Josephson junctions with tunable weak links.
Schön, J H; Kloc, C; Hwang, H Y; Batlogg, B
2001-04-13
The electrical properties of organic molecular crystals, such as polyacenes or C60, can be tuned from insulating to superconducting by application of an electric field. By structuring the gate electrode of such a field-effect switch, the charge carrier density, and therefore also the superfluid density, can be modulated. Hence, weak links that behave like Josephson junctions can be fabricated between two superconducting regions. The coupling between the superconducting regions can be tuned and controlled over a wide range by the applied gate bias. Such devices might be used in superconducting circuits, and they are a useful scientific tool to study superconducting material parameters, such as the superconducting gap, as a function of carrier concentration or transition temperature.
Mesoscopic lateral S/N/S weak links: Josephson effects and Josephson-like vortex flow
NASA Astrophysics Data System (ADS)
Carapella, G.; Sabatino, P.; Gombos, M.
2017-02-01
We report an experimental and numerical study of magneto-transport properties of mesoscopic lateral S/N/S superconducting weak links where the N region is made of the same material as the S banks, though with strongly reduced critical temperature. Magnetoresistance oscillations and clear dc and ac Josephson effects are observed. Experimental results are analyzed in the framework of the time-dependent Ginzburg-Landau model for mesoscopic type II superconductors with an inhomogeneous critical temperature. The analysis suggests that dissipative branches of the current-voltage curve of the weak link in the presence of a magnetic field are accounted for by moving ‘Josephson-like’ vortices. These relatively fast excitations are anisotropic as per the ordinary Josephson vortex in tunnel junctions, but have a normal core like the ordinary Abrikosov vortex in plain superconducting strips. Moreover, unlike the vortex in tunneling junctions, in the lateral S/N/S weak link, the extension of the moving vortex is larger than the extension of the static one. Further, we report in some detail on the lateral proximity effect, and the deviations from the ideality of the current-phase relation of this kind of lateral weak link in the Josephson regime.
Thermal transport through ac-driven transparent Josephson weak links
NASA Astrophysics Data System (ADS)
Virtanen, P.; Giazotto, F.
2014-07-01
We discuss how phase coherence manifests in the heat transport through superconducting single and multichannel Josephson junctions in time-dependent situations. We consider the heat current driven through the junction by a temperature difference in dc voltage and ac phase biased situations. At low bias, the electromagnetic driving mainly modifies the form of the coherent resonance that transports a large part of the heat current, rather than simply dissipating energy in the junction. We find a description for the heat current in terms of quasiparticle n-photon absorption and emission rates, and discuss analytical and numerical results concerning them. In addition to the ensemble average heat transport, we describe also its fluctuations.
Theory of a weak-link superconductor-ferromagnet Josephson structure
NASA Astrophysics Data System (ADS)
Gelhausen, J.; Eschrig, M.
2016-09-01
We propose a model for the theoretical description of a weak-link Josephson junction, in which the weak link is spin-polarized due to proximity to a ferromagnetic metal [S-(F |S )-S, where S is a superconductor and F is a ferromagnetic metal]. Employing Usadel transport theory appropriate for diffusive systems, we show that the weak link is described within the framework of Andreev circuit theory by an effective self-energy resulting from the implementation of spin-dependent boundary conditions. This leads to a considerable simplification of the model, and allows for an efficient numerical treatment. As an application of our model, we show numerical calculations of important physical observables such as the local density of states, proximity-induced minigaps, spin-magnetization, and the phase and temperature dependence of Josephson currents of the S-(F |S )-S system. We discuss multivalued current-phase relationships at low temperatures as well as their crossover to sinusoidal form at high temperatures. Additionally, we numerically treat (S-F-S) systems that exhibit a magnetic domain wall in the F region and calculate the temperature-dependence of the critical currents.
Carapella, G.; Sabatino, P.; Barone, C.; Pagano, S.; Gombos, M.
2016-01-01
Vortices are topological defects accounting for many important effects in superconductivity, superfluidity, and magnetism. Here we address the stability of a small number of such excitations driven by strong external forces. We focus on Abrikosov-Josephson vortex that appears in lateral superconducting S/S’/S weak links with suppressed superconductivity in S’. In such a system the vortex is nucleated and confined in the narrow S’ region by means of a small magnetic field and moves under the effect of a force proportional to an applied electrical current with a velocity proportional to the measured voltage. Our numerical simulations show that when a slow moving Abrikosov-Josephson vortex is driven by a strong constant current it becomes unstable with respect to a faster moving excitation: the Josephon-like vortex. Such a current-driven transition explains the structured dissipative branches that we observe in the voltage-current curve of the weak link. When vortex matter is strongly confined phenomena as magnetoresistance oscillations and reentrance of superconductivity can possibly occur. We experimentally observe these phenomena in our weak links. PMID:27752137
Critical-current diffraction patterns of grain-boundary Josephson weak links
Peterson, R.L.; Ekin, J.W. )
1990-11-01
We discuss the diffraction patterns and other characteristics of the critical current as a function of magnetic field in grain-boundary Josephson barriers. Diffraction patterns occur not just for {ital SIS} junctions but for all types of Josephson links, including {ital SNS} junctions, which may be present at grain boundaries in high-{Tc} superconductors. We discuss the generality of the Airy diffraction pattern, which is expected to characterize grain-boundary barriers in bulk material more accurately than the Fraunhofer pattern. The transport critical-current density in many bulk, granular high-{ital T}{sub {ital c}} superconductors has a power-law dependence on very low magnetic fields, characteristic of averaged diffraction patterns, and cannot be fitted by an exponential magnetic-field dependence, which may result from the material properties of the barriers.
NASA Astrophysics Data System (ADS)
Arjoranta, Juho; Heikkilä, Tero T.
2016-01-01
We study the effect of the intrinsic (Rashba or Dresselhaus) spin-orbit interaction in superconductor-nanowire-superconductor (SNS) weak links in the presence of a spin-splitting field that can result either from an intrinsic exchange field or the Zeeman effect of an applied field. We solve the full nonlinear Usadel equations numerically [The code used for calculating the results in this paper is available in https://github.com/wompo/Usadel-for-nanowires] and analyze the resulting supercurrent through the weak link and the behavior of the density of states in the center of the wire. We point out how the presence of the spin-orbit interaction gives rise to a long-range spin triplet supercurrent, which remains finite even in the limit of very large exchange fields. In particular, we show how rotating the field leads to a sequence of transitions between the 0 and π states as a function of the angle between the exchange field and the spin-orbit field. Simultaneously, the triplet pairing leads to a zero-energy peak in the density of states. We proceed by solving the linearized Usadel equations, showing the correspondence to the solutions of the full equations and detail the emergence of the long-range supercurrent components. Our studies are relevant for ongoing investigations of supercurrent in semiconductor nanowires in the limit of several channels and in the presence of disorder.
Nanoelectromechanics of superconducting weak links (Review Article)
NASA Astrophysics Data System (ADS)
Parafilo, A. V.; Krive, I. V.; Shekhter, R. I.; Jonson, M.
2012-04-01
Nanoelectromechanical effects in superconducting weak links are considered. Three different superconducting devices are studied: (i) a single-Cooper-pair transistor, (ii) a transparent SNS junction, and (iii) a single-level quantum dot coupled to superconducting electrodes. The electromechanical coupling is due to electrostatic or magnetomotive forces acting on a movable part of the device. It is demonstrated that depending on the frequency of mechanical vibrations the electromechanical coupling could either suppress or enhance the Josephson current. Nonequilibrium effects associated with cooling of the vibrational subsystem or pumping energy into it at low bias voltages are discussed.
Method Producing an SNS Superconducting Junction with Weak Link Barrier
NASA Technical Reports Server (NTRS)
Hunt, Brian D. (Inventor)
1999-01-01
A method of producing a high temperature superconductor Josephson element and an improved SNS weak link barrier element is provided. A YBaCuO superconducting electrode film is deposited on a substrate at a temperature of approximately 800 C. A weak link barrier layer of a nonsuperconducting film of N-YBaCuO is deposited over the electrode at a temperature range of 520 C. to 540 C. at a lower deposition rate. Subsequently a superconducting counter-electrode film layer of YBaCuO is deposited over the weak link barrier layer at approximately 800 C. The weak link barrier layer has a thickness of approximately 50 A and the SNS element can be constructed to provide an edge geometry junction.
Detection of Weak Microwave Fields with an Underdamped Josephson Junction
NASA Astrophysics Data System (ADS)
Oelsner, G.; Andersen, C. K.; Rehák, M.; Schmelz, M.; Anders, S.; Grajcar, M.; Hübner, U.; Mølmer, K.; Il'ichev, E.
2017-01-01
We construct a microwave detector based on the voltage switching of an underdamped Josephson junction that is positioned at a current antinode of a λ /4 coplanar waveguide resonator. By measuring the switching current and the transmission through a waveguide capacitively coupled to the resonator at different drive frequencies and temperatures, we are able to fully characterize the system and assess its detection efficiency and sensitivity. Testing the detector by applying a classical microwave field with the strength of a single photon yields a sensitivity parameter of 0.5, in qualitative agreement with theoretical calculations.
(abstract) Epitaxial High-T(sub c) SNS Weak Links on Silicon-on-Sapphire Substrates
NASA Technical Reports Server (NTRS)
Hunt, B. D.; Barner, J. B.; Foote, M. C.; Vasquez, R. P.; Schoelkopf, R. J.; Phillips, T. G.; Zmuidzinas, J.
1994-01-01
High-T(sub c) SNS weak links are expected to prove useful as high frequency sources and detectors. Recent studies with low-T(sub c) Josephson mixers using shunted tunnel junctions at 100 GHz show good initial performance, and modeling suggests that these results should extrapolate to higher frequencies if larger I(sub c)R(sub n) products can be achieved. Progress on this work will be reported.
Josephson magnetic rotary valve
Soloviev, I. I.; Klenov, N. V.; Bakurskiy, S. V.; Bol'ginov, V. V.; Ryazanov, V. V.; Kupriyanov, M. Yu.; Golubov, A. A.
2014-12-15
We propose a control element for a Josephson spin valve. It is a complex Josephson device containing ferromagnetic (F) layer in the weak-link area consisting of two regions, representing 0 and π Josephson junctions, respectively. The valve's state is defined by mutual orientations of the F-layer magnetization vector and boundary line between 0 and π sections of the device. We consider possible implementation of the control element by introduction of a thin normal metal layer in a part of the device area. By means of theoretical simulations, we study properties of the valve's structure as well as its operation, revealing such advantages as simplicity of control, high characteristic frequency, and good legibility of the basic states.
Phase slips in superconducting weak links
Kimmel, Gregory; Glatz, Andreas; Aranson, Igor S.
2017-01-01
Superconducting vortices and phase slips are primary mechanisms of dissipation in superconducting, superfluid, and cold-atom systems. While the dynamics of vortices is fairly well described, phase slips occurring in quasi-one- dimensional superconducting wires still elude understanding. The main reason is that phase slips are strongly nonlinear time-dependent phenomena that cannot be cast in terms of small perturbations of the superconducting state. Here we study phase slips occurring in superconducting weak links. Thanks to partial suppression of superconductivity in weak links, we employ a weakly nonlinear approximation for dynamic phase slips. This approximation is not valid for homogeneous superconducting wires and slabs. Using the numerical solution of the time-dependent Ginzburg-Landau equation and bifurcation analysis of stationary solutions, we show that the onset of phase slips occurs via an infinite period bifurcation, which is manifested in a specific voltage-current dependence. Our analytical results are in good agreement with simulations.
NASA Astrophysics Data System (ADS)
Zemlyanaya, E. V.; Bashashin, M. V.; Rahmonov, I. R.; Shukrinov, Yu. M.; Atanasova, P. Kh.; Volokhova, A. V.
2016-10-01
We consider a model of system of long Josephson junctions (LJJ) with inductive and capacitive coupling. Corresponding system of nonlinear partial differential equations is solved by means of the standard three-point finite-difference approximation in the spatial coordinate and utilizing the Runge-Kutta method for solution of the resulting Cauchy problem. A parallel algorithm is developed and implemented on a basis of the MPI (Message Passing Interface) technology. Effect of the coupling between the JJs on the properties of LJJ system is demonstrated. Numerical results are discussed from the viewpoint of effectiveness of parallel implementation.
Gravity's Weak Force Link and other thoughts
NASA Astrophysics Data System (ADS)
Aquilina, Rich
2011-10-01
Gravity is by far the weakest of the known four forces. What if that is because it is the oldest of the forces and the most decayed of them? What if that is what caused the Big Bang? The decay of gravity could no longer hold the singularity (or other forces) in check. We know there is decay, it is known as the ``Weak'' force. The idea of decaying gravity would only serve to unite the ``Weak'' force and ``Gravity.'' What if this is the elusive connection between ``Gravity'' and the ``Other Forces''? What if there have been other forces that are no longer with us because of decay or their own evolutionary process? What if these unknown decayed forces gave rise to newer and ``stronger'' forces or maybe even ``weaker'' ones? What if ``particles'' were actually a threshold of converged points of strings (like on a multi-dimensional graph), and the reason we can't seem to find one for gravity is because the convergence threshold to manifest as a particle hasn't been met, yet the strings and influence are still there.
Axion mass estimates from resonant Josephson junctions
NASA Astrophysics Data System (ADS)
Beck, Christian
2015-03-01
Recently it has been proposed that dark matter axions from the galactic halo can produce a small Shapiro step-like signal in Josephson junctions whose Josephson frequency resonates with the axion mass (Beck, 2013). Here we show that the axion field equations in a voltage-driven Josephson junction environment allow for a nontrivial solution where the axion-induced electrical current manifests itself as an oscillating supercurrent. The linear change of phase associated with this nontrivial solution implies the formal existence of a large magnetic field in a tiny surface area of the weak link region of the junction which makes incoming axions decay into microwave photons. We derive a condition for the design of Josephson junction experiments so that they can act as optimum axion detectors. Four independent recent experiments are discussed in this context. The observed Shapiro step anomalies of all four experiments consistently point towards an axion mass of (110±2) μeV. This mass value is compatible with the recent BICEP2 results and implies that Peccei-Quinn symmetry breaking was taking place after inflation.
Wendt, J.R.; Plut, T.A.; Martens, J.S.
1995-05-02
A novel method for fabricating nanometer geometry electronic devices is described. Such Josephson junctions can be accurately and reproducibly manufactured employing photolithographic and direct write electron beam lithography techniques in combination with aqueous etchants. In particular, a method is described for manufacturing planar Josephson junctions from high temperature superconducting material. 10 figs.
Wendt, Joel R.; Plut, Thomas A.; Martens, Jon S.
1995-01-01
A novel method for fabricating nanometer geometry electronic devices is described. Such Josephson junctions can be accurately and reproducibly manufactured employing photolithographic and direct write electron beam lithography techniques in combination with aqueous etchants. In particular, a method is described for manufacturing planar Josephson junctions from high temperature superconducting material.
NASA Astrophysics Data System (ADS)
Bauer, S.; Behr, R.; Hagen, T.; Kieler, O.; Lee, J.; Palafox, L.; Schurr, J.
2017-04-01
In this paper the realization of a two-terminal-pair impedance bridge based on pulse-driven Josephson arrays will be presented. This bridge was used to link a 10 nF capacitance standard to the quantized Hall resistance at 1233 Hz. With pulse-driven Josephson arrays the setup for a quadrature bridge can be reduced dramatically. For the combination of the AC quantum Hall resistance and a 10 nF capacitance standard, most of the uncertainties caused by contact resistances in a two-terminal-pair definition were circumvented by a triple-series connection of the AC quantum Hall resistance. The capacitance value obtained by the new Josephson impedance bridge was compared to the results from a transformer-based ratio bridge and agrees within 1.3 parts in 108. Sources of systematic uncertainties were investigated and the combined relative uncertainty of the bridge was determined to be less than 1× {{10}-8} (k = 1) and 13.9 nF F‑1 (k = 1) for the link of the 10 nF capacitance standard.
Stability in Real Food Webs: Weak Links in Long Loops
NASA Astrophysics Data System (ADS)
Neutel, Anje-Margriet; Heesterbeek, Johan A. P.; de Ruiter, Peter C.
2002-05-01
Increasing evidence that the strengths of interactions among populations in biological communities form patterns that are crucial for system stability requires clarification of the precise form of these patterns, how they come about, and why they influence stability. We show that in real food webs, interaction strengths are organized in trophic loops in such a way that long loops contain relatively many weak links. We show and explain mathematically that this patterning enhances stability, because it reduces maximum ``loop weight'' and thus reduces the amount of intraspecific interaction needed for matrix stability. The patterns are brought about by biomass pyramids, a feature common to most ecosystems. Incorporation of biomass pyramids in 104 food-web descriptions reveals that the low weight of the long loops stabilizes complex food webs. Loop-weight analysis could be a useful tool for exploring the structure and organization of complex communities.
Stress and Aeronautical Team Decision Making: Strengthening the Weak Links
NASA Technical Reports Server (NTRS)
Orasanu, Judith; Rosekind, Mark R. (Technical Monitor)
1996-01-01
A model that characterizes pilots'decision making in flight will be presented. Elements of the model that appear most vulnerable to stress will be examined in light of accidents and incidents. The model includes two major components: Situation assessment and choice of a course of action. While based on Klein's Recognition-Primed Decision Making, it is tailored to the aviation environment which includes certain features that may be common to other domains: Primarily, aviation is highly proceduralized and options are generally well known. What appears to make decisions difficult are ambiguity, time pressure, and risk. In addition, decisions must often be made while carrying out the standard procedures of flight, including checklists, review of approach plates, standard briefings, and communication with air traffic controllers or cabin crew. The effects of stressors on decision making by pilots with varying levels of expertise will be explored, along with strategies for strengthening the weak links.
NASA Astrophysics Data System (ADS)
Barone, Antonio; Pagano, Sergio
In this chapter we briefly review the main applications of Josephson effect together with the most successful devices realized. We will give an overview of the various devices, providing also some basic concepts of the underlying physical mechanisms involved, and the associated limit performances. Some considerations on the concrete possibilities of successful "market ready" implementation will also be given.
Modulated microwave absorption spectra from Josephson junctions on a scratched niobium wire
Rubins, R.S. |; Hutton, S.L.; Ravindran, K.; Subbaraman, K.; Drumheller, J.E.
1997-05-01
Modulated microwave absorption (MMA) spectra from Josephson junction formations on a scratched Nb wire have been studied at 9.3 GHz and 4 K. The peak-to-peak separation, {delta}H of the Josephson lines was found to vary linearly with P{sup 1/2}, where P is the applied microwave power, in contrast to a recent interpretation of junction formation in pressed lead pieces by Rubins, Drumheller, and Trybula. The interpretation of the MMA data on Nb are given in terms of the theory of Vichery, Beuneu, and Lejay for superconducting loops containing weak links. {copyright} {ital 1997} {ital The American Physical Society}
Lack of strength; Muscle weakness ... feel weak but have no real loss of strength. This is called subjective weakness. It may be ... flu. Or, you may have a loss of strength that can be noted on a physical exam. ...
Magnetically-driven colossal supercurrent enhancement in InAs nanowire Josephson junctions.
Tiira, J; Strambini, E; Amado, M; Roddaro, S; San-Jose, P; Aguado, R; Bergeret, F S; Ercolani, D; Sorba, L; Giazotto, F
2017-04-12
The Josephson effect is a fundamental quantum phenomenon where a dissipationless supercurrent is introduced in a weak link between two superconducting electrodes by Andreev reflections. The physical details and topology of the junction drastically modify the properties of the supercurrent and a strong enhancement of the critical supercurrent is expected to occur when the topology of the junction allows an emergence of Majorana bound states. Here we report charge transport measurements in mesoscopic Josephson junctions formed by InAs nanowires and Ti/Al superconducting leads. Our main observation is a colossal enhancement of the critical supercurrent induced by an external magnetic field applied perpendicular to the substrate. This striking and anomalous supercurrent enhancement cannot be described by any known conventional phenomenon of Josephson junctions. We consider these results in the context of topological superconductivity, and show that the observed critical supercurrent enhancement is compatible with a magnetic field-induced topological transition.
4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions
Wiedenmann, J.; Bocquillon, E.; Deacon, R. S.; Hartinger, S.; Herrmann, O.; Klapwijk, T. M.; Maier, L.; Ames, C.; Brüne, C.; Gould, C.; Oiwa, A.; Ishibashi, K.; Tarucha, S.; Buhmann, H.; Molenkamp, L. W.
2016-01-01
The Josephson effect describes the generic appearance of a supercurrent in a weak link between two superconductors. Its exact physical nature deeply influences the properties of the supercurrent. In recent years, considerable efforts have focused on the coupling of superconductors to the surface states of a three-dimensional topological insulator. In such a material, an unconventional induced p-wave superconductivity should occur, with a doublet of topologically protected gapless Andreev bound states, whose energies vary 4π-periodically with the superconducting phase difference across the junction. In this article, we report the observation of an anomalous response to rf irradiation in a Josephson junction made of a HgTe weak link. The response is understood as due to a 4π-periodic contribution to the supercurrent, and its amplitude is compatible with the expected contribution of a gapless Andreev doublet. Our work opens the way to more elaborate experiments to investigate the induced superconductivity in a three-dimensional insulator. PMID:26792013
Josephson effects in an alternating current biased transition edge sensor
NASA Astrophysics Data System (ADS)
Gottardi, L.; Kozorezov, A.; Akamatsu, H.; van der Kuur, J.; Bruijn, M. P.; den Hartog, R. H.; Hijmering, R.; Khosropanah, P.; Lambert, C.; van der Linden, A. J.; Ridder, M. L.; Suzuki, T.; Gao, J. R.
2014-10-01
We report the experimental evidence of the ac Josephson effect in a transition edge sensor (TES) operating in a frequency domain multiplexer and biased by ac voltage at MHz frequencies. The effect is observed by measuring the non-linear impedance of the sensor. The TES is treated as a weakly linked superconducting system and within the resistively shunted junction model framework. We provide a full theoretical explanation of the results by finding the analytic solution of the non-inertial Langevian equation of the system and calculating the non-linear response of the detector to a large ac bias current in the presence of noise.
The ω-SQUIPT as a tool to phase-engineer Josephson topological materials
NASA Astrophysics Data System (ADS)
Strambini, E.; D'Ambrosio, S.; Vischi, F.; Bergeret, F. S.; Nazarov, Yu. V.; Giazotto, F.
2016-12-01
Multi-terminal superconducting Josephson junctions based on the proximity effect offer the opportunity to tailor non-trivial quantum states in nanoscale weak links. These structures can realize exotic topologies in several dimensions, for example, artificial topological superconductors that are able to support Majorana bound states, and pave the way to emerging quantum technologies and future quantum information schemes. Here we report the realization of a three-terminal Josephson interferometer based on a proximized nanosized weak link. Our tunnelling spectroscopy measurements reveal transitions between gapped (that is, insulating) and gapless (conducting) states that are controlled by the phase configuration of the three superconducting leads connected to the junction. We demonstrate the topological nature of these transitions: a gapless state necessarily occurs between two gapped states of different topological indices, in much the same way that the interface between two insulators of different topologies is necessarily conducting. The topological numbers that characterize such gapped states are given by superconducting phase windings over the two loops that form the Josephson interferometer. As these gapped states cannot be transformed to one another continuously without passing through a gapless condition, they are topologically protected. The same behaviour is found for all of the points of the weak link, confirming that this topology is a non-local property. Our observation of the gapless state is pivotal for enabling phase engineering of different and more sophisticated artificial topological materials.
Feynman's and Ohta's Models of a Josephson Junction
ERIC Educational Resources Information Center
De Luca, R.
2012-01-01
The Josephson equations are derived by means of the weakly coupled two-level quantum system model given by Feynman. Adopting a simplified version of Ohta's model, starting from Feynman's model, the strict voltage-frequency Josephson relation is derived. The contribution of Ohta's approach to the comprehension of the additional term given by the…
Playing the role of weak clique property in link prediction: A friend recommendation model
NASA Astrophysics Data System (ADS)
Ma, Chuang; Zhou, Tao; Zhang, Hai-Feng
2016-07-01
An important fact in studying link prediction is that the structural properties of networks have significant impacts on the performance of algorithms. Therefore, how to improve the performance of link prediction with the aid of structural properties of networks is an essential problem. By analyzing many real networks, we find a typical structural property: nodes are preferentially linked to the nodes with the weak clique structure (abbreviated as PWCS to simplify descriptions). Based on this PWCS phenomenon, we propose a local friend recommendation (FR) index to facilitate link prediction. Our experiments show that the performance of FR index is better than some famous local similarity indices, such as Common Neighbor (CN) index, Adamic-Adar (AA) index and Resource Allocation (RA) index. We then explain why PWCS can give rise to the better performance of FR index in link prediction. Finally, a mixed friend recommendation index (labelled MFR) is proposed by utilizing the PWCS phenomenon, which further improves the accuracy of link prediction.
Playing the role of weak clique property in link prediction: A friend recommendation model.
Ma, Chuang; Zhou, Tao; Zhang, Hai-Feng
2016-07-21
An important fact in studying link prediction is that the structural properties of networks have significant impacts on the performance of algorithms. Therefore, how to improve the performance of link prediction with the aid of structural properties of networks is an essential problem. By analyzing many real networks, we find a typical structural property: nodes are preferentially linked to the nodes with the weak clique structure (abbreviated as PWCS to simplify descriptions). Based on this PWCS phenomenon, we propose a local friend recommendation (FR) index to facilitate link prediction. Our experiments show that the performance of FR index is better than some famous local similarity indices, such as Common Neighbor (CN) index, Adamic-Adar (AA) index and Resource Allocation (RA) index. We then explain why PWCS can give rise to the better performance of FR index in link prediction. Finally, a mixed friend recommendation index (labelled MFR) is proposed by utilizing the PWCS phenomenon, which further improves the accuracy of link prediction.
Low-noise THz MgB2 Josephson mixer
NASA Astrophysics Data System (ADS)
Cunnane, Daniel; Kawamura, Jonathan H.; Acharya, Narendra; Wolak, Matthäus A.; Xi, X. X.; Karasik, Boris S.
2016-09-01
The potential applications for high frequency operation of the Josephson effect in MgB2 include THz mixers, direct detectors, and digital circuits. Here we report on MgB2 weak links which exhibit the Josephson behavior up to almost 2 THz and using them for low-noise heterodyne detection of THz radiation. The devices are made from epitaxial film grown in the c-axis direction by the hybrid physical-chemical vapor deposition method. The current in the junctions travels parallel to the surface of the film, thus making possible a large contribution of the quasi-two-dimensional σ-gap in transport across the weak link. These devices are connected to a planar spiral antenna with a dielectric substrate lens to facilitate coupling to free-space radiation for use as a detector. The IcRn product of the junction is 5.25 mV, giving confirmation of a large gap parameter. The sensitivity of the mixer was measured from 0.6 THz to 1.9 THz. At a bath temperature of over 20 K, a mixer noise temperature less than 2000 K (DSB) was measured near 0.6 THz.
Weak Links: Stabilizers of Complex Systems from Proteins to Social Networks
NASA Astrophysics Data System (ADS)
Csermely, Peter
Why do women stabilize our societies? Why can we enjoy and understand Shakespeare? Why are fruitflies uniform? Why do omnivorous eating habits aid our survival? Why is Mona Lisa's smile beautiful? -- Is there any answer to these questions? This book shows that the statement: "weak links stabilize complex systems" holds the answers to all of the surprising questions above. The author (recipientof several distinguished science communication prizes) uses weak (low affinity, low probability) interactions as a thread to introduce a vast varietyof networks from proteins to ecosystems.
Implications of Weak Link Effects on Thermal Characteristics of Transition-Edge Sensors
NASA Technical Reports Server (NTRS)
Bailey, Catherine
2011-01-01
Weak link behavior in transition-edge sensor (TES) devices creates the need for a more careful characterization of a device's thermal characteristics through its transition. This is particularly true for small TESs where a small change in the measurement current results in large changes in temperature. A highly current-dependent transition shape makes accurate thermal characterization of the TES parameters through the transition challenging. To accurately interpret measurements, especially complex impedance, it is crucial to know the temperature-dependent thermal conductance, G(T), and heat capacity, C(T), at each point through the transition. We will present data illustrating these effects and discuss how we overcome the challenges that are present in accurately determining G and T from IV curves. We will also show how these weak link effects vary with TES size.
Field theoretical model of multilayered Josephson junction and dynamics of Josephson vortices
NASA Astrophysics Data System (ADS)
Fujimori, Toshiaki; Iida, Hideaki; Nitta, Muneto
2016-09-01
Multilayered Josephson junctions are modeled in the context of a field theory, and dynamics of Josephson vortices trapped inside insulators are studied. Starting from a theory consisting of complex and real scalar fields coupled to a U(1) gauge field which admit parallel N -1 domain-wall solutions, Josephson couplings are introduced weakly between the complex scalar fields. The N -1 domain walls behave as insulators separating N superconductors, where one of the complex scalar fields has a gap. We construct the effective Lagrangian on the domain walls, which reduces to a coupled sine-Gordon model for well-separated walls and contains more interactions for walls at short distance. We then construct sine-Gordon solitons emerging in an effective theory in which we identify Josephson vortices carrying singly quantized magnetic fluxes. When two neighboring superconductors tend to have the same phase, the ground state does not change with the positions of domain walls (the width of superconductors). On the other hand, when two neighboring superconductors tend to have π -phase differences, the ground state has a phase transition depending on the positions of domain walls; when the two walls are close to each other (one superconductor is thin), frustration occurs because of the coupling between the two superconductors besides the thin superconductor. Focusing on the case of three superconductors separated by two insulators, we find for the former case that the interaction between two Josephson vortices on different insulators changes its nature, i.e., attractive or repulsive, depending on the positions of the domain walls. In the latter case, there emerges fractional Josephson vortices when two degenerate ground states appear due to spontaneous charge-symmetry breaking, and the number of the Josephson vortices varies with the position of the domain walls. Our predictions should be verified in multilayered Josephson junctions.
Phase slips and vortex dynamics in Josephson oscillations between Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Abad, M.; Guilleumas, M.; Mayol, R.; Piazza, F.; Jezek, D. M.; Smerzi, A.
2015-02-01
We study the relation between Josephson dynamics and topological excitations in a dilute Bose-Einstein condensate confined in a double-well trap. We show that the phase slips responsible for the self-trapping regime are created by vortex rings entering and annihilating inside the weak-link region or created at the center of the barrier and expanding outside the system. Large amplitude oscillations just before the onset of self-trapping are also strictly connected with the dynamics of vortex rings at the edges of the inter-well barrier. Our results extend and analyze the dynamics of the vortex-induced phase slippages suggested a few decades ago in relation to the “ac” Josephson effect of superconducting and superfluid helium systems.
Nonlinear dynamics of Josephson vortices in a film screen under dc and ac magnetic fields
NASA Astrophysics Data System (ADS)
Sheikhzada, A.; Gurevich, A.
2014-11-01
We present detailed numerical simulations of Josephson vortices in a long Josephson junction perpendicular to a thin film screen under strong dc and ac magnetic fields. By solving the sine-Gordon equation, we calculated the threshold magnetic field for penetration of fluxons as a function of frequency, and the power dissipated by oscillating fluxons as functions of the ac field amplitude and frequency. We considered the effects of superimposed ac and dc fields, and a bi-harmonic magnetic field resulting in a vortex ratchet dynamics. The results were used to evaluate the contribution of weak-linked grain boundaries to the nonlinear surface resistance of polycrystalline superconductors under strong electromagnetic fields, particularly thin film screens and resonator cavities.
Playing the role of weak clique property in link prediction: A friend recommendation model
Ma, Chuang; Zhou, Tao; Zhang, Hai-Feng
2016-01-01
An important fact in studying link prediction is that the structural properties of networks have significant impacts on the performance of algorithms. Therefore, how to improve the performance of link prediction with the aid of structural properties of networks is an essential problem. By analyzing many real networks, we find a typical structural property: nodes are preferentially linked to the nodes with the weak clique structure (abbreviated as PWCS to simplify descriptions). Based on this PWCS phenomenon, we propose a local friend recommendation (FR) index to facilitate link prediction. Our experiments show that the performance of FR index is better than some famous local similarity indices, such as Common Neighbor (CN) index, Adamic-Adar (AA) index and Resource Allocation (RA) index. We then explain why PWCS can give rise to the better performance of FR index in link prediction. Finally, a mixed friend recommendation index (labelled MFR) is proposed by utilizing the PWCS phenomenon, which further improves the accuracy of link prediction. PMID:27439697
Enhancement of Shapiro-like steps in multiterminal Josephson structures
NASA Astrophysics Data System (ADS)
Savinov, D. A.
2016-08-01
The distinctive features of current-voltage characteristics are studied for mesoscopic multiterminal structures effected by external irradiation. Considering a simple model of applied dc+ac voltage, we calculate Shapiro-like steps in Josephson systems with several weakly coupled superconducting electrodes. Owing to the action of an external alternating signal, the dc current is found to be rather increased than it appears in the same multiterminal Josephson node without the radiation. The possible applications of our results for the experimental observation of the Shapiro-like steps in such Josephson structures are discussed.
Characterizing Weak-Link Effects in Mo/Au Transition-Edge Sensors
NASA Technical Reports Server (NTRS)
Smith, Stephen
2011-01-01
We are developing Mo/Au bilayer transition-edge sensors (TESs) for applications in X-ray astronomy. Critical current measurements on these TESs show they act as weak superconducting links exhibiting oscillatory, Fraunhofer-like, behavior with applied magnetic field. In this contribution we investigate the implications of this behavior for TES detectors, under operational bias conditions. This includes characterizing the logarithmic resistance sensitivity with temperature, (alpha, and current, beta, as a function of applied magnetic field and bias point within the resistive transition. Results show that these important device parameters exhibit similar oscillatory behavior with applied magnetic field, which in turn affects the signal responsivity, noise and energy resolution.
Weak links between fast mobility and local structure in molecular and atomic liquids
Bernini, S.; Puosi, F.; Leporini, D.
2015-03-28
We investigate by molecular-dynamics simulations, the fast mobility—the rattling amplitude of the particles temporarily trapped by the cage of the neighbors—in mildly supercooled states of dense molecular (linear trimers) and atomic (binary mixtures) liquids. The mixture particles interact by the Lennard-Jones potential. The non-bonded particles of the molecular system are coupled by the more general Mie potential with variable repulsive and attractive exponents in a range which is a characteristic of small n-alkanes and n-alcohols. Possible links between the fast mobility and the geometry of the cage (size and shape) are searched. The correlations on a per-particle basis are rather weak. Instead, if one groups either the particles in fast-mobility subsets or the cages in geometric subsets, the increase of the fast mobility with both the size and the asphericity of the cage is revealed. The observed correlations are weak and differ in states with equal relaxation time. Local forces between a tagged particle and the first-neighbour shell do not correlate with the fast mobility in the molecular liquid. It is concluded that the cage geometry alone is unable to provide a microscopic interpretation of the known, universal link between the fast mobility and the slow structural relaxation. We suggest that the particle fast dynamics is affected by regions beyond the first neighbours, thus supporting the presence of collective, extended fast modes.
Implications of Weak Link Effects on Thermal Characteristics of Transition-Edge Sensors
NASA Technical Reports Server (NTRS)
Bailey, C. N.; Adams, J. S.; Bandler, S. R.; Brekosky, R. P.; Chevenak, J. A.; Eckart, M. E.; Finkbeiner, F. M.; Kelley, R. L.; Kally, D. P.; Kilbourne, C. A.; Porter, F. S.; Sadleir, J. E.; Smith, S. J.
2012-01-01
Weak link behavior in transition-edge sensor (TES) microcalorimeters creates the need for a more careful characterization of a device's thermal characteristics through its transition. This is particularly true for small TESs where a small change in the bias current results in large changes in effective transition temperature. To correctly interpret measurements, especially complex impedance, it is crucial to know the temperature-dependent thermal conductance, G(T), and heat capacity, C(T), at each point through the transition. We present data illustrating these effects and discuss how we overcome the challenges that are present in accurately determining G and T from I-V curves. We also show how these weak link effects vary wi.th TES size. Additionally, we use this improVed understanding of G(T) to determine that, for these TES microcalorimeters. Kaptiza boundary resistance dominates the G of devices with absorbers while the electron-phonon coupling also needs to be considered when determining G for devices without absorbers
Josephson-vortex Cherenkov radiation
Mints, R.G.; Snapiro, I.B.
1995-10-01
We predict the Josephson-vortex Cherenkov radiation of an electromagnetic wave. We treat a long one-dimensional Josephson junction. We consider the wavelength of the radiated electromagnetic wave to be much less than the Josephson penetration depth. We use for calculations the nonlocal Josephson electrodynamics. We find the expression for the radiated power and for the radiation friction force acting on a Josephson vortex and arising due to the Cherenkov radiation. We calculate the relation between the density of the bias current and the Josephson vortex velocity.
Shu Deming; Maser, Jorg
2010-06-23
To use x-ray optics with nanometer resolution limit, scanning x-ray nanoprobes with corresponding mechanical positioning capability need to be designed. In particular, positioning stages with both sub-nanometer resolution and a positioning/scanning range of several millimeters are required. Based on our design of precision weak-link stages with interferometric encoders for the Center for Nanoscale Materials (CNM) hard x-ray nanoprobe at the Advanced Photon Source (APS) Sector 26, we have developed a new two-dimensional (2-D) weak-link stage system for nanopositioning of a specimen holder. This system provides sub-nanometer resolution, coupled with sub-nanometer metrology at a travel range of several millimeters. The 2-D weak-link stage system is designed with high structure stiffness using laminar overconstrained weak-link mechanisms [4-6]. In this paper we present the study of a linear precision weak-link stage system with sub-centimeter travel range and sub-nanometer positioning resolution. Design of a rotary weak-link stage system with 10-nrad resolution and 10-degree-level travel range is also discussed in this paper.
Cooling of a suspended nanowire by an ac Josephson current flow.
Sonne, Gustav; Peña-Aza, Milton E; Gorelik, Leonid Y; Shekhter, Robert I; Jonson, Mats
2010-06-04
We consider a nanoelectromechanical Josephson junction, where a suspended nanowire serves as a superconducting weak link, and show that an applied dc bias voltage can result in suppression of the flexural vibrations of the wire. This cooling effect is achieved through the transfer of vibronic energy quanta first to voltage-driven Andreev states and then to extended quasiparticle electronic states. Our analysis, which is performed for a nanowire in the form of a metallic carbon nanotube and in the framework of the density matrix formalism, shows that such self-cooling is possible down to the ground state of the flexural vibration mode of the nanowire.
Self-Oscillating Josephson Quantum Heat Engine
NASA Astrophysics Data System (ADS)
Marchegiani, G.; Virtanen, P.; Giazotto, F.; Campisi, M.
2016-11-01
The design of a mesoscopic self-oscillating heat engine that works thanks to purely quantum effects is presented. The proposed scheme is amenable to experimental implementation with current state-of-the-art nanotechnology and materials. One of the main features of the structure is its versatility: The engine can deliver work to a generic load without galvanic contact. This versatility makes it a promising building block for low-temperature on-chip energy-management applications. The heat engine consists of a circuit featuring a thermoelectric element based on a ferromagnetic insulator-superconductor tunnel junction and a Josephson weak link that realizes a purely quantum dc-ac converter. This makeup enables the contactless transfer of work to the load (a generic RL circuit). The performance of the heat engine is investigated as a function of the thermal gradient applied to the thermoelectric junction. Power up to 1 pW can be delivered to a load RL=10 Ω .
Vortices in a toroidal Bose-Einstein condensate with a rotating weak link
NASA Astrophysics Data System (ADS)
Yakimenko, A. I.; Bidasyuk, Y. M.; Weyrauch, M.; Kuriatnikov, Y. I.; Vilchinskii, S. I.
2015-03-01
Motivated by a recent experiment [K. C. Wright et al., Phys. Rev. Lett. 110, 025302 (2013), 10.1103/PhysRevLett.110.025302], we investigate deterministic discontinuous jumps between quantized circulation states in a toroidally trapped Bose-Einstein condensate. These phase slips are induced by vortex excitations created by a rotating weak link. We analyze the influence of a localized condensate density depletion and atomic superflows, governed by the rotating barrier, on the energetic and dynamical stability of the vortices in the ring-shaped condensate. We simulate in a three-dimensional dissipative mean-field model the dynamics of the condensate using parameters similar to the experimental conditions. Moreover, we consider the dynamics of the stirred condensate far beyond the experimentally explored region and reveal surprising manifestations of complex vortex dynamics.
Josephson device for voltage measurement
NASA Astrophysics Data System (ADS)
Régent, A.; Villegier, J. C.; Angénieux, G.; Monllor, C.; Delahaye, F.
This paper describes a new Josephson device with microwave integrated circuit for voltage standard. The circuit is essentially made of a resonator (Nb), the Josephson junction (Nb, NbOx, Pb-In) and a capacitive microstrip section (Pb-In) which ends the rf part; the dc connections are through Cauer Filters (Nb or Pb-In). A niobium film is deposited on the opposite side of the fused quartz substrate as a ground plane. The circuit is enclosed in a special package with outside dc and rf connections. The technology ensures very good cyclability and lifetime with storage at room temperature. In liquid helium (4.2 K) with a very weak rf power less than 0.5 milliwatts at the frequency resonance (11.5 GHz), 100 μ A high current steps were obtained near a polarization of 4.5 mV. These devices allows a precision of 1 × 10 -7 on the volt standard when used with a series-parallel divider of fixed value (ratio 225). The precise adjustment of the voltages is made by a slight drift of the rf frequency of the source, allowed by the high rf coupling factor of the device and the band width of its resonance.
Precise Heater Controller with rf-Biased Josephson Junctions
NASA Technical Reports Server (NTRS)
Green, Colin J.; Sergatskov, Dmitri A.; Duncan, R. V.
2003-01-01
Paramagnetic susceptibility thermometers used in fundamental physics experiments are capable of measuring temperature changes with a precision of a part in 2 x 10(exp 10). However, heater controllers are only able to control open-loop power dissipation to about a part in 10(exp 5). We used an array of rf-biased Josephson junctions to precisely control the electrical power dissipation in a heater resistor mounted on a thermally isolated cryogenic platform. Theoretically, this method is capable of controlling the electrical power dissipation to better than a part in 10(exp 12). However, this level has not yet been demonstrated experimentally. The experiment consists of a liquid helium cell that also functions as a high-resolution PdMn thermometer, with a heater resistor mounted on it. The cell is thermally connected to a temperature-controlled cooling stage via a weak thermal link. The heater resistor is electrically connected to the array of Josephson junctions using superconducting wire. An rf-biased array of capacitively shunted Josephson junctions drives the voltage across the heater. The quantized voltage across the resistor is Vn = nf(h/2e), where h is Planck's constant, f is the array biasing frequency, e is the charge of an electron, and n is the integer quantum state of the Josephson array. This results in an electrical power dissipation on the cell of Pn = (Vn)(sup 2/R), where R is the heater resistance. The change of the quantum state of the array changes the power dissipated in the heater, which in turn, results in the change of the cell temperature. This temperature change is compared to the expected values based on the known thermal standoff resistance of the cell from the cooling stage. We will present our initial experimental results and discuss future improvements. This work has been funded by the Fundamental Physics Discipline of the Microgravity Science Office of NASA, and supported by a no-cost equipment loan from Sandia National Laboratories.
Interactions between electrons, mesoscopic Josephson effect and asymmetric current fluctuations
NASA Astrophysics Data System (ADS)
Huard, B.
2006-07-01
This article discusses three experiments on the properties of electronic transport at the mesoscopic scale. The first one allowed to measure the energy exchange rate between electrons in a metal contaminated by a very weak concentration of magnetic impurities. The role played by magnetic impurities in the Kondo regime on those energy exchanges is quantitatively investigated, and the global measured exchange rate is larger than expected. The second experiment is a measurement of the current-phase relation in a system made of two superconductors linked through a single atom. We thus provide quantitative support for the recent description of the mesoscopic Josephson effect. The last experiment is a measurement of the asymmetry of the current fluctuations in a mesoscopic conductor, using a Josephson junction as a threshold detector. Cet ouvrage décrit trois expériences portant sur les propriétés du transport électronique à l'échelle mésoscopique. La première a permis de mesurer le taux d'échange d'énergie entre électrons dans un métal contenant une très faible concentration d'impuretés magnétiques. Nous avons validé la description quantitative du rôle des impuretés magnétiques dans le régime Kondo sur ces échanges énergétiques et aussi montré que le taux global d'échange est plus fort que prévu. La seconde expérience est une mesure de la relation courant-phase dans un système constitué de deux supraconducteurs couplés par un seul atome. Elle nous a permis de conforter quantitativement la récente description de l'effet Josephson mésoscopique. La dernière expérience est unemesure de l'asymétrie des fluctuations du courant dans un conducteur mésoscopique en utilisant une Jonction Josephson comme détecteur de seuil.
Research on characteristics of free-space optical communication link in weak atmospheric turbulence
NASA Astrophysics Data System (ADS)
Cui, Liguo; Hou, Zaihong; Li, Fei
2013-08-01
Research on characteristics of atmospheric communication link becomes a subject of current interest, and often mainly focuses on some fading parameters including the probability of fade, the mean fade number and the mean fade time. The contribution of false alarm to bit error rate has been considered, however, the temporal characteristic is rarely mentioned., To make up the deficiency, parameters integrating the influence of false alarm and fading were defined. On one hand, the laser communication link were modeled for Gamma-Gamma distribution of irradiance fluctuation subjected to weak atmospheric turbulence. Accordingly the mathematical expressions of these parameters were deduced. On the other hand, characteristic of the parameters were obtained by numerical simulation with various channel environment parameters, such as mean signal-to-noise ratio (SNR), zenith angle and detection threshold. Compared with other researches on fade characteristic, some different conclusions can be drawn from simulation results. With the same SNR and zenith angle, there is an optimum value of detection threshold corresponding to the minimum mean error number, which deviates obviously from that obtained according to the minimum error probability. Either increasing SNR or decreasing zenith angle can reduce mean error number and the optimum threshold. Different from mean error number, mean error time is slightly influenced with channel environment parameters and constant at the order of milliseconds.
Sheikhzada, Ahmad; Gurevich, Alex
2015-01-01
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids. PMID:26639165
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. In conclusion, our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.
Sheikhzada, Ahmad; Gurevich, Alex
2015-12-07
Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result,more » vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. In conclusion, our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.« less
Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces
Jabdaraghi, R. N.; Peltonen, J. T.; Saira, O.-P.; Pekola, J. P.
2016-01-25
We characterize niobium-based lateral Superconductor (S)–Normal metal (N)–Superconductor (SNS) weak links through low-temperature switching current measurements and tunnel spectroscopy. We fabricate the SNS devices in two separate lithography and deposition steps, combined with strong argon ion cleaning before the normal metal deposition in the last step. Our SNS weak link consists of high-quality sputtered Nb electrodes that have contacted with evaporated Cu. The two-step fabrication flow enables more flexibility in the choice of materials and pattern design. A comparison of the temperature-dependent equilibrium critical supercurrent with theoretical predictions indicates that the quality of the Nb-Cu interface is similar to that of evaporated Al-Cu weak links. We further demonstrate a hybrid magnetic flux sensor based on an Nb-Cu-Nb SNS junction, where the phase-dependent normal metal density of states is probed with an Al tunnel junction.
Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces
NASA Astrophysics Data System (ADS)
Jabdaraghi, R. N.; Peltonen, J. T.; Saira, O.-P.; Pekola, J. P.
2016-01-01
We characterize niobium-based lateral Superconductor (S)-Normal metal (N)-Superconductor (SNS) weak links through low-temperature switching current measurements and tunnel spectroscopy. We fabricate the SNS devices in two separate lithography and deposition steps, combined with strong argon ion cleaning before the normal metal deposition in the last step. Our SNS weak link consists of high-quality sputtered Nb electrodes that have contacted with evaporated Cu. The two-step fabrication flow enables more flexibility in the choice of materials and pattern design. A comparison of the temperature-dependent equilibrium critical supercurrent with theoretical predictions indicates that the quality of the Nb-Cu interface is similar to that of evaporated Al-Cu weak links. We further demonstrate a hybrid magnetic flux sensor based on an Nb-Cu-Nb SNS junction, where the phase-dependent normal metal density of states is probed with an Al tunnel junction.
Johnson, Jay Dean; Oberkampf, William Louis; Helton, Jon Craig
2004-12-01
Relationships to determine the probability that a weak link (WL)/strong link (SL) safety system will fail to function as intended in a fire environment are investigated. In the systems under study, failure of the WL system before failure of the SL system is intended to render the overall system inoperational and thus prevent the possible occurrence of accidents with potentially serious consequences. Formal developments of the probability that the WL system fails to deactivate the overall system before failure of the SL system (i.e., the probability of loss of assured safety, PLOAS) are presented for several WWSL configurations: (i) one WL, one SL, (ii) multiple WLs, multiple SLs with failure of any SL before any WL constituting failure of the safety system, (iii) multiple WLs, multiple SLs with failure of all SLs before any WL constituting failure of the safety system, and (iv) multiple WLs, multiple SLs and multiple sublinks in each SL with failure of any sublink constituting failure of the associated SL and failure of all SLs before failure of any WL constituting failure of the safety system. The indicated probabilities derive from time-dependent temperatures in the WL/SL system and variability (i.e., aleatory uncertainty) in the temperatures at which the individual components of this system fail and are formally defined as multidimensional integrals. Numerical procedures based on quadrature (i.e., trapezoidal rule, Simpson's rule) and also on Monte Carlo techniques (i.e., simple random sampling, importance sampling) are described and illustrated for the evaluation of these integrals. Example uncertainty and sensitivity analyses for PLOAS involving the representation of uncertainty (i.e., epistemic uncertainty) with probability theory and also with evidence theory are presented.
Krishnan, Kapil; Brown, Andrew; Wayne, Leda; Vo, Johnathan; Opie, Saul; Lim, Harn; Peralta, Pedro; Luo, Sheng-Nian; Byler, Darrin; McClellan, Kenneth J.; Koskelo, Aaron; Dickerson, Robert
2014-11-25
Local microstructural weak links for spall damage were investigated using three-dimensional (3-D) characterization in multicrystalline copper samples (grain size ≈ 450 µm) shocked with laser-driven plates at low pressures (2 to 4 GPa). The thickness of samples and flyer plates, approximately 1000 and 500 µm respectively, led to short pressure pulses that allowed isolating microstructure effects on local damage characteristics. Electron Backscattering Diffraction and optical microscopy were used to relate the presence, size, and shape of porosity to local microstructure. The experiments were complemented with 3-D finite element simulations of individual grain boundaries (GBs) that resulted in large damage volumes using crystal plasticity coupled with a void nucleation and growth model. Results from analysis of these damage sites show that the presence of a GB-affected zone, where strain concentration occurs next to a GB, correlates strongly with damage localization at these sites, most likely due to the inability of maintaining strain compatibility across these interfaces, with additional effects due to the inclination of the GB with respect to the shock. Results indicate that strain compatibility plays an important role on intergranular spall damage in metallic materials.
Sampling: the weak link in the sanitary quality control system of agricultural products.
Blanc, Michel
2006-05-01
To ensure a high level of consumer protection, the European Union has in the past years published several regulations setting very low limits for a given number of food contaminants (pesticides, mycotoxins, heavy metals) in many agricultural products (cereals, oilseeds, dry fruits, coffee, spices, etc). These new regulations regarding the sanitary quality of agricultural products, compel both economic operators and officials of different EU member states to set up sampling plans and rigorous analyses aimed at checking whether a product lot complies with the required standards prior to its release on the market. While the laboratory analysis management today is outstanding thanks to the validated and efficient detection methods and procedures available for quality assurance in laboratories (accreditation), this is not necessarily true of the sampling operation, which seems to be the weak link in the sanitary control system for agricultural products. The sampling operation is often the main source of error when assessing the sanitary quality of a lot of agricultural commodities, with both commercial (downgrading of the product) and sanitary (marketing of a product which poses a health risk for the consumer) consequences. Therefore, it is essential for the operators involved to be aware of the significance and difficulties of the sampling operation, which requires important equipment and human resources. Furthermore, drawing up specific standards and guidelines, as well as setting up quality assurance procedures, at the level in charge of carrying out this delicate and important operation, are necessary.
Krishnan, Kapil; Brown, Andrew; Wayne, Leda; ...
