its symmetry point shows a minimum in the energy splitting (the gap), providing protection against flux noise. We have fabricated a qubit of which the gap can be tuned fast and have coupled this qubit strongly to an LC oscillator. We show full spectroscopy of the qubit-oscilla
Characterization of superconducting transmission line resonators
Energy Technology Data Exchange (ETDEWEB)
Goetz, Jan; Summer, Philipp; Meier, Sebastian; Haeberlein, Max; Wulschner, Karl Friedrich; Eder, Peter; Fischer, Michael; Schwarz, Manuel; Deppe, Frank; Fedorov, Kirill; Huebl, Hans; Menzel, Edwin [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Physik-Department, TU Muenchen, Garching (Germany); Krawczyk, Marta; Marx, Achim [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Baust, Alexander; Xie, Edwar; Zhong, Ling; Gross, Rudolf [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Physik-Department, TU Muenchen, Garching (Germany); Nanosystems Initiative Munich (NIM), Muenchen (Germany)
2015-07-01
Superconducting transmission line resonators are widely used in circuit quantum electrodynamics experiments as quantum bus or storage devices. For these applications, long coherence times, which can be linked to the internal quality factor of the resonators, are crucial. Here, we show a systematic study of the internal quality factor of niobium thin film resonators. We analyze different cleaning methods and substrate parameters for coplanar waveguide as well as microstrip geometries. In addition, we investigate the impact of a niobium-aluminum interface which is necessary for galvanically coupled flux qubits made from aluminum. This interface can be avoided by fabricating the complete resonator-qubit structure using Al/AlO{sub x}/Al technology during fabrication.
Quantum and superconducting fluctuations effects in disordered Nb 1- xTa x thin films above Tc
Giannouri, M.; Papastaikoudis, C.
1999-05-01
Disordered Nb 1- xTa x thin films are prepared with e-gun coevaporation. The influence of the β-phase of tantalum in the critical temperature Tc is observed as a function of the substrate temperature. The measurements of transverse magnetoresistance at various isothermals are interpreted in terms of weak-localization and superconducting fluctuations. From the fitting procedure, the phase breaking rate τφ-1 and the Larkin parameter βL are estimated as a function of temperature. Conclusions about the dominant inelastic scattering mechanisms at various temperature regions as well as for the dominant mechanism of superconducting fluctuations near the transition temperature are extracted.
Multispectral Superconducting Quantum Detectors
1995-08-01
Molybdenum 894 SS316 2770 Iron Fe 1890 SS304 2790 Beryllium 1300 Titanium 1700 Aluminum 3910 Poly-Alumina 791 Table 3.6. Total thermal contraction...is the electron two spin density of states and p is the density of the material. This constant describes coupling of electrons with thermal phonons...antiferromagnetic spin fluctuations . Due to the presence of node lines, the low temperature behavior of a superconductor is quite sensitive to the
Takemoto, Kazuya; Nambu, Yoshihiro; Miyazawa, Toshiyuki; Sakuma, Yoshiki; Yamamoto, Tsuyoshi; Yorozu, Shinichi; Arakawa, Yasuhiko
2015-09-01
Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks.
