High Frequency Quantum Admittance and Noise Measurement with an On-chip Resonant Circuit

By coupling a quantum detector, a superconductor-insulator-superconductor junction, to a Josephson junction \textit{via} a resonant circuit we probe the high frequency properties, namely the ac complex admittance and the current fluctuations of the Josephson junction at the resonant frequencies. The admittance components show frequency dependent singularities related to the superconducting density of state while the noise exhibits a strong frequency dependence, consistent with theoretical predictions. The circuit also allows to probe separately the emission and absorption noise in the quantum regime of the superconducting resonant circuit at equilibrium. At low temperature the resonant circuit exhibits only absorption noise related to zero point fluctuations, whereas at higher temperature emission noise is also present.Comment: 15 pages, 15 figure

Double-Spin Transverse Asymmetries in Drell-Yan Processes

We calculate the double-spin transverse asymmetries for the Drell-Yan lepton pair production in p-p and p-anti p collisions. We assume the transverse and the longitudinal polarization densities to be equal at a very small scale, as it is suggested by confinement model results. Using a global fit for the longitudinal distributions, we find transverse asymmetries of order of 10^-2 at most, in the accessible kinematic regions.Comment: 8 pages, REVTeX, 6 figures included as file figures.tar.g

Zurek-Kibble Mechanism for the Spontaneous Vortex Formation in Nb−Al/Alox/NbNb-Al/Al_{ox}/Nb Josephson Tunnel Junctions: New Theory and Experiment

New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched $Nb-Al/Al_{ox}/Nb$ annular Josephson tunnel junctions as a function of the quench time, $\tau_{Q}$. The probability $f_{1}$ to trap a single defect during the N-S phase transition clearly follows an allometric dependence on $\tau_{Q}$ with a scaling exponent $\sigma = 0.5$, as predicted from the Zurek-Kibble mechanism for {\it realistic} JTJs formed by strongly coupled superconductors. This definitive experiment replaces one reported by us earlier, in which an idealised model was used that predicted $\sigma = 0.25$, commensurate with the then much poorer data. Our experiment remains the only condensed matter experiment to date to have measured a scaling exponent with any reliability.Comment: Four pages, one figur

Spontaneous Fluxon Production in Annular Josephson Tunnel Junctions in the Presence of a Magnetic Field

We report on the spontaneous production of fluxons in the presence of a symmetry-breaking magnetic field for annular Josephson tunnel junctions during a thermal quench. The dependence on field intensity $B$ of the probability $\bar{f_1}$ to trap a single defect during the N-S phase transition drastically depends on the sample circumferences. We show that the data can be understood in the framework of the Kibble-Zurek picture of spontaneous defect formation controlled by causal bounds.Comment: Submitted to Phys. Rev. B with 5 figures on Nov. 15, 200

Nonlinear dynamics, rectification, and phase locking for particles on symmetrical two-dimensional periodic substrates with dc and circular ac drives

We investigate the dynamical motion of particles on a two-dimensional symmetric periodic substrate in the presence of both a dc drive along a symmetry direction of the periodic substrate and an additional circular ac drive. For large enough ac drives, the particle orbit encircles one or more potential maxima of the periodic substrate. In this case, when an additional increasing dc drive is applied in the longitudinal direction, the longitudinal velocity increases in a series of discrete steps that are integer multiples of the lattice constant of the substrate times the frequency. Fractional steps can also occur. These integer and fractional steps correspond to distinct stable dynamical orbits. A number of these phases also show a rectification in the positive or negative transverse direction where a non-zero transverse velocity occurs in the absence of a dc transverse drive. We map out the phase diagrams of the regions of rectification as a function of ac amplitude, and find a series of tongues. Most of the features, including the steps in the longitudinal velocity and the transverse rectification, can be captured with a simple toy model and by arguments from nonlinear maps. We have also investigated the effects of thermal disorder and incommensuration on the rectification phenomena, and find that for increasing disorder, the rectification regions are gradually smeared and the longitudinal velocity steps are no longer flat but show a linearly increasing velocity.Comment: 14 pages, 17 postscript figure