2014-11-25
Local microstructural weak links for spall damage were investigated using three-dimensional (3-D) characterization in multicrystalline copper samples (grain size ≈ 450 µm) shocked with laser-driven plates at low pressures (2 to 4 GPa). The thickness of samples and flyer plates, approximately 1000 and 500 µm respectively, led to short pressure pulses that allowed isolating microstructure effects on local damage characteristics. Electron Backscattering Diffraction and optical microscopy were used to relate the presence, size, and shape of porosity to local microstructure. The experiments were complemented with 3-D finite element simulations of individual grain boundaries (GBs) that resulted in large damage volumesmore » using crystal plasticity coupled with a void nucleation and growth model. Results from analysis of these damage sites show that the presence of a GB-affected zone, where strain concentration occurs next to a GB, correlates strongly with damage localization at these sites, most likely due to the inability of maintaining strain compatibility across these interfaces, with additional effects due to the inclination of the GB with respect to the shock. Results indicate that strain compatibility plays an important role on intergranular spall damage in metallic materials.« less
NASA Astrophysics Data System (ADS)
Gallagher, Patrick; Lee, Menyoung; Williams, James R.; Goldhaber-Gordon, David
2014-10-01
Two-dimensional electron systems in gallium arsenide and graphene have enabled ground-breaking discoveries in condensed-matter physics, in part because they are easily modulated by voltages on nanopatterned gate electrodes. Electron systems at oxide interfaces hold a similarly large potential for fundamental studies of correlated electrons and novel device technologies, but typically have carrier densities too large to control by conventional gating techniques. Here we present a quantum transport study of a superconducting strontium titanate (STO) interface, enabled by a combination of electrolyte and metal-oxide gating. Our structure consists of two superconducting STO banks flanking a nanoscale STO weak link, which is tunable at low temperatures from insulating to superconducting behaviour by a local metallic gate. At low gate voltages, our device behaves as a quantum point contact that exhibits a minimum conductance plateau of e2/h in zero applied magnetic field, half the expected value for spin-degenerate electrons, but consistent with predictions and experimental signatures of a magnetically ordered ground state. The quantum point contact mediates tunnelling between normal and superconducting regions, enabling lateral tunnelling spectroscopy of the local superconducting state. Our work provides a generic scheme for quantum transport studies of STO and other surface electron liquids.
Quantum Phase Transition in Josephson Junction Arrays
NASA Astrophysics Data System (ADS)
Moon, K.; Girvin, S. M.
1997-03-01
One-dimensional Josephson junction arrays of SQUIDS exhibit a novel superconductor-insulator phase transition. The critical regime can be accessed by tuning the effective Josephson coupling energy using a weak magnetic field applied to the SQUIDS. The role of instantons induced by quantum fluctuations will be discussed. One novel feature of these systems which can be explained in terms of quantum phase slips is that in some regimes, the array resistance decreases with increasing length of the array. We calculate the finite temperature crossover function for the array resistance and compare our theoretical results with the recent experiments by D. Haviland and P. Delsing at Chalmers. This work is supported by DOE grant #DE-FG02-90ER45427 and by NSF DMR-9502555.
Merkle, K.L.; Huang, Y.
1998-01-01
The electric transport of high-temperature superconductors, such as YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO), can be strongly restricted by the presence of high-angle grain boundaries (GB). This weak-link behavior is governed by the macroscopic GB geometry and the microscopic grain boundary structure and composition at the atomic level. Whereas grain boundaries present a considerable impediment to high current applications of high T{sub c} materials, there is considerable commercial interest in exploiting the weak-link-nature of grain boundaries for the design of microelectronic devices, such as superconducting quantum interference devices (SQUIDs). The Josephson junctions which form the basis of this technology can also be formed by introducing artificial barriers into the superconductor. The authors have examined both types of Josephson junctions by EM techniques in an effort to understand the connection between microstructure/chemistry and electrical transport properties. This knowledge is a valuable resource for the design and production of improved devices.
High-T(sub c) Edge-geometry SNS Weak Links on Silicon-on-sapphire Substrates
NASA Technical Reports Server (NTRS)
Hunt, B.; Foote, M.; Pike, W.; Barner, J.; Vasquez, R.
1994-01-01
High-quality superconductor/normal-metal/superconductor(SNS) edge-geometry weak links have been produced on silicon-on-sapphire (SOS) substrates using a new SrTiO(sub 3)/'seed layer'/cubic-zirconia (YS2) buffer system.
Signatures of topological Josephson junctions
NASA Astrophysics Data System (ADS)
Peng, Yang; Pientka, Falko; Berg, Erez; Oreg, Yuval; von Oppen, Felix
2016-08-01
Quasiparticle poisoning and diabatic transitions may significantly narrow the window for the experimental observation of the 4 π -periodic dc Josephson effect predicted for topological Josephson junctions. Here, we show that switching-current measurements provide accessible and robust signatures for topological superconductivity which persist in the presence of quasiparticle poisoning processes. Such measurements provide access to the phase-dependent subgap spectrum and Josephson currents of the topological junction when incorporating it into an asymmetric SQUID together with a conventional Josephson junction with large critical current. We also argue that pump-probe experiments with multiple current pulses can be used to measure the quasiparticle poisoning rates of the topological junction. The proposed signatures are particularly robust, even in the presence of Zeeman fields and spin-orbit coupling, when focusing on short Josephson junctions. Finally, we also consider microwave excitations of short topological Josephson junctions which may complement switching-current measurements.
Josephson-CMOS Hybrid Memories
2007-04-25
Liu, X . Meng, S. R. Whiteley, and T. Van Duzer, “Characterization of 4 K CMOS devices and circuits for hybrid Josephson- CMOS systems,” IEEE Trans. on...Josephson- CMOS hybrid memories Qingguo Liu Electrical Engineering and Computer Sciences University of California at Berkeley Technical Report No. UCB...to 00-00-2007 4. TITLE AND SUBTITLE Josephson- CMOS hybrid memories 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S
Narla, A.; Sliwa, K. M.; Hatridge, M.; Shankar, S.; Frunzio, L.; Schoelkopf, R. J.; Devoret, M. H.
2014-06-09
Josephson junction parametric amplifiers are playing a crucial role in the readout chain in superconducting quantum information experiments. However, their integration with current 3D cavity implementations poses the problem of transitioning between waveguide, coax cables, and planar circuits. Moreover, Josephson amplifiers require auxiliary microwave components, like directional couplers and/or hybrids, that are sources of spurious losses and impedance mismatches that limit measurement efficiency and amplifier tunability. We have developed a wireless architecture for these parametric amplifiers that eliminates superfluous microwave components and interconnects. This greatly simplifies their assembly and integration into experiments. We present an experimental realization of such a device operating in the 9–11 GHz band with about 100 MHz of amplitude gain-bandwidth product, on par with devices mounted in conventional sample holders. The simpler impedance environment presented to the amplifier also results in increased amplifier tunability.
Protected Josephson Rhombus Chains
NASA Astrophysics Data System (ADS)
Bell, Matthew T.; Paramanandam, Joshua; Ioffe, Lev B.; Gershenson, Michael E.
2014-04-01
We have studied the low-energy excitations in a minimalistic protected Josephson circuit which contains two basic elements (rhombi) characterized by the π periodicity of the Josephson energy. Novel design of these elements, which reduces their sensitivity to the offset charge fluctuations, has been employed. We have observed that the lifetime T1 of the first excited state of this quantum circuit in the protected regime is increased up to 70 μs, a factor of ˜100 longer than that in the unprotected state. The quality factor ω01T1 of this qubit exceeds 106. Our results are in agreement with theoretical expectations; they demonstrate the feasibility of symmetry protection in the rhombus-based qubits fabricated with existing technology.
The structural role of weak and strong links in a financial market network
NASA Astrophysics Data System (ADS)
Garas, A.; Argyrakis, P.; Havlin, S.
2008-05-01
We investigate the properties of correlation based networks originating from economic complex systems, such as the network of stocks traded at the New York Stock Exchange (NYSE). The weaker links (low correlation) of the system are found to contribute to the overall connectivity of the network significantly more than the strong links (high correlation). We find that nodes connected through strong links form well defined communities. These communities are clustered together in more complex ways compared to the widely used classification according to the economic activity. We find that some companies, such as General Electric (GE), Coca Cola (KO), and others, can be involved in different communities. The communities are found to be quite stable over time. Similar results were obtained by investigating markets completely different in size and properties, such as the Athens Stock Exchange (ASE). The present method may be also useful for other networks generated through correlations.
Anomalous spin Josephson effect
NASA Astrophysics Data System (ADS)
Wang, Mei-Juan; Wang, Jun; Hao, Lei; Liu, Jun-Feng
2016-10-01
We report a theoretical study on the spin Josephson effect arising from the exchange coupling of the two ferromagnets (Fs), which are deposited on a two-dimensional (2D) time-reversal-invariant topological insulator. An anomalous spin supercurrent Js z˜sin(α +α0) is found to flow in between the two Fs and the ground state of the system is not limited to the magnetically collinear configuration (α =n π ,n is an integer) but determined by a controllable angle α0, where α is the crossed angle between the two F magnetizations. The angle α0 is the dynamic phase of the electrons traveling in between the two Fs and can be controlled electrically by a gate voltage. This anomalous spin Josephson effect, similar to the conventional φ0 superconductor junction, originates from the definite electron chirality of the helical edge states in the 2D topological insulator. These results indicate that the magnetic coupling in a topological system is different from the usual one in conventional materials.
Origin of grain boundary weak links in BaPb1 - xBixO3 superconductor
NASA Astrophysics Data System (ADS)
Takagi, T.; Chiang, Y.-M.; Roshko, A.
1990-12-01
Although BaPb0.75Bi0.25O3 (BPB) has a comparatively large superconducting coherence length of ˜7 nm and no reported anisotropy in its superconducting parameters, polycrystalline BPB exhibits the same rapid decrease in transport critical current density (Jct) with low applied field (<˜50 Oe) that is characteristic of grain boundary weak links in cuprate superconductors (e.g., La2-xSrxCuO4, YBa2Cu3O7-x ). We have studied the effects of processing thermal history on the formation and morphology of grain boundary phases, and on the composition of BPB boundaries with and without second phase, in order to understand the origin of these weak links. Scanning transmission electron microscopy and Auger electron spectroscopy results show the presence of a Pb-Bi-Ba-O phase that is wetting and liquid above ˜570 °C, but which retracts to three-grain junctions upon slow cooling or annealing at lower temperatures. However, weak-link behavior persists in materials with retracted secondary phase, as well as in hot isostatically pressed samples that never exceed the secondary phase melting temperature. It is found that the grain boundaries remain Bi- and Pb-rich even after the retraction of secondary phases; samples that never exceed the melting temperature of the secondary phase show absence of segregation at some but not all grain boundaries. The composition of the grain boundaries as well as Jct vs temperature measurements indicate that the boundaries act as SIS tunnel junctions.
Quantum circuit theory and measurements on Y-Ba-Cu-O grain-boundary weak-link bridges
NASA Astrophysics Data System (ADS)
How, H.; Jiang, H.; Widom, A.; Vittoria, C.
1994-01-01
The quantum system associated with a resistor-shunted weak-link junction circuit may be described in terms of a single Lagrangian. In this representation the degrees of freedom internal to the dissipative energy of the resistor can be systematically separated from the Hamiltonian formulation of the circuit. This allows us to solve the quantum states of the junction while the effects of the resistor on the circuit are included as a Lagrangian multiplier. In this manner the effects of the measuring apparatus or resistor on the quantum state of the junction may be calculable. The calculations are in very good agreement with experiments.
Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas
NASA Astrophysics Data System (ADS)
Happel, T.; Manz, P.; Ryter, F.; Hennequin, P.; Hetzenecker, A.; Conway, G. D.; Guimarais, L.; Honoré, C.; Stroth, U.; Viezzer, E.; The ASDEX Upgrade Team
2016-06-01
This letter shows for the first time a pronounced increase of extremely intermittent edge density turbulence behavior inside the confinement region related to the I-mode confinement regime in the ASDEX Upgrade tokamak. With improving confinement, the perpendicular propagation velocity of density fluctuations in the plasma edge increases together with the intermittency of the observed density bursts. Furthermore, it is shown that the weakly coherent mode, a fluctuation feature generally observed in I-mode plasmas, is connected to the observed bursts. It is suggested that the large amplitude density bursts could be generated by a non-linearity similar to that in the Korteweg-de-Vries equation which includes the radial temperature gradient.
Optimal spike-based communication in excitable networks with strong-sparse and weak-dense links.
Teramae, Jun-nosuke; Tsubo, Yasuhiro; Fukai, Tomoki
2012-01-01
The connectivity of complex networks and functional implications has been attracting much interest in many physical, biological and social systems. However, the significance of the weight distributions of network links remains largely unknown except for uniformly- or Gaussian-weighted links. Here, we show analytically and numerically, that recurrent neural networks can robustly generate internal noise optimal for spike transmission between neurons with the help of a long-tailed distribution in the weights of recurrent connections. The structure of spontaneous activity in such networks involves weak-dense connections that redistribute excitatory activity over the network as noise sources to optimally enhance the responses of individual neurons to input at sparse-strong connections, thus opening multiple signal transmission pathways. Electrophysiological experiments confirm the importance of a highly broad connectivity spectrum supported by the model. Our results identify a simple network mechanism for internal noise generation by highly inhomogeneous connection strengths supporting both stability and optimal communication.
Optimal spike-based communication in excitable networks with strong-sparse and weak-dense links
NASA Astrophysics Data System (ADS)
Teramae, Jun-Nosuke; Tsubo, Yasuhiro; Fukai, Tomoki
2012-07-01
The connectivity of complex networks and functional implications has been attracting much interest in many physical, biological and social systems. However, the significance of the weight distributions of network links remains largely unknown except for uniformly- or Gaussian-weighted links. Here, we show analytically and numerically, that recurrent neural networks can robustly generate internal noise optimal for spike transmission between neurons with the help of a long-tailed distribution in the weights of recurrent connections. The structure of spontaneous activity in such networks involves weak-dense connections that redistribute excitatory activity over the network as noise sources to optimally enhance the responses of individual neurons to input at sparse-strong connections, thus opening multiple signal transmission pathways. Electrophysiological experiments confirm the importance of a highly broad connectivity spectrum supported by the model. Our results identify a simple network mechanism for internal noise generation by highly inhomogeneous connection strengths supporting both stability and optimal communication.
Phase slippage and self-trapping in a self-induced bosonic Josephson junction
Abad, M.; Guilleumas, M.; Mayol, R.; Pi, M.; Jezek, D. M.
2011-09-15
A dipolar condensate confined in a toroidal trap constitutes a self-induced Josephson junction when the dipoles are oriented perpendicularly to the trap symmetry axis and the s-wave scattering length is small enough. The ring-shaped double-well potential coming from the anisotropic character of the mean-field dipolar interaction is robust enough to sustain self-trapping dynamics, which takes place when the initial population imbalance between the two wells is large. We show that, in this system, the self-trapping regime is directly related to a vortex-induced phase-slip dynamics. A vortex and antivortex are spontaneously nucleated in the low-density regions before a minimum of the population imbalance is reached and then cross the toroidal section in opposite directions through the junctions. This vortex dynamics yields a phase slip between the two weakly linked condensates causing an inversion of the particle flux.
The weak link: do muscle properties determine locomotor performance in frogs?
Roberts, Thomas J.; Abbott, Emily M.; Azizi, Emanuel
2011-01-01
Muscles power movement, yet the conceptual link between muscle performance and locomotor performance is poorly developed. Frog jumping provides an ideal system to probe the relationship between muscle capacity and locomotor performance, because a jump is a single discrete event and mechanical power output is a critical determinant of jump distance. We tested the hypothesis that interspecific variation in jump performance could be explained by variability in available muscle power. We used force plate ergometry to measure power produced during jumping in Cuban tree frogs (Osteopilus septentrionalis), leopard frogs (Rana pipiens) and cane toads (Bufo marinus). We also measured peak isotonic power output in isolated plantaris muscles for each species. As expected, jump performance varied widely. Osteopilus septentrionalis developed peak power outputs of 1047.0 ± 119.7 W kg−1 hindlimb muscle mass, about five times that of B. marinus (198.5 ± 54.5 W kg−1). Values for R. pipiens were intermediate (543.9 ± 96.2 W kg−1). These differences in jump power were not matched by differences in available muscle power, which were 312.7 ± 28.9, 321.8 ± 48.5 and 262.8 ± 23.2 W kg−1 muscle mass for O. septentrionalis, R. pipiens and B. marinus, respectively. The lack of correlation between available muscle power and jump power suggests that non-muscular mechanisms (e.g. elastic energy storage) can obscure the link between muscle mechanical performance and locomotor performance. PMID:21502120
Simple Electronic Analog of a Josephson Junction.
ERIC Educational Resources Information Center
Henry, R. W.; And Others
1981-01-01
Demonstrates that an electronic Josephson junction analog constructed from three integrated circuits plus an external reference oscillator can exhibit many of the circuit phenomena of a real Josephson junction. Includes computer and other applications of the analog. (Author/SK)
Spin-asymmetric Josephson plasma oscillations
NASA Astrophysics Data System (ADS)
Kreula, J. M.; Valtolina, G.; Törmä, P.
2017-01-01
The spin-asymmetric Josephson effect is a proposed quantum-coherent tunneling phenomenon where Cooper-paired fermionic spin-1/2 particles, which are subjected to spin-dependent potentials across a Josephson junction, undergo frequency-synchronized alternating-current Josephson oscillations with spin-dependent amplitudes. Here, in line with present-day techniques in ultracold Fermi gas setups, we consider the regime of small Josephson oscillations and show that the Josephson plasma oscillation amplitude becomes spin dependent in the presence of spin-dependent potentials, while the Josephson plasma frequency is the same for both spin components. Detecting these spin-dependent Josephson plasma oscillations provides a possible means to establish the yet-unobserved spin-asymmetric Josephson effect with ultracold Fermi gases using existing experimental tools.
Weak trophic links between a crab-spider and the effective pollinators of a rewardless orchid
NASA Astrophysics Data System (ADS)
Quintero, Carolina; Corley, Juan C.; Aizen, Marcelo A.
2015-01-01
Sit and wait predators hunting on flowers are considered to be exploiters of plant-pollinator mutualisms. Several studies have shown that plant-pollinator interactions can be highly susceptible to the impact of a third trophic level, via consumptive (direct) and non-consumptive (indirect) effects that alter pollinator behavior and, ultimately, plant fitness. However, most flowering plants attract a wide array of flower visitors, from which only a subset will be effective pollinators. Hence, a negative effect of an ambush predator on plant fitness should be expected only when: (i) the effective pollinators are part of the predators' diet and/or (ii) the non-consumptive effects of predator presence (e.g. dead prey) alter the behavior of effective pollinators and pollen movement among individual plants. We analyzed the direct and indirect effects of a crab-spider (Misumenops pallidus), on the pollination and reproductive success of Chloraea alpina, a Patagonian rewardless orchid. Our results indicate that most of the flower visitors do not behave as effective pollinators and most effective pollinators were not observed as prey for the crab-spider. In terms of non-consumptive effects, inflorescences with and without spiders and/or dead-prey did not vary the frequency of flower visitors, nor pollinia removal or deposition. Hence, it is not surprising that M. pallidus has a neutral effect on pollinia removal and deposition as well as on fruit and seed set. Similar to other rewardless orchids, the low reproductive success of C. alpina (∼6% fruit set) was associated with the limited number of visits by effective pollinators. Negative top-down effects of a flower-visitor predator on plant pollination may not be anticipated without studying the direct and indirect effects of this predator on the effective pollinators. In pollination systems where effective pollinators visited flowers erratically, such as in deceptive orchids, we expect weak or no effect of predators on
Weak beacon detection for air-to-ground optical wireless link establishment.
Han, Yaoqiang; Dang, Anhong; Tang, Junxiong; Guo, Hong
2010-02-01
In an air-to-ground free-space optical communication system, strong background interference seriously affects the beacon detection, which makes it difficult to establish the optical link. In this paper, we propose a correlation beacon detection scheme under strong background interference conditions. As opposed to traditional beacon detection schemes, the beacon is modulated by an m-sequence at the transmitting terminal with a digital differential matched filter (DDMF) array introduced at the receiving end to detect the modulated beacon. This scheme is capable of suppressing both strong interference and noise by correlation reception of the received image sequence. In addition, the DDMF array enables each pixel of the image sensor to have its own DDMF of the same structure to process its received image sequence in parallel, thus it makes fast beacon detection possible. Theoretical analysis and an outdoor experiment have been demonstrated and show that the proposed scheme can realize fast and effective beacon detection under strong background interference conditions. Consequently, the required beacon transmission power can also be reduced dramatically.
ERIC Educational Resources Information Center
Clarke, John
1970-01-01
Discusses the theory of the Josephson Effect, the derivation of the Josephson voltage-frequency relation, and methods of measuring the fundamental constatn ratio e/h. Various types of Josephson junctions are described. The impact of the measurement of e/h upin the fundamental constants and quantum electro-dynamics is briefly discussed.…
NASA Astrophysics Data System (ADS)
Aghamalyan, D.; Nguyen, N. T.; Auksztol, F.; Gan, K. S.; Martinez Valado, M.; Condylis, P. C.; Kwek, L.-C.; Dumke, R.; Amico, L.
2016-07-01
We study a physical system consisting of a Bose-Einstein condensate confined to a ring shaped lattice potential interrupted by three weak links. The system is assumed to be driven by an effective flux piercing the ring lattice. By employing path integral techniques, we explore the effective quantum dynamics of the system in a pure quantum phase dynamics regime. Moreover, the effects of the density’s quantum fluctuations are studied through exact diagonalization analysis of the spectroscopy of the Bose-Hubbard model. We demonstrate that a clear two-level system emerges by tuning the magnetic flux at degeneracy. The lattice confinement, platform for the condensate, is realized experimentally employing a spatial light modulator.
All high T sub c edge-geometry weak links utilizing Y-Ba-Cu-O barrier layers
Hunt, B.D.; Foote, M.C.; Bajuk, L.J. )
1991-08-19
High quality YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}}/normal-metal/YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} edge-geometry weak links have been fabricated using nonsuperconducting Y-Ba-Cu-O barrier layers deposited by laser ablation at reduced growth temperatures. Devices incorporating 25--100 A thick barrier layers exhibit current-voltage characteristics consistent with the resistively shunted junction model, with strong microwave and magnetic field response at temperatures up to 85 K. The critical currents vary exponentially with barrier thickness, and the resistances scale linearly with Y-Ba-Cu-O interlayer thickness and device area, indicating good barrier uniformity, with an effective normal metal coherence length of 20 A.
NASA Astrophysics Data System (ADS)
Popović, Z.; Dobrosavljević-Grujić, L.; Zikic, R.
2012-05-01
We develop a quantitative theory describing the behavior of current-voltage characteristics (CVCs) in superconductor (S)/ferromagnet (F)/superconductor (SFS) weak links with transparent S/F interfaces. The approach of Kümmel, Gunsenheimer, and Nikolsky [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.42.3992 42, 3992 (1990)], developed for S/normal metal (N)/S junctions with an N barrier and based on the solution of time-dependent Bogoliubov-de Gennes equations combined with the time-relaxation model, is generalized to the SFS case. CVCs are calculated as a function of the barrier material parameters: the exchange energy h, the barrier thickness d, and the mean free path l. CVC peculiarities, such as a steep rise in the current and negative differential conductance at a low voltage, as well as the h-dependent position of the peaks, are obtained for a weak exchange energy h lower than or comparable to the superconducting energy gap Δ=Δ(T). They are interpreted to be induced by multiple Andreev reflections, modified in the presence of h in ferromagnets.
NASA Astrophysics Data System (ADS)
Singh, Shiv Jee; Ogino, Hiraku; Shimoyama, Jun-ichi; Kishio, Kohji
2013-10-01
The synthesis of iron-based superconductors with thick perovskite-type blocking layers, (Fe2As2)(Ca4(Mg0.25,Ti0.75)3O8) (22438) and (Fe2As2)(Ca5(Sc0.5Ti0.5)4O11) (225411), has been carried out and their transport properties discussed in comparison with those of fluorine-doped SmFeAsO0.8F0.2 (Sm1111) superconductors. Microstructural observation revealed that superconducting grains have a platelet shape and are strongly coupled with each other, particularly in 22438. The onset transition temperature (Tc) of 22438 reached up to 47.5 K and its very high upper critical field at low temperatures was suggested by a steep slope (dHc2/dT) near Tc as large as -19.8 T K-1. The resistance curves under various magnetic fields showed a basically two-step-like character of the superconducting transitions, where the effect of magnetic field is weaker at the onset part near the normal state in comparison to the tail part. The broadening of the tail part suggests a weak-link connection between superconducting grains. Two distinct scales of current flow corresponding to inter- and intragranular currents were confirmed by the remanent magnetization measurement of bulk samples, and their calculated intergranular current densities are relatively low. The analysis of their superconducting properties suggests evidence of the weak-link intergrain nature and high electromagnetic anisotropy of these iron-based superconductors with thick oxide blocking layers.
Clarke, J.; Hilbert, C.; Hahn, E.L.; Sleator, T.
1986-03-25
An automatic Q-spoiler comprising at least one Josephson tunnel junction connected in an LC circuit for flow of resonant current therethrough. When in use in a system for detecting the magnetic resonance of a gyromagnetic particle system, a high energy pulse of high frequency energy irradiating the particle system will cause the critical current through the Josephson tunnel junctions to be exceeded, causing the tunnel junctions to act as resistors and thereby damp the ringing of the high-Q detection circuit after the pulse. When the current has damped to below the critical current, the Josephson tunnel junctions revert to their zero-resistance state, restoring the Q of the detection circuit and enabling the low energy magnetic resonance signals to be detected.
Clarke, John; Hilbert, Claude; Hahn, Erwin L.; Sleator, Tycho
1988-01-01
An automatic Q-spoiler comprising at least one Josephson tunnel junction connected in an LC circuit for flow of resonant current therethrough. When in use in a system for detecting the magnetic resonance of a gyromagnetic particle system, a high energy pulse of high frequency energy irradiating the particle system will cause the critical current through the Josephson tunnel junctions to be exceeded, causing the tunnel junctions to act as resistors and thereby damp the ringing of the high-Q detection circuit after the pulse. When the current has damped to below the critical current, the Josephson tunnel junctions revert to their zero-resistance state, restoring the Q of the detection circuit and enabling the low energy magnetic resonance signals to be detected.
Josephson instantons and Josephson monopoles in a non-Abelian Josephson junction
NASA Astrophysics Data System (ADS)
Nitta, Muneto
2015-08-01
The non-Abelian Josephson junction is a junction of non-Abelian color superconductors sandwiching an insulator, or a non-Abelian domain wall if flexible, whose low-energy dynamics is described by a U (N ) principal chiral model with the conventional pion mass. A non-Abelian Josephson vortex is a non-Abelian vortex (color magnetic flux tube) residing inside the junction, that is described as a non-Abelian sine-Gordon soliton. In this paper, we propose Josephson instantons and Josephson monopoles, that is, Yang-Mills instantons and monopoles inside a non-Abelian Josephson junction, respectively, and show that they are described as S U (N ) Skyrmions and U (1 )N -1 vortices in the U (N ) principal chiral model without and with a twisted-mass term, respectively. Instantons with a twisted boundary condition are reduced (or T-dual) to monopoles, implying that C PN -1 lumps are T-dual to C PN -1 kinks inside a vortex. Here we find S U (N ) Skyrmions are T-dual to U (1 )N-1 vortices inside a wall. Our configurations suggest a yet another duality between C PN -1 lumps and S U (N ) Skyrmions as well as that between C PN -1 kinks and U (1 )N-1 vortices, viewed from different host solitons. They also suggest a duality between fractional instantons and bions in the C PN -1 model and those in the S U (N ) principal chiral model.
Dynamics of Josephson pancakes in layered superconductors
Mints, R.G.; Snapiro, I.B.
1994-03-01
We consider a pointlike vortex in a layered superconductor with linear defects in the superconducting layers. We treat these defects as Josephson junctions with high critical current density. We consider the electrodynamics of these junctions within the framework of nonlocal Josephson electrodynamics. We show that Josephson current through a linear defect in a superconducting layer results in a pointlike vortex with a superconducting core residing in this layer (Josephson pancake). We find the mobility of a Josephson pancake. We consider a small amplitude wave in a Josephson junction with nonlocal electrodynamics. We treat a bending wave for an infinite stack of Josephson pancakes. We find the dispersion relation for these waves. We show that their velocities tend to a certain finite limit when the wavelength tends to infinity.
Dirk, Shawn M.; Johnson, Ross S.; Wheeler, David R.; Bogart, Gregory R.
2013-04-23
A process for making a dielectric material where a precursor polymer selected from poly(phenylene vinylene)polyacetylene, poly(p-phenylene), poly(thienylene vinylene), poly(1,4-naphthylene vinylene), and poly(p-pyridine vinylene) is energized said by exposure by radiation or increase in temperature to a level sufficient to eliminate said leaving groups contained within the precursor polymer, thereby transforming the dielectric material into a conductive polymer. The leaving group in the precursor polymer can be a chloride, a bromide, an iodide, a fluoride, an ester, an xanthate, a nitrile, an amine, a nitro group, a carbonate, a dithiocarbamate, a sulfonium group, an oxonium group, an iodonium group, a pyridinium group, an ammonium group, a borate group, a borane group, a sulphinyl group, or a sulfonyl group.
Dirk, Shawn M.; Johnson, Ross S.; Wheeler, David R.; Bogart, Gregory R.
2011-06-07
A process for making a dielectric material where a precursor polymer selected from poly(phenylene vinylene) polyacetylene, poly(p-phenylene), poly(thienylene vinylene), poly(1,4-naphthylene vinylene), and poly(p-pyridine vinylene) is energized said by exposure by radiation or increase in temperature to a level sufficient to eliminate said leaving groups contained within the precursor polymer, thereby transforming the dielectric material into a conductive polymer. The leaving group in the precursor polymer can be a chloride, a bromide, an iodide, a fluoride, an ester, an xanthate, a nitrile, an amine, a nitro group, a carbonate, a dithiocarbamate, a sulfonium group, an oxonium group, an iodonium group, a pyridinium group, an ammonium group, a borate group, a borane group, a sulphinyl group, or a sulfonyl group.
Squeezed States in Josephson Junctions.
NASA Astrophysics Data System (ADS)
Hu, X.; Nori, F.
1996-03-01
We have studied quantum fluctuation properties of Josephson junctions in the limit of large Josephson coupling energy and small charging energy, when the eigenstates of the system can be treated as being nearly localized. We have considered(X. Hu and F. Nori, preprints.) a Josephson junction in a variety of situations, e.g., coupled to one or several of the following elements: a capacitor, an inductor (in a superconducting ring), and an applied current source. By solving an effective Shrödinger equation, we have obtained squeezed vacuum (coherent) states as the ground states of a ``free-oscillating'' (linearly-driven) Josephson junction, and calculated the uncertainties of its canonical momentum, charge, and coordinate, phase. We have also shown that the excited states of the various systems we consider are similar to the number states of a simple harmonic oscillator but with different fluctuation properties. Furthermore, we have obtained the time-evolution operators for these systems. These operators can make it easier to calculate the time-dependence of the expectation values and fluctuations of various quantities starting from an arbitrary initial state.
Implications of Weak-Link Behavior on the Performance of Mo/Au Bilayer Transition-Edge Sensors
NASA Technical Reports Server (NTRS)
Smith, Stephen J.
2011-01-01
Understanding the physical properties of the superconducting-to-normal transition is fundamental for optimizing the design and performance of transition-edge sensors (TESs). Recent critical current measurements of Mol Au bilayer test structures show that they act as weak superconducting links, exhibiting oscillatory, Fraunhofer-like behavior with applied magnetic field. In this paper we investigate the implications of this behavior for TES X-ray detectors, under operational bias conditions. These devices include normal metal features used for absorber attachment and unexplained noise suppression, which result in modifications to the previously reported critical current behavior. We present measurements of the logarithmic resistance sensitivity with temperature, a, and current, b, as a function of applied magnetic field and bias point within the resistive transition. Results show that these important device parameters exhibit similar oscillatory behavior with applied magnetic field, which in turn affects the signal responsivity and noise, and hence the energy resolution. These results show the significance of the critical current in determining the performance of TESs and hold promise to improve future.
Quantum dynamics in the bosonic Josephson junction
Chuchem, Maya; Cohen, Doron; Smith-Mannschott, Katrina; Hiller, Moritz; Kottos, Tsampikos; Vardi, Amichay
2010-11-15
We employ a semiclassical picture to study dynamics in a bosonic Josephson junction with various initial conditions. Phase diffusion of coherent preparations in the Josephson regime is shown to depend on the initial relative phase between the two condensates. For initially incoherent condensates, we find a universal value for the buildup of coherence in the Josephson regime. In addition, we contrast two seemingly similar on-separatrix coherent preparations, finding striking differences in their convergence to classicality as the number of particles increases.
NASA Astrophysics Data System (ADS)
Kurter, C.; Finck, A. D. K.; English, C. D.; Hor, Y. S.; van Harlingen, D. J.
2013-03-01
It is predicted that the presence of Majorana fermions manifests itself with a 4 π periodic current-phase relation (CPR) in planar Josephson junctions formed with topological weak links. To test this proposal, we have fabricated planar junctions by depositing Nb leads on exfoliated Bi2Se3 single crystals. The temperature and magnetic field dependence of the proximity-induced supercurrent have been examined in various doping regimes accessed via top gating. The critical current modulation with magnetic field deviates from the usual Fraunhofer diffraction pattern, suggesting modifications to a sinusoidal CPR consistent with a sin (2 ϕ) component. We are corroborating those results with direct measurements of the CPR using a phase-sensitive SQUID interferometry technique.
Laser-induced modification of transport properties of Y-Ba-Cu-O step-edge weak links
NASA Astrophysics Data System (ADS)
Adam, R.; Kula, W.; Sobolewski, Roman; Murduck, J. M.; Pettiette-Hall, C.
1995-12-01
We report on the laser-induced permanent changes of the critical current (Ic) and normal resistance (Rn) of YBa2Cu3O7-x (YBCO) step-edge Josephson junctions. The 2- to 20-μm-wide junctions were prepared from a 200-nm-thick YBCO film deposited by a pulsed KrF excimer laser onto 300-nm-high steps etched in the LaAlO3 substrate. The laser modification experiments were performed by illuminating the junctions at 50 K with a focused Ar-ion laser beam of various intensities. Depending on the illumination power density, either increase or decrease of the junction Ic has been observed. In particular, after illumination at the 0.6×105 W/cm2 power level, a 75% enhancement of Ic and increase of the IcRn product up to 25% were obtained without a measurable change in the junction critical temperature. The laser-induced modifications were very reproducible and remained unchanged even after a subsequent room-temperature/helium thermal cycling of the sample. Photoassisted, thermally activated oxygen redistribution in the YBCO grain boundary region is proposed to explain the observed behavior.
Terahertz radiation from Josephson sandwiches
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2010-08-01
Basic results are presented from a study of the Cerenkov emission of electromagnetic waves by solitary vortices and Swihart waves moving in a long Josephson sandwich embedded in a dielectric. The energy fluxes of the electromagnetic field along a long sandwich are examined. The magnitudes of the fluxes are compared over a wide range of frequencies and wave numbers of surface waves in the sandwich.
Operation of NIST Josephson Array Voltage Standards
Hamilton, Clark A.; Burroughs, Charles; Chieh, Kao
1990-01-01
This paper begins with a brief discussion of the physical principles and history of Josephson effect voltage standards. The main body of the paper deals with the practical details of the array design, cryoprobe construction, bias source requirements, adjustment of the system for optimum performance, calibration algorithms, and an assessment of error sources for the NIST-developed Josephson array standard. PMID:28179776
Nonlinear Phase Dynamics in a Driven Bosonic Josephson Junction
Boukobza, Erez; Moore, Michael G.; Cohen, Doron; Vardi, Amichay
2010-06-18
We study the collective dynamics of a driven two-mode Bose-Hubbard model in the Josephson interaction regime. The classical phase space is mixed, with chaotic and regular components, which determine the dynamical nature of the fringe visibility. For a weak off-resonant drive, where the chaotic component is small, the many-body dynamics corresponds to that of a Kapitza pendulum, with the relative phase {phi} between the condensates playing the role of the pendulum angle. Using a master equation approach we show that the modulation of the intersite potential barrier stabilizes the {phi}={pi} 'inverted pendulum' coherent state, and protects the fringe visibility.
High Power Josephson Effect Sources
1994-09-01
large spacing was nsed ,along with cooling water, os Iao a d$ to ensure the substrate temperature did not rise durn theCox flow Osiltr.adsaljnto ry~ h m...Here two arra’s. a 400 s.m Josephson effect detector and an SIS mixer are "I integrated on a single silicon substrate . One array func- tions as the...junction’s shunt resistor, on array’s output power and detector’s current- voltage characteristics are also discussed. I. INTRODUCTION - U Phb &z locked
An 8-b Josephson digital signal processor
NASA Astrophysics Data System (ADS)
Kotani, Seigo; Inoue, Atsuki; Imamura, Takeshi; Hasuo, Shinya
1990-12-01
A 6.3 K-gate Josephson digital signal processor (DSP) that performs 240-psec 8-b multiplication and 410-psec 13-b addition is described. The structure of the DSP, which is based on a three-stage pipeline, and the design of the components used in the DSP are reviewed. The DSP contains 23,000 Josephson junctions on a 5 x 5-mm die and was fabricated using 1.5-micron all-niobium Josephson techniques. Measurements indicate that the DSP can attain a nonparallel processing speed of 1 gigaoperation per second with 12-mW power dissipation.
Polaritonic Rabi and Josephson Oscillations
Rahmani, Amir; Laussy, Fabrice P.
2016-01-01
The dynamics of coupled condensates is a wide-encompassing problem with relevance to superconductors, BECs in traps, superfluids, etc. Here, we provide a unified picture of this fundamental problem that includes i) detuning of the free energies, ii) different self-interaction strengths and iii) finite lifetime of the modes. At such, this is particularly relevant for the dynamics of polaritons, both for their internal dynamics between their light and matter constituents, as well as for the more conventional dynamics of two spatially separated condensates. Polaritons are short-lived, interact only through their material fraction and are easily detuned. At such, they bring several variations to their atomic counterpart. We show that the combination of these parameters results in important twists to the phenomenology of the Josephson effect, such as the behaviour of the relative phase (running or oscillating) or the occurence of self-trapping. We undertake a comprehensive stability analysis of the fixed points on a normalized Bloch sphere, that allows us to provide a generalized criterion to identify the Rabi and Josephson regimes in presence of detuning and decay. PMID:27452872
Phase-diffusion dynamics in weakly coupled bose-einstein condensates.
Boukobza, Erez; Chuchem, Maya; Cohen, Doron; Vardi, Amichay
2009-05-08
We study the phase sensitivity of collisional phase diffusion between weakly coupled Bose-Einstein condensates, using a semiclassical picture of the two-mode Bose-Hubbard model. When weak coupling is allowed, zero relative phase locking is attained in the Josephson-Fock transition regime, whereas a pi relative phase is only locked in Rabi-Josephson point. Our analytic semiclassical estimates agree well with the numerical results.
Phase-Diffusion Dynamics in Weakly Coupled Bose-Einstein Condensates
Boukobza, Erez; Vardi, Amichay; Chuchem, Maya; Cohen, Doron
2009-05-08
We study the phase sensitivity of collisional phase diffusion between weakly coupled Bose-Einstein condensates, using a semiclassical picture of the two-mode Bose-Hubbard model. When weak coupling is allowed, zero relative phase locking is attained in the Josephson-Fock transition regime, whereas a {pi} relative phase is only locked in Rabi-Josephson point. Our analytic semiclassical estimates agree well with the numerical results.
Microwave integrated circuit for Josephson voltage standards
NASA Technical Reports Server (NTRS)
Holdeman, L. B.; Toots, J.; Chang, C. C. (Inventor)
1980-01-01
A microwave integrated circuit comprised of one or more Josephson junctions and short sections of microstrip or stripline transmission line is fabricated from thin layers of superconducting metal on a dielectric substrate. The short sections of transmission are combined to form the elements of the circuit and particularly, two microwave resonators. The Josephson junctions are located between the resonators and the impedance of the Josephson junctions forms part of the circuitry that couples the two resonators. The microwave integrated circuit has an application in Josephson voltage standards. In this application, the device is asymmetrically driven at a selected frequency (approximately equal to the resonance frequency of the resonators), and a d.c. bias is applied to the junction. By observing the current voltage characteristic of the junction, a precise voltage, proportional to the frequency of the microwave drive signal, is obtained.
THz Cherenkov radiation of Josephson vortex
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2008-01-01
It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.
Josephson A/D Converter Development.
1981-10-01
by Zappe and A Landman [20]. They conclude that the simple model of the Josephson effect is applicable up to frequencies at least as high (a) as 300...GHz. B. Time-Domain Experiments 4ooF so The early high - frequency experiments with Josephson devices I .O suggested their use as very fast logic switches...exactly as for the phenomenological model . The tunneling pacitive current paths dominate the circuit at high frequencies . current is the sum of two
Ramos, Irene; Krammer, Florian; Hai, Rong; Aguilera, Domingo; Bernal-Rubio, Dabeiba; Steel, John; García-Sastre, Adolfo; Fernandez-Sesma, Ana
2013-11-01
The recent human outbreak of H7N9 avian influenza A virus has caused worldwide concerns. Receptor binding specificity is critical for viral pathogenicity, and still not thoroughly studied for this emerging virus. Here, we evaluated the receptor specificity of the haemagglutinin (HA) of two human H7N9 isolates (A/Shanghai/1/13 and A/Anhui/1/13) through a solid-phase binding assay and a flow cytometry-based assay. In addition, we compared it with those from several HAs from human and avian influenza viruses. We observed that the HAs from the novel H7 isolates strongly interacted with α2,3-linked sialic acids. Importantly, they also showed low levels of binding to α2,6-linked sialic acids, but significantly higher than other avian H7s.
Josephson and persistent spin currents in Bose-Einstein condensates of magnons
NASA Astrophysics Data System (ADS)
Nakata, Kouki; van Hoogdalem, Kevin A.; Simon, Pascal; Loss, Daniel
2014-10-01
Using the Aharonov-Casher (A-C) phase, we present a microscopic theory of the Josephson and persistent spin currents in quasiequilibrium Bose-Einstein condensates (BECs) of magnons in ferromagnetic insulators. Starting from a microscopic spin model that we map onto a Gross-Pitaevskii Hamiltonian, we derive a two-state model for the Josephson junction between the weakly coupled magnon-BECs. We then show how to obtain the alternating-current (ac) Josephson effect with magnons as well as macroscopic quantum self-trapping in a magnon-BEC. We next propose how to control the direct-current (dc) Josephson effect electrically using the A-C phase, which is the geometric phase acquired by magnons moving in an electric field. Finally, we introduce a magnon-BEC ring and show that persistent magnon-BEC currents flow due to the A-C phase. Focusing on the feature that the persistent magnon-BEC current is a steady flow of magnetic dipoles that produces an electric field, we propose a method to directly measure it experimentally.
Motion of a Josephson vortex in the field of a random potential
Mineev, M.B.; Feigel'man, M.V.; Shmidt, V.V.
1981-07-01
We consider the motion and pinning of a Josephson vortex in a field produced by random inhomogeneities in a long junction. We find the distribution function of the force of vortex pinning on the inhomogeneities. We construct the current-voltage characteristic (CVC) of the junction. For inhomogeneities which are weak compared to the ohmic losses the CVC has a single hysteresis, in the opposite case it has two.
Stability of the kink state in a stack of intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Lin, Shi-Zeng; Hu, Xiao
2010-12-01
A new dynamic state characterized by (2ml+1)π static phase kink with integers {ml} is proposed recently in a stack of inductively coupled Josephson junctions. In the present paper, the stability of the phase kink state is investigated against various perturbations and it is shown that the kink state is stable. It is also discussed that the suppression of the amplitude of superconducting order parameter caused by the kink is weak.
Wu, K.H.; Fu, C.M.; Jeng, W.J.
1994-12-31
The effects of oxygen stoichiometry on the transport properties of the pulsed laser deposited YBa{sub 2}Cu{sub 3}O{sub x} bicrystalline grain boundary weak-link junctions were studied. It is found that not only the cross boundary resistive transition foot structure can be manipulated repeatedly with oxygen annealling processes but the junction behaviors are also altered in accordance. In the fully oxygenated state i.e. with x=7.0 in YBa{sub 2}Cu{sub 3}O{sub x} stoichiometry, the junction critical current exhibits a power of 2 scaling behavior with temperature. In contrast, when annealed in the conditions of oxygen-deficient state (e.g. with x=6.9 in YBa{sub 2}Cu{sub 3}O{sub x} stoichiometry) the junction critical current switches to a linear temperature dependence behavior. The results are tentatively attributed to the modification of the structure in the boundary area upon oxygen annealing, which, in turn, will affect the effective dimension of the geometrically constrained weak-link bridges. The detailed discussion on the responsible physical mechanisms as well as the implications of the present results on device applications will be given.
Effects of oxygen stoichiometry on the scaling behaviors of YBa2Cu3O(x) grain boundary weak-links
NASA Technical Reports Server (NTRS)
Wu, K. H.; Fu, C. M.; Jeng, W. J.; Juang, J. Y.; Uen, T. M.; Gou, Y. S.
1995-01-01
The effects of oxygen stoichiometry on the transport properties of the pulsed laser deposited YBa2Cu3O(x) bicrystalline grain boundary weak-link junctions were studied. It is found that not only the cross boundary resistive transition foot structure can be manipulated repeatedly with oxygen annealing processes but the junction behaviors are also altered in accordance. In the fully oxygenated state i.e with x = 7.0 in YBa2Cu3O(x) stoichiometry, the junction critical current exhibits a power of 2 scaling behavior with temperature. In contrast, when annealed in the conditions of oxygen-deficient state (e.g with x = 6.9 in YBa2Cu3O(x) stoichiometry) the junction critical current switches to a linear temperature dependence behavior. The results are tentatively attributed to the modification of the structure in the boundary area upon oxygen annealing, which, in turn, will affect the effective dimension of the geometrically constrained weak-link bridges. The detailed discussion on the responsible physical mechanisms as well as the implications of the present results on device applications will be given.
Bobkov, A A; Reisler, E
2000-01-01
Myosin subfragment 1 (S1) with SH1 (Cys(707)) and SH2 (Cys(697)) groups cross-linked by p-phenylenedimaleimide (pPDM-S1) is thought to be an analog of the weakly bound states of myosin bound to actin. The structural properties of pPDM-S1 were compared in this study to those of S1.ADP.BeF(x) and S1.ADP.AlF(4)(-), i.e., the established structural analogs of the myosin weakly bound states. To distinguish between the conformational effects of SH1-SH2 cross-linking and those due to their monofunctional modification, we used S1 with the SH1 and SH2 groups labeled with N-phenylmaleimide (NPM-S1) as a control in our experiments. The state of the nucleotide pocket was probed using a hydrophobic fluorescent dye, 3-[4-(3-phenyl-2-pyrazolin-1-yl)benzene-1-sulfonylamido]phen ylboronic acid (PPBA). Differential scanning calorimetry (DSC) was used to study the thermal stability of S1. By both methods the conformational state of pPDM-S1 was different from that of unmodified S1 in the S1.ADP.BeF(x) and S1.ADP.AlF(4)(-) complexes and closer to that of nucleotide-free S1. Moreover, BeF(x) and AlF(4)(-) binding failed to induce conformational changes in pPDM-S1 similar to those observed in unmodified S1. Surprisingly, when pPDM cross-linking was performed on S1.ADP.BeF(x) complex, ADP.BeF(x) protected to some extent the nucleotide pocket of S1 from the effects of pPDM modification. NPM-S1 behaved similarly to pPDM-S1 in our experiments. Overall, this work presents new evidence that the conformational state of pPDM-S1 is different from that of the weakly bound state analogs, S1.ADP.BeF(x) and S1.ADP.AlF(4)(-). The similar structural effects of pPDM cross-linking of SH1 and SH2 groups and their monofunctional labeling with NPM are ascribed to the inhibitory effects of these modifications on the flexibility/mobility of the SH1-SH2 helix. PMID:10866971
NASA Astrophysics Data System (ADS)
Berdiyorov, G. R.; Savel'ev, S. E.; Milošević, M. V.; Kusmartsev, F. V.; Peeters, F. M.
2013-05-01
Nonlinear dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting Josephson junctions under simultaneously applied time-periodic ac and constant biasing dc currents is studied using the time dependent Ginzburg-Landau formalism with a Lawrence-Doniach extension. At zero external magnetic field and dc biasing current the resistive state of the system is characterized by periodic nucleation and annihilation of fluxon-antifluxon pairs, relative positions of which are determined by the state of neighboring junctions. Due to the mutual repulsive interaction, fluxons in different junctions move out of phase. Their collective motion can be synchronized by adding a small ac component to the biasing dc current. Coherent motion of fluxons is observed for a broad frequency range of the applied drive. In the coherent state the maximal output voltage, which is proportional to the number of junctions in the stack, is observed near the characteristic frequency of the system determined by the crossing of the fluxons across the sample. However, in this frequency range the dynamically synchronized state has an alternative—a less ordered state with smaller amplitude of the output voltage. Collective behavior of the junctions is strongly affected by the sloped sidewalls of the stack. Synchronization is observed only for weakly trapezoidal cross sections, whereas irregular motion of fluxons is observed for larger slopes of the sample edge.
OAM mode of the Hankel–Bessel vortex beam in weak to strong turbulent link of marine-atmosphere
NASA Astrophysics Data System (ADS)
Li, Ye; Zhang, Yixin
2017-04-01
We study the turbulent effects of maritime atmosphere on the propagation of the orbital angular momentum (OAM) modes of a vortex beam. Based on the modified Rytov approximation, we model the effective marine-atmospheric spectrum and the normalized energy weight of the vortex modes of Hankel–Bessel beams in a paraxial marine turbulent channel. Our results show that the intensity of the signal vortex modes of Hankel–Bessel beams in a non-turbulence channel increases with increasing the quantum number of the OAM of vortex modes from one to higher. We can utilize OAM eigenstates of the Hankel–Bessel vortex beam to increase the channel capacity in optical communication of the remote link. The normalized energy weight of signal OAM modes increases and that of crosstalk OAM modes decreases from the worst to the best turbulent maritime climate. The normalized energy weight of signal OAM modes reduces with the increasing of the turbulent outer scale from 0.1 \\text{m} to 0.5 \\text{m} and the receiving diameter, but it increases with increasing the turbulent outer scale when the outer scale is greater than 0.5 \\text{m} . The effects of the inner scale on the normalized energy weight of OAM modes can be ignored. We can mitigate the effects of turbulence by the choice of the longer wavelength and smaller receiver aperture.
A Josephson radiation comb generator
Solinas, P.; Gasparinetti, S.; Golubev, D.; Giazotto, F.
2015-01-01
We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation. PMID:26193628
Demonstration of an ac Josephson junction laser
NASA Astrophysics Data System (ADS)
Cassidy, M. C.; Bruno, A.; Rubbert, S.; Irfan, M.; Kammhuber, J.; Schouten, R. N.; Akhmerov, A. R.; Kouwenhoven, L. P.
2017-03-01
Superconducting electronic devices have reemerged as contenders for both classical and quantum computing due to their fast operation speeds, low dissipation, and long coherence times. An ultimate demonstration of coherence is lasing. We use one of the fundamental aspects of superconductivity, the ac Josephson effect, to demonstrate a laser made from a Josephson junction strongly coupled to a multimode superconducting cavity. A dc voltage bias applied across the junction provides a source of microwave photons, and the circuit’s nonlinearity allows for efficient down-conversion of higher-order Josephson frequencies to the cavity’s fundamental mode. The simple fabrication and operation allows for easy integration with a range of quantum devices, allowing for efficient on-chip generation of coherent microwave photons at low temperatures.
Anomalous Josephson current in superconducting topological insulator
NASA Astrophysics Data System (ADS)
Yamakage, Ai; Sato, Masatoshi; Yada, Keiji; Kashiwaya, Satoshi; Tanaka, Yukio
2013-03-01
We investigate the effect of helical Majorana fermions at the surface of superconducting topological insulators (STIs) on the Josephson current by referring to possible pairing states of Cu-doped Bi2Se3. The surface state in the present STI has a spin helicity because the directions of spin and momentum are locked to each other. The Josephson current-phase relation in an STI/s-wave superconductor junction shows robust sin(2φ) owing to mirror symmetry, where φ denotes the macroscopic phase difference between the two superconductors. In contrast, the maximum Josephson current in an STI/STI junction exhibits a nonmonotonic temperature dependence depending on the relative spin helicity of the two surface states. Detecting these features qualifies as distinct experimental evidence for the identification of the helical Majorana fermion in STIs.
Numerical Investigation of Josephson Junction Structures
Hristov, I.; Dimova, S.; Boyadjiev, T.
2009-10-29
Multilayered long Josephson Junction Structures form an interesting physical system where both nonlinearity and interaction between subsystems play an important role. Such systems allow to study physical effects that do not occur in single Josephson junction.The Sakai-Bodin-Pedersen model--a system of perturbed sine-Gordon equations--is used to study the dynamic states of stacks of inductively coupled long Josephson Junctions (LJJs). The corresponding static problem is numerically investigated as well. In order to study the stability of possible static solutions a Sturm-Liouville problem is generated and solved.The transitions from static to dynamic state and the scenario of these transitions are analyzed depending on the model parameters. Different physical characteristics--current-voltage characteristics, individual instant voltages and internal magnetic fields, are calculated and interpreted.