Realizing Controllable Quantum States
Takayanagi, Hideaki; Nitta, Junsaku
-- 4. Mesoscopic superconductivity with unconventional superconductor or ferromagnet. Ultraefficient microrefrigerators realized with ferromagnet-superconductor junctions / F. Giazotto et al. Anomalous charge transport in triplet superconductor junctions by the synergy effect of the proximity effect and the mid gap Andreev resonant states / Y. Tanaka and S. Kashiwaya. Paramagnetic and glass states in superconductive YBa[symbol]Cu[symbol]O[symbol] ceramics of sub-micron scale grains / H. Deguchi et al. Quantum properties of single-domain triplet superconductors / A. M. Gulian and K. S. Wood. A numerical study of Josephson current in p wave superconducting junctions / Y. Asano et al. Tilted bi-crystal sapphire substrates improve properties of grain boundary YBa[symbol]Cu[symbol]O[symbol] junctions and extend their Josephson response to THZ frequencies / E. Stepantsov et al. Circuit theory analysis of AB-plane tunnel junctions of unconventional superconductor Bi[symbol]Sr[symbol]Ca[symbol]Cu[symbol]O[symbol] / I. Shigeta et al. Transport properties of normal metal/anisotropic superconductor junctions in the eutectic system Sr[symbol]RuO[symbol]Ru / M. Kawamura et al. Macroscopic quantum tunneling in d-wave superconductor Josephson / S. Kawabata et al. Quasiparticle states of high-T[symbol] oxides observed by a Zeeman magnetic field response / S. Kashiwaya et al. Experimentally realizable devices for controlling the motion of magnetic flux quanta in anisotropic superconductors: vortex lenses, vortex diodes and vortex pumps / S. Savel'ev and F. Nori. Stability of vortex-antivortex "molecules" in mesoscopic superconducting triangles / V. R. Misko et al. Superconducting network with magnetic decoration - Hofstadter butterfly in spatially modulated magnetic field / Y. Iye et al. Observation of paramagnetic supercurrent in mesoscopic superconducting rings and disks using multiple-small-tunnel-junction method / A. Kanda et al. Guidance of vortices in high
European roadmap on superconductive electronics - status and perspectives
Energy Technology Data Exchange (ETDEWEB)
Anders, S. [Institute of Photonic Technology (IPHT), Department of Quantum Detection, Albert-Einstein-Str. 9, 07745 Jena (Germany); Blamire, M.G. [University of Cambridge, Department of Materials Science, Pembroke St, Cambridge CB2 3QZ (United Kingdom); Buchholz, F.-Im. [Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig (Germany); Crete, D.-G. [Unite Mixte de Physique CNRS/THALES, 1 Avenue Augustin Fresnel, 91767 Palaiseau CEDEx (France); Cristiano, R. [Istituto di Cibernetica CNR, Via Campi Flegrei 34, 80078 Napoli (Italy); Febvre, P. [University of Savoie, IMEP-LAHC, CNRS UMR 5130, Campus scientifique, 73376 Le Bourget du Lac Cedex (France); Fritzsch, L. [Institute of Photonic Technology (IPHT), Department of Quantum Detection, Albert-Einstein-Str. 9, 07745 Jena (Germany); Herr, A. [Chalmers University of Technology, Department of Microtechnology and Nanoscience - MC2, SE-412 96 Goeteborg (Sweden); Il' ichev, E. [Institute of Photonic Technology (IPHT), Department of Quantum Detection, Albert-Einstein-Str. 9, 07745 Jena (Germany); Kohlmann, J. [Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig (Germany); Kunert, J., E-mail: juergen.kunert@ipht-jena.d [Institute of Photonic Technology (IPHT), Department of Quantum Detection, Albert-Einstein-Str. 9, 07745 Jena (Germany); Meyer, H.-G. [Institute of Photonic Technology (IPHT), Department of Quantum Detection, Albert-Einstein-Str. 9, 07745 Jena (Germany); Niemeyer, J. [Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig (Germany); Ortlepp, T. [Technische Universitaet Ilmenau, Theoretische Elektrotechnik, PF 10 05 65 D-98684 Ilmenau (Germany); Rogalla, H. [University of Twente, Fac. Science and Technology, P.O. Box 217, 7500 AE Enschede (Netherlands); Schurig, T. [Physikalisch-Technische Bundesanstalt (PTB), Berlin, Abbestr. 2-12, 10587 Berlin (Germany)
2010-12-15
Executive Summary: For four decades semiconductor electronics has followed Moore's law: with each generation of integration the circuit features became smaller, more complex and faster. This development is now reaching a wall so that smaller is no longer any faster. The clock rate has saturated at about 3-5 GHz and the parallel processor approach will soon reach its limit. The prime reason for the limitation the semiconductor electronics experiences is not the switching speed of the individual transistor, but its power dissipation and thus heat. Digital superconductive electronics is a circuit- and device-technology that is inherently faster at much less power dissipation than semiconductor electronics. It makes use of superconductors and Josephson junctions as circuit elements, which can provide extremely fast digital devices in a frequency range - dependent on the material - of hundreds of GHz: for example a flip-flop has been demonstrated that operated at 750 GHz. This digital technique is scalable and follows similar design rules as semiconductor devices. Its very low power dissipation of only 0.1 {mu}W per gate at 100 GHz opens the possibility of three-dimensional integration. Circuits like microprocessors and analogue-to-digital converters for commercial and military applications have been demonstrated. In contrast to semiconductor circuits, the operation of superconducting circuits is based on naturally standardized digital pulses the area of which is exactly the flux quantum {Phi}{sub 0}. The flux quantum is also the natural quantization unit for digital-to-analogue and analogue-to-digital converters. The latter application is so precise, that it is being used as voltage standard and that the physical unit 'Volt' is defined by means of this standard. Apart from its outstanding features for digital electronics, superconductive electronics provides also the most sensitive sensor for magnetic fields: the Superconducting Quantum Interference
European roadmap on superconductive electronics - status and perspectives
Anders, S.; Blamire, M. G.; Buchholz, F.-Im.; Crété, D.-G.; Cristiano, R.; Febvre, P.; Fritzsch, L.; Herr, A.; Il'ichev, E.; Kohlmann, J.; Kunert, J.; Meyer, H.-G.; Niemeyer, J.; Ortlepp, T.; Rogalla, H.; Schurig, T.; Siegel, M.; Stolz, R.; Tarte, E.; ter Brake, H. J. M.; Toepfer, H.; Villegier, J.-C.; Zagoskin, A. M.; Zorin, A. B.