Vibrational Density Matrix Renormalization Group

Variational approaches for the calculation of vibrational wave functions and energies are a natural route to obtain highly accurate results with controllable errors. However, the unfavorable scaling and the resulting high computational cost of standard variational approaches limit their application to small molecules with only few vibrational modes. Here, we demonstrate how the density matrix renormalization group (DMRG) can be exploited to optimize vibrational wave functions (vDMRG) expressed as matrix product states. We study the convergence of these calculations with respect to the size of the local basis of each mode, the number of renormalized block states, and the number of DMRG sweeps required. We demonstrate the high accuracy achieved by vDMRG for small molecules that were intensively studied in the literature. We then proceed to show that the complete fingerprint region of the sarcosyn-glycin dipeptide can be calculated with vDMRG.Comment: 21 pages, 5 figures, 4 table

Localization of Gauge Fields and Monopole Tunnelling

We study the dynamical localization of a massless gauge field on a lower-dimensional surface (2-brane). In flat space, the necessary and sufficient condition for this phenomenon is the existence of confinement in the bulk. The resulting configuration is equivalent to a dual Josephson junction. This duality leads to an interesting puzzle, as it implies that a localized massless theory, even in the Abelian case, must become confining at exponentially large distances. Through the use of topological arguments we clarify the physics behind this large-distance confinement and identify the instantons of the brane world-volume theory that are responsible for its appearance. We show that they correspond to the (condensed) bulk magnetic charges (monopoles), that occasionally tunnel through the brane and induce weak confinement of the brane theory. We consider the possible generalization of this effect to higher dimensions and discuss phenomenological bounds on the confinement of electric charges at exponentially large distances within our Universe.Comment: 11 pages, 3 figures, improvements in the presentation, version to appear in Physical Review

High--Energy Photon--Hadron Scattering in Holographic QCD

This article provides an in-depth look at hadron high energy scattering by using gravity dual descriptions of strongly coupled gauge theories. Just like deeply inelastic scattering (DIS) and deeply virtual Compton scattering (DVCS) serve as clean experimental probes into non-perturbative internal structure of hadrons, elastic scattering amplitude of a hadron and a (virtual) "photon" in gravity dual can be exploited as a theoretical probe. Since the scattering amplitude at sufficiently high energy (small Bjorken x) is dominated by parton contributions (= Pomeron contributions) even in strong coupling regime, there is a chance to learn a lesson for generalized parton distribution (GPD) by using gravity dual models. We begin with refining derivation of Brower-Polchinski-Strassler-Tan (BPST) Pomeron kernel in gravity dual, paying particular attention to the role played by complex spin variable j. The BPST Pomeron on warped spacetime consists of a Kaluza-Klein tower of 4D Pomerons with non-linear trajectories, and we clarify the relation between Pomeron couplings and Pomeron form factor. We emphasize that the saddle point value j^* of the scattering amplitude in the complex j-plane representation is a very important concept in understanding qualitative behavior of the scattering amplitude. The total Pomeron contribution to the scattering is decomposed into the saddle point contribution and at most a finite number of pole contributions, and when the pole contributions are absent (which we call saddle point phase), kinematical variable (q,x,t) dependence of ln (1/q) evolution and ln(1/x) evolution parameters gamma_eff. and lambda_eff. in DIS and t-slope parameter B of DVCS in HERA experiment are all reproduced qualitatively in gravity dual

Are violations to temporal Bell inequalities there when somebody looks?

The possibility of observing violations of temporal Bell inequalities, originally proposed by Leggett as a mean of testing the quantum mechanical delocalization of suitably chosen macroscopic bodies, is discussed by taking into account the effect of the measurement process. A general criterion quantifying this possibility is defined and shown not to be fulfilled by the various experimental configurations proposed so far to test inequalities of different forms.Comment: 7 pages, 1 eps figure, needs europhys.sty and euromacr.tex, enclosed in the .tar.gz file; accepted for publication in Europhysics Letter

Unconventional Josephson Effect in Hybrid Superconductor-Topological Insulator Devices

We report on transport properties of Josephson junctions in hybrid superconducting-topological insulator devices, which show two striking departures from the common Josephson junction behavior: a characteristic energy that scales inversely with the width of the junction, and a low characteristic magnetic field for suppressing supercurrent. To explain these effects, we propose a phenomenological model which expands on the existing theory for topological insulator Josephson junctions