Josephson broadband spectroscopy to 1 THz
NASA Astrophysics Data System (ADS)
Edstam, J.; Olsson, H. K.
1994-05-01
We demonstrate the operation of a ``Josephson Broadband Spectrometer'' (JOBS) with a frequency range and bandwidth of 1 THz. The JOBS uses the inherent frequency tuning of the Josephson oscillations (f=2 eV/h) as a probe of the complex impedance environment, ZL(f), of the Josephson junction. Spectra taken of microstrip resonators (YBa2Cu3O7/SiO/Au) display up to nine harmonic resonances corresponding to a bandwidth of 1000 GHz. We find the surface resistance of YBa2Cu3O7 to scale as f2 over this frequency range, whereas the London penetration depth is frequency independent. The upper frequency limit of the measurement is set by the resonator loss whereas the JOBS presumably has an even larger intrinsic bandwidth.
Josephson junctions with alternating critical current density
Mints, R.G.; Kogan, V.G.
1997-04-01
The magnetic-field dependence of the critical current I{sub c}(H) is considered for a short Josephson junction with the critical current density j{sub c} alternating along the tunnel contact. Two model cases, periodic and randomly alternating j{sub c}, are treated in detail. Recent experimental data on I{sub c}(H) for grain-boundary Josephson junctions in YBa{sub 2}Cu{sub 3}O{sub x} are discussed. {copyright} {ital 1997} {ital The American Physical Society}
Flux cloning in Josephson transmission lines.
Gulevich, D R; Kusmartsev, F V
2006-07-07
We describe a novel effect related to the controlled birth of a single Josephson vortex. In this phenomenon, the vortex is created in a Josephson transmission line at a T-shaped junction. The "baby" vortex arises at the moment when a "mother" vortex propagating in the adjacent transmission line passes the T-shaped junction. In order to give birth to a new vortex, the mother vortex must have enough kinetic energy. Its motion can also be supported by an externally applied driving current. We determine the critical velocity and the critical driving current for the creation of the baby vortices and briefly discuss the potential applications of the found effect.
Phonon-Josephson resonances in atomtronic circuits
NASA Astrophysics Data System (ADS)
Bidasyuk, Y. M.; Prikhodko, O. O.; Weyrauch, M.
2016-09-01
We study the resonant excitation of sound modes from Josephson oscillations in Bose-Einstein condensates. From the simulations for various setups using the Gross-Pitaevskii mean-field equations and Josephson equations we observe additional tunneling currents induced by resonant phonons. The proposed experiment may be used for spectroscopy of phonons as well as other low-energy collective excitations in Bose-Einstein condensates. We also argue that the observed effect may mask the observation of Shapiro resonances if not carefully controlled.
Flux Cloning in Josephson Transmission Lines
Gulevich, D.R.; Kusmartsev, F.V.
2006-07-07
We describe a novel effect related to the controlled birth of a single Josephson vortex. In this phenomenon, the vortex is created in a Josephson transmission line at a T-shaped junction. The 'baby' vortex arises at the moment when a 'mother' vortex propagating in the adjacent transmission line passes the T-shaped junction. In order to give birth to a new vortex, the mother vortex must have enough kinetic energy. Its motion can also be supported by an externally applied driving current. We determine the critical velocity and the critical driving current for the creation of the baby vortices and briefly discuss the potential applications of the found effect.
Hybrid Josephson-CMOS Random Access Memory with Interfacing to Josephson Digital Circuits
2013-10-16
as reliable high-speed Josephson voltage drivers, Superconductor Science and Technology, (01 2013): 1. doi: TOTAL: 4 (b) Papers published in non...Theodore Van Duzer, ISEC, Washington, DC 2011 "Hybrid Josephson-CMOS Random Access Memory, T. Van Duzer, US Workshop on Superconductor Electronics: Devices...Proceeding publications (other than abstracts): Received Paper 08/22/2013 2.00 Thomas Ortlepp. Vortex transitional superconductor random access memory
Dressed fluxon in a Josephson window junction
NASA Astrophysics Data System (ADS)
Caputo, Jean Guy; Flytzanis, Nikos; Devoret, Michel
1994-09-01
The static fluxon solutions of a Josephson window junction have been studied numerically. We show that the effect of the idle region surrounding the junction is to ``dress'' the fluxon causing its energy to increase. This effect can be predicted accurately by a simple model.
Fu, C.M.; Chen, C.M.; Lin, H.C.
1994-12-31
We have studied systematically the effect of microwave irradiation on the temperature dependent resistivity R(T) and the current-voltage (I-V) characteristics of YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) bicrystalline grain boundary weak-links (GBWLs), with grain boundary of three different tilt angles. The superconducting transition temperature, T{sub c}, has significant enhancement upon microwave irradiation. The microwave enhanced T{sub c} is increased as a function of incidence microwave power, but limited to an optimum power level. The GBWLs of 45{degrees} tilt boundary has shown to be most sensitive to the microwave irradiation power, and the GBWLs of 36.8{degrees} tilt boundary has displayed a moderate response. In contrast, no enhancement of T{sub c} was observed in the GBWLs of 24{degrees} tilt boundary, as well as in the uniform films. Under the microwave irradiation, the R(T) dependence is hysteretic as the transition taken from superconducting state to normal state and vice versa. Mechanisms associated with the redistribution of nonequilibrium quasiparticles under microwave irradiation are discussed.
NASA Technical Reports Server (NTRS)
Fu, C. M.; Chen, C. M.; Lin, H. C.; Wu, K. H.; Juang, J. Y.; Uen, T. M.; Gou, Y. S.
1995-01-01
We have studied systematically the effect of microwave irradiation on the temperature dependent resistivity (R(I) and the current-voltage (I-V) characteristics of YBa2Gu3O(7 - x) (YBCO) bicrystalline grain boundary weak-links (GBWL's), with grain boundary of three different tilt angles. The superconducting transition temperature, T(sub c), has significant enhancement upon microwave irradiation. The microwave enhanced T(sub c) is increased as a function of incident microwave power, but limited to an optimum power level. The GBWL's of 45 deg tilt boundary has shown to be most sensitive to the microwave irradiation power, and the GBWL's of 36.8 deg tilt boundary has displayed a moderate response. In contrast, no enhancement of T(sub c) was observed in the GBWL's of 24 deg tilt boundary, as well as in the uniform films. Under the microwave irradiation, the R(T) dependent is hystertic as the transition taken from superconducting state to normal state and vice versa. Mechanisms associated with the redistribution of nonequilibrium quasiparticles under microwave irradiation are discussed.
NASA Technical Reports Server (NTRS)
Barner, J. B.; Rogers, C. T.; Inam, A.; Ramesh, R.; Bersey, S.
1991-01-01
The controllable, reproducible fabrication of nonhysteretic Josephson devices with excess-current weak-link characteristics at temperatures up to 80 K have been demonstrated. The devices are patterned from in situ deposited a-axis oriented YBa2Cu3O(7-y) - PrBa2Cu3O(7-y) - YBa2Cu3O(7-y) trilayers grown on SrTiO3(001) substrates. Control of the critical current density and resistance is achieved by varying the thickness of the PrBa2Cu3O(7-z) barrier layer. Critical current densities in excess of 10,000 A/sq cm have been reproducibly measured; good uniformity across the wafer is obtained with device parameters scaling with device area. Strong constant-voltage current steps are observed under 11.2 GHz microwave radiation at temperatures up to and above 80 K.
Polaron effects on the dc- and ac-tunneling characteristics of molecular Josephson junctions
NASA Astrophysics Data System (ADS)
Wu, B. H.; Cao, J. C.; Timm, C.
2012-07-01
We study the interplay of polaronic effect and superconductivity in transport through molecular Josephson junctions. The tunneling rates of electrons are dominated by vibronic replicas of the superconducting gap, which show up as prominent features in the differential conductance for the dc and ac current. For relatively large molecule-lead coupling, a features that appears when the Josephson frequency matches the vibron frequency can be identified with an over-the-gap structure observed by Marchenkov [Nat. Nanotech. 1748-338710.1038/nnano.2007.2182, 481 (2007)]. However, we are more concerned with the weak-coupling limit, where resonant tunneling through the molecular level dominates. We find that certain features involving both Andreev reflection and vibron emission show an unusual shift of the bias voltage V at their maximum with the gate voltage Vg as V˜(2/3)Vg. Moreover, due to the polaronic effect, the ac Josephson current shows a phase shift of π when the bias eV is increased by one vibronic energy quantum ℏωv. This distinctive even-odd effect is explained in terms of the different sign of the coupling to vibrons of electrons and of Andreev-reflected holes.
Transition from slow Abrikosov to fast moving Josephson vortices in iron pnictide superconductors
NASA Astrophysics Data System (ADS)
Moll, Philip J. W.; Balicas, Luis; Geshkenbein, Vadim; Blatter, Gianni; Karpinski, Janusz; Zhigadlo, Nikolai D.; Batlogg, Bertram
2013-02-01
Iron pnictides are layered high Tc superconductors with moderate material anisotropy and thus Abrikosov vortices are expected in the mixed state. Yet, we have discovered a distinct change in the nature of the vortices from Abrikosov-like to Josephson-like in the pnictide superconductor SmFeAs(O,F) with Tc~48-50 K on cooling below a temperature T*~41-42 K, despite its moderate electronic anisotropy γ~4-6. This transition is hallmarked by a sharp drop in the critical current and accordingly a jump in the flux-flow voltage in a magnetic field precisely aligned along the FeAs layers, indicative of highly mobile vortices. T* coincides well with the temperature where the coherence length ξc perpendicular to the layers matches half of the FeAs-layer spacing. For fields slightly out-of-plane (> 0.1°- 0.15°) the vortices are completely immobilized as well-pinned Abrikosov segments are introduced when the vortex crosses the FeAs layers. We interpret these findings as a transition from well-pinned, slow moving Abrikosov vortices at high temperatures to weakly pinned, fast flowing Josephson vortices at low temperatures. This vortex dynamics could become technologically relevant as superconducting applications will always operate deep in the Josephson regime.
Work fluctuations in bosonic Josephson junctions
NASA Astrophysics Data System (ADS)
Lena, R. G.; Palma, G. M.; De Chiara, G.
2016-05-01
We calculate the first two moments and full probability distribution of the work performed on a system of bosonic particles in a two-mode Bose-Hubbard Hamiltonian when the self-interaction term is varied instantaneously or with a finite-time ramp. In the instantaneous case, we show how the irreversible work scales differently depending on whether the system is driven to the Josephson or Fock regime of the bosonic Josephson junction. In the finite-time case, we use optimal control techniques to substantially decrease the irreversible work to negligible values. Our analysis can be implemented in present-day experiments with ultracold atoms and we show how to relate the work statistics to that of the population imbalance of the two modes.
Hybrid-free Josephson Parametric Converter
NASA Astrophysics Data System (ADS)
Frattini, N. E.; Narla, A.; Sliwa, K. M.; Shankar, S.; Hatridge, M.; Devoret, M. H.
A necessary component for any quantum computation architecture is the ability to perform efficient quantum operations. In the microwave regime of superconducting qubits, these quantum-limited operations can be realized with a non-degenerate Josephson junction based three-wave mixer, the Josephson Parametric Converter (JPC). Currently, the quantum signal of interest must pass through a lossy 180 degree hybrid to be presented as a differential drive to the JPC. This hybrid therefore places a limit on the quantum efficiency of the system and also increases the device footprint. We present a new design for the JPC eliminating the need for any external hybrid. We also show that this design has nominally identical performance to the conventional JPC. Work supported by ARO, AFOSR and YINQE.
Defect formation in long Josephson junctions
Gordeeva, Anna V.; Pankratov, Andrey L.
2010-06-01
We study numerically a mechanism of vortex formation in a long Josephson junction within the framework of the one-dimensional sine-Gordon model. This mechanism is switched on below the critical temperature. It is shown that the number of fluxons versus velocity of cooling roughly scales according to the power law with the exponent of either 0.25 or 0.5 depending on the temperature variation in the critical current density.
Josephson junction microwave modulators for qubit control
NASA Astrophysics Data System (ADS)
Naaman, O.; Strong, J. A.; Ferguson, D. G.; Egan, J.; Bailey, N.; Hinkey, R. T.
2017-02-01
We demonstrate Josephson junction based double-balanced mixer and phase shifter circuits operating at 6-10 GHz and integrate these components to implement both a monolithic amplitude/phase vector modulator and an I/Q quadrature mixer. The devices are actuated by flux signals, dissipate no power on chip, exhibit input saturation powers in excess of 1 nW, and provide cryogenic microwave modulation solutions for integrated control of superconducting qubits.
Edge currents in frustrated Josephson junction ladders
NASA Astrophysics Data System (ADS)
Marques, A. M.; Santos, F. D. R.; Dias, R. G.
2016-09-01
We present a numerical study of quasi-1D frustrated Josephson junction ladders with diagonal couplings and open boundary conditions, in the large capacitance limit. We derive a correspondence between the energy of this Josephson junction ladder and the expectation value of the Hamiltonian of an analogous tight-binding model, and show how the overall superconducting state of the chain is equivalent to the minimum energy state of the tight-binding model in the subspace of one-particle states with uniform density. To satisfy the constraint of uniform density, the superconducting state of the ladder is written as a linear combination of the allowed k-states of the tight-binding model with open boundaries. Above a critical value of the parameter t (ratio between the intra-rung and inter-rung Josephson couplings) the ladder spontaneously develops currents at the edges, which spread to the bulk as t is increased until complete coverage is reached. Above a certain value of t, which varies with ladder size (t = 1 for an infinite-sized ladder), the edge currents are destroyed. The value t = 1 corresponds, in the tight-binding model, to the opening of a gap between two bands. We argue that the disappearance of the edge currents with this gap opening is not coincidental, and that this points to a topological origin for these edge current states.
Radiation comb generation with extended Josephson junctions
Solinas, P.; Bosisio, R.; Giazotto, F.
2015-09-21
We propose the implementation of a Josephson radiation comb generator based on an extended Josephson junction subject to a time dependent magnetic field. The junction critical current shows known diffraction patterns and determines the position of the critical nodes when it vanishes. When the magnetic flux passes through one of such critical nodes, the superconducting phase must undergo a π-jump to minimize the Josephson energy. Correspondingly, a voltage pulse is generated at the extremes of the junction. Under periodic driving, this allows us to produce a comb-like voltage pulses sequence. In the frequency domain, it is possible to generate up to hundreds of harmonics of the fundamental driving frequency, thus mimicking the frequency comb used in optics and metrology. We discuss several implementations through a rectangular, cylindrical, and annular junction geometries, allowing us to generate different radiation spectra and to produce an output power up to 10 pW at 50 GHz for a driving frequency of 100 MHz.
Josephson junction in a thin film
Kogan, V. G.; Dobrovitski, V. V.; Clem, J. R.; Mawatari, Yasunori; Mints, R. G.
2001-04-01
The phase difference {phi}(y) for a vortex at a line Josephson junction in a thin film attenuates at large distances as a power law, unlike the case of a bulk junction where it approaches exponentially the constant values at infinities. The field of a Josephson vortex is a superposition of fields of standard Pearl vortices distributed along the junction with the line density {phi}'(y)/2{pi}. We study the integral equation for {phi}(y) and show that the phase is sensitive to the ratio l/{Lambda}, where l={lambda}{sub J}{sup 2}/{lambda}{sub L}, {Lambda}=2{lambda}{sub L}{sup 2}/d, {lambda}{sub L}, and {lambda}{sub J} are the London and Josephson penetration depths, and d is the film thickness. For l<<{Lambda}, the vortex ''core'' of the size l is nearly temperature independent, while the phase ''tail'' scales as l{Lambda}/y{sup 2}={lambda}{sub J}2{lambda}{sub L}/d/y{sup 2}; i.e., it diverges as T{yields}T{sub c}. For l>>{Lambda}, both the core and the tail have nearly the same characteristic length l{Lambda}.
Fluctuation of heat current in Josephson junctions
Virtanen, P.; Giazotto, F.
2015-02-15
We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.
MAR current of Josephson junctions with topological superconducting nanowires
NASA Astrophysics Data System (ADS)
Aguado, Ramon; San-Jose, Pablo; Prada, Elsa; Cayao, Jorge Luis
2013-03-01
We study Josephson junctions made with topological superconducting nanowires hosting Majorana bound states (MBS). We show that, despite the absence of a fractional Josephson effect in the steady state limit [1], the dissipative multiple Andreev reflection (MAR) current contains nontrivial features owing to the presence of MBS. In particular, the MAR steps appear at voltages eVP = Δ / q
The Josephson Effect: 50 Years of Science and Technology
ERIC Educational Resources Information Center
Warburton, Paul A.
2011-01-01
The Josephson effect, the 50th anniversary of which will be celebrated in 2012, remains one of the most spectacular manifestations of quantum mechanics in all of experimental science. It was first predicted in 1962 and then experimentally verified in 1963. At its most fundamental level the Josephson effect is nothing more than the electronic…
Target attractor tracking of relative phase in Bosonic Josephson junction
NASA Astrophysics Data System (ADS)
Borisenok, Sergey
2016-06-01
The relative phase of Bosonic Josephson junction in the Josephson regime of Bose-Hubbard model is tracked via the target attractor (`synergetic') feedback algorithm with the inter-well coupling parameter presented as a control function. The efficiency of our approach is demonstrated numerically for Gaussian and harmonic types of target phases.
External noise-induced transitions in a current-biased Josephson junction
Huang, Qiongwei; Xue, Changfeng; Tang, Jiashi
2016-01-15
We investigate noise-induced transitions in a current-biased and weakly damped Josephson junction in the presence of multiplicative noise. By using the stochastic averaging procedure, the averaged amplitude equation describing dynamic evolution near a constant phase difference is derived. Numerical results show that a stochastic Hopf bifurcation between an absorbing and an oscillatory state occurs. This means the external controllable noise triggers a transition into the non-zero junction voltage state. With the increase of noise intensity, the stationary probability distribution peak shifts and is characterised by increased width and reduced height. And the different transition rates are shown for large and small bias currents.
Metastable states and macroscopic quantum tunneling in a cold atom josephson ring
Solenov, Dmitry; Mozyrsky, Dmitry
2009-01-01
We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.
Identifying the chiral d-wave superconductivity by Josephson φ0-states
NASA Astrophysics Data System (ADS)
Liu, Jun-Feng; Xu, Yong; Wang, Jun
2017-03-01
We propose the Josephson junctions linked by a normal metal between a d + id superconductor and another d + id superconductor, a d-wave superconductor, or a s-wave superconductor for identifying the chiral d + id superconductivity. The time-reversal breaking in the chiral d-wave superconducting state is shown to result in a Josephson φ0-junction state where the current-phase relation is shifted by a phase φ0 from the sinusoidal relation, other than 0 and π. The ground-state phase difference φ0 and the critical current can be used to definitely confirm and read the information about the d + id superconductivity. A smooth evolution from conventional 0-π transitions to tunable φ0-states can be observed by changing the relative magnitude of two types of d-wave components in the d + id pairing. On the other hand, the Josephson junction involving the d + id superconductor is also the simplest model to realize a φ0- junction, which is useful in superconducting electronics and superconducting quantum computation.
Identifying the chiral d-wave superconductivity by Josephson φ0-states
Liu, Jun-Feng; Xu, Yong; Wang, Jun
2017-01-01
We propose the Josephson junctions linked by a normal metal between a d + id superconductor and another d + id superconductor, a d-wave superconductor, or a s-wave superconductor for identifying the chiral d + id superconductivity. The time-reversal breaking in the chiral d-wave superconducting state is shown to result in a Josephson φ0-junction state where the current-phase relation is shifted by a phase φ0 from the sinusoidal relation, other than 0 and π. The ground-state phase difference φ0 and the critical current can be used to definitely confirm and read the information about the d + id superconductivity. A smooth evolution from conventional 0-π transitions to tunable φ0-states can be observed by changing the relative magnitude of two types of d-wave components in the d + id pairing. On the other hand, the Josephson junction involving the d + id superconductor is also the simplest model to realize a φ0- junction, which is useful in superconducting electronics and superconducting quantum computation. PMID:28266582
Inverse ac Josephson effect at terahertz frequencies
NASA Astrophysics Data System (ADS)
Danchi, W. C.; Golightly, W. J.; Sutton, E. C.
1989-04-01
Using the Werthamer (1966) theory of superconducting tunnel junctions, it is shown that zero-crossing ac Josephson steps can occur at frequencies much higher than those expected previously, as long as the voltage waveform is nearly sinusoidal. Limits on the amount of permitted rounding of the Riedel (1964) peak were derived from analytical calculations, and numerical frequency-domain and time-domain computations for realistic junctions were carried out, yielding support for these limits. It is shown that previous arguments that zero-crossing steps could never be observed above the value of half the gap voltage are incorrect, due to the neglect of the Riedel peak.
Nonergodic metallic and insulating phases of Josephson junction chains.
Pino, Manuel; Ioffe, Lev B; Altshuler, Boris L
2016-01-19
Strictly speaking, the laws of the conventional statistical physics, based on the equipartition postulate [Gibbs J W (1902) Elementary Principles in Statistical Mechanics, developed with especial reference to the rational foundation of thermodynamics] and ergodicity hypothesis [Boltzmann L (1964) Lectures on Gas Theory], apply only in the presence of a heat bath. Until recently this restriction was believed to be not important for real physical systems because a weak coupling to the bath was assumed to be sufficient. However, this belief was not examined seriously until recently when the progress in both quantum gases and solid-state coherent quantum devices allowed one to study the systems with dramatically reduced coupling to the bath. To describe such systems properly one should revisit the very foundations of statistical mechanics. We examine this general problem for the case of the Josephson junction chain that can be implemented in the laboratory and show that it displays a novel high-temperature nonergodic phase with finite resistance. With further increase of the temperature the system undergoes a transition to the fully localized state characterized by infinite resistance and exponentially long relaxation.
Nonergodic metallic and insulating phases of Josephson junction chains
Pino, Manuel; Ioffe, Lev B.; Altshuler, Boris L.
2016-01-01
Strictly speaking, the laws of the conventional statistical physics, based on the equipartition postulate [Gibbs J W (1902) Elementary Principles in Statistical Mechanics, developed with especial reference to the rational foundation of thermodynamics] and ergodicity hypothesis [Boltzmann L (1964) Lectures on Gas Theory], apply only in the presence of a heat bath. Until recently this restriction was believed to be not important for real physical systems because a weak coupling to the bath was assumed to be sufficient. However, this belief was not examined seriously until recently when the progress in both quantum gases and solid-state coherent quantum devices allowed one to study the systems with dramatically reduced coupling to the bath. To describe such systems properly one should revisit the very foundations of statistical mechanics. We examine this general problem for the case of the Josephson junction chain that can be implemented in the laboratory and show that it displays a novel high-temperature nonergodic phase with finite resistance. With further increase of the temperature the system undergoes a transition to the fully localized state characterized by infinite resistance and exponentially long relaxation. PMID:26719416
Effect of environment fluctuations on a Josephson current
NASA Astrophysics Data System (ADS)
Galaktionov, A. V.
2017-01-01
An influence of an electromagnetic environment on a Josephson current through a tunnel junction is studied with the aid of Ambegaokar-Eckern-Schön effective action. Two types of environment are investigated: one, characterized by a resonant mode, and an ohmic one. The crossover to a Josephson π-junction is possible for both of them. In addition the resonant-mode environment results in an increase of a Josephson current when the ratio of the doubled superconducting gap to the frequency of the mode is close to an integer number.
Josephson effects in condensates of excitons and exciton polaritons
Shelykh, I. A.; Solnyshkov, D. D.; Pavlovic, G.; Malpuech, G.
2008-07-15
We analyze theoretically the phenomena related to the Josephson effect for exciton and polariton condensates, taking into account their specific spin degrees of freedom. We distinguish between two types of Josephson effects: the extrinsic effect, related to the coherent tunneling of particles with the same spin between two spatially separated potential traps, and the intrinsic effect, related to the 'tunneling' between different spinor components of the condensate within the same trap. We show that the Josephson effect in the nonlinear regime can lead to nontrivial polarization dynamics and produce spontaneous separation of the condensates with opposite polarization in real space.
Josephson effect in a Weyl SNS junction
NASA Astrophysics Data System (ADS)
Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.
2017-02-01
We calculate the Josephson current density j (ϕ ) for a Weyl superconductor-normal-metal-superconductor junction for which the outer terminals are superconducting Weyl metals and the normal layer is a Weyl (semi)metal. We describe the Weyl (semi)metal using a simple model with two Weyl points. The model has broken time-reversal symmetry, but inversion symmetry is present. We calculate the Josephson current for both zero and finite temperature for the two pairing mechanisms inside the superconductors that have been proposed in the literature, zero-momentum BCS-like pairing and finite-momentum FFLO-like pairing, and assuming the short-junction limit. For both pairing types we find that the current is proportional to the normal-state junction conductivity, with a proportionality coefficient that shows quantitative differences between the two pairing mechanisms. The current for the BCS-like pairing is found to be independent of the chemical potential, whereas the current for the FFLO-like pairing is not.
Black-Schaffer, Annica M.
2010-04-06
We use a tight-binding Bogoliubov-de Gennes (BdG) formalism to self-consistently calculate the proximity effect, Josephson current, and local density of states in ballistic graphene SNS Josephson junctions. Both short and long junctions, with respect to the superconducting coherence length, are considered, as well as different doping levels of the graphene. We show that self-consistency does not notably change the current-phase relationship derived earlier for short junctions using the non-selfconsistent Dirac-BdG formalism but predict a significantly increased critical current with a stronger junction length dependence. In addition, we show that in junctions with no Fermi level mismatch between the N and S regions superconductivity persists even in the longest junctions we can investigate, indicating a diverging Ginzburg-Landau superconducting coherence length in the normal region.
1D Josephson quantum interference grids: diffraction patterns and dynamics
NASA Astrophysics Data System (ADS)
Lucci, M.; Badoni, D.; Corato, V.; Merlo, V.; Ottaviani, I.; Salina, G.; Cirillo, M.; Ustinov, A. V.; Winkler, D.
2016-02-01
We investigate the magnetic response of transmission lines with embedded Josephson junctions and thus generating a 1D underdamped array. The measured multi-junction interference patterns are compared with the theoretical predictions for Josephson supercurrent modulations when an external magnetic field couples both to the inter-junction loops and to the junctions themselves. The results provide a striking example of the analogy between Josephson phase modulation and 1D optical diffraction grid. The Fiske resonances in the current-voltage characteristics with voltage spacing {Φ0}≤ft(\\frac{{\\bar{c}}}{2L}\\right) , where L is the total physical length of the array, {Φ0} the magnetic flux quantum and \\bar{c} the speed of light in the transmission line, demonstrate that the discrete line supports stable dynamic patterns generated by the ac Josephson effect interacting with the cavity modes of the line.
Josephson Junction spectrum analyzer for millimeter and submillimeter wavelengths
NASA Technical Reports Server (NTRS)
Larkin, S. Y.; Anischenko, S. E.; Khabayev, P. V.
1995-01-01
A prototype of the Josephson-effect spectrum analyzer developed for the millimeter wave band is described. The measurement results for spectra obtained in the frequency band from 50 to 250 GHz are presented.
Josephson effects in a Bose–Einstein condensate of magnons
Troncoso, Roberto E.; Núñez, Álvaro S.
2014-07-15
A phenomenological theory is developed, that accounts for the collective dynamics of a Bose–Einstein condensate of magnons. In terms of such description we discuss the nature of spontaneous macroscopic interference between magnon clouds, highlighting the close relation between such effects and the well known Josephson effects. Using those ideas, we present a detailed calculation of the Josephson oscillations between two magnon clouds, spatially separated in a magnonic Josephson junction. -- Highlights: •We presented a theory that accounts for the collective dynamics of a magnon-BEC. •We discuss the nature of macroscopic interference between magnon-BEC clouds. •We remarked the close relation between the above phenomena and Josephson’s effect. •We remark the distinctive oscillations that characterize the Josephson oscillations.
Josephson junction spectrum analyzer for millimeter and submillimeter wavelengths
Larkin, S.Y.; Anischenko, S.E.; Khabayev, P.V.
1994-12-31
A prototype of the Josephson-effect spectrum analyzer developed for the millimeter-wave band is described. The measurement results for spectra obtained in the frequency band from 50 to 250 GHz are presented.
Flux Cloning Anomalities in Josephson Nano-Junctions
NASA Astrophysics Data System (ADS)
Hassan, Hanaa Farhan; Kusmartsev, Feo V.
2010-12-01
The propagation of single flux quanta in T-shaped Josephson junctions gives rise to the flux cloning phenomenon. We have studied numerically the dynamics of flux cloning in cases of extended Josephson junctions. The changing thicknesses of T-junctions lead to new and interesting effects in terms of their dynamics. We have found out that when an additional Josephson transmission line is larger than the main Josephson transmission line, numerical simulations do not show the cloning phenomenon and soliton is reflected when it approaches the T junction. This strange result may be happened because the soliton losses more energy in the sharp edge. Although the vortex is moving very highly and it has huge energy but it still does not give birth to a new vortex. We have investigated conditions at which flux cloning occurs when both widths, W and W0, are changing.
Flux Cloning Anomalities in Josephson Nano-Junctions
NASA Astrophysics Data System (ADS)
Hassan, Hanaa Farhan; Kusmartsev, Feo V.
The propagation of single flux quanta in T-shaped Josephson junctions gives rise to the flux cloning phenomenon. We have studied numerically the dynamics of flux cloning in cases of extended Josephson junctions. The changing thicknesses of T-junctions lead to new and interesting effects in terms of their dynamics. We have found out that when an additional Josephson transmission line is larger than the main Josephson transmission line, numerical simulations do not show the cloning phenomenon and soliton is reflected when it approaches the T junction. This strange result may be happened because the soliton losses more energy in the sharp edge. Although the vortex is moving very highly and it has huge energy but it still does not give birth to a new vortex. We have investigated conditions at which flux cloning occurs when both widths, W and W0, are changing.
Coherent diffraction of thermal currents in long Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Guarcello, Claudio; Giazotto, Francesco; Solinas, Paolo
2016-08-01
We discuss heat transport in thermally-biased long Josephson tunnel junctions in the presence of an in-plane magnetic field. In full analogy with the Josephson critical current, the phase-dependent component of the heat current through the junction displays coherent diffraction. Thermal transport is analyzed as a function of both the length and the damping of the junction, highlighting deviations from the standard "Fraunhofer" pattern characteristic of short junctions. The heat current diffraction patterns show features strongly related to the formation and penetration of Josephson vortices, i.e., solitons. We show that a dynamical treatment of the system is crucial for the realistic description of the Josephson junction, and it leads to peculiar results. In fact, hysteretic behaviors in the diffraction patterns when the field is swept up and down are observed, corresponding to the trapping of vortices in the junction.
On the electrodynamics of Josephson effect in anisotropic superconductors
Mints, R.G.
1989-01-01
Specificities of Josephson effect electrodynamics in anisotropic superconductors are of considerable interest for the study of high temperature superconductors with strongly anisotropic layered structure. In this paper the authors give the calculation for the tunnel Josephson contact of an isolated vortex, the law of dispersion of its low-amplitude oscillations, the critical field H/sub cl/ for the penetration of magnetic flux, and the maximum current across a rectangular contact.
Josephson vortices as flexible waveguides for terahertz waves
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Savel'ev, Sergey; Yampol'skii, V. A.; Kusmartsev, F. V.; Nori, Franco
2008-09-01
We propose using the Josephson vortices (fluxons) as adjustable and malleable waveguides of electromagnetic radiation. Our theoretical and numerical calculations show that electromagnetic waves can propagate along the Josephson vortices and always follow the vortex lines. By changing external parameters, such as electric currents or magnetic fields, the shape and configuration of the guiding vortex lines can be controlled. We describe the design of a multifunctional three-terminal device that controls the transmission (redirecting or splitting) of a beam of electromagnetic waves.
Revealing topological superconductivity in extended quantum spin Hall Josephson junctions.
Lee, Shu-Ping; Michaeli, Karen; Alicea, Jason; Yacoby, Amir
2014-11-07
Quantum spin Hall-superconductor hybrids are promising sources of topological superconductivity and Majorana modes, particularly given recent progress on HgTe and InAs/GaSb. We propose a new method of revealing topological superconductivity in extended quantum spin Hall Josephson junctions supporting "fractional Josephson currents." Specifically, we show that as one threads magnetic flux between the superconductors, the critical current traces an interference pattern featuring sharp fingerprints of topological superconductivity-even when noise spoils parity conservation.
Sensitivity of Josephson-effect millimeter-wave radiometer
NASA Technical Reports Server (NTRS)
Ohta, H.; Feldman, M. J.; Parrish, P. T.; Chiao, R. Y.
1974-01-01
The noise temperature and the minimum detectable temperature of a Josephson junction in video detection of microwave and millimeter-wave radiation has been calculated. We use the well-known method based on a Fokker-Planck equation. The noise temperature can be very close to ambient temperature. Because its predetection bandwidth is very wide, a Josephson-effect radio telescope receiver can have a minimum detectable temperature better than that of a traveling-wave maser.
AC Josephson effect applications in microwave systems
NASA Astrophysics Data System (ADS)
Larkin, Serguey Y.
1996-12-01
analysis allow to get the picture of temperature distribution along the plasma cord diameter in accordance with dynamics of thermonuclear process development. Modem raclioastronomic research gives scientists the unique information on the world tructure. It is also necessary to analyze Space microwave radiation providing exclusive sensitivity of the equipment. In both cases equipment is required to be superwide band, to have high sensitivity and ability to operate at more than 300 GHz frequencies. Today all these requirements are met by the devices using the ac Josephson effect. The Josephson junctions are used as an active transforming element in such devices. At the end of 20 century the sphere of their utilization embraces medicine, communications, radiophysics, space exploration, ecology, military use, etc. The State Research Center "Fonon" ( SRC "Fonon") of the State Committee on Science and Technology of Ukraine was founded in 1991. The main aim of its creation was to concentrate the scientific and financial efforts for development and production of unique devices based on the results of fundamental study in physics of high T superconductivity. First of all we were interested in technological research on the obtaining of low impedance Josephson junctions out of the High T thin films. Using such junctions in combination with our original techniques developed in our Center we have succeed in creating the following new generation equipment: industrial set-up of the frequency meter in the range of 60 ... 600 GHz; experimental set-up of the spectrum analyzer operating in the range of 50 250 GHz; experimental model of radiometric receiver in 180...260 GHz range. All the above devices are based on the using ac Josephson effect for the receiving and processing mm- and submm- microwave signals.
Lossless, coherent Josephson three-wave combiner
NASA Astrophysics Data System (ADS)
Abdo, Baleegh; Sliwa, Katrina; Schackert, Flavius; Bergeal, Nicolas; Hatridge, Michael; Frunzio, Luigi; Stone, Douglas; Devoret, Michel
2013-03-01
We designed and operated a three-wave beam-splitter/combiner, based on Josephson parametric converters, which performs frequency conversion without introducing losses and thus adding no noise to the processed signal. We in particular show that the unitary signal-idler scattering parameters of the device can be fully modulated in-situ by varying the intensity and phase of the pump tone feeding the system. By operating the device as a 50/50 beam-combiner, we interfere coherently two input coherent microwave beams with different frequencies and demonstrate that the resulting interference fringes generated by the relative phase of the pump is in agreement with theoretical predictions. Potential applications of the device include quantum information transduction and realization of an ultra-sensitive interferometer with controllable feedback. Work supported by: IARPA, ARO, and NSF
Simplifying the circuit of Josephson parametric converters
NASA Astrophysics Data System (ADS)
Abdo, Baleegh; Brink, Markus; Chavez-Garcia, Jose; Keefe, George
Josephson parametric converters (JPCs) are quantum-limited three-wave mixing devices that can play various important roles in quantum information processing in the microwave domain, including amplification of quantum signals, transduction of quantum information, remote entanglement of qubits, nonreciprocal amplification, and circulation of signals. However, the input-output and biasing circuit of a state-of-the-art JPC consists of bulky components, i.e. two commercial off-chip broadband 180-degree hybrids, four phase-matched short coax cables, and one superconducting magnetic coil. Such bulky hardware significantly hinders the integration of JPCs in scalable quantum computing architectures. In my talk, I will present ideas on how to simplify the JPC circuit and show preliminary experimental results
Wang, Thomas T Y; Edwards, Alison J; Clevidence, Beverly A
2013-08-01
The mechanisms as well the genetics underlying the bioavailability and metabolism of carotenoids in humans remain unclear. To begin to address these questions, we used cluster analysis to examine individual temporal responses of plasma carotenoids from a controlled-diet study of subjects who consumed carotenoid-rich beverages. Treatments, given daily for 3 weeks, were watermelon juice at two levels (20-mg lycopene, 2.5-mg β-carotene, n=23 and 40-mg lycopene, 5-mg β-carotene, n=12) and tomato juice (18-mg lycopene, 0.6-mg β-carotene, n=10). Cluster analysis revealed distinct groups of subjects differing in the temporal response of plasma carotenoids and provided the basis for classifying subjects as strong responders or weak responders for β-carotene, lycopene, phytoene and phytofluene. Individuals who were strong or weak responders for one carotenoid were not necessarily strong or weak responders for another carotenoid. Furthermore, individual responsiveness was associated with genetic variants of the carotenoid metabolizing enzyme β-carotene 15,15'-monooxygenase 1. These results support the concept that individuals absorb or metabolize carotenoids differently across time and suggest that bioavailability of carotenoids may involve specific genetic variants of β-carotene 15,15'-monooxygenase 1.
NASA Astrophysics Data System (ADS)
Konschelle, François; Tokatly, Ilya V.; Bergeret, F. Sebastián
2015-09-01
Due to the spin-orbit coupling (SOC) an electric current flowing in a normal metal or semiconductor can induce a bulk magnetic moment. This effect is known as the Edelstein (EE) or magnetoelectric effect. Similarly, in a bulk superconductor a phase gradient may create a finite spin density. The inverse effect, also known as the spin-galvanic effect, corresponds to the creation of a supercurrent by an equilibrium spin polarization. Here, by exploiting the analogy between a linear-in-momentum SOC and a background SU(2) gauge field, we develop a quasiclassical transport theory to deal with magnetoelectric effects in superconducting structures. For bulk superconductors this approach allows us to easily reproduce and generalize a number of previously known results. For Josephson junctions we establish a direct connection between the inverse EE and the appearance of an anomalous phase shift φ0 in the current-phase relation. In particular we show that φ0 is proportional to the equilibrium spin current in the weak link. We also argue that our results are valid generically, beyond the particular case of linear-in-momentum SOC. The magnetoelectric effects discussed in this study may find applications in the emerging field of coherent spintronics with superconductors.
Lin, Shi-Zeng; Hu, Xiao
2011-04-01
The nano-scale intrinsic Josephson junctions in highly anisotropic cuprate superconductors have potential for generation of terahertz electromagnetic waves. When the thickness of a superconductor sample is much smaller than the wavelength of electromagnetic waves in vacuum, the superconductor renders itself as a cavity. Unlike conventional lasers, the presence of the cavity does not guarantee a coherent emission because of the internal degree of freedom of the superconductivity phase in long junctions. We study the excitation of terahertz wave by solitons in a stack of intrinsic Josephson junctions, especially for relatively short junctions. Coherent emission requires a rectangular configuration of solitons. However such a configuration is unstable against weak fluctuations, contrarily solitons favor a triangular lattice corresponding to an out-phase oscillation of electromagnetic waves. To utilize the cavity, we propose to use an array of stacks of short intrinsic Josephson junctions to generate powerful terahertz electromagnetic waves. The cavity synchronizes the plasma oscillation in different stacks and the emission intensity is predicted to be proportional to the number of stacks squared.
Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei
2017-01-01
The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy. PMID:28262731
NASA Astrophysics Data System (ADS)
Lee, Yu-Li; Lee, Yu-Wen
2016-05-01
We study the behavior of a topological Josephson junction in which two topological superconductors are coupled through a quantum dot. We focus on the case with the bulk superconducting gap being the largest energy scale. Two parameter regimes are investigated: a weak tunneling between the dot and the superconductors, with the dot near its charge degeneracy point, and a strong-tunneling regime in which the transmission between the dot and the superconductors is nearly perfect. We show that in the former situation, the Andreev spectrum for each sector with fixed fermion parity consists of only two levels, which gives rise to the nontrivial current-phase relation. Moreover, we study the Rabi oscillation between the two levels and indicate that the corresponding frequency is a 4 π -periodic function of the phase difference between the two superconductors, which is immune to the quasiparticle poisoning. In the latter case, we find that the Coulomb charging energy enhances the effect of backscattering at the interfaces between the dot and the superconductors. Both the temperature and the gate-voltage dependence of the critical Josephson current are examined.
Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current
NASA Astrophysics Data System (ADS)
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasyl; Ivanov, Boris A.; Slavin, Andrei
2017-03-01
The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.
Josephson critical current of long SNS junctions in the presence of a magnetic field
NASA Astrophysics Data System (ADS)
Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.
We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B <~Φ0 /W2 , the edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.
Quantum computing with Josephson junction circuits
NASA Astrophysics Data System (ADS)
Xu, Huizhong
This work concerns the study of Josephson junction circuits in the context of their usability for quantum computing. The zero-voltage state of a current-biased Josephson junction has a set of metastable quantum energy levels. If a junction is well isolated from its environment, it will be possible to use the two lowest states as a qubit in a quantum computer. I first examine the meaning of isolation theoretically. Using a master equation, I analyzed the effect of dissipation on escape rates and suggested a simple method, population depletion technique, to measure the relaxation time (T1). Using a stochastic Bloch equation to analyze the dependence of microwave resonance peak width on current noise, I found decoherence due to current noise depends on the noise spectrum. For high frequency noise with a cutoff frequency fc much larger than 1/T1, I found decoherence due to noise can be described by a dephasing rate that is proportional to the noise spectral density. However, for low frequency noise such that its cutoff frequency fc is much smaller than 1/T 1, decoherence due to noise depends on the total rms current noise. I then analyze and test a few qubit isolation schemes, including resistive isolation, inductor-capacitor (LC) isolation, half-wavelength resonant isolation and inductor-junction (LJ) isolation. I found the resistive isolation scheme has a severe heating problem. Macroscopic quantum tunneling and energy level quantization were observed in the LC isolated Nb/AlOx/Nb and AL/ALOx/Al junction qubits at 25 mK. Relaxation times of 4--12 ns and spectroscopic coherence times of 1--3 ns were obtained for these LC isolated qubits. I found the half-wavelength isolated junction qubit has a relaxation time of about 20 ns measured by the population-depletion techniques, but no energy levels were observed in this qubit. Experimental results suggest the LJ isolated qubit has a longer relaxation and coherence times than all my previously examined samples. Using a
Instability of Driven Josephson Vortices in Long Underdamped Junctions
NASA Astrophysics Data System (ADS)
Sheikhzada, Ahmad; Gurevich, Alex
We show that a Josephson vortex driven by a dc current can become unstable due to strong Cherenkov radiation resulting from intrinsic nonlocal electrodynamics of long underdamped Josephson junctions. This instability is not captured by the conventional sine-Gordon equation but is described by a more general integro-differential equation for the phase difference, θ (x , t) . Our numerical simulations of this nonlinear dynamic equation for different junction geometries have shown that, as the vortex reaches a critical velocity, it triggers a cascade of expanding vortex-antivortex pairs. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our results suggest that a rapidly moving Josephson vortex can destroy the superconducting long-range order in a way that is similar to the crack propagation in solids. This work was supported by DOE under Grant No. DE-SC0010081.
Micromagnetic modeling of critical current oscillations in magnetic Josephson junctions
NASA Astrophysics Data System (ADS)
Golovchanskiy, I. A.; Bol'ginov, V. V.; Stolyarov, V. S.; Abramov, N. N.; Ben Hamida, A.; Emelyanova, O. V.; Stolyarov, B. S.; Kupriyanov, M. Yu.; Golubov, A. A.; Ryazanov, V. V.
2016-12-01
In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal process in the ferromagnetic layer with introduced internal magnetic stiffness and subsequent reconstruction of the critical current value using total flux or reconstructed actual phase difference distribution. The approach is flexible and shows good agreement with experimental data obtained on Josephson junctions with ferromagnetic barriers. Based on this approach we have obtained a critical current dependence on applied magnetic field for rectangular magnetic Josephson junctions with high size aspect ratio. We have shown that the rectangular magnetic Josephson junctions can be considered for application as an effective Josephson magnetic memory element with the value of critical current defined by the orientation of magnetic moment at zero magnetic field. An impact of shape magnetic anisotropy on critical current is revealed and discussed. Finally, we have considered a curling magnetic state in the ferromagnetic layer and demonstrated its impact on critical current.
Chen, C.D.; Delsing, P.; Haviland, D.B.; Harada, Y.; Claeson, T.
1995-06-01
We have studied the superconductor-insulator (SI) phase transition for two-dimensional (2D) arrays of small Josephson junctions in a weak magnetic field. The data were analyzed within the context of the theory of the magnetic-field-tuned SI transition in 2D superconductors. We show resistance scaling curves over several orders of magnitude for the 2D arrays. The critical exponent {ital z}{sub {ital B}} is determined to be 1.05, in good agreement with the theory. Moreover, the transverse (Hall) resistance at the critical field is found to be very small in comparison to the longitudinal resistance.
In-phase motion of Josephson vortices in stacked SNS Josephson junctions: effect of ordered pinning
NASA Astrophysics Data System (ADS)
Berdiyorov, G. R.; Savel'ev, S. E.; Kusmartsev, F. V.; Peeters, F. M.
2013-12-01
The dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting Josephson junctions is investigated using the anisotropic time-dependent Ginzburg-Landau theory in the presence of a square/rectangular array of pinning centers (holes). For small values of the applied drive, fluxons in different junctions move out of phase, forming a periodic triangular lattice. A rectangular lattice of moving fluxons is observed at larger currents, which is in agreement with previous theoretical predictions (Koshelev and Aranson 2000 Phys. Rev. Lett. 85 3938). This ‘superradiant’ flux-flow state is found to be stable in a wide region of applied current. The stability range of this ordered state is considerably larger than the one obtained for the pinning-free sample. Clear commensurability features are observed in the current-voltage characteristics of the system with pronounced peaks in the critical current at (fractional) matching fields. The effect of density and strength of the pinning centers on the stability of the rectangular fluxon lattice is discussed. Predicted synchronized motion of fluxons in the presence of ordered pinning can be detected experimentally using the rf response of the system, where enhancement of the Shapiro-like steps is expected due to the synchronization.
Terahertz Josephson spectral analysis and its applications
NASA Astrophysics Data System (ADS)
Snezhko, A. V.; Gundareva, I. I.; Lyatti, M. V.; Volkov, O. Y.; Pavlovskiy, V. V.; Poppe, U.; Divin, Y. Y.
2017-04-01
Principles of Hilbert-transform spectral analysis (HTSA) are presented and advantages of the technique in the terahertz (THz) frequency range are discussed. THz HTSA requires Josephson junctions with high values of characteristic voltages I c R n and dynamics described by a simple resistively shunted junction (RSJ) model. To meet these requirements, [001]- and [100]-tilt YBa2Cu3O7‑x bicrystal junctions with deviations from the RSJ model less than 1% have been developed. Demonstrators of Hilbert-transform spectrum analyzers with various cryogenic environments, including integration into Stirling coolers, are described. Spectrum analyzers have been characterized in the spectral range from 50 GHz to 3 THz. Inside a power dynamic range of five orders, an instrumental function of the analyzers has been found to have a Lorentz form around a single frequency of 1.48 THz with a spectral resolution as low as 0.9 GHz. Spectra of THz radiation from optically pumped gas lasers and semiconductor frequency multipliers have been studied with these spectrum analyzers and the regimes of these radiation sources were optimized for a single-frequency operation. Future applications of HTSA will be related with quick and precise spectral characterization of new radiation sources and identification of substances in the THz frequency range.
Quantum interference in topological insulator Josephson junctions
NASA Astrophysics Data System (ADS)
Song, Juntao; Liu, Haiwen; Liu, Jie; Li, Yu-Xian; Joynt, Robert; Sun, Qing-feng; Xie, X. C.
2016-05-01
Using nonequilibrium Green's functions, we studied numerically the transport properties of a Josephson junction, superconductor-topological insulator-superconductor hybrid system. Our numerical calculation shows first that proximity-induced superconductivity is indeed observed in the edge states of a topological insulator adjoining two superconducting leads and second that the special characteristics of topological insulators endow the edge states with an enhanced proximity effect with a superconductor but do not forbid the bulk states to do the same. In a size-dependent analysis of the local current, it was found that a few residual bulk states can lead to measurable resistance, whereas because these bulk states spread over the whole sample, their contribution to the interference pattern is insignificant when the sample size is in the micrometer range. Based on these numerical results, it is concluded that the apparent disappearance of residual bulk states in the superconducting interference process as described by Hart et al. [Nat. Phys. 10, 638 (2014), 10.1038/nphys3036] is just due to the effects of size: the contribution of the topological edge states outweighs that of the residual bulk states.
Qubit readout with the Josephson Photomultiplier
NASA Astrophysics Data System (ADS)
Ribeill, Guilhem
Recent demonstrations of error correction in many qubit circuits, as well as efforts to build a logical qubit, have shown the need for a simple and scalable superconducting quantum bit (qubit) readout. Current solutions based on heterodyne detection and cryogenic amplification of microwave readout tones may prove difficult to scale, while photon counting presents an attractive alternative. However, the development of counters operating at these frequencies has proved technically challenging. In this thesis, we describe the development of the Josephson Photomultiplier (JPM), a microwave photon counting circuit. We discuss the JPM theoretically, and describe the fabrication of the JPM using standard thin film lithography techniques. We measure its properties as a microwave photon counter using a qubit as an in-situ calibrated source of photons. We measure a JPM quantum efficiency at the few percent level. We then use the JPM to perform readout of a transmon qubit in both the dispersive and bright regimes. We observe raw measurement fidelities of 35% and 62% respectively. We discuss how the JPM and measurement protocol could be further optimized to achieve fidelities in excess of 90%.
Superconducting qubits with semiconductor nanowire Josephson junctions
NASA Astrophysics Data System (ADS)
Petersson, K. D.; Larsen, T. W.; Kuemmeth, F.; Jespersen, T. S.; Krogstrup, P.; Nygård, J.; Marcus, C. M.
2015-03-01
Superconducting transmon qubits are a promising basis for a scalable quantum information processor. The recent development of semiconducting InAs nanowires with in situ molecular beam epitaxy-grown Al contacts presents new possibilities for building hybrid superconductor/semiconductor devices using precise bottom up fabrication techniques. Here, we take advantage of these high quality materials to develop superconducting qubits with superconductor-normal-superconductor Josephson junctions (JJs) where the normal element is an InAs semiconductor nanowire. We have fabricated transmon qubits in which the conventional Al-Al2O3-Al JJs are replaced by a single gate-tunable nanowire JJ. Using spectroscopy to probe the qubit we observe fluctuations in its level splitting with gate voltage that are consistent with universal conductance fluctuations in the nanowire's normal state conductance. Our gate-tunable nanowire transmons may enable new means of control for large scale qubit architectures and hybrid topological quantum computing schemes. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation and the European Commission.
Directional Amplification with a Josephson Circuit
NASA Astrophysics Data System (ADS)
Abdo, Baleegh; Sliwa, Katrina; Frunzio, Luigi; Devoret, Michel
2013-07-01
Nonreciprocal devices perform crucial functions in many low-noise quantum measurements, usually by exploiting magnetic effects. In the proof-of-principle device presented here, on the other hand, two on-chip coupled Josephson parametric converters (JPCs) achieve directionality by exploiting the nonreciprocal phase response of the JPC in the transmission-gain mode. The nonreciprocity of the device is controlled in situ by varying the amplitude and phase difference of two independent microwave pump tones feeding the system. At the desired working point and for a signal frequency of 8.453 GHz, the device achieves a forward power gain of 15 dB within a dynamical bandwidth of 9 MHz, a reverse gain of -6dB, and suppression of the reflected signal by 8 dB. We also find that the amplifier adds a noise equivalent to less than 1.5 photons at the signal frequency (referred back to the input). It can process up to 3 photons at the signal frequency per inverse dynamical bandwidth. With a directional amplifier operating along the principles of this device, qubit and readout preamplifier could be integrated on the same chip.
DOE R&D Accomplishments Database
Lee, T. D.
1957-06-01
Experimental results on the non-conservation of parity and charge conservation in weak interactions are reviewed. The two-component theory of the neutrino is discussed. Lepton reactions are examined under the assumption of the law of conservation of leptons and that the neutrino is described by a two- component theory. From the results of this examination, the universal Fermi interactions are analyzed. Although reactions involving the neutrino can be described, the same is not true of reactions which do not involve the lepton, as the discussion of the decay of K mesons and hyperons shows. The question of the invariance of time reversal is next examined. (J.S.R.)