2010-12-01
Executive SummaryFor four decades semiconductor electronics has followed Moore’s law: with each generation of integration the circuit features became smaller, more complex and faster. This development is now reaching a wall so that smaller is no longer any faster. The clock rate has saturated at about 3-5 GHz and the parallel processor approach will soon reach its limit. The prime reason for the limitation the semiconductor electronics experiences is not the switching speed of the individual transistor, but its power dissipation and thus heat. Digital superconductive electronics is a circuit- and device-technology that is inherently faster at much less power dissipation than semiconductor electronics. It makes use of superconductors and Josephson junctions as circuit elements, which can provide extremely fast digital devices in a frequency range - dependent on the material - of hundreds of GHz: for example a flip-flop has been demonstrated that operated at 750 GHz. This digital technique is scalable and follows similar design rules as semiconductor devices. Its very low power dissipation of only 0.1 μW per gate at 100 GHz opens the possibility of three-dimensional integration. Circuits like microprocessors and analogue-to-digital converters for commercial and military applications have been demonstrated. In contrast to semiconductor circuits, the operation of superconducting circuits is based on naturally standardized digital pulses the area of which is exactly the flux quantum Φ0. The flux quantum is also the natural quantization unit for digital-to-analogue and analogue-to-digital converters. The latter application is so precise, that it is being used as voltage standard and that the physical unit ‘Volt’ is defined by means of this standard. Apart from its outstanding features for digital electronics, superconductive electronics provides also the most sensitive sensor for magnetic fields: the Superconducting Quantum Interference Device (SQUID). Amongst
Energy Technology Data Exchange (ETDEWEB)
Singh, R.; Nisenoff, M.; Pavuna, D. (Clemson University, SC (United States) U.S. Navy, Naval Research Laboratory, Washington, DC (United States) Lausanne, Ecole Polytechnique Federale, (Switzerland))
1992-01-01
The present conference on high-temperature superconducting transistors and related devices encompasses applications of superconducting thin films, the deposition, patterning, and characterization of thin films, superconducting digital technology, two- and three-terminal devices, and superconducting devices and programs. Specific issues addressed include the application of HTSC films in hybrid optoelectronic devices, the growth and control of epitaxial Ba2YCu3O(7-delta) thin films, atomic layer epitaxy of YBaCuO for optoelectronic applications, single-flux quantum logic, and all-YBaCu3O(7-x) edge-geometry weak links. Also addressed are inverted cylindrical magnetron sputtering for HTSC thin film growth, HTSC films for novel optronic devices, large-area ion-beam-sputtered YBA2Cu3O(7-delta) films for novel device structures, and the High-temperature Superconductivity Space Experiment.
Singh, Rajendra; Nisenoff, Martin; Pavuna, Davor
The present conference on high-temperature superconducting transistors and related devices encompasses applications of superconducting thin films, the deposition, patterning, and characterization of thin films, superconducting digital technology, two- and three-terminal devices, and superconducting devices and programs. Specific issues addressed include the application of HTSC films in hybrid optoelectronic devices, the growth and control of epitaxial Ba2YCu3O(7-delta) thin films, atomic layer epitaxy of YBaCuO for optoelectronic applications, single-flux quantum logic, and all-YBaCu3O(7-x) edge-geometry weak links. Also addressed are inverted cylindrical magnetron sputtering for HTSC thin film growth, HTSC films for novel optronic devices, large-area ion-beam-sputtered YBA2Cu3O(7-delta) films for novel device structures, and the High-temperature Superconductivity Space Experiment.