Quantum Phase Slips in Topological Josephson Junction Rings
NASA Astrophysics Data System (ADS)
Rodriguez Mota, Rosa; Vishveshwara, Smitha; Pereg-Barnea, Tami
We study quantum phase slip processes (QPS) in a ring of N topological superconducting islands joined by Josephson junctions and threaded by magnetic flux. In this array, neighboring islands interact through the usual charge 2e Josephson tunneling and the Majorana assisted charge e tunneling. When the charging energy associated with the island's capacitance is zero, the energy vs. flux relation of the system is characterized by parabolas centered around even or odd multiples of the superconducting flux quantum, depending on the parity of the system. For small but non-zero charging energy, quantum fluctuations can lead to tunneling between these classical states. In this work, we calculate the amplitude of these tunneling processes, commonly known as quantum phase slips. We also add gate voltages to our system and study how the amplitude of QPS in these topological Josephson array is modified by Aharanov-Casher interference effects.
A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy
Jäck, Berthold Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R.; Hardock, Andreas; Kern, Klaus
2015-01-05
Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 10{sup 20 }cm{sup −2} s{sup −1} is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.
Novel all-high Tc epitaxial Josephson junction
NASA Astrophysics Data System (ADS)
Chin, D. K.; van Duzer, T.
1991-02-01
Josephson junctions are essential components in high-temperature superconductive integrated circuits. YBaCuO/Nb-doped SrTiO3/YBaCuO epitaxial Josephson junctions have been designed, fabricated, and tested. The YBaCuO and Nb-doped SrTiO3 films were deposited by off-axis sputtering. Both dc and ac Josephson effects have been observed and the supercurrent persists up to 80 K. The critical current density is an exponential function of the barrier layer thickness. The product of critical current and normal resistance is between one and three millivolts. A superconducting quantum interference device made of the junctions displays magnetic field modulation of critical current.
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions.
Massarotti, D; Pal, A; Rotoli, G; Longobardi, L; Blamire, M G; Tafuri, F
2015-06-09
The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits.
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions
Massarotti, D.; Pal, A.; Rotoli, G.; Longobardi, L.; Blamire, M. G.; Tafuri, F.
2015-01-01
The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits. PMID:26054495
Strong-coupling BCS models of Josephson qubits.
Alicki, R; Miklaszewski, W
2013-01-23
The strong-coupling version of the BCS theory for superconductors is used to derive microscopic models for all types of small Josephson junctions--charge qubit, flux qubit and phase qubit. Applied to Josephson qubits it yields a more complicated structure of the lowest-lying energy levels than that obtained from phenomenological models based on quantization of the Kirchhoff equations. In particular, highly degenerate levels emerge, which act as probability sinks for the qubit. The alternative formulae concerning spectra of superconducting qubits are presented and compared with the experimental data. In contrast to the existing theories those formulae contain microscopic parameters of the model. In particular, for the first time, the density of Cooper pairs at zero temperature is estimated for an Al-based flux qubit. Finally, the question whether small Josephson junctions can be treated as macroscopic quantum systems is briefly discussed.
Memory cell operation based on small Josephson junctions arrays
NASA Astrophysics Data System (ADS)
Braiman, Y.; Nair, N.; Rezac, J.; Imam, N.
2016-12-01
In this paper we analyze a cryogenic memory cell circuit based on a small coupled array of Josephson junctions. All the basic memory operations (e.g., write, read, and reset) are implemented on the same circuit and different junctions in the array can in principle be utilized for these operations. The presented memory operation paradigm is fundamentally different from conventional single quantum flux operation logics (SFQ). As an example, we demonstrate memory operation driven by a SFQ pulse employing an inductively coupled array of three Josephson junctions. We have chosen realistic Josephson junction parameters based on state-of-the-art fabrication capabilities and have calculated access times and access energies for basic memory cell operations. We also implemented an optimization procedure based on the simulated annealing algorithm to calculate the optimized and typical values of access times and access energies.
Cooper pair splitting in parallel quantum dot Josephson junctions
Deacon, R. S.; Oiwa, A.; Sailer, J.; Baba, S.; Kanai, Y.; Shibata, K.; Hirakawa, K.; Tarucha, S.
2015-01-01
Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair. PMID:26130172
Internal Josephson effects in spinor dipolar Bose-Einstein condensates
Yasunaga, Masashi; Tsubota, Makoto
2010-02-15
We theoretically study the internal Josephson effect, which is driven by spin-exchange interactions and magnetic dipole-dipole interactions, in a three-level system for spin-1 Bose-Einstein condensates, obtaining novel spin dynamics. We introduce single spatial mode approximations into the Gross-Pitaevskii equations and derive the Josephson-type equations, which are analogous to tunneling currents through three junctions between three superconductors. From an analogy with two interacting nonrigid pendulums, we identify unique varied oscillational modes, called the 0-{pi}, 0-running, running-running, 2n{pi} and running-2{pi}, single nonrigid pendulum, and two rigid pendulums phase modes. These Josephson modes in the three states are expected to be found in real atomic Bose gas systems.
HTS step-edge Josephson junction terahertz harmonic mixer
NASA Astrophysics Data System (ADS)
Du, Jia; Weily, Andrew R.; Gao, Xiang; Zhang, Ting; Foley, Cathy P.; Guo, Yingjie Jay
2017-02-01
A high-temperature superconducting (HTS) terahertz (THz) frequency down-converter or mixer based on a thin-film ring-slot antenna coupled YBa2Cu3O7-x (YBCO)/MgO step-edge Josephson junction is reported. The frequency down-conversion was achieved using higher order harmonics of an applied lower frequency (19-40 GHz) local oscillator signal in the Josephson junction mixing with a THz signal of over 600 GHz, producing a 1-3 GHz intermediate frequency signal. Up to 31st order of harmonic mixing was obtained and the mixer operated stably at temperatures up to 77 K. The design details of the antenna, HTS Josephson junction mixer, the matching and isolation circuits, and the DC and RF performance evaluation are described in this paper.
Statistics of voltage fluctuations in resistively shunted Josephson junctions
NASA Astrophysics Data System (ADS)
Marthaler, Michael; Golubev, Dmitry; Utsumi, Yasuhiro; Schön, Gerd
2011-03-01
The intrinsic nonlinearity of Josephson junctions converts Gaussian current noise in the input into non-Gaussian voltage noise in the output. For a resistively shunted Josephson junction with white input noise we determine numerically exactly the properties of the few lowest cumulants of the voltage fluctuations, and we derive analytical expressions for these cumulants in several important limits. The statistics of the voltage fluctuations is found to be Gaussian at bias currents well above the Josephson critical current, but Poissonian at currents below the critical value. In the transition region close to the critical current the higher-order cumulants oscillate and the voltage noise is strongly non-Gaussian. For coloured input noise we determine the third cumulant of the voltage.
Statistics of voltage fluctuations in resistively shunted Josephson junctions
NASA Astrophysics Data System (ADS)
Golubev, D. S.; Marthaler, M.; Utsumi, Y.; Schön, Gerd
2010-05-01
The intrinsic nonlinearity of Josephson junctions converts Gaussian current noise in the input into non-Gaussian voltage noise in the output. For a resistively shunted Josephson junction with white input noise we determine numerically exactly the properties of the few lowest cumulants of the voltage fluctuations, and we derive analytical expressions for these cumulants in several important limits. The statistics of the voltage fluctuations is found to be Gaussian at bias currents well above the Josephson critical current but Poissonian at currents below the critical value. In the transition region close to the critical current the higher-order cumulants oscillate and the voltage noise is strongly non-Gaussian. For colored input noise we determine the third cumulant of the voltage.
Macroscopic quantum effects in the zero voltage state of the current biased Josephson junction
Clarke, J.; Devoret, M.H.; Martinis, J.; Esteve, D.
1985-05-01
When a weak microwave current is applied to a current-biased Josephson tunnel junction in the thermal limit the escape rate from the zero voltage state is enhanced when the microwave frequency is near the plasma frequency of the junction. The resonance curve is markedly asymmetric because of the anharmonic properties of the potential well: this behavior is well explained by a computer simulation using a resistively shunted junction model. This phenomenon of resonant activation enables one to make in situ measurements of the capacitance and resistance shunting the junction, including contributions from the complex impedance presented by the current leads. For the relatively large area junctions studied in these experiments, the external capacitive loading was relatively unimportant, but the damping was entirely dominated by the external resistance.
NASA Astrophysics Data System (ADS)
Park, Sunghun; Recher, Patrik
2015-12-01
A phase from an adiabatic exchange of Majorana bound states (MBS) reveals their exotic anyonic nature. For detecting this exchange phase, we propose an experimental setup consisting of a Corbino geometry Josephson junction on the surface of a topological insulator, in which two MBS at zero energy can be created and rotated. We find that if a metallic tip is weakly coupled to a point on the junction, the time-averaged differential conductance of the tip-Majorana coupling shows peaks at the tip voltages e V =±(α -2 π l )ℏ/TJ, where α =π /2 is the exchange phase of the two circulating MBS, TJ is the half rotation time of MBS, and l an integer. This result constitutes a clear experimental signature of Majorana fermion exchange.
Resonant Phase Matching of Josephson Junction Traveling Wave Parametric Amplifiers
2014-10-06
Resonant Phase Matching of Josephson Junction Traveling Wave Parametric Amplifiers Kevin O’Brien,1 Chris Macklin,2 Irfan Siddiqi,2 and Xiang Zhang1,3...overcome phase mismatch in Josephson-junction traveling wave parametric amplifiers in order to achieve high gain over a broad bandwidth. Using “resonant...achieves a gain of 20 dB, an instantaneous bandwidth of 3 GHz, and a saturation power of −98 dBm. Such an amplifier is well suited to cryogenic
Effect of current injection into thin-film Josephson junctions
Kogan, V. G.; Mints, R. G.
2014-11-11
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. Our method of calculating the distribution of injected currents is also proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ=2λ2/d;λ is the bulk London penetration depth of the film material and d is the film thickness.
Effect of current injection into thin-film Josephson junctions
Kogan, V. G.; Mints, R. G.
2014-11-11
New thin-film Josephson junctions have recently been tested in which the current injected into one of the junction banks governs Josephson phenomena. One thus can continuously manage the phase distribution at the junction by changing the injected current. Our method of calculating the distribution of injected currents is also proposed for a half-infinite thin-film strip with source-sink points at arbitrary positions at the film edges. The strip width W is assumed small relative to Λ=2λ^{2}/d;λ is the bulk London penetration depth of the film material and d is the film thickness.
Spontaneous symmetry breaking and collapse in bosonic Josephson junctions
Mazzarella, Giovanni; Salasnich, Luca
2010-09-15
We investigate an attractive atomic Bose-Einstein condensate (BEC) trapped by a double-well potential in the axial direction and by a harmonic potential in the transverse directions. We obtain numerically a quantum phase diagram which includes all the three relevant phases of the system: Josephson, spontaneous symmetry breaking (SSB), and collapse. We consider also the coherent dynamics of the BEC and calculate the frequency of population-imbalance mode in the Josephson phase and in the SSB phase up to the collapse. We show that these phases can be observed by using ultracold vapors of {sup 7}Li atoms in a magneto-optical trap.
Al Kaissi, Ali; Ryabykh, Sergey; Ochirova, Polina; Kenis, Vladimir; Hofstätter, Jochen G.; Grill, Franz; Ganger, Rudolf; Kircher, Susanne Gerit
2017-01-01
Marked ligamentous hyperlaxity and muscle weakness/wasting associated with awkward gait are the main deficits confused with the diagnosis of myopathy. Seven children (6 boys and 1 girl with an average age of 8 years) were referred to our department because of diverse forms of skeletal abnormalities. No definitive diagnosis was made, and all underwent a series of sophisticated investigations in other institutes in favor of myopathy. We applied our methodology through the clinical and radiographic phenotypes followed by targeted genotypic confirmation. Three children (2 boys and 1 girl) were compatible with the diagnosis of progressive pseudorheumatoid chondrodysplasia. The genetic mutation was correlated with the WISP 3 gene actively expressed by articular chondrocytes and located on chromosome 6. Klinefelter syndrome was the diagnosis in 2 boys. Karyotyping confirmed 47,XXY (aneuploidy of Klinefelter syndrome). And 2 boys were finally diagnosed with Morquio syndrome (MPS type IV A) as both showed missense mutations in the N-acetylgalactosamine-sulfate sulfatase gene. Misdiagnosis can lead to the initiation of a long list of sophisticated investigations. PMID:28210640
Conditions for synchronization in Josephson-junction arrays
Chernikov, A.A.; Schmidt, G.
1995-12-31
An effective perturbation theoretical method has been developed to study the dynamics of Josephson Junction series arrays. It is shown that the inclusion of Junction capacitances, often ignored, has a significant impact on synchronization. Comparison of analytic with computational results over a wide range of parameters shows excellent agreement.
Dayem bridge Josephson junctions. [for millimeter wave mixer
NASA Technical Reports Server (NTRS)
Barr, D. W.; Mattauch, R. J.
1977-01-01
The Josephson junction shows great promise as a millimeter wave mixer element. This paper discusses the physical mixing process from a first-order mathematical approach. Design and fabrication of such structures tailored for use in a 80-120 GHz mixer application is presented. Testing of the structures and a discussion of their interpretation is presented.
Fluctuating pancake vortices revealed by dissipation of Josephson vortex lattice.
Koshelev, A. E.; Buzdin, A. I.; Kakeya, I.; Yamamoto, T.; Kadowaki, K.
2011-06-01
In strongly anisotropic layered superconductors in tilted magnetic fields, the Josephson vortex lattice coexists with the lattice of pancake vortices. Due to the interaction between them, the dissipation of the Josephson vortex lattice is very sensitive to the presence of the pancake vortices. If the c-axis magnetic field is smaller than the corresponding lower critical field, the pancake stacks are not formed but the individual pancakes may exist in the fluctuational regime either near the surface in large-size samples or in the central region for small-size mesas. We calculate the contribution of such fluctuating pancake vortices to the c-axis conductivity of the Josephson vortex lattice and compare the theoretical results with measurements on small mesas fabricated out of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} crystals. A fingerprint of fluctuating pancakes is a characteristic exponential dependence of the c-axis conductivity observed experimentally. Our results provide strong evidence of the existence of the fluctuating pancakes and their influence on the Josephson vortex lattice dissipation.
Cherenkov radiation by Josephson vortex travelling in the long sandwich
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2009-03-01
Vortex motion in the long Josephson sandwich embedded in dielectric media is described. It is shown that vortices traveling with velocities greater than the speed of light in the dielectric generate electromagnetic waves. Appearance of radiation is due to Cherenkov phenomenon. Radiation appearing at rather high vortex velocities has high enough frequencies. For typical sandwiches radiation frequencies fall on THz domain.
Processing of Superconductor-Normal-Superconductor Josephson Edge Junctions
NASA Technical Reports Server (NTRS)
Kleinsasser, A. W.; Barner, J. B.
1997-01-01
The electrical behavior of epitaxial superconductor-normal-superconductor (SNS) Josephson edge junctions is strongly affected by processing conditions. Ex-situ processes, utilizing photoresist and polyimide/photoresist mask layers, are employed for ion milling edges for junctions with Yttrium-Barium-Copper-Oxide (YBCO) electrodes and primarily Co-doped YBCO interlayers.
Josephson junctions in high-T/sub c/ superconductors
Falco, C.M.; Lee, T.W.
1981-01-14
The invention includes a high T/sub c/ Josephson sperconducting junction as well as the method and apparatus which provides the junction by application of a closely controlled and monitored electrical discharge to a microbridge region connecting two portions of a superconducting film.
High-frequency dynamics of hybrid oxide Josephson heterostructures
NASA Astrophysics Data System (ADS)
Komissinskiy, P.; Ovsyannikov, G. A.; Constantinian, K. Y.; Kislinski, Y. V.; Borisenko, I. V.; Soloviev, I. I.; Kornev, V. K.; Goldobin, E.; Winkler, D.
2008-07-01
We summarize our results on Josephson heterostructures Nb/Au/YBa2Cu3Ox that combine conventional (S) and oxide high- Tc superconductors with a dominant d -wave symmetry of the superconducting order parameter (D). The heterostructures were fabricated on (001) and (1 1 20) YBa2Cu3Ox films grown by pulsed laser deposition. The structural and surface studies of the (1 1 20) YBa2Cu3Ox thin films reveal nanofaceted surface structure with two facet domain orientations, which are attributed as (001) and (110)-oriented surfaces of YBa2Cu3Ox and result in S/D(001) and S/D(110) nanojunctions formed on the facets. Electrophysical properties of the Nb/Au/YBa2Cu3Ox heterostructures are investigated by the electrical and magnetic measurements at low temperatures and analyzed within the faceting scenario. The superconducting current-phase relation (CPR) of the heterostructures with finite first and second harmonics is derived from the Shapiro steps, which appear in the I-V curves of the heterostructures irradiated at frequencies up to 100 GHz. The experimental positions and amplitudes of the Shapiro steps are explained within the modified resistive Josephson junction model, where the second harmonic of the CPR and capacitance of the Josephson junctions are taken into account. We experimentally observe a crossover from a lumped to a distributed Josephson junction limit for the size of the heterostructures smaller than Josephson penetration depth. The effect is attributed to the variations of the harmonics of the superconducting CPR across the heterojunction, which may give rise to splintered vortices of magnetic flux quantum. Our investigations of parameters and phenomena that are specific for superconductors having d -wave symmetry of the superconducting order parameter may be of importance for applications such as high-frequency detectors and novel elements of a possible quantum computer.
Frequency combs with weakly lasing exciton-polariton condensates.
Rayanov, K; Altshuler, B L; Rubo, Y G; Flach, S
2015-05-15
We predict the spontaneous modulated emission from a pair of exciton-polariton condensates due to coherent (Josephson) and dissipative coupling. We show that strong polariton-polariton interaction generates complex dynamics in the weak-lasing domain way beyond Hopf bifurcations. As a result, the exciton-polariton condensates exhibit self-induced oscillations and emit an equidistant frequency comb light spectrum. A plethora of possible emission spectra with asymmetric peak distributions appears due to spontaneously broken time-reversal symmetry. The lasing dynamics is affected by the shot noise arising from the influx of polaritons. That results in a complex inhomogeneous line broadening.
Effects of the environment on the switching current in graphene-based Josephson Junctions
NASA Astrophysics Data System (ADS)
Borzenets, Ivan; Ke, Chung-Ting; Amet, Francois; Tso Wei, Ming; Yamamoto, Michihisa; Bomze, Yuriy; Tarucha, Seigo; Finkelstein, Gleb
The nature of the switching current and hysteresis (difference between switching and retrapping currents) in graphene-based Josephson junctions depends greatly on the interaction with the environment. Conventional devices result in underdamped Josephson junctions making the true critical current inaccessible. On the other hand, heavily isolating the Josephson junctions places them in the microscopic quantum tunneling regime even at high temperatures, also masking the critical current. We study the critical current, and the switching statistics in graphene Josephson junctions while varying the effects of the environment. Proper isolation of graphene Josephson junctions is necessary to measure the true critical current, especially so for the cases of small currents around the Dirac point. This is true for the case of conventional diffusive as well as the novel ballistic Josephson junctions.
Phenomena in Coupled Superconducting Weak Links.
NASA Astrophysics Data System (ADS)
Neumann, Lawrence George
Interactions between two independently biasable coupled superconducting microbridges were studied. Some bridges were fabricated within 2 (mu)m of each other. Quasiparticles from one bridge affect the other. In a second type of sample, the microbridges were separated by 10 (mu)m and coupled via a resistive shunt. The interaction results from the current flowing through the shunt. Similar effects are seen in both types of samples. In opposed biased bridges, the effective critical current is decreased because of the interaction. For series biased bridges, the effective critical current of one bridge is decreased or increased, depending on the voltage across the other bridge. These interactions lead to voltage steps in the I-V curves where, for opposed biased bridges, both voltages increase; for series bias, one voltage increases, the other decreases. Experimental results are in reasonable agreement with a second-order perturbation calculation and with an analog simulation. Voltage locking is found for both biasing configurations in both types of samples. Locking can occur simultaneously with a voltage step, resulting in nascent voltage locking which can also occur in conjunction with hysteresis. The effect of a voltage in the pad between the two proximity coupled bridges is to vary the voltage at which locking occurs, which in turn alters the shape of the locking curve. Locking range is calculated in two models for comparison with the two types of samples. The first explicitly considers the time delay for propagation of the charge -imbalance wave from one bridge to the other. The second model considers the current flowing in the resistive/inductive coupling shunt. A deviation of the critical current of planar microbridges from a linear temperature dependence can be explained as an effective length effect. Variable thickness bridges show a linear temperature dependence except very near T(,c), where fluctuations are important. The critical current of the one-dimensional indium strips shows a (1 - t('2))('3/2) temperature dependence. A negative resistance region was found in the I-V curve of one strip. It is hypothesized that this is due to increased conductivity at the gap voltage made noticeable by an extremely uniform film.
Interfaces - Weak Links, Yet Great Opportunities
NASA Technical Reports Server (NTRS)
Hendricks, Robert C.; Dimofte, Florin; Chupp, Raymond E.; Steinetz, Bruce M.
2011-01-01
Inadequate turbomachine interface design can rapidly degrade system performance, yet provide great opportunity for improvements. Engineered coatings of seals and bearing interfaces are major issues in the operational life of power systems. Coatings, films, and combined use of both metals and ceramics play a major role in maintaining component life. Interface coatings, like lubricants, are sacrificial for the benefit of the component. Bearing and sealing surfaces are routinely protected by tribologically paired coatings such as silicon diamond like coatings (SiDLC) in combination with an oil lubricated wave bearing that prolongs bearing operational life. Likewise, of several methods used or researched for detecting interface failures, dopants within coatings show failures in functionally graded ceramic coatings. The Bozzolo-Ferrante-Smith (BFS) materials models and quantum mechanical tools, employed in interface design, are discussed.
High-gain weakly nonlinear flux-modulated Josephson parametric amplifier using a SQUID array
NASA Astrophysics Data System (ADS)
Zhou, X.; Schmitt, V.; Bertet, P.; Vion, D.; Wustmann, W.; Shumeiko, V.; Esteve, D.
2014-06-01
We have developed and measured a high-gain quantum-limited microwave parametric amplifier based on a superconducting lumped LC resonator with the inductor L including an array of eight superconducting quantum interference devices (SQUIDs). This amplifier is parametrically pumped by modulating the flux threading the SQUIDs at twice the resonator frequency. Around 5 GHz, a maximum gain of 31 dB, a product amplitude gain × bandwidth above 60 MHz, and a 1 dB compression point of -123 dBm at 20 dB gain are obtained in the nondegenerate mode of operation. Phase-sensitive amplification-deamplification is also measured in the degenerate mode and yields a maximum gain of 37 dB. The compression point obtained is 18 dB above what would be obtained with a single SQUID of the same inductance, due to the smaller nonlinearity of the SQUID array.
6 π Josephson Effect in Majorana Box Devices
NASA Astrophysics Data System (ADS)
Zazunov, A.; Buccheri, F.; Sodano, P.; Egger, R.
2017-02-01
We study Majorana devices featuring a competition between superconductivity and multichannel Kondo physics. Our proposal extends previous work on single-channel Kondo systems to a topologically nontrivial setting of a non-Fermi liquid type, where topological superconductor wires (with gap Δ ) represent leads tunnel coupled to a Coulomb-blockaded Majorana box. On the box, a spin degree of freedom with Kondo temperature TK is nonlocally defined in terms of Majorana states. For Δ ≫TK, the destruction of Kondo screening by superconductivity implies a 4 π -periodic Josephson current-phase relation. Using a strong-coupling analysis in the opposite regime Δ ≪TK, we find a 6 π -periodic Josephson relation for three leads, with critical current Ic≈e Δ2/ℏTK, corresponding to the transfer of fractionalized charges e*=2 e /3 .
Coexistence of tunneling magnetoresistance and Josephson effects in SFIFS junctions
NASA Astrophysics Data System (ADS)
Vávra, O.; Soni, R.; Petraru, A.; Himmel, N.; Vávra, I.; Fabian, J.; Kohlstedt, H.; Strunk, Ch.
2017-02-01
We demonstrate an integration of tunneling magnetoresistance and the Josephson effects within one tunneling junction. Several sets of Nb-Fe-Al-Al2O3-Fe-Nb wafers with varying Al and Fe layers thickness were prepared to systematically explore the competition of TMR and Josephson effects. A coexistence of the critical current IC(dFe) and the tunneling magnetoresistance ratio T M R(dFe) is observed for iron layer dFe thickness range 1.9 and 2.9 nm. Further optimization such as thinner Al2O3 layer leads to an enhancement of the critical current and thus to an extension of the coexistence regime up to dFe≃3.9 nm Fe.
Fractional Josephson effect in number-conserving systems
NASA Astrophysics Data System (ADS)
Cheng, Meng; Lutchyn, Roman
2015-10-01
We study the fractional Josephson effect in a particle-number-conserving system consisting of a quasi-one-dimensional superconductor coupled to a nanowire or an edge carrying e /m fractional charge excitations with m being an odd integer. We show that, due to the topological ground-state degeneracy in the system, the periodicity of the supercurrent on magnetic flux through the superconducting loop is nontrivial, which provides a possibility to detect topological phases of matter by the dc supercurrent measurement. Using a microscopic model for the nanowire and quasi-one-dimensional superconductor, we derived an effective low-energy theory for the system which takes into account effects of quantum phase fluctuations. We discuss the stability of the fractional Josephson effect with respect to the quantum phase slips in a mesoscopic superconducting ring with a finite charging energy.
Dissipation in a simple model of a topological Josephson junction.
Matthews, Paul; Ribeiro, Pedro; García-García, Antonio M
2014-06-20
The topological features of low-dimensional superconductors have created a lot of excitement recently because of their broad range of applications in quantum information and their potential to reveal novel phases of quantum matter. A potential problem for practical applications is the presence of phase slips that break phase coherence. Dissipation in nontopological superconductors suppresses phase slips and can restore long-range order. Here, we investigate the role of dissipation in a topological Josephson junction. We show that the combined effects of topology and dissipation keep phase and antiphase slips strongly correlated so that the device is superconducting even under conditions where a nontopological device would be resistive. The resistive transition occurs at a critical value of the dissipation that is 4 times smaller than that expected for a conventional Josephson junction. We propose that this difference could be employed as a robust experimental signature of topological superconductivity.
Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures
NASA Astrophysics Data System (ADS)
Rudenko, E. M.
2012-04-01
Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V ≈ 2Δ/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2Δ/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect.
Mesoscopic Josephson junctions with switchable current-phase relation
NASA Astrophysics Data System (ADS)
Strambini, E.; Bergeret, F. S.; Giazotto, F.
2015-10-01
We propose and analyze a mesoscopic Josephson junction consisting of two ferromagnetic insulator-superconductors (FI-Ss) coupled through a normal metal (N) layer. The Josephson current of the junction is non-trivially affected by the spin-splitting field induced by the FIs in the two superconductors. In particular, it shows sizeable enhancement by increasing the amplitude of the exchange field (hex) and displays a switchable current-phase relation which depends on the relative orientation of h ex in the FIs. In a realistic EuS/Al-based setup this junction can be exploited as a high-resolution threshold sensor for the magnetic field as well as an on-demand tunable kinetic inductor.
Josephson photonics with a two-mode superconducting circuit
NASA Astrophysics Data System (ADS)
Armour, A. D.; Kubala, B.; Ankerhold, J.
2015-05-01
We analyze the quantum dynamics of two electromagnetic oscillators coupled in series to a voltage-biased Josephson junction. When the applied voltage leads to a Josephson frequency across the junction which matches the sum of the two mode frequencies, tunneling Cooper pairs excite photons in both modes simultaneously leading to far-from-equilibrium states. These states display highly nonclassical features including strong antibunching, violation of Cauchy-Schwartz inequalities, and number squeezing. We obtain approximate analytic results for both the regimes of low and high photon occupancies which are supported by a full numerical treatment. The impact of asymmetries between the two modes is explored, revealing a pronounced enhancement of number squeezing when the modes are damped at different rates.
Evidence for nonlocal electrodynamics in planar Josephson junctions.
Boris, A A; Rydh, A; Golod, T; Motzkau, H; Klushin, A M; Krasnov, V M
2013-09-13
We study the temperature dependence of the critical current modulation I(c)(H) for two types of planar Josephson junctions: a low-Tc Nb/CuNi/Nb and a high-Tc YBa2Cu3O(7-δ) bicrystal grain-boundary junction. At low T both junctions exhibit a conventional behavior, described by the local sine-Gordon equation. However, at elevated T the behavior becomes qualitatively different: the I(c)(H) modulation field ΔH becomes almost T independent and neither ΔH nor the critical field for the penetration of Josephson vortices vanish at Tc. Such an unusual behavior is in good agreement with theoretical predictions for junctions with nonlocal electrodynamics. We extract absolute values of the London penetration depth λ from our data and show that a crossover from local to nonlocal electrodynamics occurs with increasing T when λ(T) becomes larger than the electrode thickness.
Dissipation in microwave quantum circuits with hybrid nanowire Josephson elements
NASA Astrophysics Data System (ADS)
Mugnai, D.; Ranfagni, A.; Agresti, A.
2017-04-01
Recent experiments on hybrid Josephson junctions have made the argument a topical subject. However, a quantity which remains still unknown is the tunneling (or response) time, which is strictly connected to the role that dissipation plays in the dynamics of the complete system. A simple way for evaluating dissipation in microwave circuits, previously developed for describing the dynamics of conventional Josephson junctions, is now presented as suitable for application even to non-conventional junctions. The method is based on a stochastic model, as derived from the telegrapher's equation, and is particularly devoted to the case of junctions loaded by real transmission lines. When the load is constituted by lumped-constant circuits, a connection with the stochastic model is also maintained. The theoretical model demonstrated its ability to analyze both classically-allowed and forbidden processes, and has found a wide field of applicability, namely in all cases in which dissipative effects cannot be ignored.
Effets Josephson generalises entre antiferroaimants et entre supraconducteurs antiferromagnetiques
NASA Astrophysics Data System (ADS)
Chasse, Dominique
L'effet Josephson est generalement presente comme le resultat de l'effet tunnel coherent de paires de Cooper a travers une jonction tunnel entre deux supraconducteurs, mais il est possible de l'expliquer dans un contexte plus general. Par exemple, Esposito & al. ont recemment demontre que l'effet Josephson DC peut etre decrit a l'aide du boson pseudo-Goldstone de deux systemes couples brisant chacun la symetrie abelienne U(1). Puisque cette description se generalise de facon naturelle a des brisures de symetries continues non-abeliennes, l'equivalent de l'effet Josephson devrait donc exister pour des types d'ordre a longue portee differents de la supraconductivite. Le cas de deux ferroaimants itinerants (brisure de symetrie 0(3)) couples a travers une jonction tunnel a deja ete traite dans la litterature Afin de mettre en evidence la generalite du phenomene et dans le but de faire des predictions a partir d'un modele realiste, nous etudions le cas d'une jonction tunnel entre deux antiferroaimants itinerants. En adoptant une approche Similaire a celle d'Ambegaokar & Baratoff pour une jonction Josephson, nous trouvons un courant d'aimantation alternee a travers la jonction qui est proportionnel a sG x sD ou fG et sD sont les vecteurs de Neel de part et d'autre de la jonction. La fonction sinus caracteristique du courant Josephson standard est donc remplacee.ici par un produit vectoriel. Nous montrons que, d'un point de vue microscopique, ce phenomene resulte de l'effet tunnel coherent de paires particule-trou de spin 1 et de vecteur d'onde net egal au vecteur d'onde antiferromagnetique Q. Nous trouvons egalement la dependance en temperature de l'analogue du courant critique. En presence d'un champ magnetique externe, nous obtenons l'analogue de l'effet Josephson AC et la description complete que nous en donnons s'applique aussi au cas d'une jonction tunnel entre ferroaimants (dans ce dernier cas, les traitements anterieurs de cet effet AC s'averent incomplets). Nous
Josephson Junction Arrays with Positional Disorder: Experiments and Simulations
1988-02-01
Caislinuo an loe*@*. old* it no.ee.q Aid taoncitI y IOcA flMwb~wJ Josephson junctions Positional disorder Monta Carlo simulations 20. AUSTRACT (Conoidiie an...both experiments and Monte Carlo siimulations. We have fabricated 50 x 50 arrays of Pb/Cu proximity-effect junctions, with controlled positional...However, our experiments show no evidence for the predicted reentrant phase transition. Our Monte Carlo simulations of XY spin systems with positional
Evidence for a minigap in YBCO grain boundary Josephson junctions.
Lucignano, P; Stornaiuolo, D; Tafuri, F; Altshuler, B L; Tagliacozzo, A
2010-10-01
Self-assembled YBaCuO diffusive grain boundary submicron Josephson junctions offer a realization of a special regime of the proximity effect, where normal state coherence prevails on the superconducting coherence in the barrier region. Resistance oscillations from the current-voltage characteristic encode mesoscopic information on the junction and more specifically on the minigap induced in the barrier. Their persistence at large voltages is evidence of the long lifetime of the antinodal (high energy) quasiparticles.
Identification of the periodic processes in Josephson junctions p
Zagrodzinski, J.
1984-02-01
It is shown that different forms of the same quasiperiodic solution of the sine-Gordon equation can be obtained by applying to the Riemann-theta function a transformation determined by a matrix belonging to a certain subgroup of the symplectic group Sp(g,Z). A few examples important for classification of the processes occurring in the Josephson junction illustrate the essential statement.
Quantum Dynamics of a d-wave Josephson Junction
NASA Astrophysics Data System (ADS)
Bauch, Thilo
2007-03-01
Thilo Bauch ^1, Floriana Lombardi ^1, Tobias Lindstr"om ^2, Francesco Tafuri ^3, Giacomo Rotoli ^4, Per Delsing ^1, Tord Claeson ^1 1 Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, S-412 96 G"oteborg, Sweden. 2 National Physical Laboratory, Queens Road, Teddington, Middlesex TW11 0LW, UK. 3 Istituto Nazionale per la Fisica della Materia-Dipartimento Ingegneria dell'Informazione, Seconda Universita di Napoli, Aversa (CE), Italy. 4 Dipartimento di Ingegneria Meccanica, Energetica e Gestionale, Universita of L'Aquila, Localita Monteluco, L'Aquila, Italy. We present direct observation of macroscopic quantum properties in an all high critical temperature superconductor d-wave Josephson junction. Although dissipation caused by low energy excitations is expected to strongly suppress quantum effects we demonstrate macroscopic quantum tunneling [1] and energy level quantization [2] in our d-wave Josephson junction. The results clearly indicate that the role of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for a new class of solid state ``quiet'' quantum bit with superior coherence time. We show that the dynamics of the YBCO grain boundary Josephson junctions fabricated on a STO substrate are strongly affected by their environment. As a first approximation we model the environment by the stray capacitance and stray inductance of the junction electrodes. The total system consisting of the junction and stray elements has two degrees of freedom resulting in two characteristic resonance frequencies. Both frequencies have to be considered to describe the quantum mechanical behavior of the Josephson circuit. [1] T. Bauch et al, Phys. Rev. Lett. 94, 087003 (2005). [2] T. Bauch et al, Science 311, 57 (2006).
Josephson inplane and tunneling currents in bilayer quantum Hall system
Ezawa, Z. F.; Tsitsishvili, G.; Sawada, A.
2013-12-04
A Bose-Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (–e). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ν = 1. We show the existence of the critical current for the tunneling current to be coherent and dissipationless in tunneling experiments with various geometries.
Josephson effect without superconductivity: realization in quantum Hall bilayers.
Fogler, M M; Wilczek, F
2001-02-26
We show that a quantum Hall bilayer with the total filling nu = 1 should exhibit a dynamical regime similar to the flux flow in large Josephson junctions. This analogy may explain a conspicuous peak in the interlayer tunneling conductance [Phys. Rev. Lett. 84, 5808 (2000)]. The flux flow is likely to be spatiotemporally chaotic at low-bias voltage, which will manifest itself through broadband noise. The peak position can be controlled by an in-plane magnetic field.
Low-Loss Materials for Josephson Qubits
2014-10-09
quantum circuit. It also intuitively explains how for a linear circuit the standard results for electrical circuits are obtained, justifying the use of... linear concepts for a weakly non- linear device such as the transmon. It has also become common to use a double sided noise spectrum to represent...loss tangent of large area pad junction. (c) Effective linearized circuit for the double junction, which makes up the admittance $Y$. $L_j$ is the
Josephson Coupling in Nb/SmB6/Nb Junctions
NASA Astrophysics Data System (ADS)
Zhang, Xiaohang; Lee, Seunghun; Drisko, Jasper; Cumings, John; Greene, Richard; Takeuchi, Ichiro
Josephson coupling of superconductors through a topological surface has attracted considerable attention because it may provide device applications of topological insulators with implications for Majorana fermions. However, the results of previous Josephson junction studies on topological insulators have not been fully understood due to complications arising from the conducting bulk and the non-pristine nature of the surfaces/interfaces of the topological insulator materials used. In this work, SmB6 thin films with a highly insulating bulk were adopted to minimize the influence of the bulk carriers while in-situ deposition of Nb film on SmB6 surface was used to ensure the interface quality. The bilayer structure was then patterned into Nb/SmB6/Nb lateral junctions by e-beam lithography and ion milling. The Nb electrodes in our junctions had a typical width of ~1 μm and the gap between the two Nb electrodes was varied from 50 nm to 200 nm. A critical current up to 40 μA has been observed in junctions with a gap around 50 nm at 2.0 K. In this talk, I will discuss the implication of our results to the desired Josephson coupling through topological surface states. This work was supported by NSF under Grant No. DMR-1410665 and conducted at CNAM and at the Maryland NanoCenter.
Measurement of Quantum Phase-Slips in Josephson Junction Chains
NASA Astrophysics Data System (ADS)
Guichard, Wiebke
2011-03-01
Quantum phase-slip dynamics in Josephson junction chains could provide the basis for the realization of a new type of topologically protected qubit or for the implementation of a new current standard. I will present measurements of the effect of quantum phase-slips on the ground state of a Josephson junction chain. We can tune in situ the strength of the phase-slips. These phase-slips are the result of fluctuations induced by the finite charging energy of each junction in the chain. Our measurements demonstrate that a Josephson junction chain under phase bias constraint behaves in a collective way. I will also show evidence of coherent phase-slip interference, the so called Aharonov-Casher effect. This phenomenon is the dual of the well known Aharonov-Bohm interference. In collaboration with I.M. Pop, Institut Neel, C.N.R.S. and Universite Joseph Fourier, BP 166, 38042 Grenoble, France; I. Protopopov, L. D. Landau Institute for Theoretical Physics, Kosygin str. 2, Moscow 119334, Russia and Institut fuer Nanotechnologie, Karlsruher Institut fuer Technologie, 76021 Karlsruhe, Germany; and F. Lecocq, Z. Peng, B. Pannetier, O. Buisson, Institut Neel, C.N.R.S. and Universite Joseph Fourier. European STREP MIDAS, ANR QUANTJO.
Fractional Josephson current through a Luttinger liquid with topological excitations
Wang, Rui; Wang, Baigeng Xing, D.Y.
2015-07-15
Recently, the Majorana fermion has received great attentions due to its promising application in the fault-tolerant quantum computation. This application requires more accessible methods to detect the motion and braiding of the Majorana fermions. We use a Luttinger liquid ring to achieve this goal, where the ring geometry is nontrivial in the sense that it leads to fermion-parity-dependent topological excitations. First, we briefly review the essential physics of the Luttinger liquid and the Majorana fermion, in order to give an introduction of the general framework used in the following main work. Then, we theoretically investigated the DC Josephson effect between two topological superconductors via a Luttinger liquid ring. A low-energy effective Hamiltonian is derived to show the existence of the fractional Josephson current. Also, we find that the amplitude of the Josephson current, which is determined by the correlation function of Luttinger liquid, exhibits different behaviors in terms of the parity of Luttinger liquid due to the topological excitations. Our results suggest a possible method to detect the Majorana fermions and their tunneling process.
Generalized parafermions and nonlocal Josephson effect in multilayer systems
NASA Astrophysics Data System (ADS)
Ebisu, Hiromi; Sagi, Eran; Tanaka, Yukio; Oreg, Yuval
2017-02-01
We theoretically investigate the effects of backscattering and superconducting proximity terms between the edges of two multilayer fractional quantum Hall (FQH) systems. While the different layers are strongly interacting, we assume that tunneling between them is absent. Studying the boundaries between regions gapped by the two mechanisms in an N -layer system, we find N localized zero-mode operators, realizing a generalized parafermionic algebra. We further propose an experiment capable of probing imprints of the generalized parafermionic bound states. This is done by coupling different superconducting contacts to different layers and examining the periodicity of the Josephson effect as a function of the various relative superconducting phases. Remarkably, even if we apply a phase difference between the superconductors in one layer, we induce a Josephson current at the other layers due to interlayer interactions. Furthermore, while the Josephson effect is commonly used to probe only charged degrees of freedom, the possibility of independently controlling the superconducting phase differences between the layers allows us to find imprints of the neutral modes of the underlying multilayer system. In particular, we propose two configurations, one of which is capable of isolating the signal associated with the charge modes while the other probes the neutral modes.
Thin-film Josephson junctions with alternating critical current density
NASA Astrophysics Data System (ADS)
Moshe, Maayan; Kogan, V. G.; Mints, R. G.
2009-01-01
We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions with alternating critical current density. Im(H) is evaluated within nonlocal Josephson electrodynamics taking into account the stray fields that affect the difference of the order-parameter phases across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density gc , i.e., it is universal. An explicit form for this universal function is derived for small currents through junctions of the width W≪Λ , the Pearl length. The result is used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant but only in high fields. We find that the spacing between zeros is proportional to 1/W2 . The general approach is applied to calculate Im(H) for a superconducting quantum interference device with two narrow edge-type junctions. If gc changes sign periodically or randomly, as it does in grain boundaries of high- Tc materials and superconductor-ferromagnet-superconductor heterostructures, Im(H) not only acquires the major side peaks, but due to nonlocality the following peaks decay much slower than in bulk junctions.
Josephson radiation from InSb-nanowire junction
NASA Astrophysics Data System (ADS)
van Woerkom, David; Proutski, Alexander; Krivachy, Tamas; Bouman, Daniel; van Gulik, Ruben; Gul, Onder; Cassidy, Maja; Car, Diana; Bakkers, Erik; Kouwenhoven, Leo; Geresdi, Attila
Semiconducting nanowire Josephson junctions has recently gained interest as building blocks for Majorana circuits and gate-tuneable superconducting qubits . Here we investigate the rich physics of the Andreev bound state spectrum of InSb nanowire junctions utilizing the AC Josephson relation 2eV_bias =hf . We designed and characterized an on-chip microwave circuit coupling the nanowire junction to an Al/AlOx/Al tunnel junction. The DC response of the tunnel junction is affected by photon-assisted quasiparticle current, which gives us the possibility to measure the radiation spectrum of the nanowire junction up to several tens of GHz in frequency. Our circuit design allows for voltage or phase biasing of the Josephson junction enabling direct mapping of Andreev bound states. We discuss our fabrication methods and choice of materials to achieve radiation detection up to a magnetic field of few hundred milliTesla, compatible with Majorana states in spin-orbit coupled nanowires. This work has been supported by the Netherlands Foundations FOM, Abstract NWO and Microsoft Corporation Station Q.
Model for large arrays of Josephson junctions with unconventional superconductors
NASA Astrophysics Data System (ADS)
Khveshchenko, D. V.; Crooks, R.
2011-10-01
We study large arrays of mesoscopic junctions made out of gapless unconventional superconductors where the tunneling processes of both particle-hole and Cooper pairs give rise to a strongly retarded effective action which, contrary to the standard case, cannot be readily characterized in terms of a local Josephson energy. This action can be relevant, for example, to grain boundary and c-axis junctions in layered high-Tc superconductors. By using a particular functional representation, we describe emergent collective phenomena in this system, ascertain its phase diagram, and compute electrical conductivity.
Strong environmental coupling in a Josephson parametric amplifier
Mutus, J. Y.; White, T. C.; Barends, R.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Cleland, A. N.; Martinis, John M.; Megrant, A.; Sundqvist, K. M.
2014-06-30
We present a lumped-element Josephson parametric amplifier designed to operate with strong coupling to the environment. In this regime, we observe broadband frequency dependent amplification with multi-peaked gain profiles. We account for this behavior using the “pumpistor” model which allows for frequency dependent variation of the external impedance. Using this understanding, we demonstrate control over the complexity of gain profiles through added variation in the environment impedance at a given frequency. With strong coupling to a suitable external impedance, we observe a significant increase in dynamic range, and large amplification bandwidth up to 700 MHz giving near quantum-limited performance.
Soft nanostructuring of YBCO Josephson junctions by phase separation.
Gustafsson, D; Pettersson, H; Iandolo, B; Olsson, E; Bauch, T; Lombardi, F
2010-12-08
We have developed a new method to fabricate biepitaxial YBa2 Cu3 O7-δ (YBCO) Josephson junctions at the nanoscale, allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures. By using the competition between the superconducting YBCO and the insulating Y2 BaCuO5 phases during film growth, we formed nanometer sized grain boundary junctions in the insulating Y2 BaCuO5 matrix as confirmed by high-resolution transmission electron microscopy. Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries.
Microwave quantum refrigeration based on the Josephson effect
NASA Astrophysics Data System (ADS)
Solinas, Paolo; Bosisio, Riccardo; Giazotto, Francesco
2016-06-01
We present a microwave quantum refrigeration principle based on the Josephson effect. When a superconducting quantum interference device (SQUID) is pierced by a time-dependent magnetic flux, it induces changes in the macroscopic quantum phase and an effective finite bias voltage appears across the SQUID. This voltage can be used to actively cool, well below the lattice temperature, one of the superconducting electrodes forming the interferometer. The achievable cooling performance combined with the simplicity and scalability intrinsic to the structure pave the way to a number of applications in quantum technology.
Classical Bifurcation at the Transition from Rabi to Josephson Dynamics
Zibold, Tilman; Nicklas, Eike; Gross, Christian; Oberthaler, Markus K.
2010-11-12
We report on the experimental demonstration of the internal bosonic Josephson effect in a rubidium spinor Bose-Einstein condensate. The measurement of the full time dynamics in phase space allows the characterization of the theoretically predicted {pi}-phase modes and quantitatively confirms analytical predictions, revealing a classical bifurcation. Our results suggest that this system is a model system which can be tuned from classical to the quantum regime and thus is an important step towards the experimental investigation of entanglement generation close to critical points.
Observation of Soliton Fusion in a Josephson Array
Pfeiffer, J.; Schuster, M.; Abdumalikov, A.A. Jr.; Ustinov, A.V.
2006-01-27
The behavior of topological solitons in a parallel array of a Josephson junction is studied experimentally. We observe the fusion of two relativistic 2{pi} solitons of the same polarity into a single 4{pi} soliton. The 4{pi} soliton carries two quanta of magnetic flux and, most strikingly, travels 18% faster than an ordinary 2{pi} soliton under the same driving force. We also find a variety of bunched states composed of 2{pi} solitons of the same polarity, moving with fixed separation.
New fluxon resonant mechanism in annular Josephson tunnel structures.
Nappi, C; Lisitskiy, M P; Rotoli, G; Cristiano, R; Barone, A
2004-10-29
A novel dynamical state has been observed in the dynamics of a perturbed sine-Gordon system. This resonant state has been experimentally observed as a singularity in the dc current-voltage characteristic of an annular Josephson tunnel junction, excited in the presence of a magnetic field. In this respect it can be assimilated to self-resonances known as Fiske steps. Differently from these, however, we demonstrate, on the basis of numerical simulations, that its detailed dynamics involves rotating fluxon pairs, a mechanism associated, so far, to self-resonances known as zero-field steps. This occurs because the size of nonlinear excitations is comparable with that of the system.
Fabrication and measurement of multi-terminal mesoscopic Josephson junctions
NASA Astrophysics Data System (ADS)
Solovyeva, Natalya; Tetsuya, Mishima; Santos, Michael; Shabani, Javad; Manucharyan, Vladimir
We present fabrication and characterization of 3- and 4-terminal mesoscopic Josephson junctions involving InAs quantum well heterostructures and superconducting Al contacts. A cross-shaped nanowire junction region with dimensions of order a few 100 nm is dry-etched in the 2DEG, followed by deposition of superconducting contacts and gating electrodes. These novel 0D devices have been recently predicted to have topological features in their Andreev spectra and finite-bias transport; they may also be useful in efforts towards observation and braiding of Majorana fermions in the solid state. // This material is based upon work supported by the NSF under Grant No. DMR-1207537.
Strong environmental coupling in a Josephson parametric amplifier
NASA Astrophysics Data System (ADS)
Mutus, J. Y.; White, T. C.; Barends, R.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Sundqvist, K. M.; Cleland, A. N.; Martinis, John M.
2014-06-01
We present a lumped-element Josephson parametric amplifier designed to operate with strong coupling to the environment. In this regime, we observe broadband frequency dependent amplification with multi-peaked gain profiles. We account for this behavior using the "pumpistor" model which allows for frequency dependent variation of the external impedance. Using this understanding, we demonstrate control over the complexity of gain profiles through added variation in the environment impedance at a given frequency. With strong coupling to a suitable external impedance, we observe a significant increase in dynamic range, and large amplification bandwidth up to 700 MHz giving near quantum-limited performance.
Adjustable Josephson Coupler for Transmon Qubit Measurement
NASA Astrophysics Data System (ADS)
Jeffrey, Evan
2015-03-01
Transmon qubits are measured via a dispersive interaction with a linear resonator. In order to be scalable this measurement must be fast, accurate, and not disrupt the state of the qubit. Speed is of particular importance in a scalable architecture with error correction as the measurement accounts for substantial portion of the cycle time and waiting time associated with measurement is a major source of decoherence. We have found that measurement speed and accuracy can be improved by driving the qubit beyond the critical photon number ncrit = Δ/4g by a factor of 2-3 without compromising the QND nature of the measurement. While it is expected that such strong drive will cause qubit state transitions, we find that as long as the readout is sufficiently fast, those transitions are negligible, however they grow rapidly with time, and are not described by a simple rate. Measuring in this regime requires parametric amplifiers with very high saturation power, on the order of -105 dBm in order to avoid losing SNR when increasing the power. It also requires a Purcell filter to allow fast ring-up and ring-down. Adjustable couplers can be used to further increase the measurement performance, by switching the dispersive interaction on and off much faster than the cavity ring-down time. This technique can also be used to investigate the dynamics of the qubit cavity interaction beyond the weak dispersive limit ncavity >=ncrit not easily accessible to standard dispersive measurement due to the cavity time constant.
Lin, Z R; Inomata, K; Koshino, K; Oliver, W D; Nakamura, Y; Tsai, J S; Yamamoto, T
2014-07-25
The parametric phase-locked oscillator (PPLO) is a class of frequency-conversion device, originally based on a nonlinear element such as a ferrite ring, that served as a fundamental logic element for digital computers more than 50 years ago. Although it has long since been overtaken by the transistor, there have been numerous efforts more recently to realize PPLOs in different physical systems such as optical photons, trapped atoms, and electromechanical resonators. This renewed interest is based not only on the fundamental physics of nonlinear systems, but also on the realization of new, high-performance computing devices with unprecedented capabilities. Here we realize a PPLO with Josephson-junction circuitry and operate it as a sensitive phase detector. Using a PPLO, we demonstrate the demodulation of a weak binary phase-shift keying microwave signal of the order of a femtowatt. We apply PPLO to dispersive readout of a superconducting qubit, and achieved high-fidelity, single-shot and non-destructive readout with Rabi-oscillation contrast exceeding 90%.
Signatures of time-reversal-invariant topological superconductivity in the Josephson effect
NASA Astrophysics Data System (ADS)
Mellars, Ehren; Béri, Benjamin
2016-11-01
For Josephson junctions based on s -wave superconductors, time-reversal symmetry is known to allow for powerful relations between the normal-state junction properties, the excitation spectrum, and the Josephson current. Here we provide analogous relations for Josephson junctions involving one-dimensional time-reversal-invariant topological superconductors supporting Majorana-Kramers pairs, considering both topological-topological and s -wave-topological junctions. Working in the regime where the junction is much shorter than the superconducting coherence length, we obtain a number of analytical and numerical results that hold for arbitrary normal-state conductance and the most general forms of spin-orbit coupling. The signatures of topological superconductivity we find include the fractional ac Josephson effect, which arises in topological-topological junctions provided that the energy relaxation is sufficiently slow. We also show, for both junction types, that robust signatures of topological superconductivity arise in the dc Josephson effect in the form of switches in the Josephson current due to zero-energy crossings of Andreev levels. The junction spin-orbit coupling enters the Josephson current only in the topological-topological case and in a manner determined by the switch locations, thereby allowing quantitative predictions for experiments with the normal-state conductance, the induced gaps, and the switch locations as inputs.
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio; Matsumoto, Hideki
2009-06-12
Using the functional integral method, we construct a theory of heterotic superconductor-insulator-superconductor Josephson junctions between one- and two-gap superconductors. The theory predicts the presence of in-phase and out-of-phase collective oscillation modes of superconducting phases. The former corresponds to the Josephson plasma mode whose frequency is drastically reduced for +/- s-wave symmetry, and the latter is a counterpart of Leggett's mode in Josephson junctions. We also reveal that the critical current and the Fraunhofer pattern strongly depend on the symmetry type of the two-gap superconductor.
Two-channel Kondo physics in a Majorana island coupled to a Josephson junction
NASA Astrophysics Data System (ADS)
Landau, L. A.; Sela, E.
2017-01-01
We study a Majorana island coupled to a bulk superconductor via a Josephson junction and to multiple external normal leads. In the absence of the Josephson coupling, the system displays a topological Kondo state, which had been largely studied recently. However, we find that this state is unstable even to small Josephson coupling, which instead leads at low temperature T to a new fixed point. Most interesting is the case of three external leads, forming a minimal electronic realization of the long sought two-channel Kondo effect. While the T =0 conductance corresponds to simple resonant Andreev reflection, the leading T dependence forms an experimental fingerprint for non-Fermi-liquid properties.
Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers.
Flowers-Jacobs, Nathan E; Fox, Anna E; Dresselhaus, Paul D; Schwall, Robert E; Benz, Samuel P
2016-09-01
The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors.
Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers
Flowers-Jacobs, Nathan E.; Fox, Anna E.; Dresselhaus, Paul D.; Schwall, Robert E.; Benz, Samuel P.
2016-01-01
The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors. PMID:27453676
Two Superconducting Charge Qubits Coupled by a Josephson Inductance
NASA Astrophysics Data System (ADS)
Watanabe, Michio; Yamamoto, Tsuyoshi; Pashkin, Yuri A.; Astafiev, Oleg; Nakamura, Yasunobu; Tsai, Jaw-Shen
2007-03-01
When the quantum oscillations [Pashkin et al., Nature 421, 823 (2003)] and the conditional gate operation [Yamamoto et al., Nature 425, 941 (2003)] were demonstrated using superconducting charge qubits, the charge qubits were coupled capacitively, where the coupling was always on and the coupling strength was not tunable. This fixed coupling, however, is not ideal because for example, it makes unconditional gate operations difficult. In this work, we aimed to tunably couple two charge qubits. We fabricated circuits based on the theoretical proposal by You, Tsai, and Nori [PRB 68, 024510 (2003)], where the inductance of a Josephson junction, which has a much larger junction area than the qubit junctions, couples the qubits and the coupling strength is controlled by the external magnetic flux. We confirmed by spectroscopy that the large Josephson junction was indeed coupled to the qubits and that the coupling was turned on and off by the external magnetic flux. In the talk, we will also discuss the quantum oscillations in the circuits.
NASA Astrophysics Data System (ADS)
Hikino, S.; Yunoki, S.
2015-07-01
We theoretically study the magnetization inside a normal metal induced in an s -wave superconductor/ferromagnetic metal/normal metal/ferromagnetic metal/s -wave superconductor (S /F 1 /N /F 2 /S ) Josephson junction. Using the quasiclassical Green's function method, we show that the magnetization becomes finite inside the N . The origin of this magnetization is due to odd-frequency spin-triplet Cooper pairs formed by electrons of equal and opposite spins, which are induced by the proximity effect in the S /F 1 /N /F 2 /S junction. We find that the magnetization M (d ,θ ) in the N can be decomposed into two parts, M (d ,θ ) =MI(d ) +MII(d ,θ ) , where θ is the superconducting phase difference between the two S s and d is the thickness of N . The θ -independent magnetization MI(d ) exists generally in S /F junctions, while MII(d ,θ ) carries all θ dependence and represents the fingerprint of the phase coherence between the two S s in Josephson junctions. The θ dependence thus allows us to control the magnetization in the N by tuning θ for a fixed d . We show that the θ -independent magnetization MI(d ) weakly decreases with increasing d , while the θ -dependent magnetization MII(d ,θ ) rapidly decays with d . Moreover, we find that the time-averaged magnetization
Shape Waves in 2D Josephson Junctions: Exact Solutions and Time Dilation
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Kusmartsev, F. V.; Savel'Ev, Sergey; Yampol'Skii, V. A.; Nori, Franco
2008-09-01
We predict a new class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line and have an analogy with shear waves in solid mechanics. Their shapes can have an arbitrary profile, which is retained when propagating. We derive a universal analytical expression for the energy of arbitrary shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically moving Josephson vortex and suggest an experiment to measure a time dilation effect analogous to that in special relativity.
Shape waves in 2D Josephson junctions: exact solutions and time dilation.
Gulevich, D R; Kusmartsev, F V; Savel'ev, Sergey; Yampol'skii, V A; Nori, Franco
2008-09-19
We predict a new class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line and have an analogy with shear waves in solid mechanics. Their shapes can have an arbitrary profile, which is retained when propagating. We derive a universal analytical expression for the energy of arbitrary shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically moving Josephson vortex and suggest an experiment to measure a time dilation effect analogous to that in special relativity.
NASA Astrophysics Data System (ADS)
Malishevskiĭ, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskiĭ, S. G.
2007-06-01
It is demonstrated that when the velocity of vortices in a Josephson junction magnetically coupled to a waveguide approaches the limits of the allowed ranges, the relative contribution of the Cherenkov losses to the transport current density increases drastically.
Dicke-Josephson effect in a cross-typed triple-quantum-dot junction
NASA Astrophysics Data System (ADS)
Wang, Xiao-Qi; Yi, Guang-Yu; Gong, Wei-Jiang
2016-12-01
We investigate the Dicke-Josephson effect in a superconductor/triple-quantum-dot/superconductor junction in which the central dot is coupled to the superconductors. It is found that the Dicke effect can modulate the Josephson effect in a nontrivial way. In the noninteracting case, the Dicke effect induces a subpeak in the supercurrent spectrum around the energy zero point. When intradot interactions are taken into account, the role of the Dicke effect changes completely. Namely, it tends to suppress the π-phase current near the position of electron-hole symmetry. With the increase of the Coulomb strength, it has an opportunity to reverse the current direction. We thus conclude that the Dicke-Josephson effect is also an important part in describing the Josephson effect in coupled-dot junctions.
Controlled dynamics of sine-Gordon breather in long Josephson junctions
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Gaifullin, M. B.; Kusmartsev, F. V.
2012-01-01
We describe a method of controlled creation and detection of breathers in long Josephson Junctions. We show how a breather can be detected and investigated by measuring switching of the current biased Josephson junction to a resistive state. The complete theoretical description of the switching events associated with the decay of a breather into a fluxon-antifluxon pair is developed. Eventually, we propose several designs of the systems where breathers can be observed.
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Gaifullin, M.; Kusmartseva, O. E.; Kusmartsev, F. V.; Hirata, K.
2008-09-01
We propose a device able to generate trains of Josephson fluxons without application of external magnetic field - fluxon pump. The pulses of individual fluxons are generated by cloning single fluxons trapped inside a reservoir. When an electric current is applied, a flow of fluxons is generated in the long attachment connected to the reservoir of fluxons. The role of a reservoir is played by Josephson junctions in the form of a loop where one or several fluxons are permanently trapped.
Role of phonons in Josephson oscillations of excitonic and polaritonic condensates
Magnusson, E. B.; Flayac, H.; Malpuech, G.; Shelykh, I. A.
2010-11-15
We analyze theoretically the role of the exciton-phonon interactions in phenomena related to the Josephson effect between two spatially separated exciton and exciton-polariton condensates. We consider the role of the dephasing introduced by phonons in such phenomena as Josephson tunneling, self-trapping and spontaneous polarization separation. In the regime of cw pumping we find a remarkable bistability effect arising from exciton-exciton interactions as well as regimes of self-sustained regular and chaotic oscillations.
Light-modulated 0-π transition in a silicene-based Josephson junction
NASA Astrophysics Data System (ADS)
Zhou, Xingfei; Jin, Guojun
2016-10-01
We investigate the Andreev bound states (ABSs) and Josephson current in a silicene-based superconductor-normal-superconductor junction modulated by a perpendicular electric field and an off-resonant circularly polarized light. Based on the Dirac-Bogoliubov-de Gennes equation, we analytically derive the ABS levels and show they have different phase-difference dependences, which will remarkably influence the velocity of Cooper pairs and then the Josephson current. In the pristine or gated silicene, the ABS levels always show negative slope, which means that the Josephson current is irreversible because of the time-reversal symmetry. When an off-resonant circularly polarized light is applied, whether or not there is a perpendicular electric field, the ABS levels will have positive slope, leading to the emergence of reversed Josephson current due to the nonzero center-of-mass wave vector of Cooper pairs. In this light-modulated silicene-based Josephson junction, valley polarization provides an alternative mechanism for 0-π transition, very different from that for the conventional ferromagnetic Josephson junctions where the spin polarization is essential.
Microwave response and photon emission of a voltage baised Josephson junction
NASA Astrophysics Data System (ADS)
Jebari, Salha; Grimm, Alexander; Hazra, Dibyendu; Hofheinz, Max
The readout of superconducting qubits requires amplifiers combining noise close to the quantum limit, high gain, large bandwidth, and sufficient dynamic range. Josephson parametric amplifiers using Josephson junctions in the 0-voltage state, driven by a large microwave signals, begin to perform sufficiently well in all 4 of these aspects to be of practical use, but remain difficult to optimize and use. Recent experiments with superconducting circuits consisting of a DC voltage-biased Josephson junction in series with a resonator, showed that a tunneling Cooper pair can emit one or several photons with a total energy of 2e times the applied voltage. We present microwave reflection measurements on this device indicating that amplification is possible with a simple DC voltage-biased Josephson junction. We compare these measurements with the noise power emitted by the junction and show that, for low Josephson energy, transmission and noise emission can be explained within the framework of P(E) theory of inelastic Cooper pair tunneling. Combined with a theoretical model, our results indicate that voltage-biased Josephson junctions might be useful for amplification near the quantum limit, offering simpler design and a different trade-off between gain, bandwidth and dynamic range.
Topological transconductance quantization in a four-terminal Josephson junction
NASA Astrophysics Data System (ADS)
Eriksson, Erik; Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2017-02-01
Recently we predicted that the Andreev bound-state spectrum of four-terminal Josephson junctions may possess topologically protected zero-energy Weyl singularities, which manifest themselves in a quantized transconductance in units of 4 e2/h when two of the terminals are voltage biased [R.-P. Riwar, M. Houzet, J. S. Meyer, and Y. V. Nazarov, Nature Commun. 7, 11167 (2016), 10.1038/ncomms11167]. Here, using the Landauer-Büttiker scattering theory, we compute numerically the currents flowing through such a structure in order to assess the conditions for observing this effect. We show that the voltage below which the transconductance becomes quantized is determined by the interplay of nonadiabatic transitions between Andreev bound states and inelastic relaxation processes. We demonstrate that the topological quantization of the transconductance can be observed at voltages of the order of 10-2Δ /e ,Δ being the the superconducting gap in the leads.
Observing Majorana bound states of Josephson vortices in topological superconductors
Grosfeld, Eytan; Stern, Ady
2011-01-01
In recent years there has been an intensive search for Majorana fermion states in condensed matter systems. Predicted to be localized on cores of vortices in certain nonconventional superconductors, their presence is known to render the exchange statistics of bulk vortices non-Abelian. Here we study the equations governing the dynamics of phase solitons (fluxons) in a Josephson junction in a topological superconductor. We show that the fluxon will bind a localized zero energy Majorana mode and will consequently behave as a non-Abelian anyon. The low mass of the fluxon, as well as its experimentally observed quantum mechanical wave-like nature, will make it a suitable candidate for vortex interferometry experiments demonstrating non-Abelian statistics. We suggest two experiments that may reveal the presence of the zero mode carried by the fluxon. Specific experimental realizations will be discussed as well. PMID:21730165
The current-phase relation in HTS Josephson junctions
NASA Astrophysics Data System (ADS)
Il'ichev, E.; Zakosarenko, V.; Ijsselsteijn, R. P. J.; Schultze, V.; Meyer, H.-G.; Hoenig, H. E.
The current-phase relation of YBa2Cu3O7-x step-edge as well as 24° and 45° grain boundary Josephson junctions has been investigated experimentally. The junctions were incorporated into a washer-shaped superconducting ring with inductance L≈80-300 pH. The ring was inductively coupled to a tank circuit with a resonance frequency 9…40 MHz. The current-phase relation was obtained from the measurement of the impedance of the phase-biased junction. It is shown, that experimentally observed deviations from harmonic behavior of the apparent current-phase relation for step-edge and 24° grain boundary junctions can be explained by the influence of thermal noise. The current-phase relation of 45° grain boundary junctions was found to be extremely non-harmonic. The reasons of this unusual behavior are discussed.
Quasi-optical Josephson-junction oscillator arrays
NASA Technical Reports Server (NTRS)
Stern, J. A.; Leduc, H. G.; Zmuidzinas, J.
1993-01-01
Josephson junctions are natural voltage-controlled oscillators capable of generating submillimeter-wavelength radiation, but a single junction usually can produce only 100 nW of power and often has a broad spectral linewidth. The authors are investigating 2D quasi-optical power combining arrays of 103 and 104 NbN/MgO/NbN and Nb/Al-AlO(x)/Nb junctions to overcome these limitations. The junctions are dc-biased in parallel and are distributed along interdigitated lines. The arrays couple to a resonant mode of a Fabry-Perot cavity to achieve mutual phase-locking. The array configuration has a relatively low impedance, which should allow the capacitance of the junctions to be tuned out at the oscillation frequency.
Manipulating Josephson junctions in thin-films by nearby vortices
Kogan, V G; Mints, R G
2014-07-01
It is shown that a vortex trapped in one of the banks of a planar edge-type Josephson junction in a narrow thin-film superconducting strip can change drastically the dependence of the junction critical current on the applied field, I-c(H). When the vortex is placed at certain discrete positions in the strip middle, the pattern I-c(H) has zero at H = 0 instead of the traditional maximum of '0-type' junctions. The number of these positions is equal to the number of vortices trapped at the same location. When the junction-vortex separation exceeds similar to W, the strip width, I-c(H) is no longer sensitive to the vortex presence. The same is true for any separation if the vortex approaches the strip edges. (C) 2014 Elsevier B.V. All rights reserved.
Dispersive Thermometry with a Josephson Junction Coupled to a Resonator
NASA Astrophysics Data System (ADS)
Saira, O.-P.; Zgirski, M.; Viisanen, K. L.; Golubev, D. S.; Pekola, J. P.
2016-08-01
We embed a small Josephson junction in a microwave resonator that allows simultaneous dc biasing and dispersive readout. Thermal fluctuations drive the junction into phase diffusion and induce a temperature-dependent shift in the resonance frequency. By sensing the thermal noise of a remote resistor in this manner, we demonstrate primary thermometry in the range of 300 mK to below 100 mK, and high-bandwidth (7.5 MHz) operation with a noise-equivalent temperature of better than 10 μ K /√{Hz } . At a finite bias voltage close to a Fiske resonance, amplification of the microwave probe signal is observed. We develop an accurate theoretical model of our device based on the theory of dynamical Coulomb blockade.
Multi-terminal Josephson junctions as topological matter
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2016-01-01
Topological materials and their unusual transport properties are now at the focus of modern experimental and theoretical research. Their topological properties arise from the bandstructure determined by the atomic composition of a material and as such are difficult to tune and naturally restricted to ≤3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n−1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n≥4, the Andreev subgap spectrum of the junction can accommodate Weyl singularities in the space of the n−1 independent superconducting phases, which play the role of bandstructure quasimomenta. The presence of these Weyl singularities enables topological transitions that are manifested experimentally as changes of the quantized transconductance between two voltage-biased leads, the quantization unit being 4e2/h, where e is the electric charge and h is the Planck constant. PMID:27040917
All-MgB2 Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Ueda, K.; Saito, S.; Semba, K.; Makimoto, T.; Naito, M.
2005-04-01
Sandwich-type all-MgB2 Josephson tunnel junctions (MgB2/AlOx/MgB2) have been fabricated with as-grown MgB2 films formed by molecular-beam epitaxy. The junctions exhibit substantial superconducting current (IcRN product ˜0.8mV at 4.2 K), a well-defined superconducting gap (Δ=2.2-2.3mV), and clear Fraunhofer patterns. The superconducting gap voltage of Δ agrees well with the smaller gap in the multigap scenario. The results demonstrate that MgB2 has great promise for superconducting electronics that can be operated at T ˜20K.
Josephson phase diffusion in the superconducting quantum interference device ratchet
Spiechowicz, Jakub; Łuczka, Jerzy
2015-05-15
We study diffusion of the Josephson phase in the asymmetric superconducting quantum interference device (SQUID) subjected to a time-periodic current and pierced by an external magnetic flux. We analyze a relation between phase diffusion and quality of transport characterized by the dc voltage across the SQUID and efficiency of the device. In doing so, we concentrate on the previously reported regime [J. Spiechowicz and J. Łuczka, New J. Phys. 17, 023054 (2015)] for which efficiency of the SQUID attains a global maximum. For long times, the mean-square displacement of the phase is a linear function of time, meaning that diffusion is normal. Its coefficient is small indicating rather regular phase evolution. However, it can be magnified several times by tailoring experimentally accessible parameters like amplitudes of the ac current or external magnetic flux. Finally, we prove that in the deterministic limit this regime is essentially non-chaotic and possesses an unexpected simplicity of attractors.
High-performance passive microwave survey on Josephson junctions
Denisov, A.G.; Radzikhovsky, V.N.; Kudeliya, A.M.
1994-12-31
The quasi-optical generations of image of objects with their internal structure in millimeter (MM) and submillimeter (SMM) bands is one of the prime problems of modern radioelectronics. The main advantage of passive MM imaging systems in comparison with visible and infrared (IR) systems is small attenuation of signals in fog, cloud, smoke, dust and other obscurants. However at a panoramic scanning of space the observation time lengthens and thereby the information processing rate becomes restricted. So that single-channel system cannot image in real time. Therefore we must use many radiometers in parallel to reduce the observation time. Such system must contain receiving sensors as pixels in multibeam antenna. The use of Josephson Junctions (JJ) for this purpose together with the cryoelectronic devices like GaAs FET or SQUIDS for signal amplifications after JJ is of particular interest in this case.
Majorana dc Josephson current mediated by a quantum dot.
Xu, Luting; Li, Xin-Qi; Sun, Qing-Feng
2017-05-17
The Josephson supercurrent through a hybrid Majorana-quantum dot-Majorana junction is investigated. We particularly analyze the effect of spin-selective coupling between the Majorana and quantum dot states, which only emerges in the topological phase and will influence the current through bent junctions and/or in the presence of magnetic fields in the quantum dot. We find that the characteristic behavior of the supercurrent through this system is quite counterintuitive, differing remarkably from the resonant tunneling, e.g. through the similar (normal phase) superconductor-quantum dot-superconductor junction. Our analysis is carried out under the influence of the full set-up parameters and for both the [Formula: see text] and [Formula: see text] periodic currents. The present study is expected to be relevant to the future exploration of applications of Majorana-nanowire circuits.
Vortex dynamics in an annular Josephson ratchet ladder
NASA Astrophysics Data System (ADS)
Lee, Ki Ho
2016-11-01
We present numerically the motion of vortices placed in an annular Josephson ladder which has a periodic ratchet potential along the annular direction. The ratchet characteristics are provided by assigning both alternate critical currents and alternate plaquette areas. The vortices are subject to an external current applied uniformly from each superconducting grain in the inner ring to each grain in the outer ring. The current-voltage (I-V) curves show asymmetric features because of the spatially broken symmetry of the potential. When an alternating current is added to the external current, Shapiro steps appear in the I-V curves, showing asymmetric values of the step widths and on-set currents. For a certain range of the alternating currents, vortices rotate to the easy direction, even at zero driving current, that corresponds to the direction away from the steep slope and toward the gentle slope of the ratchet potential.
Observation of the Bloch oscillations in an ultrasmall Josephson junction
Kuzmin, L.S.; Haviland, D.B. Laboratory of Cryoelectronics, Physics Department, Moscow State University, Moscow 119 899 GSP )
1991-11-11
We have studied the low-temperature behavior of lead-alloy Josephson tunnel junctions with area {ital S}{approx}0.01 {mu}m{sup 2}, isolated from their electromagnetic environment by high-resistance metallic resistors inserted into the current and voltage leads. Under irradiation with microwaves frequencies, {ital f}=3.5--10 GHz, the dc differential resistance {ital dV}/{ital dI}, as a function of the dc current {ital I}, showed peaks at {ital I}={plus minus}2{ital ef}. This effect, and other observations, arises due to the periodic electrical recharging of the junction by discrete Cooper pairs, and can be explained by the orthodox'' theory of Bloch oscillations.
Characteristics of strong ferromagnetic Josephson junctions with epitaxial barriers
NASA Astrophysics Data System (ADS)
Bell, C.; Loloee, R.; Burnell, G.; Blamire, M. G.
2005-05-01
We present the measurement of superconductor/ferromagnetic Josephson junctions, based on an epitaxial Nb bottom electrode and epitaxial Fe20Ni80 barrier. Uniform junctions have been fabricated with a barrier thicknesses in the range 2-12nm . The maximum critical current density ˜2.4±0.2×109Am-2 was found for a device with a 3-nm -thick barrier at 4.2K , corresponding to an average characteristic voltage ICRN˜16μV . The ICRN showed a nonmonotonic behavior with Fe20Ni80 thickness. The variation of the resistance of a unit area ARN , of the junctions with barrier thickness gave a Nb/Py specific interface resistance of 6.0±0.5fΩm2 and Fe20Ni80 resistivity of 174±50nΩm , consistent with other studies in polycrystalline samples.
Thermal depinning of fluxons in discrete Josephson rings
Mazo, J. J.; Naranjo, F.; Segall, K.
2008-11-01
We study the thermal depinning of single fluxons in rings made of Josephson junctions. Due to thermal fluctuations a fluxon can be excited from its energy minima and move through the array, causing a voltage across each junction. We find that for the initial depinning, the fluxon behaves as a single particle and follows a Kramers-type escape law. However, under some conditions this single-particle description breaks down. At low values of the discreteness parameter and low values of the damping, the depinning rate is larger than what the single-particle result would suggest. In addition, for some values of the parameters the fluxon can undergo low-voltage diffusion before switching to the high-voltage whirling mode. This type of diffusion is similar to phase diffusion in a single junction but occurs without frequency-dependent damping. We study the switching to the whirling state as well.
High-efficiency thermal switch based on topological Josephson junctions
NASA Astrophysics Data System (ADS)
Sothmann, Björn; Giazotto, Francesco; Hankiewicz, Ewelina M.
2017-02-01
We propose theoretically a thermal switch operating by the magnetic-flux controlled diffraction of phase-coherent heat currents in a thermally biased Josephson junction based on a two-dimensional topological insulator. For short junctions, the system shows a sharp switching behavior while for long junctions the switching is smooth. Physically, the switching arises from the Doppler shift of the superconducting condensate due to screening currents induced by a magnetic flux. We suggest a possible experimental realization that exhibits a relative temperature change of 40% between the on and off state for realistic parameters. This is a factor of two larger than in recently realized thermal modulators based on conventional superconducting tunnel junctions.
The a.c. Josephson effect without superconductivity
Gaury, Benoit; Weston, Joseph; Waintal, Xavier
2015-01-01
Superconductivity derives its most salient features from the coherence of the associated macroscopic wave function. The related physical phenomena have now moved from exotic subjects to fundamental building blocks for quantum circuits such as qubits or single photonic modes. Here we predict that the a.c. Josephson effect—which transforms a d.c. voltage Vb into an oscillating signal cos (2eVbt/ħ)—has a mesoscopic counterpart in normal conductors. We show that when a d.c. voltage Vb is applied to an electronic interferometer, there exists a universal transient regime where the current oscillates at frequency eVb/h. This effect is not limited by a superconducting gap and could, in principle, be used to produce tunable a.c. signals in the elusive 0.1–10-THz ‘terahertz gap’. PMID:25765929
High-performance passive microwave survey on Josephson Junctions
NASA Technical Reports Server (NTRS)
Denisov, A. G.; Radzikhovsky, V. N.; Kudeliya, A. M.
1995-01-01
The quasi-optical generations of images of objects with their internal structure in millimeter (MM) and submillimeter (SMM) bands is one of prime problems of modern radioelectronics. The main advantage of passive MM imaging systems in comparison with visible and infrared (IR) systems is small attenuation of signals in fog, cloud, smoke, dust and other obscurants. However, at a panoramic scanning of space the observation time lengthens and thereby the information processing rate becomes restricted so that single-channel system cannot image in real time. Therefore we must use many radiometers in parallel to reduce the observation time. Such system must contain receiving sensors as pixels in multibeam antenna. The use of Josephson Junctions (JJ) for this purpose together with the cryoelectronic devices like GaAs FET (field effect transistors) or SQUIDS for signal amplifications after JJ is of particular interest in this case.
Optimal control of quantum superpositions in a bosonic Josephson junction
NASA Astrophysics Data System (ADS)
Lapert, M.; Ferrini, G.; Sugny, D.
2012-02-01
We show how to optimally control the creation of quantum superpositions in a bosonic Josephson junction within the two-site Bose-Hubbard-model framework. Both geometric and purely numerical optimal-control approaches are used, the former providing a generalization of the proposal of Micheli [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.67.013607 67, 013607 (2003)]. While this method is shown not to lead to significant improvements in terms of time of formation and fidelity of the superposition, a numerical optimal-control approach appears more promising, as it allows creation of an almost perfect superposition, within a time short compared to other existing protocols. We analyze the robustness of the optimal solution against atom-number variations. Finally, we discuss the extent to which these optimal solutions could be implemented with state-of-the-art technology.
Multi-terminal Josephson junctions as topological matter
NASA Astrophysics Data System (ADS)
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
Topological materials and their unusual transport properties are now at the focus of modern experimental and theoretical research. Their topological properties arise from the bandstructure determined by the atomic composition of a material and as such are difficult to tune and naturally restricted to <= 3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n - 1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n >= 4 , the Andreev subgap spectrum of the junction can accommodate Weyl singularities in the space of the n - 1 independent superconducting phases, which play the role of bandstructure quasimomenta. The presence of these Weyl singularities enables topological transitions that are manifested experimentally as changes of the quantized transconductance between two voltage-biased leads, the quantization unit being 4e2 / h .
Multi-terminal Josephson junctions as topological matter
NASA Astrophysics Data System (ADS)
Riwar, Roman-Pascal; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2016-04-01
Topological materials and their unusual transport properties are now at the focus of modern experimental and theoretical research. Their topological properties arise from the bandstructure determined by the atomic composition of a material and as such are difficult to tune and naturally restricted to <=3 dimensions. Here we demonstrate that n-terminal Josephson junctions with conventional superconductors may provide novel realizations of topology in n-1 dimensions, which have similarities, but also marked differences with existing 2D or 3D topological materials. For n>=4, the Andreev subgap spectrum of the junction can accommodate Weyl singularities in the space of the n-1 independent superconducting phases, which play the role of bandstructure quasimomenta. The presence of these Weyl singularities enables topological transitions that are manifested experimentally as changes of the quantized transconductance between two voltage-biased leads, the quantization unit being 4e2/h, where e is the electric charge and h is the Planck constant.
Parallel arrays of Josephson junctions for submillimeter local oscillators
NASA Technical Reports Server (NTRS)
Pance, Aleksandar; Wengler, Michael J.
1992-01-01
In this paper we discuss the influence of the DC biasing circuit on operation of parallel biased quasioptical Josephson junction oscillator arrays. Because of nonuniform distribution of the DC biasing current along the length of the bias lines, there is a nonuniform distribution of magnetic flux in superconducting loops connecting every two junctions of the array. These DC self-field effects determine the state of the array. We present analysis and time-domain numerical simulations of these states for four biasing configurations. We find conditions for the in-phase states with maximum power output. We compare arrays with small and large inductances and determine the low inductance limit for nearly-in-phase array operation. We show how arrays can be steered in H-plane using the externally applied DC magnetic field.
NASA Astrophysics Data System (ADS)
Hui, Hoi-Yin; Sau, Jay D.
2017-01-01
Time-reversal invariance places strong constraints on the properties of the quantum spin Hall edge. One such restriction is the inevitability of dissipation in a Josephson junction between two superconductors formed on such an edge without the presence of interaction. Interactions and spin-conservation breaking are key ingredients for the realization of the dissipationless ac Josephson effect on such quantum spin Hall edges. We present a simple quantum impurity model that allows us to create a dissipationless fractional Josephson effect on a quantum spin Hall edge. We then use this model to substantiate a general argument that shows that any such nondissipative Josephson effect must necessarily be 8 π periodic.
Chaos and related nonlinear noise phenomena in Josephson tunnel junctions
Miracky, R.F.
1984-07-01
The nonlinear dynamics of Josephson tunnel junctions shunted by a resistance with substantial self-inductance have been thoroughly investigated. The current-voltage characteristics of these devices exhibit stable regions of negative differential resistance. Very large increases in the low-frequency voltage noise with equivalent noise temperatures of 10/sup 6/ K or more, observed in the vicinity of these regions, arise from switching, or hopping, between subharmonic modes. Moderate increases in the noise, with temperatures of about 10/sup 3/ K, arise from chaotic behavior. Analog and digital simulations indicate that under somewhat rarer circumstances the same junction system can sustain a purely deterministic hopping between two unstable subharmonic modes, accompanied by excess low-frequency noise. Unlike the noise-induced case, this chaotic process occurs over a much narrower range in bias current and is destroyed by the addition of thermal noise. The differential equation describing the junction system can be reduced to a one-dimensional mapping in the vicinity of one of the unstable modes. A general analytical calculation of switching processes for a class of mappings yields the frequency dependence of the noise spectrum in terms of the parameters of the mapping. Finally, the concepts of noise-induced hopping near bifurcation thresholds are applied to the problem of the three-photon Josephson parametric amplifier. Analog simulations indicate that the noise rise observed in experimental devices arises from occasional hopping between a mode at the pump frequency ..omega../sub p/ and a mode at the half harmonic ..omega../sub p//2. The hopping is induced by thermal noise associated with the shunt resistance. 71 references.
High-performance DC SQUIDs with submicrometer niobium Josephson junctions
de Waal, V.J.; Klapwijk, T.M.; van den Hamer, P.
1983-11-01
We report on the fabrication and performance of low-noise, all-niobium, thin-film planar dc SQUIDs with submicrometer Josephson junctions. The junctions are evaporated obliquely through a metal shadow evaporation mask, which is made using optical lithography with 0.5 ..mu..m tolerance. The Josephson junction barrier is formed by evaporating a thin silicon film and with a subsequent oxidation in a glow discharge. The junction parameters can be reproduced within a factor of two. Typical critical currents of the SQUIDs are about 3 ..mu..A and the resistances are about 100 ..cap omega... With SQUIDs having an inductance of 1 nH the voltage modulation is a least 60 ..mu..V. An intrinsic energy resolution of 4 x 10/sup -32/ J/Hz has been reached. The SQUIDs are coupled to wire-wound input coils or with thin-film input coils. The thin-film input coil consists of a niobium spiral of 20 turns on a separate substrate. In both cases the coil is glued onto a 2-nH SQUID with a coupling efficiency of at least 0.5. Referred to the thin-film input coil, the best coupled energy resolution achieved is 1.2 x 10/sup -30/ J/Hz measured in a flux-locked loop at frequencies above 10 Hz. As far as we know, this is the best figure achieved with an all-refractory-metal thin-film SQUID. The fabrication technique used is suited for making circuits with SQUID and pickup coil on the same substrate. We describe a compact, planar, first-order gradiometer integrated with a SQUID on a single substrate. The gradient noise of this device is 3 x 10/sup -12/ Tm/sup -1/. The gradiometer has a size of 12 mm x 17 mm, is simple to fabricate, an is suitable for biomedical applications.
Resonant tunneling in small current-biased Josephson Junctions
Schmidt, John Mark
1994-05-01
Effects of resonant tunneling between bound quantum states of a current-biased Josephson tunnel junction is studied both theoretically and experimentally. Several effects are predicted to arise from resonant tunneling, including a series of voltage peaks along the supercurrent branch of the current-voltage characteristic, and enhanced rate of escape from zero voltage state to voltage state at particular values of bias current. A model is developed to estimate magnitude and duration of voltage peaks, and to estimate enhancement of the escape rate, which appears as peaks in the rate as a function of bias current. An experimental investigation was carried out in an attempt to observe these predicted peaks in the escape rate distribution in a current-biased DC SQUID, which is shown to be dynamically equivalent to a Josephson junction with adjustable critical current. Electrical contact to each SQUID (fabricated from aluminium) was made through high resistance thin film leads located on the substrate. These resistors provided a high impedance at the plasma frequency which is for the isolation of the SQUID from its electromagnetic environment. Measurements were carried out on a dilution refrigerator at temperatures as low as 19 mK. No evidence was found for resonant tunneling; this is attributed to effective temperatures of hundreds of millikelvin. The behavior is well explained by a heating model where the high effective temperatures are generated by ohmic heating of the electron gas of the isolation resistors, which decouples from the phonon system (hot electron effect). The prospects for further theoretical and experimental research are discussed.
Postselected weak measurement beyond the weak value
Geszti, Tamas
2010-04-15
Closed expressions are derived for the quantum measurement statistics of pre- and postselected Gaussian particle beams. The weakness of the preselection step is shown to compete with the nonorthogonality of postselection in a transparent way. The approach is shown to be useful in analyzing postselection-based signal amplification, allowing measurements to be extended far beyond the range of validity of the well-known Aharonov-Albert-Vaidman limit. Additionally, the present treatment connects postselected weak measurement to the topic of phase-contrast microscopy.
Shunted Josephson tunnel junctions: High-frequency, self-pumped low noise amplifiers
NASA Astrophysics Data System (ADS)
Calander, N.; Claeson, T.; Rudner, S.
1982-07-01
The high-frequency amplification properties of transformer coupled, resistively shunted Josephson tunnel junctions have been investigated. The importance of the shunt loop inductance is stressed. It allows a high cutoff frequency, of significance for good high-frequency performance. The self-pumped parametric amplifier showed none of the excessive noise rise, which has hitherto plagued the development of externally pumped Josephson junction amplifiers. Around 10 GHz, we estimated a noise temperature less than 30 K for an amplifier pumped by a Josephson oscillation with a frequency well above twice the signal frequency. The corresponding gain of 5 dB may be increased in a better impedance matched circuit. The gain was very stable against variations in the bias conditions. A gain-bandwidth product as high as 0.3 was registered. The experimental results agreed well with the established theory for self-pumped parametric Josephson amplifiers. It should be possible to extend the low noise amplification by this device to mm wave frequencies. A relaxation oscillation occurred at a subharmonic of the Josephson frequency when the shunt loop inductance became large. The amplification in this mode followed closely the predictions of a simple model, where the signal modulated the switching of the sawtooth-like (relatively low frequency) relaxation current. Gains of about 15 dB were measured around 10 GHz, but the amplification was sensitive to bias conditions and noisy in this case where the relaxation frequency fell well below the signal frequency. Much improved properties were registered when the inductance was decreased so that the relaxation frequency approached the Josephson frequency and exceeded twice the signal frequency. The behavior then resembled that of a Josephson mode parametric amplifier, but the high content of harmonics of a relaxation oscillation meant that the amplifier became noisier due to converted noise from the many idler frequencies.
Intrinsic Josephson Junctions in the Superconducting Compound Fe (Se_{1-x }Tex )y
NASA Astrophysics Data System (ADS)
Ionov, Aleksander N.; Melekh, Bernard A.-T.
2016-12-01
Transport of Cooper pairs in the direction perpendicular to the layers of an Fe (Se_{0.3 }Te_{0.7})_{0.9} superconductor proceeds through the weak link via the proximity effect. We observed radiation from the chalcogen Fe (Se_{0.3 }Te_{0.7})_{0.9} superconductor in its resistive state.
NASA Astrophysics Data System (ADS)
Tollaksen, Jeff; Aharonov, Yakir
2006-03-01
We introduce a new type of weak measurement which yields a quantum average of weak values that is robust, outside the range of eigenvalues, extends the valid regime for weak measurements, and for which the probability of obtaining the pre- and post-selected ensemble is not exponentially rare. This result extends the applicability of weak values, shifts the statistical interpretation previously attributed to weak values and suggests that the weak value is a property of every pre- and post-selected ensemble. We then apply this new weak measurement to Hardy's paradox. Usually the paradox is dismissed on grounds of counterfactuality, i.e., because the paradoxical effects appear only when one considers results of experiments which do not actually take place. We suggest a new set of measurements in connection with Hardy's scheme, and show that when they are actually performed, they yield strange and surprising outcomes. More generally, we claim that counterfactual paradoxes point to a deeper structure inherent to quantum mechanics characterized by weak values (Aharonov Y, Botero A, Popescu S, Reznik B, Tollaksen J, Physics Letters A, 301 (3-4): 130-138, 2002).
0-π Transition Driven by Magnetic Proximity Effect in a Josephson Junction
NASA Astrophysics Data System (ADS)
Hikino, Shin-ichi; Yunoki, Seiji
2015-02-01
We theoretically study the Josephson effect in a superconductor/normal metal/superconductor (S/N/S) Josephson junction composed of s-wave Ss with N which is sandwiched by two ferromagnetic insulators (Fs), forming a spin valve, in the vertical direction of the junction. We show that the 0-π transition of the Josephson critical current occurs with increasing the thickness of N along the junction. This transition is due to the magnetic proximity effect (MPE) which induces ferromagnetic magnetization in the N. Moreover, we find that, even for fixed thickness of N, the proposed Josephson junction with the spin valve can be switched from π to 0 states and vice versa by varying the magnetization configuration (parallel or antiparallel) of two Fs. We also examine the effect of spin-orbit scattering on the Josephson critical current and argue that the 0-π transition found here can be experimentally observed within the current nanofabrication techniques, thus indicating a promising potential of this junction as a 0-π switching device operated reversibly with varying the magnetic configuration in the spin valve by, e.g., applying an external magnetic field. Our results not only provide possible applications in superconducting electronics but also suggest the importance of a fundamental concept of MPE in nanostructures of multilayer N/F systems.
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Kusmartsev, F. V.; Savel'Ev, Sergey; Yampol'Skii, V. A.; Nori, Franco
2009-09-01
We predict a class of excitations propagating along a Josephson vortex in two-dimensional Josephson junctions. These excitations are associated with the distortion of a Josephson vortex line of an arbitrary profile. We derive a universal analytical expression for the energy of arbitrary-shape excitations, investigate their influence on the dynamics of a vortex line, and discuss conditions where such excitations can be created. Finally, we show that such excitations play the role of a clock for a relativistically-moving Josephson vortex and suggest an experiment to measure a time-dilation effect analogous to that in special relativity. The position of the shape excitation on a Josephson vortex acts like a “minute hand” showing the time in the rest frame associated with the vortex. Remarkably, at some conditions, the shape wave can carry negative energy: a vortex with the shape excitation can have less energy than the same vortex without it.
NASA Astrophysics Data System (ADS)
Gallemí, A.; Guilleumas, M.; Mayol, R.; Mateo, A. Muñoz
2016-03-01
We analyze the dynamics of Josephson vortex states in two-component Bose-Einstein condensates with Rashba-Dresselhaus spin-orbit coupling by using the Gross-Pitaevskii equation. In one dimension, both in homogeneous and harmonically trapped systems, we report on stationary states containing doubly charged, static Josephson vortices. In multidimensional systems, we find stable Josephson vortices in a regime of parameters typical of current experiments with 87Rb atoms. In addition, we discuss the instability regime of Josephson vortices in disk-shaped condensates, where the snake instability operates and vortex dipoles emerge. We study the rich dynamics that they exhibit in different regimes of the spin-orbit-coupled condensate depending on the orientation of the Josephson vortices.
Structured chaos in a devil's staircase of the Josephson junction
Shukrinov, Yu. M.; Botha, A. E.; Medvedeva, S. Yu.; Kolahchi, M. R.; Irie, A.
2014-09-01
The phase dynamics of Josephson junctions (JJs) under external electromagnetic radiation is studied through numerical simulations. Current-voltage characteristics, Lyapunov exponents, and Poincaré sections are analyzed in detail. It is found that the subharmonic Shapiro steps at certain parameters are separated by structured chaotic windows. By performing a linear regression on the linear part of the data, a fractal dimension of D = 0.868 is obtained, with an uncertainty of ±0.012. The chaotic regions exhibit scaling similarity, and it is shown that the devil's staircase of the system can form a backbone that unifies and explains the highly correlated and structured chaotic behavior. These features suggest a system possessing multiple complete devil's staircases. The onset of chaos for subharmonic steps occurs through the Feigenbaum period doubling scenario. Universality in the sequence of periodic windows is also demonstrated. Finally, the influence of the radiation and JJ parameters on the structured chaos is investigated, and it is concluded that the structured chaos is a stable formation over a wide range of parameter values.
Josephson junction detectors for Majorana modes and Dirac fermions
NASA Astrophysics Data System (ADS)
Maiti, M.; Kulikov, K. M.; Sengupta, K.; Shukrinov, Yu. M.
2015-12-01
We demonstrate that the current-voltage (I -V ) characteristics of resistively and capacitively shunted Josephson junctions (RCSJs) hosting localized subgap Majorana states provide a phase-sensitive method for their detection. The I -V characteristics of such RCSJs, in contrast to their resistively shunted counterparts, exhibit subharmonic odd Shapiro steps. These steps, owing to their subharmonic nature, exhibit qualitatively different properties compared to harmonic odd steps of conventional junctions. In addition, the RCSJs hosting Majorana bound states also display an additional sequence of steps in the devil's staircase structure seen in their I -V characteristics; such a sequence of steps makes their I -V characteristics qualitatively distinct from that of their conventional counterparts. A similar study for RCSJs with graphene superconducting junctions hosting Dirac-like quasiparticles reveals that the Shapiro step width in their I -V curves bears a signature of the transmission resonance phenomenon of their underlying Dirac quasiparticles; consequently, these step widths exhibit a π periodic oscillatory behavior with variation of the junction barrier potential. We discuss experiments which can test our theory.
Generating entangled quantum microwaves in a Josephson-photonics device
NASA Astrophysics Data System (ADS)
Dambach, Simon; Kubala, Björn; Ankerhold, Joachim
2017-02-01
When connecting a voltage-biased Josephson junction in series to several microwave cavities, a Cooper-pair current across the junction gives rise to a continuous emission of strongly correlated photons into the cavity modes. Tuning the bias voltage to the resonance where a single Cooper pair provides the energy to create an additional photon in each of the cavities, we demonstrate the entangling nature of these creation processes by simple witnesses in terms of experimentally accessible observables. To characterize the entanglement properties of the such created quantum states of light to the fullest possible extent, we then proceed to more elaborate entanglement criteria based on the knowledge of the full density matrix and provide a detailed study of bi- and multipartite entanglement. In particular, we illustrate how due to the relatively simple design of these circuits changes of experimental parameters allow one to access a wide variety of entangled states differing, e.g., in the number of entangled parties or the dimension of state space. Such devices, besides their promising potential to act as a highly versatile source of entangled quantum microwaves, may thus represent an excellent natural testbed for classification and quantification schemes developed in quantum information theory.
Phase dynamics of low critical current density YBCO Josephson junctions
NASA Astrophysics Data System (ADS)
Massarotti, D.; Stornaiuolo, D.; Rotoli, G.; Carillo, F.; Galletti, L.; Longobardi, L.; Beltram, F.; Tafuri, F.
2014-08-01
High critical temperature superconductors (HTS) based devices can have impact in the study of the phase dynamics of Josephson junctions (JJs) thanks to the wide range of junction parameters they offer and to their unconventional properties. Measurements of current-voltage characteristics and of switching current distributions constitute a direct way to classify different regimes of the phase dynamics and of the transport, also in nontrivial case of the moderately damped regime (MDR). MDR is going to be more and more common in JJs with advances in nanopatterning superconductors and synthesizing novel hybrid systems. Distinctive signatures of macroscopic quantum tunneling and of thermal activation in presence of different tunable levels of dissipation have been detected in YBCO grain boundary JJs. Experimental data are supported by Monte Carlo simulations of the phase dynamics, in a wide range of temperatures and dissipation levels. This allows us to quantify dissipation in the MDR and partially reconstruct a phase diagram as guideline for a wide range of moderately damped systems.
Squeezing with a flux-driven Josephson parametric amplifier
NASA Astrophysics Data System (ADS)
Menzel, E. P.; Zhong, L.; Eder, P.; Baust, A.; Haeberlein, M.; Hoffmann, E.; Deppe, F.; Marx, A.; Gross, R.; di Candia, R.; Solano, E.; Ihmig, M.; Inomata, K.; Yamamoto, T.; Nakamura, Y.
2014-03-01
Josephson parametric amplifiers (JPA) are promising devices for the implementation of continuous-variable quantum communication protocols. Operated in the phase-sensitive mode, they allow for amplifying a single quadrature of the electromagnetic field without adding any noise. While in practice internal losses introduce a finite amount of noise, our device still adds less noise than an ideal phase-insensitive amplifier. This property is a prerequisite for the generation of squeezed states. In this work, we reconstruct the Wigner function of squeezed vacuum, squeezed thermal and squeezed coherent states with our dual-path method [L. Zhong et al. arXiv:1307.7285 (2013); E. P. Menzel et al. Phys. Rev. Lett. 105 100401 (2010)]. In addition, we illuminate the physics of squeezed coherent microwave fields. This work is supported by SFB 631, German Excellence Initiative via NIM, EU projects SOLID, CCQED, PROMISCE and SCALEQIT, MEXT Kakenhi ``Quantum Cybernetics,'' JSPS FIRST Program, the NICT Commissioned Research, Basque Government IT472-10, Spanish MINECO FIS2012-36673-C03-02, and UPV/EHU UFI 11/55.
Correlating quantum decoherence and material defects in a Josephson qubit
NASA Astrophysics Data System (ADS)
Hite, D. A.; McDermott, R.; Simmonds, R. W.; Cooper, K. B.; Steffen, M.; Nam, S.; Pappas, D. P.; Martinis, J. M.
2004-03-01
Superconducting tunnel junction devices are promising candidates for constructing quantum bits (qubits) for quantum computation because of their inherently low dissipation and ease of scalability by microfabrication. Recently, the Josephson phase qubit has been characterized spectroscopically as having spurious microwave resonators that couple to the qubit and act as a dominant source of decoherence. While the origin of these spurious resonances remains unknown, experimental evidence points to the material system of the tunnel barrier. Here, we focus on our materials research aimed at elucidating and eliminating these spurious resonators. In particular, we have studied the use of high quality Al films epitaxially grown on Si(111) as the base electrode of the tunnel junction. During each step in the Al/AlOx/Al trilayer growth, we have investigated the structure in situ by AES, AED and LEED. While tunnel junctions fabricated with these epitaxial base electrodes prove to be of non-uniform oxide thickness and too thin, I-V characteristics have shown a lowering of subgap currents by a factor of two. Transport measurements will be correlated with morphological structure for a number of devices fabricated with various degrees of crystalline quality.
Diffusion current in a system of coupled Josephson junctions
Shukrinov, Yu. M. Rahmonov, I. R.
2012-08-15
The role of a diffusion current in the phase dynamics of a system of coupled Josephson junctions (JJs) has been analyzed. It is shown that, by studying the temporal dependences of the superconducting, quasi-particle, diffusion, and displacement currents and the dependences of average values of these currents on the total current, it is possible to explain the main features of the current-voltage characteristic (CVC) of the system. The effect of a diffusion current on the character of CVC branching in the vicinity of a critical current and in the region of hysteresis, as well as on the part of CVC branch corresponding to a parametric resonance in the system is demonstrated. A clear interpretation of the differences in the character of CVC branching in a model of capacitively coupled JJs (CCJJ model) and a model of capacitive coupling with diffusion current (CCJJ+DC model) is proposed. It is shown that a decrease in the diffusion current in a JJ leads to the switching of this junction to an oscillating state. The results of model calculations are qualitatively consistent with the experimental data.
Diffusion current in a system of coupled Josephson junctions
NASA Astrophysics Data System (ADS)
Shukrinov, Yu. M.; Rahmonov, I. R.
2012-08-01
The role of a diffusion current in the phase dynamics of a system of coupled Josephson junctions (JJs) has been analyzed. It is shown that, by studying the temporal dependences of the superconducting, quasi-particle, diffusion, and displacement currents and the dependences of average values of these currents on the total current, it is possible to explain the main features of the current-voltage characteristic (CVC) of the system. The effect of a diffusion current on the character of CVC branching in the vicinity of a critical current and in the region of hysteresis, as well as on the part of CVC branch corresponding to a parametric resonance in the system is demonstrated. A clear interpretation of the differences in the character of CVC branching in a model of capacitively coupled JJs (CCJJ model) and a model of capacitive coupling with diffusion current (CCJJ+DC model) is proposed. It is shown that a decrease in the diffusion current in a JJ leads to the switching of this junction to an oscillating state. The results of model calculations are qualitatively consistent with the experimental data.
Josephson frequency meter for millimeter and submillimeter wavelengths
Anischenko, S.E.; Larkin, S.Y.; Chaikovsky, V.I.
1994-12-31
Frequency measurements of electromagnetic oscillations of millimeter and submillimeter wavebands with frequency growth due to a number of reasons become more and more difficult. First, these frequencies are considered to be cutoff for semiconductor converting devices and one has to use optical measurement methods instead of traditional ones with frequency transfer. Second, resonance measurement methods are characterized by using relatively narrow bands and optical ones are limited in frequency and time resolution due to the limited range and velocity of movement of their mechanical elements as well as the efficiency of these optical techniques decreases with the increase of wavelength due to diffraction losses. That requires the apriori information on the radiation frequency band of the source involved. Method of measuring frequency of harmonic microwave signals in millimeter and submillimeter wavebands based on the ac Josephson effect in superconducting contacts is devoid of all the above drawbacks. This approach offers a number of major advantages over the more traditional measurement methods, that is the one based on frequency conversion, resonance and interferrometric techniques. It can be characterized by high potential accuracy, wide range of frequencies measured, prompt measurement and the opportunity to obtain panoramic display of the results as well as full automation of the measuring process.
Multi-qubit measurements with a Josephson Photomultiplier
NASA Astrophysics Data System (ADS)
Howington, Caleb; Hutchings, M.; Ribeill, Guilhem; Pechenezhskiy, Ivan; Vavilov, Maxim G.; Wilhelm, Frank K.; McDermott, R.; Plourde, Blt
The ability to measure multi-qubit parity is critical for the realization of a fault-tolerant quantum information processor. For a system of transmon qubits coupled to a superconducting cavity, a threshold photon detector can provide an efficient path towards the digital readout of qubit parity after the parity information is mapped onto the cavity photon occupation. We will describe progress towards the implementation of such a scheme for measuring the parity of two transmon qubits. On-chip flux bias lines allow us to tune the dispersive cavity shifts related to the state of the two qubits and an appropriately shaped pulse driven to the cavity results in a bright state for one parity but not the other. A Josephson Photomultiplier then serves as a phase-insensitive digital detector of the microwave photons that leak out of the cavity. Future improvements and various technical difficulties will be discussed. We acknowledge support from ARO under Contract W911NF-14-1-0080.
Resonant subgap current transport in Josephson field effect transistor
NASA Astrophysics Data System (ADS)
Bezuglyi, E. V.; Bratus', E. N.; Shumeiko, V. S.
2017-01-01
We study theoretically the current-voltage characteristics (IVCs) of the Josephson field effect transistor—a ballistic SNINS junction with superconducting (S) electrodes confining a planar normal-metal region (N), which is controlled by the gate-induced potential barrier (I). Using the computation technique developed earlier for long single-channel junctions in the coherent multiple Andreev reflection (MAR) regime, we find a significant difference of the subgap current structure compared to the subharmonic gap structure in tunnel junctions and atomic-size point contacts. For long junctions, whose lengths significantly exceed the coherence length, the IVC exhibits current peaks at multiples (harmonics) of the distance δm between the static Andreev levels e Vn=n δm . Moreover, the averaged IVC follows the powerlike behavior rather than the exponential one and has a universal scaling with the junction transparency. This result is qualitatively understood using an analytical approach based on the concept of resonant MAR trajectories. In shorter junctions having lengths comparable to the coherence length, the IVC has an exponential form common for point contacts, however the current structures appear at the subharmonics of the interlevel distance e Vn=δm/n rather than the gap subharmonics 2 Δ /n .
ac Josephson Effect in Finite-Length Nanowire Junctions with Majorana Modes
NASA Astrophysics Data System (ADS)
San-Jose, Pablo; Prada, Elsa; Aguado, Ramón
2012-06-01
It has been predicted that superconducting junctions made with topological nanowires hosting Majorana bound states (MBS) exhibit an anomalous 4π-periodic Josephson effect. Finding an experimental setup with these unconventional properties poses, however, a serious challenge: for finite-length wires, the equilibrium supercurrents are always 2π periodic as anticrossings of states with the same fermionic parity are possible. We show, however, that the anomaly survives in the transient regime of the ac Josephson effect. Transients are, moreover, protected against decay by quasiparticle poisoning as a consequence of the quantum Zeno effect, which fixes the parity of Majorana qubits. The resulting long-lived ac Josephson transients may be effectively used to detect MBS.