Javerzac-Galy, Clément; Bernier, Nathan; Toth, Laszlo D; Feofanov, Alexey K; Kippenberg, Tobias J
2015-01-01
We propose a device architecture capable of direct quantum electro-optical conversion of microwave to optical photons. The hybrid system consists of a planar superconducting microwave circuit coupled to an integrated whispering-gallery-mode microresonator made from an electro-optical material. We show that electro-optical (vacuum) coupling rates $g_0$ as large as$\\sim 2\\pi \\, \\mathcal{O}(10-100)$ kHz are achievable with currently available technology, due to the small mode volume of the planar microwave resonator. Operating at millikelvin temperatures, such a converter would enable high-efficiency conversion of microwave to optical photons. We analyze the added noise, and show that maximum conversion efficiency is achieved for a multi-photon cooperativity of unity which can be reached with optical power as low as $ \\mathcal{O}(1)\\,\\mathrm{mW} $.
Tsukada, Keiji; Matsunaga, Yasuaki; Isshiki, Ryota; Nakamura, Yuta; Sakai, Kenji; Kiwa, Toshihiko
2017-05-01
The magnetic characteristics of ethanol-water mixtures were investigated using our newly developed hybrid-type magnetometer based on a high-temperature superconducting quantum-interference device. The magnetization (M-H) curves of ethanol-water mixtures show good diamagnetic characteristics. The magnetic moments of the mixture show ethanol concentration dependence. However, the variation in magnetic moment differs from the characteristics expected by considering the magnetic moment ratio between water and ethanol, and volume-reduction rate. It showed two decrement regions separated at approximately 50-60% concentration values. It is also observed that the concentration dependence of the magnetic moment measured using the sample vibration method under a uniform magnetic field and that by the sample rotation method showed slightly different characteristics. These anomalies are attributed to the formation of clustered structures in the mixture.
Evidence for quantum annealing with more than one hundred qubits
Boixo, Sergio; Rønnow, Troels F.; Isakov, Sergei V.; Wang, Zhihui; Wecker, David; Lidar, Daniel A.; Martinis, John M.; Troyer, Matthias
2014-03-01
Quantum technology is maturing to the point where quantum devices, such as quantum communication systems, quantum random number generators and quantum simulators may be built with capabilities exceeding classical computers. A quantum annealer, in particular, solves optimization problems by evolving a known initial configuration at non-zero temperature towards the ground state of a Hamiltonian encoding a given problem. Here, we present results from tests on a 108 qubit D-Wave One device based on superconducting flux qubits. By studying correlations we find that the device performance is inconsistent with classical annealing or that it is governed by classical spin dynamics. In contrast, we find that the device correlates well with simulated quantum annealing. We find further evidence for quantum annealing in the form of small-gap avoided level crossings characterizing the hard problems. To assess the computational power of the device we compare it against optimized classical algorithms.
Zhang, Zhedong
2015-01-01
We provide a quantitative description of the nonequilibriumness based on the model of coupled oscillators interacting with multiple energy sources. This can be applied to the study of vibrational energy transport in molecules. The curl quantum flux quantifying the nonequilibriumness and time-irreversibility is quantified in the coherent representation and we find the geometric description of the shape and polarization of the flux which provides the connection between the microscopic description of quantum nonequilibriumness and the macroscopic observables, i.e., correlation function. We use the Wilson loop integral to quantify the magnitude of curl flux, which is shown to be correlated to the correlation function as well. Coherence contribution is explicitly demonstrated to be non-trivial and to considerably promote the heat transport quantified by heat current and efficiency. This comes from the fact that coherence effect is microscopically reflected by the geometric description of the flux. To uncover the e...
Exotic Magnetic Orders and Their Interplay with Superconductivity
DEFF Research Database (Denmark)
Christensen, Morten Holm
Superconductivity represents one of the most important scientific discoveries of the 20th century. The practical applications are numerous ranging from clean energy storage and MRI machines to quantum computers. However, the low temperatures required for superconductivity prohibits many practical...