Josephson effect in CeCoIn{sub 5} microbridges as seen via quantum interferometry
Foyevtsov, Oleksandr; Porrati, Fabrizio; Huth, Michael
2011-07-15
A superconducting quantum interference device (SQUID) was prepared on a micron-sized single crystal using a selected growth domain of a thin film of CeCoIn{sub 5} grown by molecular beam epitaxy. SQUID voltage oscillations of good quality were obtained as well as interference effects stemming from the individual Josephson microbridges. The transport characteristics in the superconducting state exhibited several peculiarities which we ascribe to the periodic motion of vortices in the microbridges. The temperature dependence of the Josephson critical current shows good correspondence to the Ambegaokar-Baratoff relation, expected for the ideal Josephson junction. The results indicate a promising pathway to identify the type of order parameter in CeCoIn{sub 5} by means of phase-sensitive measurements on microbridges.
High-quality planar high-T{sub c} Josephson junctions
Bergeal, N.; Grison, X.; Lesueur, J.; Faini, G.; Aprili, M.; Contour, J.P.
2005-09-05
Reproducible high-T{sub c} Josephson junctions have been made in a rather simple two-step process using ion irradiation. A microbridge (1 to 5 {mu}m wide) is firstly designed by ion irradiating a c-axis-oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} film through a gold mask such as the nonprotected part becomes insulating. A lower T{sub c} part is then defined within the bridge by irradiating with a much lower fluence through a narrow slit (20 nm) opened in a standard electronic photoresist. These planar junctions, whose settings can be finely tuned, exhibit reproducible and nearly ideal Josephson characteristics. This process can be used to produce complex Josephson circuits.
Statistics of avalanches in the self-organized criticality state of a Josephson junction
Matizen, E. V.; Martynets, V. G. Bezverkhii, P. P.
2010-08-15
Magnetic flux avalanches in Josephson junctions that include superconductor-insulator-superconductor (SIS) tunnel junctions and are magnetized at temperatures lower than approximately 5 K have been studied in detail. Avalanches are of stochastic character and appear when the magnetic field penetration depth {lambda} into a junction becomes equal to the length a of the Josephson junction with a decrease in the temperature. The statistical properties of such avalanches are presented. The size distribution of the avalanches is a power law with a negative noninteger exponent about unity, indicating the self-organized criticality state. The self-organized criticality state is not observed in Josephson junctions with a superconductor-normal metal-superconductor (SNS) junction.
Non-equilibrium 8π Josephson effect in atomic Kitaev wires
Laflamme, C.; Budich, J. C.; Zoller, P.; Dalmonte, M.
2016-01-01
The identification of fractionalized excitations, such as Majorana quasi-particles, would be a striking signal of the realization of exotic quantum states of matter. While the paramount demonstration of such excitations would be a probe of their non-Abelian statistics via controlled braiding operations, alternative proposals exist that may be easier to access experimentally. Here we identify a signature of Majorana quasi-particles, qualitatively different from the behaviour of a conventional superconductor, which can be detected in cold atom systems using alkaline-earth-like atoms. The system studied is a Kitaev wire interrupted by an extra site, which gives rise to super-exchange coupling between two Majorana-bound states. We show that this system hosts a tunable, non-equilibrium Josephson effect with a characteristic 8π periodicity of the Josephson current. The visibility of the 8π periodicity of the Josephson current is then studied including the effects of dephasing and particle losses. PMID:27481540
Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface
NASA Astrophysics Data System (ADS)
Pang, Yuan; Wang, Junhua; Lyu, Zhaozheng; Yang, Guang; Fan, Jie; Liu, Guangtong; Ji, Zhongqing; Jing, Xiunian; Yang, Changli; Lu, Li
2016-11-01
Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface. In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi2Te3 surface. Project supported by the National Basic Research Program of China (Grant Nos. 2009CB929101 and 2011CB921702), the National Natural Science Foundation of China (Grant Nos. 91221203, 11174340, 11174357, 91421303, and 11527806), and the Strategic Priority Research Program B of the Chinese Academy of Sciences (Grant No. XDB07010100).
Synchronization dynamics on the picosecond time scale in coupled Josephson junction neurons
NASA Astrophysics Data System (ADS)
Segall, K.; LeGro, M.; Kaplan, S.; Svitelskiy, O.; Khadka, S.; Crotty, P.; Schult, D.
2017-03-01
Conventional digital computation is rapidly approaching physical limits for speed and energy dissipation. Here we fabricate and test a simple neuromorphic circuit that models neuronal somas, axons, and synapses with superconducting Josephson junctions. The circuit models two mutually coupled excitatory neurons. In some regions of parameter space the neurons are desynchronized. In others, the Josephson neurons synchronize in one of two states, in-phase or antiphase. An experimental alteration of the delay and strength of the connecting synapses can toggle the system back and forth in a phase-flip bifurcation. Firing synchronization states are calculated >70 000 times faster than conventional digital approaches. With their speed and low energy dissipation (10-17J /spike ), this set of proof-of-concept experiments establishes Josephson junction neurons as a viable approach for improvements in neuronal computation as well as applications in neuromorphic computing.
DOE R&D Accomplishments Database
Lee, T. D.
1970-07-01
While the phenomenon of beta-decay was discovered near the end of the last century, the notion that the weak interaction forms a separate field of physical forces evolved rather gradually. This became clear only after the experimental discoveries of other weak reactions such as muon-decay, muon-capture, etc., and the theoretical observation that all these reactions can be described by approximately the same coupling constant, thus giving rise to the notion of a universal weak interaction. Only then did one slowly recognize that the weak interaction force forms an independent field, perhaps on the same footing as the gravitational force, the electromagnetic force, and the strong nuclear and sub-nuclear forces.
NASA Astrophysics Data System (ADS)
Probst, B.; Domínguez, F.; Schroer, A.; Yeyati, A. Levy; Recher, P.
2016-10-01
We study the critical Josephson current flowing through a double quantum dot weakly coupled to two superconducting leads. We use analytical as well as numerical methods to investigate this setup in the limit of small and large bandwidth leads in all possible charging states, where we account for on-site interactions exactly. Our results provide clear signatures of nonlocal spin-entangled pairs, which support interpretations of recent experiments [R. S. Deacon, A. Oiwa, J. Sailer, S. Baba, Y. Kanai, K. Shibata, K. Hirakawa, and S. Tarucha, Nat. Commun. 6, 7446 (2015), 10.1038/ncomms8446]. In addition, we find that the ground state with one electron on each quantum dot can undergo a tunable singlet-triplet phase transition in the regime where the superconducting gap in the leads is not too large, which gives rise to an additional new signature of nonlocal Cooper-pair transport.
NASA Astrophysics Data System (ADS)
Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.
2016-03-01
On the basis of the Usadel equation we study a multiterminal Josephson junction. This junction is composed by "magnetic" superconductors Sm, which have singlet pairing and are separated from the normal n wire by spin filters so that the Josephson coupling is caused only by fully polarized triplet components. We show that there is no interaction between triplet Cooper pairs with antiparallel total spin orientations. The presence of an additional singlet superconductor S attached to the n wire leads to a finite Josephson current IQ with an unusual current-phase relation. The density of states in the n wire for different orientations of spins of Cooper pairs is calculated. We derive a general formula for the current IQ in a multiterminal Josephson contact and apply this formula for analysis of two four-terminal Josephson junctions of different structures. It is shown in particular that both the "nematic" and the "magnetic" cases can be realized in these junctions. In a two-terminal structure with parallel filter orientations and in a three-terminal structure with antiparallel filter orientations of the "magnetic" superconductors with attached additional singlet superconductor, we find a nonmonotonic temperature dependence of the critical current. Also, in these structures, the critical current shows a Riedel peak like dependence on the exchange field in the "magnetic" superconductors. Although there is no current through the S/n interface due to orthogonality of the singlet and triplet components, the phase of the order parameter in the superconuctor S is shown to affect the Josephson current in a multiterminal structure.
Measurement of Aharonov-Casher effect in a Josephson junction chain
NASA Astrophysics Data System (ADS)
Pop, Ioan Mihai; Lecocq, Florent; Pannetier, Bernard; Buisson, Olivier; Guichard, Wiebke
2011-03-01
We have recently measured the effect of superconducting phase-slips on the ground state of a Josephson junction chain and a rhombi chain. Here we report clear evidence of Aharonov-Casher effect in a chain of Josephson junctions. This phenomenon is the dual of the well known Aharonov-Bohm interference. Using a capacitively coupled gate to the islands of the chain, we induce oscillations of the supercurrent by tuning the polarization charges on the islands. We observe complex interference patterns for different quantum phase slip amplitudes, that we understand quantitatively as Aharonov-Casher vortex interferences. European STREP MIDAS.
Pure second harmonic current-phase relation in spin-filter Josephson junctions.
Pal, Avradeep; Barber, Z H; Robinson, J W A; Blamire, M G
2014-01-01
Higher harmonics in current-phase relations of Josephson Junctions are predicted to be observed when the first harmonic is suppressed. Conventional theoretical models predict higher harmonics to be extremely sensitive to changes in barrier thickness, temperature, and so on. Here we report experiments with Josephson junctions incorporating a spin-dependent tunnelling barrier, revealing a current-phase relation for highly spin polarized barriers that is purely second harmonic in nature and is insensitive to changes in barrier thickness. This observation implies that the standard theory of Cooper pair transport through tunnelling barriers is not applicable for spin-dependent tunnelling barriers.
Simulation and measurement of a Ka-band HTS MMIC Josephson junction mixer
NASA Astrophysics Data System (ADS)
Zhang, Ting; Pegrum, Colin; Du, Jia; Guo, Yingjie Jay
2017-01-01
We report modeling and simulation results for a Ka band high-temperature superconducting (HTS) monolithic microwave integrated circuit (MMIC) Josephson junction mixer. A Verilog-A model of a Josephson junction is established and imported into the system simulator to realize a full HTS MMIC circuit simulation containing the HTS passive circuit models. Impedance matching optimization between the junction and passive devices is investigated. Junction DC I-V characteristics, current and local oscillator bias conditions and mixing performance are simulated and compared with the experimental results. Good agreement is obtained between the simulation and measurement results.
NASA Astrophysics Data System (ADS)
Denisenko, M. V.; Munyaev, V. O.; Satanin, A. M.
2016-11-01
The parametric frequency division in a coplanar waveguide line with an integrated single-contact rf SQUID (Josephson oscillator) is discussed. It is assumed that the oscillator is excited by pump pulses whose carrier frequency can be a multiple of the plasma frequency of the oscillator. It is shown that the Josephson oscillator excited at the pump frequency can induce frequency division by emitting subharmonics that are multiples of the fundamental frequency (fractional resonances). Parameters for which parametric frequency transformation occurs are determined. The possible generalization of this effect to the quantum case in which correlated microwave photons (entangled photon states) can be generated is discussed.
Thin-film metal coated insulation barrier in a Josephson tunnel junction. [Patent application
Hawkins, G.A.; Clarke, J.
1975-10-31
A highly stable, durable, and reproducible Josephson tunnel junction consists of a thin-film electrode of a hard superconductor, a thin oxide insulation layer over the electrode constituting a Josephson tunnel junction barrier, a thin-film layer of stabilizing metal over the barrier, and a second thin-film hard superconductive electrode over the stabilizing film. The thin stabilizing metal film is made only thick enough to limit penetration of the electrode material through the insulation layer so as to prevent a superconductive short.
Free and Induced Vortices Motion in the Josephson Junction Coupled with Waveguide
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
A model for the analytic description of vortices in a system consisting of a long Josephson junction and a waveguide is formulated. For this system all types of elementary vortices and its chains are listed. The allowed range of velocities of an elementary vortex is found. It is established that a free vortex can be a fast one which moves with velocity much greater than the Swihart velocity of Josephson junction. The effect of the waveguide on the induced vortices motion is studied. It is shown that fast vortex can be generated by relatively small values of bias current density. The effect of vortex Cherenkov losses on the bias current is described.
Free and Induced Vortices Motion in the Josephson Junction Coupled with Waveguide
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2010-12-01
A model for the analytic description of vortices in a system consisting of a long Josephson junction and a waveguide is formulated. For this system all types of elementary vortices and its chains are listed. The allowed range of velocities of an elementary vortex is found. It is established that a free vortex can be a fast one which moves with velocity much greater than the Swihart velocity of Josephson junction. The effect of the waveguide on the induced vortices motion is studied. It is shown that fast vortex can be generated by relatively small values of bias current density. The effect of vortex Cherenkov losses on the bias current is described.
Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions
NASA Astrophysics Data System (ADS)
Peng, Yang; Vinkler-Aviv, Yuval; Brouwer, Piet W.; Glazman, Leonid I.; von Oppen, Felix
2016-12-01
We study the Josephson effect in a quantum spin Hall system coupled to a localized magnetic impurity. As a consequence of the fermion parity anomaly, the spin of the combined system of impurity and spin-Hall edge alternates between half-integer and integer values when the superconducting phase difference across the junction advances by 2 π . This leads to characteristic differences in the splittings of the spin multiplets by exchange coupling and single-ion anisotropy at phase differences, for which time-reversal symmetry is preserved. We discuss the resulting 8 π -periodic (or Z4) fractional Josephson effect in the context of recent experiments.
Defect motion and lattice pinning barriers in Josephson-junction ladders
Kang, H.; Lim, Jong Soo; Fortin, J.-Y.; Choi, J.; Choi, M. Y.
2006-01-01
We study the motion of domain wall defects in a fully frustrated Josephson-junction ladder system, driven by small applied currents. For small system sizes, the energy barrier E{sub B} to the defect motion is computed analytically via symmetry and topological considerations. More generally, we perform numerical simulations directly on the equations of motion, based on the resistively-shunted junction model, to study the dynamics of defects, varying the system size. Coherent motion of domain walls is observed for large system sizes. In the thermodynamical limit, we find E{sub B}=0.1827 in units of the Josephson coupling energy.
NASA Astrophysics Data System (ADS)
Lombardi, Marco; Bertin, Giuseppe
1999-02-01
Recently, it has been shown that it is possible to reconstruct the projected mass distribution of a cluster from weak lensing provided that both the geometry of the universe and the probability distribution of galaxy redshifts are known; actually, when additional photometric data are taken to be available, the galaxy redshift distribution could be determined jointly with the cluster mass from the weak lensing analysis. In this paper we develop, in the spirit of a ``thought experiment,'' a method to constrain the geometry of the universe from weak lensing, provided that the redshifts of the source galaxies are measured. The quantitative limits and merits of the method are discussed analytically and with a set of simulations, in relation to point estimation, interval estimation, and test of hypotheses for homogeneous Friedmann-Lema\\^\\i tre models. The constraints turn out to be significant when a few thousand source galaxies are used.
Fluxons in a triangular set of coupled long Josephson junctions
NASA Astrophysics Data System (ADS)
Yukon, Stanford P.; Malomed, Boris A.
2015-09-01
We report results of an analysis of the dynamics of magnetic flux solitons in the system of three long Josephson junctions between three bulk superconductors that form a prism. The system is modeled by coupled sine-Gordon equations for the phases of the junctions. The Aharonov-Bohm constraint takes into account the axial magnetic flux enclosed by the prism and reduces the system from three independent phases to two. The equations of motion for the phases include dissipative terms, and a control parameter δ which accounts for the deviation of the enclosed flux from half a quantum. Analyzing the effective potential of the coupled equations, we identify different species of topological and non-topological phase solitons (fluxons) in this system. In particular, subkinks with fractional topological charges ±1/3 and ±2/3, confined inside integer-charge fluxons, may be mapped onto the root diagrams for mesons and baryons in the original quark model of hadrons. Solutions for straight-line kinks and for two types of non-topological solitons are obtained in an explicit analytical form. Numerical tests demonstrate that the former species is unstable against breakup into pairs of separating single-fluxon kinks. The non-topological kinks feature metastability, eventually breaking up into fluxon-antifluxon pairs. Free fractional-fluxon kinks, that connect different potential minima and are, accordingly, pulled by the potential difference, are also considered. Using the momentum-balance method, we predict the velocity at which these kinks should move in the presence of the dissipation. Numerical tests demonstrate that the analysis predicts the velocity quite closely. Higher-energy static solutions for all of the stable kink types mentioned above, as well as kinks connecting false vacua, are found by means of the shooting method. Inelastic collisions among the stable fractional and single-fluxon kinks are investigated numerically.
Fluxons in a triangular set of coupled long Josephson junctions
Yukon, Stanford P.; Malomed, Boris A.
2015-09-15
We report results of an analysis of the dynamics of magnetic flux solitons in the system of three long Josephson junctions between three bulk superconductors that form a prism. The system is modeled by coupled sine-Gordon equations for the phases of the junctions. The Aharonov-Bohm constraint takes into account the axial magnetic flux enclosed by the prism and reduces the system from three independent phases to two. The equations of motion for the phases include dissipative terms, and a control parameter δ which accounts for the deviation of the enclosed flux from half a quantum. Analyzing the effective potential of the coupled equations, we identify different species of topological and non-topological phase solitons (fluxons) in this system. In particular, subkinks with fractional topological charges ±1/3 and ±2/3, confined inside integer-charge fluxons, may be mapped onto the root diagrams for mesons and baryons in the original quark model of hadrons. Solutions for straight-line kinks and for two types of non-topological solitons are obtained in an explicit analytical form. Numerical tests demonstrate that the former species is unstable against breakup into pairs of separating single-fluxon kinks. The non-topological kinks feature metastability, eventually breaking up into fluxon-antifluxon pairs. Free fractional-fluxon kinks, that connect different potential minima and are, accordingly, pulled by the potential difference, are also considered. Using the momentum-balance method, we predict the velocity at which these kinks should move in the presence of the dissipation. Numerical tests demonstrate that the analysis predicts the velocity quite closely. Higher-energy static solutions for all of the stable kink types mentioned above, as well as kinks connecting false vacua, are found by means of the shooting method. Inelastic collisions among the stable fractional and single-fluxon kinks are investigated numerically.
Cedergren, K; Kirtley, J R; Bauch, T; Rotoli, G; Troeman, A; Hilgenkamp, H; Tafuri, F; Lombardi, F
2010-04-30
We have investigated the static and dynamic properties of long YBa2Cu3O(7-delta) 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions.
Golick, V A; Kadygrob, D V; Yampol'skii, V A; Rakhmanov, A L; Ivanov, B A; Nori, Franco
2010-05-07
We predict a new branch of surface Josephson plasma waves (SJPWs) in layered superconductors for frequencies higher than the Josephson plasma frequency. In this frequency range, the permittivity tensor components along and transverse to the layers have different signs, which is usually associated with negative refraction. However, for these frequencies, the bulk Josephson plasma waves cannot be matched with the incident and reflected waves in the vacuum, and, instead of the negative-refractive properties, abnormal surface modes appear within the frequency band expected for bulk modes. We also discuss the excitation of high-frequency SJPWs by means of the attenuated-total-reflection method.
Fischer, G M; Mayer, B; Gross, R; Nissel, T; Husemann, K D; Huebener, R P; Freltoft, T; Shen, Y; Vase, P
1994-02-25
With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with YBa(2)Cu(3)O(7-delta) thin-film grain boundary Josephson junctions fabricated on [001] tilt SrTiO(3) bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction. The spatial modulation of the Josephson current density by the external magnetic field is imaged directly with a spatial resolution of about 1 micrometer.
Control of Josephson current by Aharonov-Casher phase in a Rashba ring
NASA Astrophysics Data System (ADS)
Liu, Xin; Borunda, M. F.; Liu, Xiong-Jun; Sinova, Jairo
2009-11-01
We study the interference effect induced by the Aharonov-Casher phase on the Josephson current through a semiconducting ring attached to superconducting leads. Using a one-dimensional model that incorporates spin-orbit coupling in the semiconducting ring, we calculate the Andreev levels analytically and numerically, and predict oscillations of the Josephson current due to the AC phase. This result is valid from the point-contact limit to the long channel-length case, as defined by the ratio of the junction length and the BCS healing length. We show in the long channel-length limit that the impurity scattering has no effect on the oscillation of the Josephson current, in contrast to the case of conductivity oscillations in a spin-orbit-coupled ring system attached to normal leads where impurity scattering reduces the amplitude of oscillations. Our results suggest a scheme to measure the AC phase with, in principle, higher sensitivity. In addition, this effect allows for control of the Josephson current through the gate-voltage-tuned AC phase.
2016-09-01
to the characteristics and extract the non-ideality. These capabilities and calibration results will assist in the characterization of advanced...superconductor-ionic quantum memory and computation devices. iv CONTENTS EXECUTIVE SUMMARY...Josephson effect makes these measurements useful for characterization and calibration of superconducting quantum memory and computational devices
NASA Astrophysics Data System (ADS)
Costa, Andreas; Högl, Petra; Fabian, Jaroslav
2017-01-01
We study theoretically the effects of interfacial Rashba and Dresselhaus spin-orbit coupling in superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions—with allowing for tunneling barriers between the ferromagnetic and superconducting layers—by solving the Bogoljubov-de Gennes equation for realistic heterostructures and applying the Furusaki-Tsukada technique to calculate the electric current at a finite temperature. The presence of spin-orbit couplings leads to out-of-plane and in-plane magnetoanisotropies of the Josephson current, which are giant in comparison to current magnetoanisotropies in similar normal-state ferromagnet/normal metal (F/N) junctions. Especially huge anisotropies appear in the vicinity of 0 -π transitions, caused by the exchange-split bands in the ferromagnetic metal layer. We also show that the direction of the Josephson critical current can be controlled (inducing 0 -π transitions) by the strength of the spin-orbit coupling and, more crucial, by the orientation of the magnetization. Such a control can bring new functionalities into Josephson junction devices.
Wendt, J.R.; Tigges, C.P.; Hietala, V.M.; Plut, T.A.; Martens, J.S.; Char, K.; Johansson, M.E.
1994-03-01
A well-controlled, high-yield Josephson junction process in high temperature superconductors (HTS) is necessary for the demonstration of ultra-high-speed devices and circuits which exceed the capabilities of conventional electronics. The authors developed nanobridge Josephson junctions in high quality thin-film YBaCuO with dimensions below 100 nm fabricated using electron-beam nanolithography. They characterized this Josephson junction technology for process yield, junction parameter uniformity, and overall applicability for use in high-performance circuits. To facilitate the determination of junction parameters, they developed a measurement technique based on spectral analysis in the range of 90--160 GHz of phase-locked, oscillating arrays of up to 2,450 Josephson junctions. Because of the excellent yield and uniformity of the nanobridge junctions, they successfully applied the junction technology to a wide variety of circuits. These circuits included transmission-line pulse formers and 32 and 64-bit shift registers. The 32-bit shift register was shown to operate at clock speeds near 100 GHz and is believed to be one of the faster and more complex digital circuit demonstrated to date using high temperature superconductor technology.
Resonance tunneling of cooper pairs in a superconductor-polymer-superconductor josephson junction
Ionov, A. I.
2013-05-15
It is shown that the superconducting current flowing though a polymer in a superconductor-polymer-superconductor Josephson structure is due to resonant tunneling of Cooper pairs. The critical current and the thickness of the polymer in which the superconducting current is observed depend on the coherence length of a Cooper pair in the superconductor contacting the polymer.
Josephson current through a quantum dot coupled to a Majorana zero mode
NASA Astrophysics Data System (ADS)
Tang, Han-Zhao; Zhang, Ying-Tao; Liu, Jian-Jun
2016-05-01
Employing the Green’s function method, we investigate the Josephson current through a quantum dot side coupled to a topological superconducting nanowire sustaining a pair of Majorana zero modes. It is found that the Josephson current is blocked when the quantum dot is side coupled to a superconducting nanowire in a topologically trivial phase. However, when the topological superconducting nanowire transitions from a topologically trivial to a topologically non-trivial phase, an Andreev bound state arises at the zero Fermi energy of the quantum dot due to leakage of the Majorana zero mode. Thus a Josephson current can be induced by leakage of the Majorana zero mode into the quantum dot. The Josephson current shows a plateau-like structure and a clear-cut trivial/non-trivial phase transition, as a function of a Zeeman field imposed on the system. The transition and plateau-like structure can be used to probe the existence of the Majorana zero mode. The current-phase relation has also been studied.
Josephson Phase Qubit Circuit for the Evaluation of Advanced Tunnel Barrier Materials
2008-11-21
gradiometer loop. An overlapped gradiometer three- junction direct current superconducting quantum interference device (SQUID) with 64 pH mutual...qubit circuit. (a) Micrograph of an individual qubit circuit consisting of a Josephson junction in a gradiometer loop, state readout measurement
Magnetic Field Dependence of the Critical Current of Planar Geometry Josephson Junctions
NASA Astrophysics Data System (ADS)
Ma, Meng; Cho, Ethan; Huynh, Chuong; Cybart, Shane; Dynes, Robert
2015-03-01
We report a study on the magnetic field dependence of the critical current of planar geometry Josephson junctions. We have fabricated Josephson junctions by using a focused helium ion beam to irradiate a narrow barrier in the plane of a 25 nm thick Y-Ba-Cu-O film. The London penetration depth λL is large (~1 μm) because of the ultra-thin thickness of the film. As a result, calculations of the Josephson penetration depth λJ are not realistic nor physical. Therefore in this work, we measure λJ experimentally. We tested devices with bridge widths ranging from 4 to 50 μm, and present measurements of the Fraunhofer quantum diffraction pattern (IC (B)). We observe a crossover from short to long junction behavior, which gives an experimentally measured λJ that ranges between 3 μm to 5 μm. The shape of the IC (B) pattern is strongly affected by the width of the bridge because of self-field effects. As the bridge width increases, Josephson vortices enter the junction and skew the patterns. This work shows that the electronic properties of the planar junctions are very different than those classical ``sandwich'' junctions due to the differences in geometry.
High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O
Ginley, David S.; Hietala, Vincent M.; Hohenwarter, Gert K. G.; Martens, Jon S.; Plut, Thomas A.; Tigges, Chris P.; Vawter, Gregory A.; Zipperian, Thomas E.
1994-10-25
A process for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO.sub.3 crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O.sub.3, followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry.
High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O
Ginley, D.S.; Hietala, V.M.; Hohenwarter, G.K.G.; Martens, J.S.; Plut, T.A.; Tigges, C.P.; Vawter, G.A.; Zipperian, T.E.
1994-10-25
A process is disclosed for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO[sub 3] crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O[sub 3], followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry. 8 figs.
A closed cycle cascade Joule Thomson refrigerator for cooling Josephson junction magnetometers
NASA Technical Reports Server (NTRS)
Tward, E.; Sarwinski, R.
1985-01-01
A closed cycle cascade Joule Thomson refrigerator designed to cool Josephson Junction magnetometers to liquid helium temperature is being developed. The refrigerator incorporates 4 stages of cooling using the working fluids CF4 and He. The high pressure gases are provided by a small compressor designed for this purpose. The upper stages have been operated and performance will be described.
NbN Josephson and Tunnel Junctions for Space THz Observation and Signal Processing
2005-07-13
jonctions Josephson en nitrures supraconducteurs (TiN et NbN) ; application à la logique RSFQ, Ph.D. thesis, SPSMS/LCP CEA - Grenoble and DEMIRM...Accepted for Publication in June 2005. [14] V. Larrey, Etude et réalisation de jonctions SIS à base de nitrure de niobium et d’une barrière tunnel
Weaknesses in Underperforming Schools
ERIC Educational Resources Information Center
van de Grift, Wim; Houtveen, Thoni
2007-01-01
In some Dutch elementary schools, the average performance of students over several years is significantly below the level that could be expected of them. This phenomenon is known as "underperformance." The most important identifiable weaknesses that go along with this phenomenon are that (a) learning material offered at school is…
Fluxon dynamics in two-gap superconductor-based long Josephson junction
NASA Astrophysics Data System (ADS)
Ghimire, Bal Ram
A superconducting tunnel junction with two-gap superconductors, such as MgB2 and iron-based superconductors, can lead to more interesting phase dynamics than those with one-gap superconductors. The phase dynamics in a long Josephson junction (LJJ) may be described by using the sine-Gordon equation. The difference in the phase dynamics between the LJJ with two-gap superconductors and that with the one-gap superconductors arises due to the presence of multiple tunneling channels between the superconductor (S) layers and the inter-band Josephson effect within the same S layer. The inter-band Josephson effect leads to both spatial and temporal modulation of the critical current between the two adjacent S layers. In this work, the effects of critical current modulation on the trajectories of the single Josephson vortex (i.e., fluxon) and the current-voltage characteristics of the two-gap superconductor-based LJJ are estimated. Also, the possibility of a broken time-reversal symmetry state ground state of a single LJJ due to the presence of additional tunneling channels is investigated by using a microscopic model for two-gap superconductors. The consequence of this broken time reversal ground state is discussed. Finally, the equation of motion for fluxon for coupled LJJs interacting via both the magnetic induction effect and charging effect is investigated. As the inter-band Josephson effect is found to affect the dynamics of a single fluxon in a single LJJ, this effect is explicitly taken into account for a two-coupled LJJ stack. This equation of motion is expected to be an excellent starting point for exploring interesting LJJ properties such as collective dynamics of fluxons as well as fractional fluxons.
Weak Finsler structures and the Funk weak metric
NASA Astrophysics Data System (ADS)
Papadopoulos, Athanase; Troyanov, Marc
2009-04-01
We discuss general notions of metrics and of Finsler structures which we call weak metrics and weak Finsler structures. Any convex domain carries a canonical weak Finsler structure, which we call its tautological weak Finsler structure. We compute distances in the tautological weak Finsler structure of a domain and we show that these are given by the so-called Funk weak metric. We conclude the paper with a discussion of geodesics, of metric balls and of convexity properties of the Funk weak metric.
NASA Astrophysics Data System (ADS)
Pires, Sandrine; Starck, Jean-Luc; Leonard, Adrienne; Réfrégier, Alexandre
2012-03-01
This chapter reviews the data mining methods recently developed to solve standard data problems in weak gravitational lensing. We detail the different steps of the weak lensing data analysis along with the different techniques dedicated to these applications. An overview of the different techniques currently used will be given along with future prospects. Until about 30 years ago, astronomers thought that the Universe was composed almost entirely of ordinary matter: protons, neutrons, electrons, and atoms. The field of weak lensing has been motivated by the observations made in the last decades showing that visible matter represents only about 4-5% of the Universe (see Figure 14.1). Currently, the majority of the Universe is thought to be dark, that is, does not emit electromagnetic radiation. The Universe is thought to be mostly composed of an invisible, pressure less matter - potentially relic from higher energy theories - called "dark matter" (20-21%) and by an even more mysterious term, described in Einstein equations as a vacuum energy density, called "dark energy" (70%). This "dark" Universe is not well described or even understood; its presence is inferred indirectly from its gravitational effects, both on the motions of astronomical objects and on light propagation. So this point could be the next breakthrough in cosmology. Today's cosmology is based on a cosmological model that contains various parameters that need to be determined precisely, such as the matter density parameter Omega_m or the dark energy density parameter Omega_lambda. Weak gravitational lensing is believed to be the most promising tool to understand the nature of dark matter and to constrain the cosmological parameters used to describe the Universe because it provides a method to directly map the distribution of dark matter (see [1,6,60,63,70]). From this dark matter distribution, the nature of dark matter can be better understood and better constraints can be placed on dark energy
Paik, Hanhee; Schuster, D I; Bishop, Lev S; Kirchmair, G; Catelani, G; Sears, A P; Johnson, B R; Reagor, M J; Frunzio, L; Glazman, L I; Girvin, S M; Devoret, M H; Schoelkopf, R J
2011-12-09
Superconducting quantum circuits based on Josephson junctions have made rapid progress in demonstrating quantum behavior and scalability. However, the future prospects ultimately depend upon the intrinsic coherence of Josephson junctions, and whether superconducting qubits can be adequately isolated from their environment. We introduce a new architecture for superconducting quantum circuits employing a three-dimensional resonator that suppresses qubit decoherence while maintaining sufficient coupling to the control signal. With the new architecture, we demonstrate that Josephson junction qubits are highly coherent, with T2 ∼ 10 to 20 μs without the use of spin echo, and highly stable, showing no evidence for 1/f critical current noise. These results suggest that the overall quality of Josephson junctions in these qubits will allow error rates of a few 10(-4), approaching the error correction threshold.
Suzuki, M.
1988-04-01
Dynamical mechanism of composite W and Z is studied in a 1/N field theory model with four-fermion interactions in which global weak SU(2) symmetry is broken explicitly by electromagnetic interaction. Issues involved in such a model are discussed in detail. Deviation from gauge coupling due to compositeness and higher order loop corrections are examined to show that this class of models are consistent not only theoretically but also experimentally.
Weakly supervised glasses removal
NASA Astrophysics Data System (ADS)
Wang, Zhicheng; Zhou, Yisu; Wen, Lijie
2015-03-01
Glasses removal is an important task on face recognition, in this paper, we provide a weakly supervised method to remove eyeglasses from an input face image automatically. We choose sparse coding as face reconstruction method, and optical flow to find exact shape of glasses. We combine the two processes iteratively to remove glasses more accurately. The experimental results reveal that our method works much better than these algorithms alone, and it can remove various glasses to obtain natural looking glassless facial images.
Transport in arrays of submicron Josephson junctions over a ground plane
Ho, Teressa Rae
1997-12-01
One-dimensional (1D) and two-dimensional (2D) arrays of Al islands linked by submicron Al/Al_{x}O_{y}/Al tunnel junctions were fabricated on an insulating layer grown on a ground plane. The arrays were cooled to temperatures as low as 20 mK where the Josephson coupling energy E_{J} of each junction and the charging energy E_{C} of each island were much greater than the thermal energy k_{B}T. The capacitance C_{g} between each island and the ground plane was much greater than the junction capacitance C. Two classes of arrays were studied. In the first class, the normal state tunneling resistance of the junctions was much larger than the resistance quantum for single electrons, R_{N}>> R_{Qe}≡ h/e^{2} ~ 25.8 kΩ, and the islands were driven normal by an applied magnetic field such that E_{J} = 0 and the array was in the Coulomb blockade regime. The arrays were made on degenerately-doped Si, thermally oxidized to a thickness of approximately 100 nm. The current-voltage (I - V) characteristics of a 1D and a 2D array were measured and found to display a threshold voltage V_{T} below which little current flows. In the second class of arrays, the normal state tunneling resistance of the junctions was close to the resistance quantum for Cooper pairs, R_{N}≈R_{Q}≡h/4e^{2}≈6.45kΩ, such that E_{J}/E_{C}≈1. The arrays were made on GaAs/Al_{0.3}Ga_{0.7}As heterostructures with a two-dimensional electron gas approximately 100 nm below the surface. One array displayed superconducting behavior at low temperature. Two arrays displayed insulating behavior at low temperature, and the size of the Coulomb gap increased with increasing R_{g}.
Josephson Parametric Amplification for Circuit Quantum Electrodynamics: Theory and Implementation
2013-05-01
cavity’s resonance frequency. By probing the cavity near resonance with a signal weak enough not to disturb the qubit, one can reliably read out the...amplifier having its own strengths and weaknesses . As a result, in very recent years, impressive experiments have been enabled by such amplifiers...T = 10 mK, ∆AlkT is a few hundred. For niobium , ∆Nb ≈ 31 × 10−4 eV [52], so that ∆NbkT is a few thousand. Also, compared to cavity drive photon
NASA Astrophysics Data System (ADS)
Tsui, Ophelia Kwan Chui
A novel magnetic resonance is observed in Bi_2Sr_2CaCu_2O_{8+ delta} single crystals exposed to microwave radiation (26 to 95 GHz) in the presence of a magnetic field. The resonance exhibits unconventional field and temperature dependence. At a fixed temperature below the melting transition of the vortex solid, T_ {m}(B), the resonance frequency decreases with the applied field and displays a power-law dependence, viz. omega~ B^{-mu }. The exponent was found to be 0.8 within 10% across all samples and temperatures studied. However, when the temperature is increased above T_ {m}(B), mu becomes sample dependent and is equal to 0.64 and 1.08 for the two samples studied. At fixed microwave frequencies, the resonance field, B_0 increases exponentially with temperature to a maximum at T_{m }(B) and decreases slowly with temperature above. We attribute the resonance to Josephson plasma oscillations excited along the sample c-axis. The model explains many features of the experiment. Recently, Bulaevskii et al. proposed an explanation for the field dependence of the Josephson plasma frequency. By assuming that disorder in vortex pancakes is caused by strong pinning at low temperatures, the authors obtained the power-law dependence of omega on B, which agrees with the experiment. Rotating the microwave E-field, { bf E}_{rf} relatively to the sample, we find maximum resonance absorption when {bf E}_{rf} has the maximum projection along the sample c-axis, and minimum when there is none. This identification of {bf E}_{rf} parallel to the sample c-axis as the one responsible for the resonance, supports the Josephson plasma hypothesis. The strongest evidence for the Josephson plasma model is obtained by tilting the magnetic field close to alignment with the ab-plane of the crystal. In that case, an unusual re-entrant cusp in B_0 is observed when the tilt angle is in the range -5.5^circ to 5.5^circ. This is consistent with Bulaevskii et al.'s calculation. They propose that pancake
Weakly broken galileon symmetry
Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico; Vernizzi, Filippo
2015-09-01
Effective theories of a scalar ϕ invariant under the internal galileon symmetryϕ→ϕ+b{sub μ}x{sup μ} have been extensively studied due to their special theoretical and phenomenological properties. In this paper, we introduce the notion of weakly broken galileon invariance, which characterizes the unique class of couplings of such theories to gravity that maximally retain their defining symmetry. The curved-space remnant of the galileon’s quantum properties allows to construct (quasi) de Sitter backgrounds largely insensitive to loop corrections. We exploit this fact to build novel cosmological models with interesting phenomenology, relevant for both inflation and late-time acceleration of the universe.
Cartron, J. P.; Gerbal, A.; Hughes-Jones, N. C.; Salmon, C.
1974-01-01
Thirty-five weak A samples including fourteen A3, eight Ax, seven Aend, three Am and three Ae1 were studied in order to determine their A antigen site density, using an IgG anti-A labelled with 125I. The values obtained ranged between 30,000 A antigen sites for A3 individuals, and 700 sites for the Ae1 red cells. The hierarchy of values observed made it possible to establish a quantitative relationship between the red cell agglutinability of these phenotypes measured under standard conditions, and their antigen site density. PMID:4435836
Superconducting quantum-interference devices
NASA Technical Reports Server (NTRS)
Peters, P. N.; Holdeman, L. B.
1975-01-01
Published document discusses devices which are based on weak-link Josephson elements that join superconductors. Links can take numerous forms, and circuitry utilizing links can perform many varied functions with unprecedented sensitivity. Theoretical review of Josephson's junctions include tunneling junctions, point contact devices, microbridges, and proximity-effect devices.
Experimental demonstration of Aharonov-Casher interference in a Josephson junction circuit
NASA Astrophysics Data System (ADS)
Pop, I. M.; Douçot, B.; Ioffe, L.; Protopopov, I.; Lecocq, F.; Matei, I.; Buisson, O.; Guichard, W.
2012-03-01
A neutral quantum particle with magnetic moment encircling a static electric charge acquires a quantum-mechanical phase (Aharonov-Casher effect). In superconducting electronics, the neutral particle becomes a fluxon that moves around superconducting islands connected by Josephson junctions. The full understanding of this effect in systems of many junctions is crucial for the design of novel quantum circuits. Here, we present measurements and quantitative analysis of fluxon interference patterns in a six Josephson junction chain. In this multijunction circuit, the fluxon can encircle any combination of charges on five superconducting islands, resulting in a complex pattern. We compare the experimental results with predictions of a simplified model that treats fluxons as independent excitations and with the results of the full diagonalization of the quantum problem. Our results demonstrate the accuracy of the fluxon interference description and the quantum coherence of these arrays.
Traveling wave parametric amplifier with Josephson junctions using minimal resonator phase matching
White, T. C.; Mutus, J. Y.; Hoi, I.-C.; Barends, R.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Martinis, John M.; Megrant, A.; Chaudhuri, S.; and others
2015-06-15
Josephson parametric amplifiers have become a critical tool in superconducting device physics due to their high gain and quantum-limited noise. Traveling wave parametric amplifiers (TWPAs) promise similar noise performance, while allowing for significant increases in both bandwidth and dynamic range. We present a TWPA device based on an LC-ladder transmission line of Josephson junctions and parallel plate capacitors using low-loss amorphous silicon dielectric. Crucially, we have inserted λ/4 resonators at regular intervals along the transmission line in order to maintain the phase matching condition between pump, signal, and idler and increase gain. We achieve an average gain of 12 dB across a 4 GHz span, along with an average saturation power of −92 dBm with noise approaching the quantum limit.
Josephson-based full digital bridge for high-accuracy impedance comparisons
NASA Astrophysics Data System (ADS)
Overney, Frédéric; Flowers-Jacobs, Nathan E.; Jeanneret, Blaise; Rüfenacht, Alain; Fox, Anna E.; Underwood, Jason M.; Koffman, Andrew D.; Benz, Samuel P.
2016-08-01
This paper describes a Josephson-based full digital impedance bridge capable of comparing any two impedances, regardless of type (R-C, R-L, or L-C), over a large frequency range (from 1 kHz to 20 kHz). At the heart of the bridge are two Josephson arbitrary waveform synthesizer systems that offer unprecedented flexibility in high-precision impedance calibration, that is, it can compare impedances with arbitrary ratios and phase angles. Thus this single bridge can fully cover the entire complex plane. In the near future, this type of instrument will considerably simplify the realization and maintenance of the various impedance scales in many National Metrology Institutes around the world. Contribution of the National Institute of Standards and Technology, US Department of Commerce, not subject to copyright in the United States.
Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes
NASA Astrophysics Data System (ADS)
Gharavi, Kaveh; Holloway, Gregory W.; LaPierre, Ray R.; Baugh, Jonathan
2017-02-01
The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies t∼ 0.7 are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterised by a dissipationless current up to ∼100 nA, and (ii) the quantum dot (QD) regime, characterised by the formation of Andreev bound states (ABS) associated with spontaneous QDs inside the nanowire channel. In regime (i), the behaviour of the critical current I c versus an axial magnetic field {B}| | shows an unexpected modulation and persistence to fields > 2 T. In the QD regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed.
Modeling the switching processes in the Josephson AND and OR logic gates
NASA Astrophysics Data System (ADS)
Tyhanskyi, M. V.; Krysko, R. R.
2013-02-01
We propose a design principle of digital logic gates based on Josephson cryotrons. The operation mode of digital logic gates AND and OR based on tunnel junctions "superconductor-insulator-superconductor" was described. Mathematical models of the switching processes in the logic elements were developed, the transient characteristics during the logic state change were calculated, and the basic parameters of these models were determined. It was shown that digital logic gates "AND" and "OR" can be realized based on individual Josephson cryotrons and their logic state can be controlled by using current pulses as control inputs. Such logic gates satisfy all the requirements for digital logic elements and have switching time of about 2-3 ps.
Thickness dependent interlayer transport in vertical MoS2 Josephson junctions
NASA Astrophysics Data System (ADS)
Island, Joshua O.; Steele, Gary A.; van der Zant, Herre S. J.; Castellanos-Gomez, Andres
2016-09-01
We report on observations of thickness dependent Josephson coupling and multiple Andreev reflections (MAR) in vertically stacked molybdenum disulfide (MoS2)—molybdenum rhenium (MoRe) Josephson junctions. MoRe, a chemically inert superconductor, allows for oxide free fabrication of high transparency vertical MoS2 devices. Single and bilayer MoS2 junctions display relatively large critical currents (up to 2.5 μA) and the appearance of sub-gap structure given by MAR. In three and four layer thick devices we observe orders of magnitude lower critical currents (sub-nA) and reduced quasiparticle gaps due to proximitized MoS2 layers in contact with MoRe. We anticipate that this device architecture could be easily extended to other 2D materials.
One-dimensional Josephson arrays as superlattices for single Cooper pairs
NASA Astrophysics Data System (ADS)
Odintsov, A. A.
1996-07-01
We investigate uniform one-dimensional arrays of small Josephson junctions [EJ<
One-dimensional Josephson arrays as superlattices for single Cooper pairs
NASA Astrophysics Data System (ADS)
Odintsov, Arkadi
1996-03-01
We investigate uniform one-dimensional arrays of small Josephson junctions (EJ << E_C, EC = (2e)^2/2C) with a realistic Coulomb interaction U(x) = EC λ exp( - |x|/λ) (here λ >> 1 is the screening length in units of the lattice constant of the array). At low energies this system can be described in terms of interacting Bose particles (extra single Cooper pairs) on the lattice. With increasing concentration ν of extra Cooper pairs, a crossover from the Bose gas phase to the Wigner crystal phase and then to the superlattice regime occurs. The phase diagram in the superlattice regime consists of commensurable insulating phases with ν = 1/l (l is integer) separated by superconducting regions where the current is carried by excitations with fractional electric charge q = ± 2e/l. The Josephson current through a ring-shaped array pierced by magnetic flux is calculated for all of the phases.
Phase retrapping in a φ Josephson junction: Onset of the butterfly effect
NASA Astrophysics Data System (ADS)
Menditto, R.; Sickinger, H.; Weides, M.; Kohlstedt, H.; Žonda, M.; Novotný, T.; Koelle, D.; Kleiner, R.; Goldobin, E.
2016-05-01
We investigate experimentally the retrapping of the phase in a φ Josephson junction upon return of the junction to the zero-voltage state. Since the Josephson energy profile U0(ψ ) in φ JJ is a 2 π periodic double-well potential with minima at ψ =±φ mod2 π , the question is at which of the two minima -φ or +φ the phase will be trapped upon return from a finite voltage state during quasistatic decrease of the bias current (tilt of the potential). By measuring the relative population of two peaks in escape histograms, we determine the probability of phase trapping in the ±φ wells for different temperatures. Our experimental results agree qualitatively with theoretical predictions. In particular, we observe an onset of the butterfly effect with an oscillating probability of trapping. Unexpectedly, this probability saturates at a value different from 50% at low temperatures.
Band-gaps in long Josephson junctions with periodic phase-shifts
NASA Astrophysics Data System (ADS)
Ahmad, Saeed; Susanto, Hadi; Wattis, Jonathan A. D.
2017-04-01
We investigate analytically and numerically a long Josephson junction on an infinite domain, having arbitrary periodic phase shift of κ, that is, the so-called 0-κ long Josephson junction. The system is described by a one-dimensional sine-Gordon equation and has relatively recently been proposed as artificial atom lattices. We discuss the existence of periodic solutions of the system and investigate their stability both in the absence and presence of an applied bias current. We find critical values of the phase-discontinuity and the applied bias current beyond which static periodic solutions cease to exist. Due to the periodic discontinuity in the phase, the system admits regions of allowed and forbidden bands. We perturbatively investigate the Arnold tongues that separate the region of allowed and forbidden bands, and discuss the effect of an applied bias current on the band-gap structure. We present numerical simulations to support our analytical results.
Yokoyama, Tomohiro; Eto, Mikio; Nazarov, Yuli V.
2013-12-04
We theoretically study the current-phase relation in semiconductor nanowire Josephson junction in the presence of spin-orbit interaction. In the nanowire, the impurity scattering with strong SO interaction is taken into account using the random matrix theory. In the absence of magnetic field, the Josephson current I and phase difference φ between the superconductors satisfy the relation of I(φ) = –I(–φ). In the presence of magnetic field along the nanowire, the interplay between the SO interaction and Zeeman effect breaks the current-phase relation of I(φ) = –I(–φ). In this case, we show that the critical current depends on the current direction, which qualitatively agrees with recent experimental findings.
Understanding the Josephson current through a Kondo-correlated quantum dot.
Luitz, D J; Assaad, F F; Novotný, T; Karrasch, C; Meden, V
2012-06-01
We study the Josephson current 0-π transition of a quantum dot tuned to the Kondo regime. The physics can be quantitatively captured by the numerically exact continuous time quantum Monte Carlo method applied to the single-impurity Anderson model with Bardeen-Cooper-Schrieffer superconducting leads. For a comparison to an experiment, the tunnel couplings are determined by fitting the normal-state linear conductance. Excellent agreement for the dependence of the critical Josephson current on the level energy is achieved. For increased tunnel couplings the Kondo scale becomes comparable to the superconducting gap, and the regime of the strongest competition between superconductivity and Kondo correlations is reached; we predict the gate voltage dependence of the critical current in this regime.
Quantum state engineering with flux-biased Josephson phase qubits by rapid adiabatic passages
NASA Astrophysics Data System (ADS)
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.
Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K
NASA Astrophysics Data System (ADS)
Du, Jia; Hellicar, A. D.; Hanham, S. M.; Li, L.; Macfarlane, J. C.; Leslie, K. E.; Foley, C. P.
2011-05-01
A high-Tc superconducting (HTS) broadband Josephson detector has been developed and applied to millimetre wave (mm-wave) and terahertz (THz) imaging. The detector is based on a YBa2Cu3O7-x (YBCO) step-edge Josephson junction, which is coupled to a thin-film log-periodic antenna, designed for operation at 200-600 GHz, and a hemispheric silicon lens. The junction parameters have been optimised to achieve a high IcRn value so that the detector responds well to the specified frequencies at liquid nitrogen temperature (77 K). Images at ˜200 GHz and ˜600 GHz were acquired with the same detector; each demonstrated their unique properties. The results demonstrate the potential of achieving a cheaper, compact and portable multi-spectral imager based on a HTS detector.
Nambu-Goldstone modes and the Josephson supercurrent in the bilayer quantum Hall system
NASA Astrophysics Data System (ADS)
Hama, Yusuke; Tsitsishvili, George; Ezawa, Zyun F.
2013-05-01
An interlayer phase coherence develops spontaneously in the bilayer quantum Hall system at the filling factor ν = 1. On the other hand, the spin and pseudospin degrees of freedom are entangled coherently in the canted antiferromagnetic phase of the bilayer quantum Hall system at the filling factor ν = 2. There emerges a complex Nambu-Goldstone mode with a linear dispersion in the zero tunneling-interaction limit for both cases. Then its phase field provokes a Josephson supercurrent in each layer, which is dissipationless as in a superconductor. We study what kind of phase coherence the Nambu-Goldstone mode develops in association with the Josephson supercurrent and its effect on the Hall resistance in the bilayer quantum Hall system at ν = 1, 2, by employing the Grassmannian formalism.
Traveling wave parametric amplifier with Josephson junctions using minimal resonator phase matching
NASA Astrophysics Data System (ADS)
White, T. C.; Mutus, J. Y.; Hoi, I.-C.; Barends, R.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; Chaudhuri, S.; Gao, J.; Martinis, John M.
2015-06-01
Josephson parametric amplifiers have become a critical tool in superconducting device physics due to their high gain and quantum-limited noise. Traveling wave parametric amplifiers (TWPAs) promise similar noise performance, while allowing for significant increases in both bandwidth and dynamic range. We present a TWPA device based on an LC-ladder transmission line of Josephson junctions and parallel plate capacitors using low-loss amorphous silicon dielectric. Crucially, we have inserted λ/4 resonators at regular intervals along the transmission line in order to maintain the phase matching condition between pump, signal, and idler and increase gain. We achieve an average gain of 12 dB across a 4 GHz span, along with an average saturation power of -92 dBm with noise approaching the quantum limit.
Weakly relativistic plasma expansion
Fermous, Rachid Djebli, Mourad
2015-04-15
Plasma expansion is an important physical process that takes place in laser interactions with solid targets. Within a self-similar model for the hydrodynamical multi-fluid equations, we investigated the expansion of both dense and under-dense plasmas. The weakly relativistic electrons are produced by ultra-intense laser pulses, while ions are supposed to be in a non-relativistic regime. Numerical investigations have shown that relativistic effects are important for under-dense plasma and are characterized by a finite ion front velocity. Dense plasma expansion is found to be governed mainly by quantum contributions in the fluid equations that originate from the degenerate pressure in addition to the nonlinear contributions from exchange and correlation potentials. The quantum degeneracy parameter profile provides clues to set the limit between under-dense and dense relativistic plasma expansions at a given density and temperature.
Cleland, A.N.
1991-04-01
Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q {approx} 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement.
Aharonov-Casher effect for plasmons in a ring of Josephson junctions
NASA Astrophysics Data System (ADS)
Süsstrunk, Roman; Garate, Ion; Glazman, Leonid I.
2013-08-01
Phase slips in a one-dimensional closed array of Josephson junctions hybridize the persistent current states and plasmon branches of excitations. The interference between phase slips passing through different junctions of the array makes the hybridization sensitive to the charges of the superconducting islands comprising the array. This in turn results in the Aharonov-Casher effect for plasmons, which in the absence of phase slips are insensitive to island charges.
Dynamical simulations of fractional giant Shapiro steps in two-dimensional Josephson arrays
Free, J.U.; Benz, S.P.; Rzchowski, M.S.; Tinkham, M.; Lobb, C.J. Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 ); Octavio, M. )
1990-04-01
We have performed computer simulations of arrays of resistively shunted Josephson junctions in the presence of commensurate magnetic fields and alternating and direct currents. We have found {ital fractional} giant Shapiro steps in the simulated current-voltage characteristics in agreement with recent experimental measurements. The detailed motion of the magnetic-field-induced vortices is shown to be in agreement with a previously proposed phenomenological model of Benz {ital et} {ital al}. (Phys. Rev. Lett. 64, 693 (1990)).