Duality, Confinement and Supersymmetry in Restricted Quantum Chromodynamics (rcd)
Rana, J. M. S.
Electromagnetic duality has been utilized to study the isocolor charge-dyon interactions in Restricted Quantum Chromodynamics (RCD),in terms of current-current correlation (in magnetic gauge)using dielectric and permeability parameters of the associated vacuum. In the state of dyonic superconductivity, it has been shown that the dual propagators behave as 1/k4 (for small k2), which in analogy with superconductivity (dual superconductivity) leads to the confinement of colored fluxes associated with dyonic quarks vide generalized Meissner effect. Based on semi-quantitative analysis of vortex solutions of RCD and by calculating the masses for the massive collective modes of the condensed vacuum, the expressions for the London penetration depth, coherence length and the associated flux energy functions for the type I and type II superconducting media have been obtained. It has further been demonstrated that in the type I medium, vortices tend to coalesce and hence are attractive, while the energy function supports repulsive forces between vortices in the type II superconducting medium. The RCD has been supersymmetrized in N=1 limit and the supersymmetric dyonic solutions have been obtained. In the dyonic background gauge one-loop quantum corrections to the dyonic mass have been calculated and it has been shown that the one-loop quantum corrections lead no change in classical mass of the dyon.
Statistical mechanics of superconductivity
Kita, Takafumi
2015-01-01
This book provides a theoretical, step-by-step comprehensive explanation of superconductivity for undergraduate and graduate students who have completed elementary courses on thermodynamics and quantum mechanics. To this end, it adopts the unique approach of starting with the statistical mechanics of quantum ideal gases and successively adding and clarifying elements and techniques indispensible for understanding it. They include the spin-statistics theorem, second quantization, density matrices, the Bloch–De Dominicis theorem, the variational principle in statistical mechanics, attractive interaction, and bound states. Ample examples of their usage are also provided in terms of topics from advanced statistical mechanics such as two-particle correlations of quantum ideal gases, derivation of the Hartree–Fock equations, and Landau’s Fermi-liquid theory, among others. With these preliminaries, the fundamental mean-field equations of superconductivity are derived with maximum mathematical clarity based on ...
Takeuchi, Naoki; Nagasawa, Shuichi; China, Fumihiro; Ando, Takumi; Hidaka, Mutsuo; Yamanashi, Yuki; Yoshikawa, Nobuyuki
2017-03-01
Adiabatic quantum-flux-parametron (AQFP) logic is an energy-efficient superconductor logic with zero static power consumption and very small switching energy. In this paper, we report a new AQFP cell library designed using the AIST 10 kA cm-2 Nb high-speed standard process (HSTP), which is a high-critical-current-density version of the AIST 2.5 kA cm-2 Nb standard process (STP2). Since the intrinsic damping of the Josephson junction (JJ) of HSTP is relatively strong, shunt resistors for JJs were removed and the energy efficiency improved significantly. Also, excitation transformers in the new cells were redesigned so that the cells can operate in a four-phase excitation mode. We described the detail of HSTP and the AQFP cell library designed using HSTP, and showed experimental results of cell test circuits.
Emergent Higgsless Superconductivity
Directory of Open Access Journals (Sweden)
Cristina Diamantini M.
2017-01-01
Full Text Available We present a new Higgsless model of superconductivity, inspired from anyon superconductivity but P- and T-invariant and generalizable to any dimension. While the original anyon superconductivity mechanism was based on incompressible quantum Hall fluids as average field states, our mechanism involves topological insulators as average field states. In D space dimensions it involves a (D-1-form fictitious pseudovector gauge field which originates from the condensation of topological defects in compact lowenergy effective BF theories. There is no massive Higgs scalar as there is no local order parameter. When electromagnetism is switched on, the photon acquires mass by the topological BF mechanism. Although the charge of the gapless mode (2 and the topological order (4 are the same as those of the standard Higgs model, the two models of superconductivity are clearly different since the origins of the gap, reflected in the high-energy sectors are totally different. In 2D thi! s type of superconductivity is explicitly realized as global superconductivity in Josephson junction arrays. In 3D this model predicts a possible phase transition from topological insulators to Higgsless superconductors.
Fingerprints of Mott Superconductivity
Institute of Scientific and Technical Information of China (English)
王强华
2003-01-01
We improve a previous theory of doped Mott insulators with duality between pairing and magnetism by a further duality transform. As the result we obtained a quantum Ginzburg-Landau theory describing the Cooper pair condensate and the dual of spin condensate. We address the superconductivity by doping a Mott insulator,which we call the Mott superconductivity. Some fingerprints of such novelty in cuprates are the scaling between neutron resonance energy and superfluid density, and the induced quantized spin moment by vortices or Zn impurity (together with circulating charge super-current to be checked by experiments).
Morgenstern Horing, Norman J
2017-01-01
This book provides an introduction to the methods of coupled quantum statistical field theory and Green's functions. The methods of coupled quantum field theory have played a major role in the extensive development of nonrelativistic quantum many-particle theory and condensed matter physics. This introduction to the subject is intended to facilitate delivery of the material in an easily digestible form to advanced undergraduate physics majors at a relatively early stage of their scientific development. The main mechanism to accomplish this is the early introduction of variational calculus and the Schwinger Action Principle, accompanied by Green's functions. Important achievements of the theory in condensed matter and quantum statistical physics are reviewed in detail to help develop research capability. These include the derivation of coupled field Green's function equations-of-motion for a model electron-hole-phonon system, extensive discussions of retarded, thermodynamic and nonequilibrium Green's functions...
Gray, Kenneth E.
1979-01-01
A superconducting transistor is formed by disposing three thin films of superconducting material in a planar parallel arrangement and insulating the films from each other by layers of insulating oxides to form two tunnel junctions. One junction is biased above twice the superconducting energy gap and the other is biased at less than twice the superconducting energy gap. Injection of quasiparticles into the center film by one junction provides a current gain in the second junction.
Eichler, C.; Mlynek, J.; Butscher, J.; Kurpiers, P.; Hammerer, K.; Osborne, T. J.; Wallraff, A.
2015-10-01
Improving the understanding of strongly correlated quantum many-body systems such as gases of interacting atoms or electrons is one of the most important challenges in modern condensed matter physics, materials research, and chemistry. Enormous progress has been made in the past decades in developing both classical and quantum approaches to calculate, simulate, and experimentally probe the properties of such systems. In this work, we use a combination of classical and quantum methods to experimentally explore the properties of an interacting quantum gas by creating experimental realizations of continuous matrix product states—a class of states that has proven extremely powerful as a variational ansatz for numerical simulations. By systematically preparing and probing these states using a circuit quantum electrodynamics system, we experimentally determine a good approximation to the ground-state wave function of the Lieb-Liniger Hamiltonian, which describes an interacting Bose gas in one dimension. Since the simulated Hamiltonian is encoded in the measurement observable rather than the controlled quantum system, this approach has the potential to apply to a variety of models including those involving multicomponent interacting fields. Our findings also hint at the possibility of experimentally exploring general properties of matrix product states and entanglement theory. The scheme presented here is applicable to a broad range of systems exploiting strong and tunable light-matter interactions.
Suitability of quantum cascade laser spectroscopy for CH4 and N2O eddy covariance flux measurements
Directory of Open Access Journals (Sweden)
A. T. Vermeulen
2007-08-01
Full Text Available A quantum cascade laser spectrometer was evaluated for eddy covariance flux measurements of CH4 and N2O using three months of continuous measurements at a field site. The required criteria for eddy covariance flux measurements including continuity, sampling frequency, precision and stationarity were examined. The system operated continuously at a dairy farm on peat grassland in the Netherlands from 17 August to 6 November 2006. An automatic liquid nitrogen filling system for the infrared detector was employed to provide unattended operation of the system. The electronic sampling frequency was 10 Hz, however, the flow response time was 0.08 s, which corresponds to a bandwidth of 2 Hz. A precision of 2.9 and 0.5 ppb Hz−1/2 was obtained for CH4 and N2O, respectively. Accuracy was assured by frequent calibrations using low and high standard additions. Drifts in the system were compensated by using a 120 s running mean filter. The average CH4 and N2O exchange was 512 ngC m−2 s−1 (2.46 mg m−2 hr−1 and 52 ngN m−2 s−1 (0.29 mg m−2 hr−1. Given that 40% of the total N2O emission was due to a fertilizing event.
Superconductivity and superconductive electronics
Beasley, M. R.