The Bose-Hubbard model: from Josephson junction arrays to optical lattices
NASA Astrophysics Data System (ADS)
Bruder, C.; Fazio, R.; Schön, G.
2005-09-01
[Dedicated to Bernhard Mühlschlegel on the occasion ofhis 80th birthday]The Bose-Hubbard model is a paradigm for the study of strongly correlated bosonic systems. We review some of its properties with emphasis on the implications on quantum phase transitions of Josephson junction arrays and quantum dynamics of topological excitations as well as the properties of ultra-cold atoms in optical lattices.
Vortex motion rectification in Josephson junction arrays with a ratchet potential.
Shalóm, D E; Pastoriza, H
2005-05-06
By means of electrical transport measurements we have studied the rectified motion of vortices in ratchet potentials engineered on overdamped Josephson junction arrays. The rectified voltage as a function of the vortex density shows a maximum efficiency close a matching condition to the period of the ratchet potential indicating a collective vortex motion. Vortex current reversals were detected varying the driving force and vortex density revealing the influence of vortex-vortex interaction in the ratchet effect.
A high-speed Analog-to-Digital converter using Josephson Self-Gating-AND comparators
NASA Astrophysics Data System (ADS)
Petersen, D. A.; Ho, H.; Jewett, R. E.; Nakajima, K.; Nandakumar, V.; Spargo, J. W.; van Duzer, T.
1985-03-01
A Josephson Analog-to-Digital (A/D) converter which employs Self-Gating-AND (SGA) circuits as comparators has been designed and experimentally investigated. A functional description of the SGA is presented and the design of a four-bit A/D converter is described. High-speed measurements demonstrate four-bit quantization of 280 MHz sinusiodal inputs, and three-bit quantization of 499 MHz inputs at a 1.0 GHz conversion rate.
Monaco, R; Mygind, J; Rivers, R J
2002-08-19
Phase transitions create a domain structure with defects, which has been argued by Zurek and Kibble (ZK) to depend in a characteristic way on the quench rate. We present an experiment to measure the ZK scaling exponent sigma. Using long symmetric Josephson tunnel junctions, for which the predicted index is sigma=0.25, we find sigma=0.27+/-0.05. Further, we agree with the ZK prediction for the overall normalization.
Octavio, M. ); Free, J.U. Physics Department, Harvard University, Cambridge, Massachusetts ); Benz, S.P. ); Newrock, R.S.; Mast, D.B. ); Lobb, C.J. )
1991-09-01
We present simulations of two-dimensional Josephson-junction arrays to study giant Shapiro steps in these arrays. The amplitude and frequency dependence of the step widths is found to be more complex than in single junctions. The fractional step widths are found to decrease more rapidly with increasing frequency or rf current than conventional steps in single junctions. The washboard model of single junctions is extended to arrays to explain these differences between arrays and single junctions.
Universal quantum fluctuations of a cavity mode driven by a Josephson junction.
Armour, A D; Blencowe, M P; Brahimi, E; Rimberg, A J
2013-12-13
We analyze the quantum dynamics of a superconducting cavity coupled to a voltage-biased Josephson junction. The cavity is strongly excited at resonances where the voltage energy lost by a Cooper pair traversing the circuit is a multiple of the cavity photon energy. We find that the resonances are accompanied by substantial squeezing of the quantum fluctuations of the cavity over a broad range of parameters and are able to identify regimes where the fluctuations in the system take on universal values.
Horizontal gene transfer in eukaryotes: The weak-link model
Huang, Jinling
2013-01-01
The significance of horizontal gene transfer (HGT) in eukaryotic evolution remains controversial. Although many eukaryotic genes are of bacterial origin, they are often interpreted as being derived from mitochondria or plastids. Because of their fixed gene pool and gene loss, however, mitochondria and plastids alone cannot adequately explain the presence of all, or even the majority, of bacterial genes in eukaryotes. Available data indicate that no insurmountable barrier to HGT exists, even in complex multicellular eukaryotes. In addition, the discovery of both recent and ancient HGT events in all major eukaryotic groups suggests that HGT has been a regular occurrence throughout the history of eukaryotic evolution. A model of HGT is proposed that suggests both unicellular and early developmental stages as likely entry points for foreign genes into multicellular eukaryotes. PMID:24037739
Strengthening the weak link: Built Environment modelling for loss analysis
NASA Astrophysics Data System (ADS)
Millinship, I.
2012-04-01
Methods to analyse insured losses from a range of natural perils, including pricing by primary insurers and catastrophe modelling by reinsurers, typically lack sufficient exposure information. Understanding the hazard intensity in terms of spatial severity and frequency is only the first step towards quantifying the risk of a catastrophic event. For any given event we need to know: Are any structures affected? What type of buildings are they? How much damaged occurred? How much will the repairs cost? To achieve this, detailed exposure information is required to assess the likely damage and to effectively calculate the resultant loss. Modelling exposures in the Built Environment therefore plays as important a role in understanding re/insurance risk as characterising the physical hazard. Across both primary insurance books and aggregated reinsurance portfolios, the location of a property (a risk) and its monetary value is typically known. Exactly what that risk is in terms of detailed property descriptors including structure type and rebuild cost - and therefore its vulnerability to loss - is often omitted. This data deficiency is a primary source of variations between modelled losses and the actual claims value. Built Environment models are therefore required at a high resolution to describe building attributes that relate vulnerability to property damage. However, national-scale household-level datasets are often not computationally practical in catastrophe models and data must be aggregated. In order to provide more accurate risk analysis, we have developed and applied a methodology for Built Environment modelling for incorporation into a range of re/insurance applications, including operational models for different international regions and different perils and covering residential, commercial and industry exposures. Illustrated examples are presented, including exposure modelling suitable for aggregated reinsurance analysis for the UK and bespoke high resolution modelling for industrial sites in Germany. A range of attributes are included following detailed claims analysis and engineering research with property type, age and condition identified as important differentiators of damage from flood, wind and freeze events.
Horizontal gene transfer in eukaryotes: the weak-link model.
Huang, Jinling
2013-10-01
The significance of horizontal gene transfer (HGT) in eukaryotic evolution remains controversial. Although many eukaryotic genes are of bacterial origin, they are often interpreted as being derived from mitochondria or plastids. Because of their fixed gene pool and gene loss, however, mitochondria and plastids alone cannot adequately explain the presence of all, or even the majority, of bacterial genes in eukaryotes. Available data indicate that no insurmountable barrier to HGT exists, even in complex multicellular eukaryotes. In addition, the discovery of both recent and ancient HGT events in all major eukaryotic groups suggests that HGT has been a regular occurrence throughout the history of eukaryotic evolution. A model of HGT is proposed that suggests both unicellular and early developmental stages as likely entry points for foreign genes into multicellular eukaryotes.
Modeling of LC-shunted intrinsic Josephson junctions in high-T c superconductors
NASA Astrophysics Data System (ADS)
Shukrinov, Yu M.; Rahmonov, I. R.; Kulikov, K. V.; Botha, A. E.; Plecenik, A.; Seidel, P.; Nawrocki, W.
2017-02-01
Resonance phenomena in a model of intrinsic Josephson junctions shunted by LC-elements (L-inductance, C-capacitance) are studied. The phase dynamics and IV-characteristics are investigated in detail when the Josephson frequency approaches the frequency of the resonance circuit. A realization of parametric resonance through the excitation of a longitudinal plasma wave, within the bias current interval corresponding to the resonance circuit branch, is demonstrated. It is found that the temporal dependence of the total voltage of the stack, and the voltage measured across the shunt capacitor, reflect the charging of superconducting layers, a phenomenon which might be useful as a means of detecting such charging experimentally. Thus, based on the voltage dynamics, a novel method for the determination of charging in the superconducting layers of coupled Josephson junctions is proposed. A demonstration and discussion of the influence of external electromagnetic radiation on the IV-characteristics and charge-time dependence is given. Over certain parameter ranges the radiation causes an interesting new type of temporal splitting in the charge-time oscillations within the superconducting layers.
Incipient Berezinskii-Kosterlitz-Thouless transition in two-dimensional coplanar Josephson junctions
NASA Astrophysics Data System (ADS)
Massarotti, D.; Jouault, B.; Rouco, V.; Charpentier, S.; Bauch, T.; Michon, A.; De Candia, A.; Lucignano, P.; Lombardi, F.; Tafuri, F.; Tagliacozzo, A.
2016-08-01
Superconducting hybrid junctions are revealing a variety of effects. Some of them are due to the special layout of these devices, which often use a coplanar configuration with relatively large barrier channels and the possibility of hosting Pearl vortices. A Josephson junction with a quasi-ideal two-dimensional barrier has been realized by growing graphene on SiC with Al electrodes. Chemical vapor deposition offers centimeter size monolayer areas where it is possible to realize a comparative analysis of different devices with nominally the same barrier. In samples with a graphene gap below 400 nm, we have found evidence of Josephson coherence in the presence of an incipient Berezinskii-Kosterlitz-Thouless transition. When the magnetic field is cycled, a remarkable hysteretic collapse and revival of the Josephson supercurrent occurs. Similar hysteresis are found in granular systems and are usually justified within the Bean critical state model (CSM). We show that the CSM, with appropriate account for the low-dimensional geometry, can partly explain the odd features measured in these junctions.
Josephson Supercurrent through the Topological Surface States of Strained Bulk HgTe
NASA Astrophysics Data System (ADS)
Oostinga, Jeroen B.; Maier, Luis; Schüffelgen, Peter; Knott, Daniel; Ames, Christopher; Brüne, Christoph; Tkachov, Grigory; Buhmann, Hartmut; Molenkamp, Laurens W.
2013-04-01
Strained bulk HgTe is a three-dimensional topological insulator, whose surface electrons have a high mobility (˜30000cm2/Vs), while its bulk is effectively free of mobile charge carriers. These properties enable a study of transport through its unconventional surface states without being hindered by a parallel bulk conductance. Here, we show transport experiments on HgTe-based Josephson junctions to investigate the appearance of the predicted Majorana states at the interface between a topological insulator and a superconductor. Interestingly, we observe a dissipationless supercurrent flow through the topological surface states of HgTe. The current-voltage characteristics are hysteretic at temperatures below 1 K, with critical supercurrents of several microamperes. Moreover, we observe a magnetic-field-induced Fraunhofer pattern of the critical supercurrent, indicating a dominant 2π-periodic Josephson effect in the unconventional surface states. Our results show that strained bulk HgTe is a promising material system to get a better understanding of the Josephson effect in topological surface states, and to search for the manifestation of zero-energy Majorana states in transport experiments.
Josephson current in finite-lenght nanowire SNS junctions with Majorana fermions
NASA Astrophysics Data System (ADS)
Aguado, Ramon; Prada, Elsa; San Jose, Pablo
2012-02-01
The dc Josephson effect (JE) through infinite-lenght junctions of one-dimensional topological superconductors exhibits an anomalous 4π periodic phase (φ) dependence which originates from a parity-protected level crossing of zero-energy Majorana bound states (MBS) at φ=π. This ``fractional'' JE provides an important experimental detection tool for MBS. In this talk, I will discuss the JE in more realistic SNS junctions of arbitrary transparency and when both the normal and the nanowire regions are of finite length, namely beyond the short-junction and infinite topological superconductor limits. In general, the spectrum of Andreev bound states can become rather intricate and dense as opposed to the infinite-lenght case. Moreover, the low-energy spectrum around φ=π shows always anticrossings, originated from hybridization of four MBS, which may preclude the experimental observation of the fractional JE. At finite bias voltages, Landau-Zener dynamics involving the MBS and quasi-continuum Andreev levels gives rise to a nontrivial ac Josephson current. Interestingly, the ac current phase diagram as a function of the Josephson frequency/normal transmission shows fractional JE regions which are tunable through bias/gate voltages.
Fabrication of Small Edge Josephson Junctions Between Sr2RuO4 and Al
NASA Astrophysics Data System (ADS)
Zakrzewski, Brian; Cai, Xinxin; Ying, Yiqun; Fobes, David; Liu, Tijiang; Mao, Zhiqiang; Liu, Ying
2015-03-01
Sr2RuO4 is predicted to have a chiral p-wave orbital pairing. However, attempts to measure the chiral edge currents have yielded results inconsistent with theoretical predictions. Josephson junctions between Sr2RuO4 and an s-wave superconductor such as Al may provide an avenue for directly measuring the edge currents. We report progress on fabricating these junctions, using Al electrodes with no oxide barrier. The Josephson junctions are placed on the naturally formed edges of cleaved Sr2RuO4 thin crystal, which is expected to feature a surface less disordered than ramped junctions prepared by focused ion beam and ion mills. Transmission electron microscope studies provide a powerful tool to characterize the interface. We have systematically investigated the effects of nanofabrication processes on the quality of the junction interface. In particular, several post-lithography processes appear to cause irreversible damage to the surface layer of Sr2RuO4, which highlights potential issues for general small scale device fabrication. We also report preliminary measurements of Josephson tunneling from these devices.
ac Josephson effects in Nb/InAs/Nb junctions with integrated resonators
NASA Astrophysics Data System (ADS)
Biedermann, K.; Chrestin, A.; Matsuyama, T.; Merkt, U.
2001-04-01
Investigations of the ac Josephson effect in Nb/p-type InAs/Nb junctions are presented. Two distinguished features of these devices are an integrated resonator formed by the overlap of two Nb electrodes with an intermediate anodic oxide and their high characteristic voltages IcRN of about 1 mV. Under radio-frequency irradiation, we observe Shapiro steps whose widths follow Bessel functions for high irradiated power. Because of the integrated resonator, self-resonances of the ac Josephson effect can be studied in the current-voltage characteristics. Using a modified resistively shunted junction model which accounts for the presence of the resonator and a nonuniform lateral current distribution, we can describe the magnetic-field dependence of the resonance amplitude. A resonance is also observed when the Josephson frequency is exactly half the lowest resonance frequency, which is beyond the simple model. A possible explanation is provided by a nonsinusoidal current-phase relation established under nonequilibrium conditions.
Heteroclinic chaos in a Josephson-junction system perturbed by dichotomous noise excitation
NASA Astrophysics Data System (ADS)
Lei, Youming; Fu, Rui
2015-12-01
The chaotic behavior in a Josephson-junction system perturbed by dichotomous noise excitation is discussed in detail. Conditions for the onsets of chaos are derived by virtue of the random Melnikov method together with the mean-square criterion. It is shown that with the increase of the noise transition rate, the threshold of the dichotomous noise amplitude for the onset of chaos in the system increases. The effects of dichotomous noise on the Josephson-junction system are also determined by numerical simulations via the mean largest Lyapunov exponents, which verifies that the injection of the dichotomous noise can cause the change of the sign of the largest Lyapunov exponent and lead to noise-induced chaos. Phase portraits and time histories are further used to verify these results. It can be concluded that by changing the internal parameters of the dichotomous noise, we can adjust the threshold for the onset of the chaos and then control dynamical behaviors in the Josephson-junction system subjected to dichotomous noise excitation.
Kimura, Hikari; Dynes, Robert; Barber Jr., Richard. P.; Ono, S.; Ando, Y.
2009-09-01
Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8+delta (BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a novel scanning tunneling microscope (STM) equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wavefunction of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe2. The relevant measurement parameter, the Josephson ICRN product, is discussed within the context of both BCS superconductors and the high transition temperature superconductors. The local relationship between the ICRN product and the quasiparticle density of states (DOS) gap are presented within the context of phase diagrams for BSCCO. Excessive current densities can be produced with these measurements and have been found to alter the local DOS in the BSCCO. Systematic studies of this effect were performed to determine the practical measurement limits for these experiments. Alternative methods for preparation of the BSCCO surface are also discussed.
Parametric amplification of vortex-antivortex pair generation in a Josephson junction
NASA Astrophysics Data System (ADS)
Berdiyorov, G. R.; Milošević, M. V.; Savel'ev, S.; Kusmartsev, F.; Peeters, F. M.
2014-10-01
Using advanced three-dimensional simulations, we show that an Abrikosov vortex, trapped inside a cavity perpendicular to an artificial Josephson junction, can serve as a very efficient source for generation of Josephson vortex-antivortex pairs in the presence of the applied electric current. In such a case, the nucleation rate of the pairs can be tuned in a broad range by an out-of-plane ac magnetic field in a broad range of frequencies. This parametrically amplified vortex-antivortex nucleation can be considered as a macroscopic analog of the dynamic Casimir effect, where fluxon pairs mimic the photons and the ac magnetic field plays the role of the oscillating mirrors. The emerging vortex pairs in our system can be detected by the pronounced features in the measured voltage characteristics, or through the emitted electromagnetic radiation, and exhibit resonant dynamics with respect to the frequency of the applied magnetic field. Reported tunability of the Josephson oscillations can be useful for developing high-frequency emission devices.
Local dissipation effects in two-dimensional quantum Josephson junction arrays with a magnetic field
Polak, T.P.; Kopec, T.K.
2005-07-01
We study the quantum phase transitions in two-dimensional arrays of Josephson-couples junctions with short range Josephson couplings (given by the Josephson energy E{sub J}) and the charging energy E{sub C}. We map the problem onto the solvable quantum generalization of the spherical model that improves over the mean-field theory method. The arrays are placed on the top of a two-dimensional electron gas separated by an insulator. We include effects of the local dissipation in the presence of an external magnetic flux f={phi}/{phi}{sub 0} in square lattice for several rational fluxes f=0,(1/2),(1/3),(1/4), and (1/6). We also have examined the T=0 superconducting-insulator phase boundary as a function of a dissipation {alpha}{sub 0} for two different geometry of the lattice: square and triangular. We have found a critical value of the dissipation parameter independent on geometry of the lattice and presence magnetic field.
Nonideal quantum measurement effects on the switching-current distribution of Josephson junctions
NASA Astrophysics Data System (ADS)
Pierro, Vincenzo; Filatrella, Giovanni
2016-10-01
The quantum character of Josephson junctions is ordinarily revealed through the analysis of the switching currents, i.e., the current at which a finite voltage appears: A sharp rise of the voltage signals the passage (tunnel) from a trapped state (the zero voltage solution) to a running state (the finite voltage solution). In this context, we investigate the probability distribution of the Josephson-junction switching current taking into account the effect of the bias sweeping rate and introducing a simple nonideal quantum measurement scheme. The measurements are modeled as repeated voltage samplings at discrete time intervals, that is, with repeated projections of the time-dependent quantum solutions on the static or the running states, to retrieve the probability distribution of the switching currents. The distribution appears to be immune to the quantum Zeno effect, and it is close to, but distinguishable from, the Wentzel-Kramers-Brillouin approximation. For energy barriers comparable to the quantum fundamental energy state and in the fast bias current ramp rate the difference is neat, and remains sizable in the asymptotic slow rate limit. This behavior is a consequence of the quantum character of the system that confirms the presence of a backreaction of quantum measurements on the outcome of mesoscopic Josephson junctions.
Josephson current through a quantum dot coupled to a molecular magnet
NASA Astrophysics Data System (ADS)
Stadler, P.; Holmqvist, C.; Belzig, W.
2013-09-01
Josephson currents are carried by sharp Andreev states within the superconducting energy gap. We theoretically study the electronic transport of a magnetically tunable nanoscale junction consisting of a quantum dot connected to two superconducting leads and coupled to the spin of a molecular magnet. The exchange interaction between the molecular magnet and the quantum dot modifies the Andreev states due to a spin-dependent renormalization of the quantum dot's energy level and the induction of spin flips. A magnetic field applied to the central region of the quantum dot and the molecular magnet further tunes the Josephson current and starts a precession of the molecular magnet's spin. We use a nonequilibrium Green's function approach to evaluate the transport properties of the junction. Our calculations reveal that the energy level of the dot, the magnetic field, and the exchange interaction between the molecular magnet and the electrons occupying the energy level of the quantum dot can trigger transitions from a 0 to a π state of the Josephson junction. The redistribution of the occupied states induced by the magnetic field strongly modifies the current-phase relation. The critical current exhibits a sharp increase as a function of either the energy level of the dot, the magnetic field, or the exchange interaction.
NASA Astrophysics Data System (ADS)
Blackburn, James A.; Cirillo, Matteo; Grønbech-Jensen, Niels
2016-02-01
For decades following its introduction in 1968, the resistively and capacitively shunted junction (RCSJ) model, sometimes referred to as the Stewart-McCumber model, was successfully applied to study the dynamics of Josephson junctions embedded in a variety of superconducting circuits. In 1980 a theoretical conjecture by A.J. Leggett suggested a possible new and quite different behavior for Josephson junctions at very low temperatures. A number of experiments seemed to confirm this prediction and soon it was taken as given that junctions at tens of millikelvins should be regarded as macroscopic quantum entities. As such, they would possess discrete levels in their effective potential wells, and would escape from those wells (with the appearance of a finite junction voltage) via a macroscopic quantum tunneling process. A zeal to pursue this new physics led to a virtual abandonment of the RCSJ model in this low temperature regime. In this paper we consider a selection of essentially prototypical experiments that were carried out with the intention of confirming aspects of anticipated macroscopic quantum behavior in Josephson junctions. We address two questions: (1) How successful is the non-quantum theory (RCSJ model) in replicating those experiments? (2) How strong is the evidence that data from these same experiments does indeed reflect macroscopic quantum behavior?
Samokhvalov, A. V.
2007-03-15
Commensurability effects have been theoretically studied in a hybrid system consisting of a Josephson junction located in a nonuniform field induced by an array of magnetic particles. A periodic phase-difference distribution in the junction that is caused by the formation of a regular lattice of Abrikosov vortices generated by the magnetic field of the particles in superconducting electrodes is calculated. The dependence of the critical current through the junction I{sub c} on the applied magnetic field H is shown to differ strongly from the conventional Fraunhofer diffraction pattern because of the periodic modulation of the Josephson phase difference created by the vortices. More specifically, the I{sub c}(H) pattern contains additional resonance peaks, whose positions and heights depend on the parameters and magnetic state of the particles in the array. These specific features of the I{sub c}(H) dependence are observed when the period of the Josephson current modulation by the field of the magnetic particles and the characteristic scale of the change in the phase difference by the applied magnetic field are commensurable. The conditions that determine the positions of the commensurability peaks are obtained, and they are found to agree well with experimental results.
Edge-type Josephson junctions in narrow thin-film strips
NASA Astrophysics Data System (ADS)
Moshe, Maayan; Kogan, V. G.; Mints, R. G.
2008-07-01
We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions. We calculate Im(H) within nonlocal Josephson electrodynamics taking into account the stray fields. These fields affect the difference of phases of the order parameter across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density, i.e., it is universal. An explicit formula for this universal function is derived and used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant only in high fields. We find that the spacing between the zeros is proportional to 1/w2 , where w is the width of the junction. The general approach is applied to calculate Im(H) for a superconducting quantum interference device (SQUID) with two narrow edge-type junctions.
Noise performance of superconductive magnetometers based on long Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Granata, Carmine; Vettoliere, Antonio; Monaco, Roberto
2014-09-01
The low-current fluctuations at cryogenic temperatures together with the low dynamical resistance in the resonant states of Josephson tunnel junctions allow for the realization of superconducting oscillators up to the THz range with ultra-low spectral linewidth. By virtue of the Josephson frequency-voltage relationship, we show that the same properties can be exploited for the practical realization of magnetic flux-to-voltage transducers based on the flux-flow in long Josephson tunnel junctions whose intrinsic low-frequency voltage fluctuations at 4.2\\;K amount to few pV/H{{z}^{1/2}}, that is, too small to be measured by any present semiconductor electronics. Nevertheless, by using a double transformer SQUID amplifier we demonstrate that the (amplitude) voltage spectral density, S_{V}^{1/2}, of an all-niobium sensor does not exceed the level of 10\\;pV/H{{z}^{1/2}} and is not affected by 1/f excess noise at least down to few hertz. Such ultra-low white noise, corresponding to a magnetic field noise S_{B}^{1/2}\\leqslant 10\\;fT/H{{z}^{1/2}}, together with a highly linear and broadband voltage responsivity over a wide magnetic flux range, makes the flux-flow magnetometers potentially competitive with SQUID-based devices.
NASA Astrophysics Data System (ADS)
Cedergren, K.; Kafanov, S.; Smirr, J.-L.; Cole, J. H.; Duty, T.
2015-09-01
We have made a systematic investigation of charge transport in one-dimensional chains of Josephson junctions where the characteristic Josephson energy is much less than the single-junction Cooper-pair charging energy, EJ≪EC P . Such chains are deep in the insulating state, where superconducting phase coherence across the chain is absent, and a voltage threshold for conduction is observed at the lowest temperatures. We find that Cooper-pair tunneling in such chains is completely suppressed. Instead, charge transport is dominated by tunneling of single electrons, which is very sensitive to the presence of BCS quasiparticles on the superconducting islands of the chain. Consequently, we observe a strong parity effect, where the threshold voltage vanishes sharply at a characteristic parity temperature T*, which is significantly lower than the critical temperature Tc. A measurable and thermally activated zero-bias conductance appears above T*, with an activation energy equal to the superconducting gap, confirming the role of thermally excited quasiparticles. Conduction below T* and above the voltage threshold occurs via injection of single electrons/holes into the Cooper-pair insulator, forming a nonequilibrium steady state with a significantly enhanced effective temperature. Our results explicitly show that single-electron transport dominates deep in the insulating state of Josephson junction arrays. This conduction process has mostly been ignored in previous studies of both superconducting junction arrays and granular superconducting films below the superconductor-insulator quantum phase transition.
Josephson coupling between superconducting islands on single- and bi-layer graphene
NASA Astrophysics Data System (ADS)
Mancarella, Francesco; Fransson, Jonas; Balatsky, Alexander
2016-05-01
We study the Josephson coupling of superconducting (SC) islands through the surface of single-layer graphene (SLG) and bilayer graphene (BLG) in the long-junction regime, as a function of the distance between the grains, temperature, chemical potential and external (transverse) gate-voltage. For SLG, we provide a comparison with existing literature. The proximity effect is analyzed through a Matsubara Green’s function approach. This represents the first step in a discussion of the conditions for the onset of a granular superconductivity within the film, made possible by Josephson currents flowing between superconductors. To ensure phase coherence over the 2D sample, a random spatial distribution can be assumed for the SC islands on the SLG sheet (or intercalating the BLG sheets). The tunable gate-voltage-induced band gap of BLG affects the asymptotic decay of the Josephson coupling-distance characteristic for each pair of SC islands in the sample, which results in a qualitatively strong field dependence of the relation between Berezinskii-Kosterlitz-Thouless transition critical temperature and gate voltage.
Engineering double-well potentials with variable-width annular Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Monaco, Roberto
2016-11-01
Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.
Engineering double-well potentials with variable-width annular Josephson tunnel junctions.
Monaco, Roberto
2016-11-09
Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.
NASA Astrophysics Data System (ADS)
Berdiyorov, Golibjon R.; Savel'ev, Sergey; Kusmartsev, Feodor V.; Peeters, François M.
2015-11-01
We use the anisotropic time-dependent Ginzburg-Landau theory to investigate the effect of a square array of out-of-plane magnetic dots on the dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting (SNS) Josephson junctions in the presence of external DC and AC currents. Periodic pinning due to the magnetic dots distorts the triangular lattice of fluxons and results in the appearance of commensurability features in the current-voltage characteristics of the system. For the larger values of the magnetization, additional peaks appear in the voltage-time characteristics of the system due to the creation and annihilation of vortex-antivortex pairs. Peculiar changes in the response of the system to the applied current is found resulting in a "superradiant" vortex-flow state at large current values, where a rectangular lattice of moving vortices is formed. Synchronizing the motion of fluxons by adding a small ac component to the biasing dc current is realized. However, we found that synchronization becomes difficult for large magnetization of the dots due to the formation of vortex-antivortex pairs.
Caldwell, Jane C; Chiale, Pablo A; Gonzalez, Mario D; Baranchuk, Adrian
2013-01-01
We present 2 cases of the slow-fast form of AVNRT with initially narrow QRS complexes followed by sudden unexpected transition to persistently wide QRS complexes due to aberrant intraventricular conduction. Introduction of a properly timed extrastimulus in one case and critical oscillations in cycle length due to short-long coupling in the second case set the stage for the initial bundle branch block. However, persistence of the aberrancy pattern once the initial event abated was maintained by the "linking" phenomenon. Delayed, retrograde concealed activation from the contralateral bundle branch perpetuated the initial bundle branch block. PMID:23840106
Caldwell, Jane C; Chiale, Pablo A; Gonzalez, Mario D; Baranchuk, Adrian
2013-05-01
We present 2 cases of the slow-fast form of AVNRT with initially narrow QRS complexes followed by sudden unexpected transition to persistently wide QRS complexes due to aberrant intraventricular conduction. Introduction of a properly timed extrastimulus in one case and critical oscillations in cycle length due to short-long coupling in the second case set the stage for the initial bundle branch block. However, persistence of the aberrancy pattern once the initial event abated was maintained by the "linking" phenomenon. Delayed, retrograde concealed activation from the contralateral bundle branch perpetuated the initial bundle branch block.
NASA Astrophysics Data System (ADS)
Kim, Jihoon
MgB2 is an unusual binary metallic superconductor in that it has a transition temperature of almost twice that of other metallic compounds and possesses two superconductor gaps. It has proven to be difficult to fabricate in thin film form, predominantly as a result of the high volatility of Mg. In this thesis, critical factors involved in MgB2 thin film growth and the synthesis of multilayer MgB2 Josephson junctions have been studied. The thermochemistry of MgB2 thin film growth has been investigated. The low Mg sticking coefficient at temperatures over 300°C prevents high temperature synthesis with traditional vacuum growth methods. However, as a result of the large kinetic barrier to MgB2 decomposition, metastable growth and subsequent thermal processing is possible. The Mg sticking coefficient is found to be strongly dependent upon B flux. High Mg and B fluxes make it possible to extend the processing window to elevated temperatures by enhancing the Mg sticking coefficient. A transition temperature of 37˜38K was achieved using molecular beam epitaxy (MBE). For the fabrication of Josephson junctions, various barrier layers including native oxide, boron, AIN, and thermal oxide were explored. Cross-bridge junction structures were fabricated using shadow masks. Repeatable tunneling characteristics were observed from metal/native oxide/MgB2 junctions. MgB 2 energy gaps and density of states, as well as the barrier's height and thickness, have been inferred from tunneling conductance measurements. MgB2/native oxide or boron/MgB2 junctions with 1mm 2 areas were fabricated and also exhibited tunneling characteristics. The junctions produced with the cross geometry process have a Josephson coupling energy that is too small compared to the thermal energy to exhibit supercurrent as a result of the junction's large size and high resistance. To overcome this limitation, planar type junctions were prepared using conventional microfabrication techniques. MgB2,/AlN/MgB2 and
Josephson effect studies of pairing symmetry in Fe-based superconductors
NASA Astrophysics Data System (ADS)
Zhang, Xiaohang
2010-03-01
To investigate the pairing symmetry in the recently discovered Fe-based superconductors, Josephson effect studies have been performed on two types of c-axis junctions incorporating 122-type iron pnictide superconductors: junctions between s-wave superconductors and iron pnictide superconductors [1] and junctions between electron-doped and hole-doped iron pnictide superconductors [2]. The ac Josephson effect was observed in the I-V characteristics for both types of junctions under microwave irradiation. By applying external magnetic fields parallel to the junction interfaces, Fraunhofer-like patterns were obtained. Analysis based on the obtained modulation patterns suggests that the Josephson current is flowing along the c-axis direction within a typical area of 10 x 10 (μm)^2. The presence of Josephson coupling between an s-wave superconductor and a 122-type iron pnictide superconductor along the c-axis strongly supports an s-wave symmetry in the iron pnictide superconductor. Moreover, our observed Josephson effect in the bicrystal junctions indicates that phase coherence can be established between electron-doped and hole-doped iron pnictide superconductors. Such a phase-coherent p-n structure is an important component [3] for performing definitive phase-sensitive tests for the proposed s± symmetry in Fe-based superconductors. Progress in carrying out such tests will be discussed. Recent results on systematic measurements of the energy gap using Andreev reflection spectroscopy with highly transparent contacts will also be presented. This work is supported by the NSF (DMR-0653535) and performed in collaboration with S. R. Saha, N. P. Butch, K. Kirshenbaum, J. Paglione, R. L. Greene, I. Takeuchi at UMD, and Y. S. Oh, Y. Liu, L. Q. Yan, K. H. Kim at SNU. [4pt] [1] X. H. Zhang et al., Phys. Rev. Lett. 102, 147002 (2009).[0pt] [2] X. H. Zhang et al., Appl. Phy. Lett. 95, 062510 (2009).[0pt] [3] D. Parker and I. I. Mazin, Phys. Rev. Lett. 102, 227007 (2009).
Weak neutral current chemistry
Mohan, R.
1996-07-01
Metal cluster organic complexes, neither atomic nor solid but in analogy to atomic nuclei and to mesoscopic systems, have unusual dynamics and catalytic properties. Organo-metal clusters as quintessence prebiotic enzymes could have originated the homochirality of the molecules from achiral precursors, controlled from the atomic-nucleus, with the initial product itself serving subsequently as chiral auxiliary transferring and amplifying the chirality in the autocatalytic process now. High resolution spectroscopic studies of diatomic molecules beginning now may lead to upper estimates of the interaction strength of weak neutral currents (WNG) with valence electrons of metal clusters and suggest kinetic pathways to dynamic symmetry breaking in the asymmetric synthesis of chiral molecules. An estimate of 10{sup {minus}5} kT (thousand times larger than for radiolysis) for the parity violating energy (PVE) could be sufficient to run an entropy driven spin-catalyzed asymmetric synthesis. Expect then, wherever there are metal clusters in interstellar dust or under the sea chiral molecular production. {copyright} {ital 1996 American Institute of Physics.}
Weak neutral current chemistry
NASA Astrophysics Data System (ADS)
Mohan, R.
1996-07-01
Metal cluster organic complexes, neither atomic nor solid but in analogy to atomic nuclei and to mesoscopic systems, have unusual dynamics and catalytic properties. Organo-metal clusters as quintessence prebiotic enzymes could have originated the homochirality of the molecules from achiral precursors, controlled from the atomic-nucleus, with the initial product itself serving subsequently as chiral auxiliary transferring and amplifying the chirality in the autocatalytic process now. High resolution spectroscopic studies of diatomic molecules beginning now may lead to upper estimates of the interaction strength of weak neutral currents (WNG) with valence electrons of metal clusters and suggest kinetic pathways to dynamic symmetry breaking in the asymmetric synthesis of chiral molecules. An estimate of 10-5 kT (thousand times larger than for radiolysis) for the parity violating energy (PVE) could be sufficient to run an entropy driven spin-catalyzed asymmetric synthesis. Expect then, wherever there are metal clusters in interstellar dust or under the sea chiral molecular production.
NASA Astrophysics Data System (ADS)
Gong, Wei-Jiang; Gao, Zhen; Shan, Wan-Fei; Yi, Guang-Yu
2016-03-01
One Majorana doublet can be realized at each end of the time-reversal-invariant Majorana nanowires. We investigate the Josephson effect in the Majorana-doublet-presented junction modified by different inter-doublet coupling manners. It is found that when the Majorana doublets couple indirectly via a non-magnetic quantum dot, only the normal Josephson effect occurs, and the fermion parity in the system just affects the current direction and amplitude. However, one magnetic field applied on the dot can induce the fractional Josephson effect in the odd-parity case. Next if the direct and indirect couplings between the Majorana doublets coexist, no fractional Josephson effect takes place, regardless of the presence of magnetic field. Instead, there almost appears the π-period-like current in some special cases. All the results are clarified by analyzing the influence of the fermion occupation in the quantum dot on the parity conservation in the whole system. We ascertain that this work will be helpful for describing the dot-assisted Josephson effect between the Majorana doublets.
NASA Astrophysics Data System (ADS)
Ngabonziza, Prosper; Stehno, Martin, P.; Myoren, Hiroaki; Brinkman, Alexander
In recent years, extensive efforts have been made to improve the coupling between topological insulators and s-wave superconductors in topological insulator Josephson devices (TIJDs). Despite significant progress, essential questions remain open such as the bulk contribution to the Josephson critical current or the existence (and number) of 4 π -periodic bound states (Majoranas) in TIJDs. To address these issues, we fabricated Nb/Bi2Te3/Nb Josephson junctions alongside Hall bar devices on MBE-grown Bi2Te3 topological insulator thin films. Using the SrTiO3 [111] substrate as a gate dielectric, we tuned the carrier density electrostatically and measured the Josephson supercurrent and the normal state transport properties of our thin film devices. We identify three gate voltage ranges with distinct behavior: A region of intermediate gate bias where the measured quantities change rapidly with the applied electric field, and two saturation regions for large bias of either polarity. We discuss carrier distribution and band alignment in the material as well as implications for the effective Josephson coupling in TIJDs. This work is financially supported by the Dutch Foundation for Fundamental Research on Matter (FOM), the Netherlands Organization for Scientific Research (NWO), and by the European Research Council (ERC).
NASA Astrophysics Data System (ADS)
Otten, Daniel; Rubbert, Sebastian; Ulrich, Jascha; Hassler, Fabian
2016-09-01
Josephson junctions are the most prominent nondissipative and at the same time nonlinear elements in superconducting circuits allowing Cooper pairs to tunnel coherently between two superconductors separated by a tunneling barrier. Due to this, physical systems involving Josephson junctions show highly complex behavior and interesting novel phenomena. Here, we consider an infinite one-dimensional chain of superconducting islands where neighboring islands are coupled by capacitances. We study the effect of Josephson junctions shunting each island to a common ground superconductor. We treat the system in the regime where the Josephson energy exceeds the capacitive coupling between the islands. For the case of two offset charges on two distinct islands, we calculate the interaction energy of these charges mediated by quantum phase slips due to the Josephson nonlinearities. We treat the phase slips in an instanton approximation and map the problem onto a classical partition function of interacting particles. Using the Mayer cluster expansion, we find that the interaction potential of the offset charges decays with a universal inverse-square power-law behavior.
NASA Astrophysics Data System (ADS)
Chien, Wei-Chen; Lin, Kuan-Yu; Liou, Saxon; Ho, I.-Lin; Kuo, Watson
2017-04-01
We conduct microwave impedance measurements on a one-dimensional (1D) array of Josephson junctions to experimentally determine the Josephson inductance and shunt resistance of the constituent junctions. The effective Josephson energy provides an estimate of the environmental impedance, which is greatly increased due to phase fluctuations in the neighboring junctions. This enhancement is attributed to the charge solitons in the 1D system. In general, the environmental impedance is dominated by the junction’s normal resistance in the superconducting phase coherent regime, but overwhelmed by zero-bias resistance and differential resistance, respectively, in the Coulomb blockaded regime and in the phase fluctuating regime. The change in phase fluctuations owing to a dc bias agrees with the finite temperature phase diffusion model.
Fano-Josephson effect in the junction with DIII-class topological and s-wave superconductors
NASA Astrophysics Data System (ADS)
Jiang, Cui; Yi, Guang-Yu; Meng, Guang-Yi; Gong, Wei-Jiang
2017-04-01
We investigate the Josephson effects in the junction formed by the direct and indirect couplings between DIII-class topological and s-wave superconductors. As a result, the Josephson current is found to oscillate in period 2 π . The presence of Majorana doublet in the DIII-class superconductor renders the current finite at the case of zero phase difference, with its sign determined by the fermion parity of such a junction. In addition to the dot level and intradot Coulomb interaction, the Fano interference is an important factor to adjust the Josephson current. It is believed that these results will be helpful in understanding the transport properties of the DIII-class superconductor.
NASA Astrophysics Data System (ADS)
Bellver, Fernando Gimeno; Garratón, Manuel Caravaca; Soto Meca, Antonio; López, Juan Antonio Vera; Guirao, Juan L. G.; Fernández-Martínez, Manuel
In this paper, we explore the chaotic behavior of resistively and capacitively shunted Josephson junctions via the so-called Network Simulation Method. Such a numerical approach establishes a formal equivalence among physical transport processes and electrical networks, and hence, it can be applied to efficiently deal with a wide range of differential systems. The generality underlying that electrical equivalence allows to apply the circuit theory to several scientific and technological problems. In this work, the Fast Fourier Transform has been applied for chaos detection purposes and the calculations have been carried out in PSpice, an electrical circuit software. Overall, it holds that such a numerical approach leads to quickly computationally solve Josephson differential models. An empirical application regarding the study of the Josephson model completes the paper.
Phase-dependent magnetoconductance fluctuations in a chaotic Josephson junction
NASA Astrophysics Data System (ADS)
Brouwer, P. W.; Beenakker, C. W. J.
1996-11-01
Motivated by recent experiments by Den Hartog et al., we present a random-matrix theory for the magnetoconductance fluctuations of a chaotic quantum dot that is coupled by point contacts to two superconductors and one or two normal metals. There are aperiodic conductance fluctuations as a function of the magnetic field through the quantum dot and 2π-periodic fluctuations as a function of the phase difference φ of the superconductors. If the coupling to the superconductors is weak compared to the coupling to the normal metals, the φ dependence of the conductance is harmonic, as observed in the experiment. In the opposite regime, the conductance becomes a random 2π-periodic function of φ, in agreement with the theory of Altshuler and Spivak. The theoretical method employs an extension of the circular ensemble which can describe the magnetic-field dependence of the scattering matrix.
Link direction for link prediction
NASA Astrophysics Data System (ADS)
Shang, Ke-ke; Small, Michael; Yan, Wei-sheng
2017-03-01
Almost all previous studies on link prediction have focused on using the properties of the network to predict the existence of links between pairs of nodes. Unfortunately, previous methods rarely consider the role of link direction for link prediction. In fact, many real-world complex networks are directed and ignoring the link direction will mean overlooking important information. In this study, we propose a phase-dynamic algorithm of the directed network nodes to analyse the role of link directions and demonstrate that the bi-directional links and the one-directional links have different roles in link prediction and network structure formation. From this, we propose new directional prediction methods and use six real networks to test our algorithms. In real networks, we find that compared to a pair of nodes which are connected by a one-directional link, a pair of nodes which are connected by a bi-directional link always have higher probabilities to connect to the common neighbours with only bi-directional links (or conversely by one-directional links). We suggest that, in the real networks, the bi-directional links will generally be more informative for link prediction and network structure formation. In addition, we propose a new directional randomized algorithm to demonstrate that the direction of the links plays a significant role in link prediction and network structure formation.
NASA Astrophysics Data System (ADS)
Kawabata, Shiro; Kato, Takeo; Bauch, Thilo
2009-03-01
We investigate classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a Josephson junction coupled with an LC circuit theoretically. The TA and MQT escape rate are calculated analytically by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling gives rise to slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in grain boundary YBCO Josephson junctions.
Josephson vortex motion as a source for dissipation of superflow of e-h pairs in bilayers.
Fil, D V; Shevchenko, S I
2009-05-27
It is shown that in a bilayer excitonic superconductor dissipative losses emerge under transmission of the current from the source to the load. These losses are proportional to the square of the interlayer tunneling amplitude and are independent of the value of the input current. The case of a quantum Hall bilayer is considered. The bilayer may work as a transmission line if the input current exceeds a certain critical value. An input current higher than the critical one induces Josephson vortices in the bilayer. The difference in electrochemical potentials is required to feed the load and it forces Josephson vortices to move. The state becomes non-stationary which leads to dissipation.
Effect of light irradiation on Fiske resonances and the Josephson effect in high-T{sub c} junctions
Elly, J.; Medici, M.G.; Gilabert, A.; Schmidl, F.; Seidel, P.; Hoffmann, A.; Schuller, I.K.
1997-10-01
We have performed photoexcitation experiments in high T{sub c} YBa{sub 2}Cu{sub 3}O{sub x} grain-boundary Josephson junctions. While the Josephson critical current is substantially enhanced, the normal state resistance decreases, and the positions of the extreme in the Fraunhofer diffraction pattern remain unchanged. These measurements show that the magnetic field penetration depth is not affected by light irradiation. On the other hand, the position and intensity of Fiske steps due to electromagnetic resonances increase substantially, which implies that the ratio of the thickness barrier to the dielectric constant changes by a factor of 2. {copyright} {ital 1997} {ital The American Physical Society}
Spin supercurrent, magnetization dynamics, and φ-state in spin-textured Josephson junctions
NASA Astrophysics Data System (ADS)
Kulagina, Iryna; Linder, Jacob
2014-08-01
The prospect of combining the dissipationless nature of superconducting currents with the spin polarization of magnetic materials is interesting with respect to exploring superconducting analogs of topics in spintronics. In order to accomplish this aim, it is pivotal to understand not only how such spin supercurrents can be created, but also how they interact dynamically with magnetization textures. In this paper, we investigate the appearance of a spin supercurrent and the resulting magnetization dynamics in a textured magnetic Josephson current by using three experimentally relevant models: (i) a superconductor∣ferromagnet∣superconductor (S∣F∣S) junction with spin-active interfaces, (ii) a S∣F1∣F2∣F3∣S Josephson junction with a ferromagnetic trilayer, and (iii) a Josephson junction containing a domain wall. In all of these cases, the supercurrent is spin polarized and exerts a spin-transfer torque on the ferromagnetic interlayers which causes magnetization dynamics. Using a scattering matrix formalism in the clean limit, we compute the Andreev bound states and resulting free energy of the system which in turn is used to solve the Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous magnetism influences the phase dependence of the charge supercurrent and the magnetization dynamics caused by the spin polarization of the supercurrent. Using a realistic experimental parameter set, we find that the spin supercurrent can induce magnetization switching that is controlled by the superconducting phase difference. Moreover, we demonstrate that the combined effect of chiral spin symmetry breaking of the system as a whole with interface scattering causes the systems above to act as phase batteries that may supply any superconducting phase difference φ in the ground state. Such a φ-junction is accompanied by an anomalous supercurrent appearing even at zero phase difference, and we demonstrate that the flow direction of this current is
Experiments on non-equilibrium superconductor-normal metal-superconductor Josephson junctions
NASA Astrophysics Data System (ADS)
Crosser, Michael S.
By controlling the distribution function within the normal metal of a superconductor/normal metal/superconductor (SNS) Josephson junction, one can reverse the supercurrent-phase relation in the normal wire, creating a pi-junction. This manipulation is done by injecting normal quasiparticle current into the wire, via one or more leads attached at the middle of the junction. Two experiments evolve from this concept. First, in a sample of four reservoirs, two normal and two superconducting, all connected by a wire cross of normal metal, one may inject current either antisymmetrically (AS) or symmetrically (S). In the AS case, current is injected into one normal lead and extracted from the other, creating normal current flow that does not interact with the supercurrent except at the junction. In the S case, current is injected into both normal leads and extracted from the superconductors. Theory predicts that, in the absence of electron energy relaxation in the normal part of the junction, these two situations should result in identical behavior of the Josephson junction. However, due to Joule heating, the S case shows a slightly larger maximum pi-current than the AS case. The second experiment considers a more subtle effect resulting from normal current being injected symmetrically into a SNS Josephson junction. One side of the SNS junction has both normal current and supercurrent flowing in the same direction while the other side has opposing current flows. This situation creates an effective energy gradient across the SNS junction that can appear in the distribution function of the normal wire. Using superconductor/insulator/normal metal tunnelling spectroscopy, it is possible to extract these changes to the distribution function.
Spin superconductivity and ac-Josephson effect in Graphene system under strong magnetic field
NASA Astrophysics Data System (ADS)
Liu, Haiwen; Jiang, Hua; Sun, Qing-Feng; Xie, X. C.; Collaborative Innovation Center of Quantum Matter, Beijing, China Collaboration
We study the spin superconductivity in Graphene system under strong magnetic field. From the microscopically Gor'kov method combined with the Aharonov-Casher effect, we derive the effective Landau-Ginzburg free energy and analyze the time evolution of order parameter, which is confirmed to be the off-diagonal long range order. Meanwhile, we compare the ground state of spin superconductivity to the canted-antiferromagnetic state, and demonstrate the equivalence between these two states. Moreover, we give out the pseudo-field flux quantization condition of spin supercurrent, and propose an experimental measurable ac-Josephson effect of spin superconductivity in this system.
Synchronization of a Josephson junction array in terms of global variables.
Vlasov, Vladimir; Pikovsky, Arkady
2013-08-01
We consider an array of Josephson junctions with a common LCR load. Application of the Watanabe-Strogatz approach [Physica D 74, 197 (1994)] allows us to formulate the dynamics of the array via the global variables only. For identical junctions this is a finite set of equations, analysis of which reveals the regions of bistability of the synchronous and asynchronous states. For disordered arrays with distributed parameters of the junctions, the problem is formulated as an integro-differential equation for the global variables; here stability of the asynchronous states and the properties of the transition synchrony-asynchrony are established numerically.
Coherent energy transport in classical nonlinear oscillators: An analogy with the Josephson effect.
Borlenghi, Simone; Iubini, Stefano; Lepri, Stefano; Bergqvist, Lars; Delin, Anna; Fransson, Jonas
2015-04-01
By means of a simple theoretical model and numerical simulations, we demonstrate the presence of persistent energy currents in a lattice of classical nonlinear oscillators with uniform temperature and chemical potential. In analogy with the well-known Josephson effect, the currents are proportional to the sine of the phase differences between the oscillators. Our results elucidate general aspects of nonequilibrium thermodynamics and point towards a way to practically control transport phenomena in a large class of systems. We apply the model to describe the phase-controlled spin-wave current in a bilayer nanopillar.
High-T{sub c} superconducting Josephson mixers for terahertz heterodyne detection
Malnou, M.; Feuillet-Palma, C.; Olanier, L.; Lesueur, J.; Bergeal, N.; Ulysse, C.; Faini, G.; Febvre, P.; Sirena, M.
2014-08-21
We report on an experimental and theoretical study of the high-frequency mixing properties of ion-irradiated YBa{sub 2}Cu{sub 3}O{sub 7} Josephson junctions embedded in THz antennas. We investigated the influence of the local oscillator power and frequency on the device performances. The experimental data are compared with theoretical predictions of the general three-port model for mixers in which the junction is described by the resistively shunted junction model. A good agreement is obtained for the conversion efficiency in different frequency ranges, spanning above and below the characteristic frequencies f{sub c} of the junctions.
Two-Point Phase Correlations of a One-Dimensional Bosonic Josephson Junction
Betz, T.; Manz, S.; Buecker, R.; Berrada, T.; Koller, Ch.; Schmiedmayer, J.; Kazakov, G.; Mazets, I. E.; Stimming, H.-P.; Perrin, A.; Schumm, T.
2011-01-14
We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows us to measure the coupling strength and temperature and hence a full characterization of the system.
A compact design for the Josephson mixer: The lumped element circuit
Pillet, J.-D.; Flurin, E.; Mallet, F. Huard, B.
2015-06-01
We present a compact and efficient design in terms of gain, bandwidth, and dynamical range for the Josephson mixer, the superconducting circuit performing three-wave mixing at microwave frequencies. In an all lumped-element based circuit with galvanically coupled ports, we demonstrate nondegenerate amplification for microwave signals over a bandwidth up to 50 MHz for a power gain of 20 dB. The quantum efficiency of the mixer is shown to be about 70%, and its saturation power reaches −112 dBm.
NASA Astrophysics Data System (ADS)
Shukrinov, Yu. M.; Rahmonov, I. R.; Plecenik, A.; Streltsova, O. I.; Zuev, M. I.; Ososkov, G. A.
2016-02-01
The current-voltage (IV) characteristics of the intrinsic Josephson junctions in high temperature superconductors under external electromagnetic radiation are calculated numerically in the parametric resonance region. We discuss a numerical method for calculation of the Shapiro step width on the amplitude of radiation. In order to accelerate computations we used parallelization by task parameter via Simple Linux Utility for Resource Management (SLURM) arrays and tested it in the case of a single junction. An analysis of the junction transitions between rotating and oscillating states in the branching region of IV-characteristics is presented.
Cherenkov radiation of a Josephson vortex moving in a sandwich embedded in a dielectric medium
Malishevskii, A. S. Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2008-08-15
A motion of a Josephson vortex in a long sandwich embedded in a dielectric medium is described. If the velocity of the vortex is greater than the velocity of light in the dielectric, terahertz-band Cherenkov radiation is generated and emitted from the lateral surface of the sandwich. The radiation loss power is determined. In the case when radiation loss is compensated for by the energy gain due to transport current, a relation between the current and the velocity of the vortex is obtained.
Using ion irradiation to make high-T{sub c} Josephson junctions
Bergeal, N.; Lesueur, J.; Sirena, M.; Faini, G.; Aprili, M.; Contour, J. P.; Leridon, B.
2007-10-15
In this article we describe the effect of ion irradiation on high-T{sub c} superconductor thin film and its interest for the fabrication of Josephson junctions. In particular, we show that these alternative techniques allow to go beyond most of the limitations encountered in standard junction fabrication methods, both in the case of fundamental and technological purposes. Two different geometries are presented: a planar one using a single high-T{sub c} film and a mesa one defined in a trilayer structure.