1990-12-01
The Stanford Center for Research on Superconductivity and Superconductive Electronics is currently focused on developing techniques for producing increasingly improved films and multilayers of the high-temperature superconductors, studying their physical properties and using these films and multilayers in device physics studies. In general the thin film synthesis work leads the way. Once a given film or multilayer structure can be made reasonably routinely, the emphasis shifts to studying the physical properties and device physics of these structures and on to the next level of film quality or multilayer complexity. The most advanced thin films synthesis work in the past year has involved developing techniques to deposit a-axis and c-axis YBCO/PBCO superlattices and related structures. The in-situ feature is desirable because no solid state reactions with accompanying changes in volume, morphology, etc., that degrade the quality of the film involved.
Energy Technology Data Exchange (ETDEWEB)
Jiang Shuai; Xing Hui; Xuan Guofang; Wang Cao; Ren Zhi; Dai Jianhui; Xu Zhu' an; Cao Guanghan [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Feng, Chunmu, E-mail: ghcao@zju.edu.c [Test and Analysis Center, Zhejiang University, Hangzhou 310027 (China)
2009-09-23
We report bulk superconductivity induced by an isovalent doping of phosphorus in BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}. The P-for-As substitution results in shrinkage of the lattice, especially for the FeAs block layers. The resistivity anomaly associated with the spin-density-wave (SDW) transition in the undoped compound is gradually suppressed by the P doping. Superconductivity with a maximum T{sub c} of 30 K emerges at x = 0.32, coinciding with a magnetic quantum critical point (QCP) which is shown by the disappearance of SDW order and the linear temperature-dependent resistivity in the normal state. The T{sub c} values were found to decrease with further P doping and no superconductivity was observed down to 2 K for x>=0.77. The appearance of superconductivity in the vicinity of QCP hints at the superconductivity mechanism in iron-based arsenides. (fast track communication)
石墨烯带正常-超导结的量子输运%Quantum transport through normal-superconducting graphene nanoribbons
Institute of Scientific and Technical Information of China (English)
王斌; 李健伟; 卫亚东; 王健
2014-01-01
The first principles calculation has been carried out to investigate the quantum transport properties of normal-superconducting graphene nanoribbons ( GNRs) within the combination of non-equilibrium Green’s function ( NEGF) and density functional theory ( DFT) . The Andreev reflection coefficient TA and quasi-particle transmission probability T1 of normal-superconducting system of a series of defective configurations were investigated in detail. As a comparison, the electric transmission coefficient TN of normal system was also calculated. In the pristine graphene nanoribbons, The Andreev reflection coefficient TA is a constant and exactly equals to electric transmission coefficient TN of the normal system in the superconducting energy gap, which indicates that the Andreev conductance is twice of the normal electric conductance. In the defective configurations of graphene nanoribbons, TA shows two sharp peaks at E =± Δ, and the peak values are larger than the electric conductance of normal system. Outside the superconducting energy gap, Andreev conductance decays to zero, and quasi-particle transmission probability increases to the normal electric transmission coefficient gradually. Different defective configurations give different influence to the Andreev reflection of the normal-superconducting graphene nanoribbons.%基于非平衡格林函数( non-equilibrium Green’s function, NEGF )和密度泛函理论( density functional theory, DFT),从第一性原理出发研究Armchair型和Zigzag型的石墨烯带正常-超导结的电子输运性质,计算了缺陷对这两种正常-超导结输运性质的影响。计算表明,对无缺陷正常-超导石墨烯带,在超导能隙内, Andreev反射系数TA恰好等于正常石墨烯带的电子透射系数TN 。当石墨烯带存在缺陷时, Andreev反射系数TA不再是一个常数,而在超导能隙边缘出现两个尖锐的峰,其峰值大于正常系统的电子透射系数。在超导能隙之外, Andreev
Yahya, Noorhana; Zakariah, Muhammad Hanis
2012-10-01
Electromagnetic (EM) waves transmitted by Horizontal Electric Dipole (HED) source to detect contrasts in subsurface resistivity termed Seabed Logging (SBL) is now an established method for hydrocarbon exploration. However, currently used EM wave detectors for SBL have several challenges including the sensitivity and its bulk size. This work exploits the benefit of superconductor technology in developing a magnetometer termed Superconducting Quantum Interference Device (SQUID) which can potentially be used for SBL. A SQUID magnetometer was fabricated using hexagon shape-niobium wire with YBa2Cu37O, (YBCO) as a barrier. The YBa2Cu37O, samples were synthesized by sol-gel method and were sintered using a furnace and conventional microwave oven. The YBCO gel was dried at 120 degrees C in air for 72 hours. It was then ground and divided into 12 parts. Four samples were sintered at 750 degrees C, 850 degrees C, 900 degrees C, and 950 degrees C for 12 hours in a furnace to find the optimum temperature. The other eight samples were sintered in a microwave with 1100 Watt (W) with a different sintering time, 5, 15, 45 minutes, 1 hour, 1 hour 15 minutes, 1 hour 30 minutes, 1 hour 45 minutes and 2 hours. A DEWAR container was designed and fabricated using fiberglass material. It was filled with liquid nitrogen (LN2) to ensure the superconducting state of the magnetometer. XRD results showed that the optimum sintering temperature for the formation of orthorhombic Y-123 phase was at 950 degrees C with the crystallite size of 67 nm. The morphology results from Field Emission Scanning Electron Microscopy (FESEM) showed that the grains had formed a rod shape with an average diameter of 60 nm. The fabricated SQUID magnetometer was able to show an increment of approximately 249% in the intensity of the EM waves when the source receiver offset was one meter apart.
Energy Technology Data Exchange (ETDEWEB)
Lee, N.; Wetzstein, H.Y.; Sommer, H.E.
1985-07-01
Liquidambar styraciflua L. seedlings and tissue-cultured plantlets were grown under high, medium, or low quantum flux densities. Net photosynthesis, chlorophyll content, and chloroplast ultrastructure of leaves differentiated from these conditions were investigated. Seedling photosynthetic rates at light saturation were positively related to light pretreatments. Cultured plantlets under all light conditions had appreciably higher photosynthetic rates than noncultured seedlings. Chlorophyll in seedlings and plantlets was significantly higher in low light-treated plants. Seedling leaves had chloroplasts with abundant starch regardless of light pretreatment. In high light, starch granules were predominant and associated with disrupted granal structure. Low light seedling chloroplasts had smaller starch grains and well-formed grana. In contrast, tissue culture-differentiated leaves were devoid of starch; grana were well organized in higher quantum flux density treatments, but disorganized at low flux densities. 29 references, 7 figures, 1 table.
Nonlinear Superconducting Metamaterials in Free-Space at mm-wave Frequencies
Anlage, Steven; Zhang, Daimeng; Trepanier, Melissa; Mukhanov, Oleg; Delfanazari, K.; Savinov, V.; Zheludev, N.
2014-03-01
Superconducting metamaterials show the promise of low loss, compact size and extreme tunability and nonlinearity, allowing for new applications. Most demonstrations of these metamaterials have been conducted in waveguide geometries, either in co-planar form or three-dimensional single-conductor structures. Here we demonstrate for the first time a widely tunable superconducting metamaterial operating under the free-space illumination of a quasi-optical beam in the 100 GHz regime. The meta-atoms are Radio Frequency Superconducting QUantum Interference Devices (RF SQUIDs) that form compact self-resonant objects endowed with the nonlinearity of the Josephson effect. The metamaterial is tuned with dc magnetic flux, temperature and mm-wave power, and holds promise for a new generation of mm-wave agile devices. This work is supported by the NSF-GOALI and OISE programs through grant # ECCS-1158644, and CNAM.
Connectivity and superconductivity
Rubinstein, Jacob
2000-01-01
The motto of connectivity and superconductivity is that the solutions of the Ginzburg--Landau equations are qualitatively influenced by the topology of the boundaries, as in multiply-connected samples. Special attention is paid to the "zero set", the set of the positions (also known as "quantum vortices") where the order parameter vanishes. The effects considered here usually become important in the regime where the coherence length is of the order of the dimensions of the sample. It takes the intuition of physicists and the awareness of mathematicians to find these new effects. In connectivity and superconductivity, theoretical and experimental physicists are brought together with pure and applied mathematicians to review these surprising results. This volume is intended to serve as a reference book for graduate students and researchers in physics or mathematics interested in superconductivity, or in the Schrödinger equation as a limiting case of the Ginzburg--Landau equations.
Superconductivity in a chiral nanotube
Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.
2017-02-01
Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity--unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.