Mathematical modeling of intrinsic Josephson junctions with capacitive and inductive couplings
NASA Astrophysics Data System (ADS)
Rahmonov, I. R.; Shukrinov, Yu M.; Zemlyanaya, E. V.; Sarhadov, I.; Andreeva, O.
2012-11-01
We investigate the current voltage characteristics (CVC) of intrinsic Josephson junctions (IJJ) with two types of couplings between junctions: capacitive and inductive. The IJJ model is described by a system of coupled sine-Gordon equations which is solved numerically by the 4th order Runge-Kutta method. The method of numerical simulation and numerical results are presented. The magnetic field distribution is calculated as the function of coordinate and time at different values of the bias current. The influence of model parameters on the CVC is studied. The behavior of the IJJ in dependence on coupling parameters is discussed.
A programmable quantum current standard from the Josephson and the quantum Hall effects
Poirier, W. Lafont, F.; Djordjevic, S.; Schopfer, F.; Devoille, L.
2014-01-28
We propose a way to realize a programmable quantum current standard (PQCS) from the Josephson voltage standard and the quantum Hall resistance standard (QHR) exploiting the multiple connection technique provided by the quantum Hall effect (QHE) and the exactness of the cryogenic current comparator. The PQCS could lead to breakthroughs in electrical metrology like the realization of a programmable quantum current source, a quantum ampere-meter, and a simplified closure of the quantum metrological triangle. Moreover, very accurate universality tests of the QHE could be performed by comparing PQCS based on different QHRs.
Strongly-coupled Josephson junction array for simulation of frustrated one-dimensional spin models
NASA Astrophysics Data System (ADS)
Zhou, Zhengwei; Du, Lianghui; Zhou, Xingxiang; Han, Yongjian; Guo, Guangcan
2013-03-01
We study the capacitance-coupled Josephson-junction array beyond the small-coupling limit. We find that, when the scale of the system is large, its Hamiltonian can be obtained without the small-coupling approximation and the system can be used to simulate strongly frustrated one-dimensional Ising spin problems. To engineer the system Hamiltonian for an ideal theoretical model, we apply a dynamical-decoupling technique to eliminate undesirable couplings in the system. Using a six-site junction array as an example, we numerically evaluate the system to show that it exhibits important characteristics of the frustrated spin model.
Cherenkov radiation of a Josephson vortex moving in a sandwich embedded in a dielectric medium
NASA Astrophysics Data System (ADS)
Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.
2008-08-01
A motion of a Josephson vortex in a long sandwich embedded in a dielectric medium is described. If the velocity of the vortex is greater than the velocity of light in the dielectric, terahertz-band Cherenkov radiation is generated and emitted from the lateral surface of the sandwich. The radiation loss power is determined. In the case when radiation loss is compensated for by the energy gain due to transport current, a relation between the current and the velocity of the vortex is obtained.
Symmetrical Josephson vortex interferometer as an advanced ballistic single-shot detector
Soloviev, I. I.; Klenov, N. V.; Bakurskiy, S. V.; Pankratov, A. L.; Kuzmin, L. S.
2014-11-17
We consider a ballistic detector formed in an interferometer manner which operational principle relies on Josephson vortex scattering at a measurement potential. We propose an approach to symmetrize the detector scheme and explore arising advantages in the signal-to-noise ratio and in the back-action on a measured object by means of recently presented numerical and analytical methods for modeling of a soliton scattering dynamics in the presence of thermal fluctuations. The obtained characteristics for experimentally relevant parameters reveal practical applicability of the considered schemes including possibility of coupling with standard digital rapid single flux quantum circuits.
Verification of the Model of Inductive Coupling between a Josephson Oscillator and a Stripline
NASA Astrophysics Data System (ADS)
Kudo, Keisuke; Yoshida, Keiji; Enpuku, Keiji; Yamafuji, Kaoru
1993-01-01
In order to realize an efficient coupling between a flux-flow-type Josephson oscillator (FFO) and a stripline, we have carried out experiments to verify the mathematical model of the inductive coupling scheme between FFO and a stripline resonator in the frequency range between 50 GHz and 350 GHz. It is shown that the simulation using the proposed equivalent circuit for the inductive coupling scheme well explains the experimental results. The experimentally obtained center frequency and the bandwidth of the matching circuit were as large as 120 GHz and 40 GHz, respectively, which are also in reasonable agreement with those obtained in the simulation.
Niobium nitride Josephson Junction studies and devices. Final report, 1 Jul-31 Dec 90
Sinclair, W.R.
1991-02-26
We suggest here a novel class of molecules for use in making monolayer thick insulating barriers for Josephson junctions employing all NbN conductors. For the experiments discussed here the smallest member of that class has been chosen. From sessile drop experiments we determine that this compound indeed reacts with NbN as postulated. Measurements of the electrical properties are less definitive. In no couple is shorting noted but the superconductivity of the bottom layer is eliminated near the junction presumably due to diffusion of the reactant molecule into the film.
Granato, Enzo
2008-07-11
Phase coherence and vortex order in a Josephson-junction array at irrational frustration are studied by extensive Monte Carlo simulations using the parallel-tempering method. A scaling analysis of the correlation length of phase variables in the full equilibrated system shows that the critical temperature vanishes with a power-law divergent correlation length and critical exponent nuph, in agreement with recent results from resistivity scaling analysis. A similar scaling analysis for vortex variables reveals a different critical exponent nuv, suggesting that there are two distinct correlation lengths associated with a decoupled zero-temperature phase transition.
Temporal stability of Y Ba Cu O nano Josephson junctions from ion irradiation
Cybart, Shane A.; Roediger, Peter; Chen, Ke; Parker, J. M.; Cho, Ethan Y.; Wong, Travis J.; Dynes, R. C.
2012-11-29
We investigate the temporal stability of YBa2Cu3O7 Josephson junctions created by ion irradiation through a nano-scale implant mask fabricated using electron beam lithography and reactive ion etching. A comparison of current-voltage characteristics measured for junctions after fabrication and eight years of storage at room temperature show a slight decrease in critical current and increase in normal state resistance consistent with broadening of the weaklink from diffusion of defects. Shapiro step measurements performed 8 years after fabrication reveal that device uniformity is maintained and is strong evidence that these devices have excellent temporal stability for applications.
NASA Astrophysics Data System (ADS)
Waintal, Xavier; Gaury, Benoit; Weston, Joseph
With single coherent electron sources and electronic interferometers now available in the lab, the time resolved dynamics of electrons can now be probed directly. I will discuss how a fast raise of voltage propagates inside an electronic interferometer and leads to an oscillating current of well controled frequency. This phenomena is the normal counterpart to the AC josephson effect. I will also briefly advertize our software for computing quantum transport properties, Kwant (http://kwant-project.org) and its time-dependent extension T-Kwant.
Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes
NASA Astrophysics Data System (ADS)
Borzenets, I. V.; Amet, F.; Ke, C. T.; Draelos, A. W.; Wei, M. T.; Seredinski, A.; Watanabe, K.; Taniguchi, T.; Bomze, Y.; Yamamoto, M.; Tarucha, S.; Finkelstein, G.
2016-12-01
We investigate the critical current IC of ballistic Josephson junctions made of encapsulated graphene-boron-nitride heterostructures. We observe a crossover from the short to the long junction regimes as the length of the device increases. In long ballistic junctions, IC is found to scale as ∝exp (-kBT /δ E ). The extracted energies δ E are independent of the carrier density and proportional to the level spacing of the ballistic cavity. As T →0 the critical current of a long (or short) junction saturates at a level determined by the product of δ E (or Δ ) and the number of the junction's transversal modes.
Unpaired Majorana modes in Josephson-Junction Arrays with gapless bulk excitations
Pino, M.; Tsvelik, A.; Ioffe, L. B.
2015-11-06
In this study, the search for Majorana bound states in solid-state physics has been limited to materials that display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson-junction arrays with gapless bulk excitations. The bulk modes mediate a coupling between Majorana bound states via the Ruderman-Kittel-Yosida-Kasuya mechanism. As a consequence, the lowest energy doublet acquires a finite energy difference. For a realistic set of parameters this energy splitting remains much smaller than the energy of the bulk eigenstates even for short chains of length L~10.
NASA Astrophysics Data System (ADS)
Mishra, Arindam; Saha, Suman; Hens, Chittaranjan; Roy, Prodyot K.; Bose, Mridul; Louodop, Patrick; Cerdeira, Hilda A.; Dana, Syamal K.
2017-01-01
An array of excitable Josephson junctions under a global mean-field interaction and a common periodic forcing shows the emergence of two important classes of coherent dynamics, librational and rotational motion, in the weaker and stronger coupling limits, respectively, with transitions to chimeralike states and clustered states in the intermediate coupling range. In this numerical study, we use the Kuramoto complex order parameter and introduce two measures, a libration index and a clustering index, to characterize the dynamical regimes and their transitions and locate them in a parameter plane.
Intestinal Transport of Weak Electrolytes
Jackson, Michael J.; Shiau, Yih-Fu; Bane, Susan; Fox, Margaret
1974-01-01
A study has been made of the transmural fluxes of benzoic, phenylacetic, and pentanoic acids, benzylamine, hexylamine, and D-amphetamine across rat jejunum incubated in vitro. The M to S fluxes of the weak acids were greater than their corresponding S to M fluxes, and the S to M fluxes of the weak bases were larger than their M to S fluxes. These patterns of asymmetric movements were observed when the transmural electrical potential difference was clamped at 0 mV, and when the pH values of the mucosal and serosal fluids were identical. The effects of a weak acid on the fluxes of other weak electrolytes were qualitatively similar when the effector weak acid was added to the mucosal fluid, and when it was added to the serosal fluid. But the effects of a weak base on the fluxes of other weak electrolytes were dependent upon its location, and the interactions observed when the effector weak base was added to the mucosal fluid were qualitatively different than those seen when it was added to the serosal fluid. The interactions between weak electrolytes could readily be explained in terms of the function of a system of three compartments in series, in which the pH of the intermediate compartment is greater than that of the bulk phases. But these observations could not be explained in terms of an analogous system involving an intermediate compartment of low pH, or in terms of a carrier mediated system. The transport function of the three-compartment system can be described in the form of an equation, and it is found that a pH difference of less than 0.5 unit may explain our observations on weak electrolyte transport. PMID:4812635
ERIC Educational Resources Information Center
Stewig, John Warren
Blacksmiths and their craft have changed with the times, and as times change for teachers, they too should be forgers of links. Teacher-to-teacher links should extend beyond the faculty lounge to support systems and active groups of individuals concerned about each other. Another personal link can be made by developing a grade level, system-wide…
Experimental investigations of weak definite and weak indefinite noun phrases.
Klein, Natalie M; Gegg-Harrison, Whitney M; Carlson, Greg N; Tanenhaus, Michael K
2013-08-01
Definite noun phrases typically refer to entities that are uniquely identifiable in the speaker and addressee's common ground. Some definite noun phrases (e.g., the hospital in Mary had to go the hospital and John did too) seem to violate this uniqueness constraint. We report six experiments that were motivated by the hypothesis that these "weak definite" interpretations arise in "incorporated" constructions. Experiments 1-3 compared nouns that seem to allow for a weak definite interpretation (e.g., hospital, bank, bus, radio) with those that do not (e.g., farm, concert, car, book). Experiments 1 and 2 used an instruction-following task and picture-judgment task, respectively, to demonstrate that a weak definite need not uniquely refer. In Experiment 3 participants imagined scenarios described by sentences such as The Federal Express driver had to go to the hospital/farm. Scenarios following weak definite noun phrases were more likely to include conventional activities associated with the object, whereas following regular nouns, participants were more likely to imagine scenarios that included typical activities associated with the subject; similar effects were observed with weak indefinites. Experiment 4 found that object-related activities were reduced when the same subject and object were used with a verb that does not license weak definite interpretations. In Experiment 5, a science fiction story introduced an artificial lexicon for novel concepts. Novel nouns that shared conceptual properties with English weak definite nouns were more likely to allow weak reference in a judgment task. Experiment 6 demonstrated that familiarity for definite articles and anti-familiarity for indefinite articles applies to the activity associated with the noun, consistent with predictions made by the incorporation analysis.
Experimental investigations of weak definite and weak indefinite noun phrases
Klein, Natalie M.; Gegg-Harrison, Whitney M.; Carlson, Greg N.; Tanenhaus, Michael K.
2013-01-01
Definite noun phrases typically refer to entities that are uniquely identifiable in the speaker and addressee’s common ground. Some definite noun phrases (e.g. the hospital in Mary had to go the hospital and John did too) seem to violate this uniqueness constraint. We report six experiments that were motivated by the hypothesis that these “weak definite” interpretations arise in “incorporated” constructions. Experiments 1-3 compared nouns that seem to allow for a weak definite interpretation (e.g. hospital, bank, bus, radio) with those that do not (e.g. farm, concert, car, book). Experiments 1 and 2 used an instruction-following task and picture-judgment task, respectively, to demonstrate that a weak definite need not uniquely refer. In Experiment 3 participants imagined scenarios described by sentences such as The Federal Express driver had to go to the hospital/farm. The imagined scenarios following weak definite noun phrases were more likely to include conventional activities associated with the object, whereas following regular nouns, participants were more likely to imagine scenarios that included typical activities associated with the subject; similar effects were observed with weak indefinites. Experiment 4 found that object-related activities were reduced when the same subject and object were used with a verb that does not license weak definite interpretations. In Experiment 5, a science fiction story introduced an artificial lexicon for novel concepts. Novel nouns that shared conceptual properties with English weak definite nouns were more likely to allow weak reference in a judgment task. Experiment 6 demonstrated that familiarity for definite articles and anti- familiarity for indefinite articles applies to the activity associated with the noun, consistent with predictions made by the incorporation analysis. PMID:23685208
Reichenbach, H.; Kuhl, A.L.
1993-09-07
The purpose of this paper is to compare reflection factors for weak shocks from various surfaces, and to focus attention on some unsolved questions. Three different cases are considered: square-wave planar shock reflection from wedges; square-wave planar shock reflection from cylinders; and spherical blast wave reflection from a planar surface. We restrict ourselves to weak shocks. Shocks with a Mach number of M{sub O} < 1.56 in air or with an overpressure of {Delta}{sub PI} < 25 psi (1.66 bar) under normal ambient conditions are called weak.
NASA Astrophysics Data System (ADS)
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio
2009-10-01
We microscopically examine the intergrain Josephson current in iron-pnictide superconductors in order to solve the puzzle of why the intergrain current is much lower than the intragrain one. The theory predicts that the intergrain Josephson current is significantly reduced by the ±s-wave symmetry when the incoherent tunneling becomes predominant and the density of states and the gap amplitude between two bands are identical. We find in such a situation that the temperature dependence of the intergrain Josephson current shows an anomalously flat curve over a wide temperature range. Finally, we suggest important points for increasing the intergrain current.
Oelze, B.; Ruck, B.; Sodtke, E.; Kirichenko, A.F.; Kupriyanov, M.Y.; Prusseit, W.
1997-02-01
A 3 bit single flux quantum (SFQ) shift register based on high-T{sub c} bicrystal Josephson junctions has been designed, fabricated, and experimentally tested. The circuit consists of 26 bicrystal Josephson junctions and includes the shift register itself, two dc-SFQ converters, one readout superconducting quantum interference device, serving as a SFQ-dc converter, and three Josephson transmission lines. The correct operation of all circuit components has been demonstrated by low frequency testing at a temperature of 50 K. {copyright} {ital 1997 American Institute of Physics.}
Time dependent weak localization of a 2DEG in the presence of Andreev reflections
Drexler, H.; Harris, J.; Yuh, E.L.
1995-12-31
Experiments on superconducting-normal-superconducting, SNS, junctions, comprised of Nb-2D InAs - Nb, exhibit AC currents at v = 4eV/h, twice the Josephson frequency. These currents can be ascribed to time dependent weak localization in the 2D InAs electron gas modulated by the presence of superconducting electrodes. The change of the current-voltage characteristic of a SNS structure under far-infrared (FIR) illumination (180GHz, 300GHz) has been investigated as a function of temperature, FIR power and magnetic field. The sample is an InAs/AlSb quantum well with a 1{mu}m-period Nb grating contacting the InAs. In the experiments a series connection of N = 300 junctions is measured. The differential resistance of the sample shows a very clear subharmonic gap structure, indicating multiple Andreev reflections between the SN-interfaces. Below a temperature of about T = 5K the sample is superconductive. At sufficiently high temperatures (T > 6K) the photoresponse of the sample under FIR illumination exhibits only a single resonance. This resonance is at V = Nhv/4e, that is half the voltage at which the first step of the AC Josephson effect would occur. B.Z. Spivak and D.E. Khmel`nitskii predicted this effect which arises from the quantum correction of the conductivity of a normal state electron gas due to Andreev reflections. Electrons and holes that are Andreev reflected at the superconductor interface acquire a phase shift that is determined by the phase {Phi} of the superconductor. Interference terms of time reversed paths that include Andreev reflections on adjacent superconductor stripes oscillate with 2({Phi}{sub 2}-{Phi}{sub 1}) = 4eVt/h and therefore lead to a time-dependent conductivity. The manifestation of the oscillating conductivity in the experiments is similar to the Shapiro steps of the AC Josephson effect but with twice the frequency. The experiments show that this effect is very sensitive to an applied magnetic field.
Side Gate Tunable Josephson Junctions at the LaAlO3/SrTiO3 Interface
2017-01-01
Novel physical phenomena arising at the interface of complex oxide heterostructures offer exciting opportunities for the development of future electronic devices. Using the prototypical LaAlO3/SrTiO3 interface as a model system, we employ a single-step lithographic process to realize gate-tunable Josephson junctions through a combination of lateral confinement and local side gating. The action of the side gates is found to be comparable to that of a local back gate, constituting a robust and efficient way to control the properties of the interface at the nanoscale. We demonstrate that the side gates enable reliable tuning of both the normal-state resistance and the critical (Josephson) current of the constrictions. The conductance and Josephson current show mesoscopic fluctuations as a function of the applied side gate voltage, and the analysis of their amplitude enables the extraction of the phase coherence and thermal lengths. Finally, we realize a superconducting quantum interference device in which the critical currents of each of the constriction-type Josephson junctions can be controlled independently via the side gates. PMID:28071920
Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions
NASA Astrophysics Data System (ADS)
Rakyta, Péter; Kormányos, Andor; Cserti, József
2016-06-01
We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.
Controllable 0–π Josephson junctions containing a ferromagnetic spin valve
Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; ...
2016-03-14
Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such ‘π-junctions’ were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relativemore » orientation of the two magnetizations. These controllable 0–π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Here, phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting ‘programmable logic’, where they could function in superconducting analogues to field-programmable gate arrays.« less
NASA Astrophysics Data System (ADS)
Guarcello, Claudio; Valenti, Davide; Spagnolo, Bernardo
2015-11-01
We study by numerical methods the phase dynamics in ballistic graphene-based short Josephson junctions. A superconductor-graphene-superconductor system exhibits superconductive quantum metastable states similar to those present in normal current-biased Josephson junctions. We investigate the effects of thermal and correlated fluctuations on the escape time from these metastable states, when the system is driven by an oscillating bias current in the presence of Gaussian white and colored noise sources. Varying the intensity and the correlation time of the noise source, it is possible to analyze the behavior of the escape time, or switching time, from a superconductive metastable state in different temperature regimes. Moreover, we are able to clearly distinguish dynamical regimes characterized by the dynamic resonant activation effect, in the absence of noise source, and the stochastic resonant activation phenomenon induced by the noise. For low initial values of the bias current, the dynamic resonant activation shows double-minimum structures, strongly dependent on the value of the damping parameter. Noise-enhanced stability is also observed in the system investigated. We analyze the probability density function (PDF) of the switching times. The PDFs for frequencies within the dynamic resonant activation minima are characterized by single peaks with exponential tails. The PDFs for noise intensities around the maxima of the switching time, peculiarity of the noise-enhanced stability phenomenon, are composed of regular sequences of two peaks for each period of the driving current, with exponentially decaying envelopes.
Quantum decay of the persistent current in a Josephson junction ring
NASA Astrophysics Data System (ADS)
Garanin, D. A.; Chudnovsky, E. M.
2016-03-01
We study the persistent current in a ring consisting of N ≫1 Josephson junctions threaded by the magnetic flux. When the dynamics of the ring is dominated by the capacitances of the superconducting islands the system is equivalent to the x y spin system in 1 +1 dimensions at the effective temperature T*=√{2 J U } , with J being the Josephson energy of the junction and U being the charging energy of the superconducting island. The numerical problem is challenging due to the absence of thermodynamic limit and slow dynamics of the Kosterlitz-Thouless transition. It is investigated on lattices containing up to ×106 sites. At T*≪J the quantum phase slips are frozen. The low-T* dependence of the persistent current computed numerically agrees quantitatively with the analytical formula provided by the spin-wave approximation. The high-T* behavior depends strongly on the magnetic flux and on the number of superconducting islands N . We present a detailed numerical study of the unbinding of vortex-antivortex pairs responsible for the phase slips, the superconductor-insulator transition, and evolution of the persistent current in a finite-size system.
A Nanoscale-Localized Ion Damage Josephson Junction Using Focused Ion Beam and Ion Implanter.
Wu, C H; Ku, W S; Jhan, F J; Chen, J H; Jeng, J T
2015-05-01
High-T(c) Josephson junctions were fabricated by nanolithography using focused ion beam (FIB) milling and ion implantation. The junctions were formed in a YBa2Cu3O7-x, thin film in regions defined using a gold-film mask with 50-nm-wide (top) slits, engraved by FIB. The focused ion beam system parameters for dwell time and passes were set to remove gold up to a precise depth. 150 keV oxygen ions were implanted at a nominal dose of up to 5 x 10(13) ions/cm2 into YBa2Cu3O7-x microbridges through the nanoscale slits. The current-voltage curves of the ion implantation junctions exhibit resistive-shunted-junction-like behavior at 77 K. The junction had an approximately linear temperature dependence of critical current. Shapiro steps were observed under microwave irradiation. A 50-nm-wide slit and 0-20-nm-thick buffer layers were chosen in order to make Josephson junctions due to the V-shape of the FIB-milled trench.
Controllable 0–π Josephson junctions containing a ferromagnetic spin valve
Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; Wang, Yixing; Miller, D. L.; Loloee, Reza; Pratt, Jr., W. P.; Birge, Norman O.
2016-03-14
Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such ‘π-junctions’ were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relative orientation of the two magnetizations. These controllable 0–π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Here, phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting ‘programmable logic’, where they could function in superconducting analogues to field-programmable gate arrays.
NASA Astrophysics Data System (ADS)
Antonenko, Daniil S.; Skvortsov, Mikhail A.
2015-12-01
A nondissipative supercurrent state of a Josephson junction is metastable with respect to the formation of a finite-resistance state. This transition is driven by fluctuations, thermal at high temperatures and quantum at low temperatures. We evaluate the lifetime of such a state due to quantum fluctuations in the limit when the supercurrent is approaching the critical current. The decay probability is determined by the instanton action for the superconducting phase difference across the junction. At low temperatures, the dynamics of the phase is massive and is determined by the effective capacitance, which is a sum of the geometric and intrinsic capacitance of the junction. We model the central part of the Josephson junction either by an arbitrary short mesoscopic conductor described by the set of its transmission coefficients, or by a diffusive wire of an arbitrary length. The intrinsic capacitance can generally be estimated as C*˜G /Eg , where G is the normal-state conductance of the junction and Eg is the proximity minigap in its normal part. The obtained capacitance is sufficiently large to qualitatively explain the hysteretic behavior of the current-voltage characteristic even in the absence of overheating.
Noise properties of nanoscale YBa2Cu3O7-δ Josephson junctions
NASA Astrophysics Data System (ADS)
Gustafsson, D.; Lombardi, F.; Bauch, T.
2011-11-01
We present electric noise measurements of nanoscale biepitaxial YBa2Cu3O7-δ (YBCO) Josephson junctions fabricated by two different lithographic methods. The first (conventional) technique defines the junctions directly by ion milling etching through an amorphous carbon mask. The second (soft patterning) method makes use of the phase competition between the superconducting YBCO (Y123) and the insulating Y2BaCuO5 (Y211) phase at the grain boundary interface on MgO (110) substrates. The voltage noise properties of the two methods are compared in this study. For all junctions (having a thickness of 100 nm and widths of 250-500 nm), we see a significant amount of individual charge traps. We have extracted an approximate value for the effective area of the charge traps from the noise data. From the noise measurements, we infer that the soft-patterned junctions with a grain-boundary (GB) interface manifesting a large c-axis tunneling component have a uniform barrier and a superconductor-insulator-superconductor (SIS) -like behavior. The noise properties of soft-patterned junctions having a GB interface dominated by transport parallel to the ab planes are in accordance with a resonant tunneling barrier model. The conventionally patterned junctions, instead, have suppressed superconducting transport channels with an area much less than the nominal junction area. These findings are important for the implementation of nanosized Josephson junctions in quantum circuits.
Observation of 0–π transition in SIsFS Josephson junctions
Ruppelt, N. Vavra, O.; Kohlstedt, H.; Sickinger, H.; Menditto, R.; Goldobin, E.; Koelle, D.; Kleiner, R.
2015-01-12
The 0–π transition in Superconductor-Insulator-superconductor-Ferromagnet-Superconductor (SIsFS) Josephson junctions (JJs) was investigated experimentally. As predicted by theory, an s-layer inserted into a ferromagnetic SIFS junction can enhance the critical current density up to the value of an SIS tunnel junction. We fabricated Nb′ | AlO{sub x} | Nb | Ni{sub 60}Cu{sub 40} | Nb JJs with wedge-like s (Nb) and F (Ni{sub 60}Cu{sub 40}) layers and studied the Josephson effect as a function of the s- and F-layer thickness, d{sub s} and d{sub F}, respectively. For d{sub s} = 11 nm, π-JJs with SIFS-type j{sub c}(d{sub F}) and critical current densities up to j{sub c}{sup π}=60 A/cm{sup 2} were obtained at 4.2 K. Thicker d{sub s} led to a drastic increase of the critical current decay length, accompanied by the unexpected disappearance of the 0–π transition dip in the j{sub c}(d{sub F}) dependence. Our results are relevant for superconducting memories, rapid single flux quantum logic circuits, and solid state qubits.
Sub-terahertz sound excitation and detection by a long Josephson junction
NASA Astrophysics Data System (ADS)
Koshelets, V. P.
2014-06-01
The paper reports on experimental observations of sub-terahertz sound wave generation and detection by a long Josephson junction. This effect was discovered in spectral measurements of sub-terahertz electromagnetic emission from a flux-flow oscillator (FFO) deposited on an optically polished Si substrate. The ‘back action’ of the acoustic waves generated by the FFO and reflected by the bottom surface of the Si substrate results in the appearance of resonant steps in the FFO IVCs with spacings as small as 29 nV for a 0.3 mm substrate thickness; these steps manifest themselves in a pronounced resonant structure in the emission spectra, with spacings of about 14 MHz, precisely according to the Josephson relation. The mechanism of acoustic wave generation and detection by the FFO is discussed; a possibility for employing the discovered effect for FFO frequency stabilization has been demonstrated. A simple and reliable way to suppress the superfine resonant structure has been developed and proved; this invention allows continuous frequency tuning and FFO phase locking at any desired frequency, all of which are vitally important for most applications.
Design and Characterization of a millikelvin dual-tip Josephson STM
NASA Astrophysics Data System (ADS)
Roychowdhury, A.; Dreyer, M.; Anderson, J. R.; Lobb, C. J.; Wellstood, F. C.
2014-03-01
We describe the design and characterization of a dual-tip Josephson STM that operates at millikelvin temperatures. We report an effective noise temperature for the STM on the order of 200 mK. In addition to the expected phase diffusive super current in the ultra-small Nb-Nb junction formed by one tip and the sample, our high resolution spectroscopy at mK temperatures reveals resonant coupling between the STM junction and the electromagnetic environment it is embedded in, as predicted by P(E) theory. We have for the first time, observed Shapiro-like steps in this limit by measuring the response of the P(E) supercurrent to microwave radiation as a function of amplitude. Fits to theory indicate that the coupling of an ultra-small Josephson junction to its environment/circuit may be used to a) directly measure dissipation channels associated with circuit resonances and b) calibrate the frequency dependent microwave attenuation in cryogenic circuits as seen by the junction.
Nb/InAs nanowire proximity junctions from Josephson to quantum dot regimes.
Gharavi, Kaveh; Holloway, Gregory W; LaPierre, Ray R; Baugh, Jonathan
2017-02-24
The superconducting proximity effect is probed experimentally in Josephson junctions fabricated with InAs nanowires contacted by Nb leads. Contact transparencies [Formula: see text] are observed. The electronic phase coherence length at low temperatures exceeds the channel length. However, the elastic scattering length is a few times shorter than the channel length. Electrical measurements reveal two regimes of quantum transport: (i) the Josephson regime, characterised by a dissipationless current up to ∼100 nA, and (ii) the quantum dot (QD) regime, characterised by the formation of Andreev bound states (ABS) associated with spontaneous QDs inside the nanowire channel. In regime (i), the behaviour of the critical current I c versus an axial magnetic field [Formula: see text] shows an unexpected modulation and persistence to fields [Formula: see text] T. In the QD regime, the ABS are modelled as the current-biased solutions of an Anderson-type model. The applicability of devices in both transport regimes to Majorana fermion experiments is discussed.
Nonreciprocal Microwave Signal Processing with a Field-Programmable Josephson Amplifier
NASA Astrophysics Data System (ADS)
Lecocq, F.; Ranzani, L.; Peterson, G. A.; Cicak, K.; Simmonds, R. W.; Teufel, J. D.; Aumentado, J.
2017-02-01
We report on the design and implementation of a field-programmable Josephson amplifier (FPJA)—a compact and lossless superconducting circuit that can be programmed in situ by a set of microwave drives to perform reciprocal and nonreciprocal frequency conversion and amplification. In this work, we demonstrate four modes of operation: frequency conversion (transmission of -0.5 dB, reflection of -30 dB), circulation (transmission of -0.5 dB, reflection of -30 dB, isolation of 30 dB), phase-preserving amplification (gain >20 dB , one photon of added noise) and directional phase-preserving amplification (reflection of -10 dB, forward gain of 18 dB, reverse isolation of 8 dB, one photon of added noise). The system exhibits quantitative agreement with the theoretical prediction. Based on a gradiometric superconducting quantum-interference device with Nb /Al -Al Ox/Nb Josephson junctions, the FPJA is first-order insensitive to flux noise and can be operated without magnetic shielding at low temperature. Owing to its flexible design and compatibility with existing superconducting fabrication techniques, the FPJA offers a straightforward route toward on-chip integration with superconducting quantum circuits such as qubits and microwave optomechanical systems.
Fraunhofer pattern arising from an edge-stepped topological surface Josephson current distribution
NASA Astrophysics Data System (ADS)
Lee, Jae Hyeong; Lee, Gil-Ho; Lee, Janghee; Park, Joonbum; Nam, Seung-Geol; Shin, Yun-Sok; Kim, Jun Sung; Lee, Hu-Jong
2015-03-01
We report a surface-dominant Josephson effect in superconductor-topological insulator-superconductor (S-TI-S) devices, where a Bi1.5Sb0.5Te1.7Se1.3 (BSTS) crystal flake was adopted as an intervening TI between Al superconducting electrodes. We observed a Fraunhofer critical current modulation in a perpendicular magnetic field in an Al-TI-Al junction for both local and nonlocal current biasing. For the local biasing, the Fraunhofer signal was highly robust to the magnetic field up to the critical field of the Al electrodes, corresponding to the edge-stepped nonuniform supercurrent distribution arising from the top and rough side surfaces of the BSTS flake. A Fraunhofer-like pattern was also observed in a neighboring Au-TI-Au normal junction when it was nonlocally biased by the Al-TI-Al junction. All these strongly suggest Josephson coupling established via topologically robust conducting channels present on the surface of the 3D topological insulator. Current: Department of Physics, Harvard University, Cambridge, USA.
Nanoscale phase engineering of thermal transport with a Josephson heat modulator.
Fornieri, Antonio; Blanc, Christophe; Bosisio, Riccardo; D'Ambrosio, Sophie; Giazotto, Francesco
2016-03-01
Macroscopic quantum phase coherence has one of its pivotal expressions in the Josephson effect, which manifests itself both in charge and energy transport. The ability to master the amount of heat transferred through two tunnel-coupled superconductors by tuning their phase difference is the core of coherent caloritronics, and is expected to be a key tool in a number of nanoscience fields, including solid-state cooling, thermal isolation, radiation detection, quantum information and thermal logic. Here, we show the realization of the first balanced Josephson heat modulator designed to offer full control at the nanoscale over the phase-coherent component of thermal currents. Our device provides magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a maximum of the flux-to-temperature transfer coefficient reaching 200 mK per flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the exact correspondence in the phase engineering of charge and heat currents, breaking ground for advanced caloritronic nanodevices such as thermal splitters, heat pumps and time-dependent electronic engines.
Energy Band and Josephson Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Zhang, Xin; Yu, Zi-Fa; Xue, Ju-Kui
2015-10-01
We theoretically investigate the energy band structure and Josephson dynamics of a spin-orbit coupled Bose-Einstein condensate in a double-well potential. We study the energy band structure and the corresponding tunneling dynamics of the system by properly adjusting the SO coupling, Raman coupling, Zeeman field and atomic interactions. The coupled effects of SO coupling, Raman coupling, Zeeman field and atomic interactions lead to the appearance of complex energy band structure including the loop structure. Particularly, the emergence of the loop structure in energy band also depends on SO coupling, Raman coupling, Zeeman field and atomic interactions. Correspondingly, the Josephson dynamics of the system are strongly related to the energy band structure. Especially, the emergence of the loop structure results in complex tunneling dynamics, including suppression-revival transitions and self-trapping of atoms transfer between two spin states and two wells. This engineering provides a possible means for studying energy level and corresponding dynamics of two-species SO coupled BECs. Supported by the National Natural Science Foundation of China under Grant Nos. 11274255 and 11305132, by Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20136203110001, by the Natural Science Foundation of Gansu province under Grant No. 2011GS04358, and by Creation of Science and Technology of Northwest Normal University under Grant Nos. NWNU-KJCXGC-03-48, NWNU-LKQN-12-12
Amplitude control of the spin-triplet supercurrent in S/F/S Josephson junctions
Martinez, William M.; Pratt, Jr., W. P.; Birge, Norman O.
2016-02-17
Josephson junctions made with conventional s-wave superconductors and containing multiple layers of ferromagnetic materials can carry spin-triplet supercurrent in the presence of certain types of magnetic inhomogeneity. In junctions containing three ferromagnetic layers, the triplet supercurrent is predicted to be maximal when the magnetizations of the adjacent layers are orthogonal, and zero when the magnetizations of any two adjacent layers are parallel. Here we demonstrate on-off control of the spin-triplet supercurrent in such junctions, achieved by rotating the magnetization direction of one of the three layers by 90°. We obtain “on-off” ratios of 5, 7, and 19 for the supercurrentmore » in the three samples that have been studied so far. In conclusion, these observations directly confirm one of the most salient predictions of the theory, and they pave the way for applications of spin-triplet Josephson junctions in the nascent area of “superconducting spintronics”.« less
An ion-beam-assisted process for high-T{sub c} Josephson junctions
Huang, M.Q.; Chen, L.; Zhao, Z.X.; Yang, T.; Nie, J.C.; Wu, P.J.; Xiong, X.M.
1997-10-01
We have developed a non-ion-etching ion-beam-assisted-deposition (IBAD) process for fabricating high critical-temperature (T{sub c}) grain boundary Josephson junctions through a photoresist liftoff mask. The YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) junctions fabricated through this process exhibited the resistively-shunted-junction (RSJ)-like I{endash}V characteristics. The well-defined Shapiro steps have been seen on the I{endash}V curves under microwave radiation. The magnetic modulation of critical current of a 4 {mu}m width YBCO junction tallied with the prior simulated Fraunhofer diffraction pattern of a Josephson junction with a spatially homogeneous critical current density. The maximum peak-to-peak modulation voltage across the dc superconducting quantum interference device (SQUID) fabricated by using these junctions reached up to 32 {mu}V at 77 K. The magnetic modulation of the SQUID exhibited periodic behavior with the observed modulation period of 5.0{times}10{sup {minus}4}G. {copyright} {ital 1997 American Institute of Physics.}
Nanoscale phase engineering of thermal transport with a Josephson heat modulator
NASA Astrophysics Data System (ADS)
Fornieri, Antonio; Blanc, Christophe; Bosisio, Riccardo; D'Ambrosio, Sophie; Giazotto, Francesco
2016-03-01
Macroscopic quantum phase coherence has one of its pivotal expressions in the Josephson effect, which manifests itself both in charge and energy transport. The ability to master the amount of heat transferred through two tunnel-coupled superconductors by tuning their phase difference is the core of coherent caloritronics, and is expected to be a key tool in a number of nanoscience fields, including solid-state cooling, thermal isolation, radiation detection, quantum information and thermal logic. Here, we show the realization of the first balanced Josephson heat modulator designed to offer full control at the nanoscale over the phase-coherent component of thermal currents. Our device provides magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a maximum of the flux-to-temperature transfer coefficient reaching 200 mK per flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the exact correspondence in the phase engineering of charge and heat currents, breaking ground for advanced caloritronic nanodevices such as thermal splitters, heat pumps and time-dependent electronic engines.
Sonne, Gustav; Gorelik, Leonid Y
2011-04-22
We demonstrate that a suspended nanowire forming a weak link between two superconductors can be cooled to its motional ground state by a supercurrent flow. The predicted cooling mechanism has its origins in magnetic field induced inelastic tunneling of the macroscopic superconducting phase associated with the junction. Furthermore, we show that the voltage drop over the junction is proportional to the average population of the vibrational modes in the stationary regime, a phenomenon which can be used to probe the level of cooling.
Weak interactions and presupernova evolution
Aufderheide, M.B. State Univ. of New York . Dept. of Physics)
1991-02-19
The role of weak interactions, particularly electron capture and {beta}{sup {minus}} decay, in presupernova evolution is discussed. The present uncertainty in these rates is examined and the possibility of improving the situation is addressed. 12 refs., 4 figs.
[Acute muscle weakness: differential diagnoses].
Antoniuk, Sérgio A
2013-09-06
Acute muscle weakness, a common disorder in pediatrics, can occur from impairment of any part of the motor unit, including the upper motor neuron, lower motor neuron, peripheral nerve, neuromuscular junction or muscle. It usually manifests itself as an acute or hyperacute motor disorder of progressive or rapidly progressive course. Acute muscle weakness is a neuromuscular emergency, especially if it affects the respiratory or oropharyngeal musculature. The location of the motor weakness and associated neurological signs and symptoms usually indicate the location of the lesion. The onset, speed and clinical evolution, as well as other data from the patient's history, suggest the pathophysiological differential diagnosis. Successful treatment depends on the immediate and correct differential diagnosis. This paper presents the main differential diagnosis of main neuromuscular diseases that cause acute muscle weakness in children.
Weak Deeply Virtual Compton Scattering
Ales Psaker; Wolodymyr Melnitchouk; Anatoly Radyushkin
2007-03-01
We extend the analysis of the deeply virtual Compton scattering process to the weak interaction sector in the generalized Bjorken limit. The virtual Compton scattering amplitudes for the weak neutral and charged currents are calculated at the leading twist within the framework of the nonlocal light-cone expansion via coordinate space QCD string operators. Using a simple model, we estimate cross sections for neutrino scattering off the nucleon, relevant for future high intensity neutrino beam facilities.
Topics in the Theory of Josephson Arrays and Disordered Magnetic Systems
NASA Astrophysics Data System (ADS)
Porter, Christopher D.
This thesis consists of two parts. In the first part, we discuss several topics in the theory of Josephson junction arrays. The second part is concerned with two problems in the theory of magnetic systems: charge transfer ferromagnetism, and the clustering of Fe adatoms on graphene. In the field of Josephson arrays we consider three topics. First, the effects of a current bias on arrays of underdamped junctions are considered, for several junction geometries including both 2D and 3D systems. Approximate phase diagrams are constructed for various values of the ratio of charging energy to Josephson coupling. The effects of finite temperature are also discussed. Next, we examine the rich response of Josephson arrays to magnetic fields in the case of Josephson ladders with nonuniform spacing, known as superconducting quantum interference filters (SQIFs). Such ladders are already used for the detection of DC magnetic fields, but here their applicability to detecting AC fields is also discussed. It is shown that, for sufficiently low frequencies, the voltage produced by an AC field is equivalent to a convolution of the DC voltage response with the sinusoidal field oscillation. These SQIFs are studied in an effort to greatly increase the period of their response to external magnetic fields. Finally, we investigate underdamped 2D and 3D arrays with a special inhomogeneity. Specifically, insulating regions of varying width are sandwiched between superconducting regions of the arrays. The phase ordering in the superconducting regions is shown to penetrate into the insulating regions, leading to an unusual type of proximity effect. Our calculations for these arrays are done using mean field and perturbation theory, mean field theory and numerical methods, and our results are quantitatively confirmed by quantum Monte Carlo calculations. The superconducting correlation length is calculated inside the insulating region and it is found that the structure yields multiple layers of
Precision metrology using weak measurements.
Zhang, Lijian; Datta, Animesh; Walmsley, Ian A
2015-05-29
Weak values and measurements have been proposed as a means to achieve dramatic enhancements in metrology based on the greatly increased range of possible measurement outcomes. Unfortunately, the very large values of measurement outcomes occur with highly suppressed probabilities. This raises three vital questions in weak-measurement-based metrology. Namely, (Q1) Does postselection enhance the measurement precision? (Q2) Does weak measurement offer better precision than strong measurement? (Q3) Is it possible to beat the standard quantum limit or to achieve the Heisenberg limit with weak measurement using only classical resources? We analyze these questions for two prototypical, and generic, measurement protocols and show that while the answers to the first two questions are negative for both protocols, the answer to the last is affirmative for measurements with phase-space interactions, and negative for configuration space interactions. Our results, particularly the ability of weak measurements to perform at par with strong measurements in some cases, are instructive for the design of weak-measurement-based protocols for quantum metrology.
Weak Energy: Form and Function
NASA Astrophysics Data System (ADS)
Parks, Allen D.
The equation of motion for a time-dependent weak value of a quantum mechanical observable contains a complex valued energy factor—the weak energy of evolution. This quantity is defined by the dynamics of the pre-selected and post-selected states which specify the observable's weak value. It is shown that this energy: (i) is manifested as dynamical and geometric phases that govern the evolution of the weak value during the measurement process; (ii) satisfies the Euler-Lagrange equations when expressed in terms of Pancharatnam (P) phase and Fubini-Study (FS) metric distance; (iii) provides for a PFS stationary action principle for quantum state evolution; (iv) time translates correlation amplitudes; (v) generalizes the temporal persistence of state normalization; and (vi) obeys a time-energy uncertainty relation. A similar complex valued quantity—the pointed weak energy of an evolving quantum state—is also defined and several of its properties in PFS coordinates are discussed. It is shown that the imaginary part of the pointed weak energy governs the state's survival probability and its real part is—to within a sign—the Mukunda-Simon geometric phase for arbitrary evolutions or the Aharonov-Anandan (AA) geometric phase for cyclic evolutions. Pointed weak energy gauge transformations and the PFS 1-form are defined and discussed and the relationship between the PFS 1-form and the AA connection 1-form is established. [Editors note: for a video of the talk given by Prof. Parks at the Aharonov-80 conference in 2012 at Chapman University, see http://quantum.chapman.edu/talk-25.
Charge segregation in weakly ionized microgels
NASA Astrophysics Data System (ADS)
Hyatt, John S.; Douglas, Alison M.; Stanley, Chris; Do, Changwoo; Barker, Thomas H.; Fernández-Nieves, Alberto
2017-01-01
We investigate microgels synthesized from N -isopropylacrylamide (NIPAM) copolymerized with a large mol% of acrylic acid, finding that when the acid groups are partially ionized at high temperatures, competition between ion-induced swelling and hydrophobic deswelling of poly(NIPAM) chains results in microphase separation. In cross-linked microgels, this manifests as a dramatic decrease in the ratio between the radius of gyration and the hydrodynamic radius to ˜0.2 , indicating that almost all the mass of the microgel is concentrated near the particle center. We also observe a concurrent decrease of the polymer network length scale via small-angle neutron scattering, confirming the presence of a dense, deswollen core surrounded by a diffuse, charged periphery. We compare these results to those obtained for a system of charged ultralow-cross-linked microgels; the form factor shows a distinct peak at high q when the temperature exceeds a threshold value. We successfully fit the form factor to theory developed to describe scattering from weakly charged gels in poor solvents, and we tie this behavior to charge segregation in the case of the cross-linked microgels.
NASA Astrophysics Data System (ADS)
Gouchi, Jun; Sumiyama, Akihiko; Motoyama, Gaku; Yamaguchi, Akira; Kimura, Noriaki; Yamamoto, Etsuji; Haga, Yoshinori; Ōnuki, Yoshichika
2012-11-01
The Josephson critical current Ic between a single-crystal UPt3 and Al has been measured for the junctions on the UPt3 surface perpendicular to the hexagonal a[11\\bar{2}0], b[10\\bar{1}0], and c[0001] axes. The magnetic field dependence of Ic shows a Fraunhofer diffraction pattern for a current flow parallel to the c-axis, suggesting that the Josephson coupling is uniform throughout the junction. Small modifications applied to the Fraunhofer pattern have been observed for a current flow parallel to the a- and b-axes. These results contradict the E2u scenario for the odd-parity order parameter in UPt3, in which the Josephson effect is forbidden in the three directions, whereas the recently proposed E1u scenario permits, at least, the a- and c-axis Josephson couplings.
Josephson effect in Nb/Al2O3/Al/MgB2 large-area thin-film heterostructures
NASA Astrophysics Data System (ADS)
Carapella, G.; Martucciello, N.; Costabile, G.; Ferdeghini, C.; Ferrando, V.; Grassano, G.
2002-04-01
We report the demonstration of dc and ac Josephson effects in Nb/Al2O3/Al/MgB2 thin-film heterostructure. The heterostructure exhibits moderately hysteretic current-voltage characteristic with a dc Josephson current branch and regular microwave-induced Shapiro steps. From conductance spectrum, a gap of about 2 meV at 7.7 K is estimated for the proximized surface of MgB2 electrode.
Warping the Weak Gravity Conjecture
NASA Astrophysics Data System (ADS)
Kooner, Karta; Parameswaran, Susha; Zavala, Ivonne
2016-08-01
The Weak Gravity Conjecture, if valid, rules out simple models of Natural Inflation by restricting their axion decay constant to be sub-Planckian. We revisit stringy attempts to realise Natural Inflation, with a single open string axionic inflaton from a probe D-brane in a warped throat. We show that warped geometries can allow the requisite super-Planckian axion decay constant to be achieved, within the supergravity approximation and consistently with the Weak Gravity Conjecture. Preliminary estimates of the brane backreaction suggest that the probe approximation may be under control. However, there is a tension between large axion decay constant and high string scale, where the requisite high string scale is difficult to achieve in all attempts to realise large field inflation using perturbative string theory. We comment on the Generalized Weak Gravity Conjecture in the light of our results.
Weak values in continuous weak measurements of qubits
NASA Astrophysics Data System (ADS)
Qin, Lupei; Liang, Pengfei; Li, Xin-Qi
2015-07-01
For continuous weak measurements of qubits, we obtain exact expressions for weak values (WVs) from the postselection restricted average of measurement outputs, by using both the quantum-trajectory equation (QTE) and the quantum Bayesian approach. The former is applicable to short-time weak measurement, while the latter can relax the measurement strength to finite. We find that even in the "very" weak limit the result can be essentially different from the one originally proposed by Aharonov, Albert, and Vaidman (AAV), in the sense that our result incorporates nonperturbative correction which could be important when the AAV WV is large. Within the Bayesian framework, we obtain also elegant expressions for finite measurement strength and find that the amplifier's noise in quantum measurement has no effect on the WVs. In particular, we obtain very useful results for homodyne measurement in a circuit-QED system, which allows for measuring the real and imaginary parts of the AAV WV by simply tuning the phase of the local oscillator. This advantage can be exploited as an efficient state-tomography technique.
Weak localization and weak antilocalization in doped germanium epilayers
NASA Astrophysics Data System (ADS)
Newton, P. J.; Mansell, R.; Holmes, S. N.; Myronov, M.; Barnes, C. H. W.
2017-02-01
The magnetoresistance of 50 nm thick epilayers of doped germanium is measured at a range of temperatures down to 1.6 K. Both n- and p-type devices show quantum corrections to the conductivity in an applied magnetic field, with n-type devices displaying weak localization and p-type devices showing weak antilocalization. From fits to these data using the Hikami-Larkin-Nagaoka model, the phase coherence length of each device is extracted, as well as the spin diffusion length of the p-type device. We obtain phase coherence lengths as large as 325 nm in the highly doped n-type device, presenting possible applications in quantum technologies. The decay of the phase coherence length with temperature is found to obey the same power law of lϕ ∝ Tc, where c = -0.68 ± 0.03, for each device, in spite of the clear differences in the nature of the conduction. In the p-type device, the measured spin diffusion length does not change over the range of temperatures for which weak antilocalization can be observed. The presence of a spin-orbit interaction manifested as weak antilocalization in the p-type epilayer suggests that these structures could be developed for use in spintronic devices such as the spin-FET, where significant spin lifetimes would be important for efficient device operation.
Cosmology and the weak interaction
NASA Technical Reports Server (NTRS)
Schramm, David N.
1989-01-01
The weak interaction plays a critical role in modern Big Bang cosmology. Two of its most publicized comological connections are emphasized: big bang nucleosynthesis and dark matter. The first of these is connected to the cosmological prediction of neutrine flavors, N(sub nu) is approximately 3 which in now being confirmed. The second is interrelated to the whole problem of galacty and structure formation in the universe. The role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure is demonstrated.
Cosmology and the weak interaction
Schramm, D.N. ):)
1989-12-01
The weak interaction plays a critical role in modern Big Bang cosmology. This review will emphasize two of its most publicized cosmological connections: Big Bang nucleosynthesis and Dark Matter. The first of these is connected to the cosmological prediction of Neutrino Flavours, N{sub {nu}} {approximately} 3 which is now being confirmed at SLC and LEP. The second is interrelated to the whole problem of galaxy and structure formation in the universe. This review will demonstrate the role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure. 87 refs., 3 figs., 5 tabs.
Adaptive antenna arrays for weak interfering signals
NASA Technical Reports Server (NTRS)
Gupta, I. J.
1985-01-01
The interference protection provided by adaptive antenna arrays to an Earth station or satellite receive antenna system is studied. The case where the interference is caused by the transmission from adjacent satellites or Earth stations whose signals inadverently enter the receiving system and interfere with the communication link is considered. Thus, the interfering signals are very weak. To increase the interference suppression, one can either decrease the thermal noise in the feedback loops or increase the gain of the auxiliary antennas in the interfering signal direction. Both methods are examined. It is shown that one may have to reduce the noise correlation to impractically low values and if directive auxiliary antennas are used, the auxiliary antenna size may have to be too large. One can, however, combine the two methods to achieve the specified interference suppression with reasonable requirements of noise decorrelation and auxiliary antenna size. Effects of the errors in the steering vector on the adaptive array performance are studied.
NASA Astrophysics Data System (ADS)
Nakhmedov, E.; Mammadova, S.; Alekperov, O.
2016-01-01
A time-reversal invariant topological superconductivity is suggested to be realized in a quasi-one-dimensional structure on a plane, which is fabricated by filling the superconducting materials into the periodic channel of dielectric matrices like zeolite and asbestos under high pressure. The topological superconducting phase sets up in the presence of large spin-orbit interactions when intra-wire s-wave and inter-wire d-wave pairings take place. Kramers pairs of Majorana bound states emerge at the edges of each wire. We analyze effects of the Zeeman magnetic field on Majorana zero-energy states. In-plane magnetic field was shown to make asymmetric the energy dispersion, nevertheless Majorana fermions survive due to protection of a particle-hole symmetry. Tunneling of Majorana quasiparticle from the end of one wire to the nearest-neighboring one yields edge fractional Josephson current with 4π-periodicity.
Quantum vortices near the superconductor-insulator transition in Josephson junction arrays
NASA Astrophysics Data System (ADS)
van Otterlo, Anne; Fazio, Rosario; Scho¨n, Gerd
1994-02-01
We investigate the properties of vortices in Josephson junction arrays in the regime close to the superconductor-insulator transition. We derive general expressions for the vortex mass and the vortex-spinwave coupling in terms of the charge-charge correlation function, which we evaluate in a self consistent harmonic approximation, as well as by means of Monte Carlo simulations. Our main conclusions are that close to the transition to the insulating phase the vortex mass vanishes and the threshold velocity above which vortices couple to spinwaves diverges. Thus, in the quantum regime close to the phase transition there is a velocity window in which vortices may move ballistically without damping, this in contrast to the flux flow behaviour in classical arrays.