159,492 research outputs found

    Nonequilibrium finite-frequency noise of a resonance-level quantum dot close to a dissipative quantum phase transition: Functional Renormalization Group approaches

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    We calculate the finite-frequency current noise of a nonequilibrium resonance-level quantum dot close to a dissipative quantum phase transition of the Kosterlitz-Thouless (KT) type between a de-localized phase for weak dissipation and a localized phase for strong dissipation. The resonance-level is coupled to two spinless fermionic baths with a finite bias voltage and an Ohmic boson bath representing the dissipative environment. The system is equivalent to an effective anisotropic Kondo model out of equilibrium. To compute the finite-frequency noise, we combine two recently developed Functional Renormalization Group (FRG) approaches in Refs.[17,22] and in Ref.[23]. The nonequilibrium current noise at zero-temperature and finite frequencies shows a singular dip in the de-localized phase for the magnitude of frequencies equal to the bias voltage; while the dip is smeared out as the system moves to the localized phase. The corresponding peak-to-dip crossover is found in the AC conductance for the magnitude of frequencies equal to the bias voltage. The relevance and applications of our results for the experiments and for tunnelings between Fractional Quantum Hall Edge (FQHE) states and chiral Luttinger liquids are discussed.Comment: This paper has been withdrawn by the author as it has been combined in another more extended work on the similar topi

    Quantum criticality of the two-channel pseudogap Anderson model: Universal scaling in linear and non-linear conductance

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    The quantum criticality of the two-lead two-channel pseudogap Anderson model is studied. Based on the non-crossing approximation, we calculate both the linear and nonlinear conductance of the model at finite temperatures with a voltage bias and a power-law vanishing conduction electron density of states, ωμFr\propto |\omega-\mu_F|^r (0<r<10<r<1) near the Fermi energy. Equilibrium and non-equilibrium quantum critical properties at the two-channel Kondo (2CK) to local moment (LM) phase transition are addressed by extracting universal scaling functions in both linear and non-linear conductances, respectively. Clear distinctions are found on the critical exponents between linear and non-linear conductance. The implications of these two distinct quantum critical properties for the non-equilibrium quantum criticality in general are discussed.Comment: 8 pages, 9 figure

    Optimal Experimental Design for Constrained Inverse Problems

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    In this paper, we address the challenging problem of optimal experimental design (OED) of constrained inverse problems. We consider two OED formulations that allow reducing the experimental costs by minimizing the number of measurements. The first formulation assumes a fine discretization of the design parameter space and uses sparsity promoting regularization to obtain an efficient design. The second formulation parameterizes the design and seeks optimal placement for these measurements by solving a small-dimensional optimization problem. We consider both problems in a Bayes risk as well as an empirical Bayes risk minimization framework. For the unconstrained inverse state problem, we exploit the closed form solution for the inner problem to efficiently compute derivatives for the outer OED problem. The empirical formulation does not require an explicit solution of the inverse problem and therefore allows to integrate constraints efficiently. A key contribution is an efficient optimization method for solving the resulting, typically high-dimensional, bilevel optimization problem using derivative-based methods. To overcome the lack of non-differentiability in active set methods for inequality constraints problems, we use a relaxed interior point method. To address the growing computational complexity of empirical Bayes OED, we parallelize the computation over the training models. Numerical examples and illustrations from tomographic reconstruction, for various data sets and under different constraints, demonstrate the impact of constraints on the optimal design and highlight the importance of OED for constrained problems.Comment: 19 pages, 8 figure

    Evaluation of a Class of Two-Scale Three-Loop Vacuum Diagrams

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    As a generalization of a previous work [Phys. Rev. D. {\bf 59}, 105014 (1999)], we compute analytically a class of three-loop vacuum diagrams with two {\em arbitrarily} different mass scales. We use a decomposition algorithm in which the integrand of the final integral for the third momentum vector, say, kk, becomes independent of the angles of kk-vector in spherical polar coordinates. This algorithm proves to be very efficient in obtaining exclusively all \e-pole terms of the given diagram.Comment: 12 pages, no figur

    Network topology: detecting topological phase transitions in the Kitaev chain and the rotor plane

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    We propose a novel network measure of topological invariants, called small-worldness, for identifying topological phase transitions of quantum and classical spin models. Small-worldness is usually defined in the study of social networks based on the best known discovery that one can find a short chain of acquaintances connecting almost any two people on the planet. Here we demonstrate that the small-world effect provides a useful description to distinguish topologically trivial and non-trivial phases in the Kitaev chain and accurately capture the Kosterlitz-Thouless transition in the rotor plane. Our results further suggest that the small-worldness containing both locality and non-locality of the network topology can be a practical approach to extract characteristic quantities of topological states of matter.Comment: 7 pages, 5 figure

    Concept of spinsonde for multi-cycle measurement of vertical wind profile of tropical cyclones

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    Tropical cyclones and cyclogenesis are active areas of research. Chute-operated dropsondes jointly developed by NASA and NCAR are capable of acquiring high resolution vertical wind profile of tropical cyclones. This paper proposes a chute-free vertical retardation technique (termed as spinsonde) that can accurately measure vertical wind profile. Unlike the expendable dropsondes, the spinsonde allows multi-cycle measurement to be performed within a single flight. Proof of principle is demonstrated using a simulation software and results indicate that the GPS ground speed correlates with the wind speeds to within +/-5 km/h. This technique reduces flying weight and increases payload capacity by eliminating bulky chutes. Maximum cruising speed (Vh) achieved by the spinsonde UAV is 372 km/h.Comment: arXiv admin note: substantial text overlap with arXiv:1407.845

    Competing Orders and Superconductivity in the Doped Mott Insulator on the Shastry-Sutherland Lattice

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    Quantum antiferromagnets on geometrically frustrated lattices often allow a number of unusual paramagnetic ground states. The fate of these Mott insulators upon doping is an important issue that may shed some light on the high TcT_c cuprate problem. We consider the doped Mott insulator on the Shastry-Sutherland lattice via the t-J model. The U(1) slave-boson mean field theory reveals the strong competition between different broken symmetry states. It is found that, in some ranges of doping, there exist superconducting phases with or without coexisting translational-symmetry- breaking orders such as the staggered flux or dimerization. Our results will be directly relevant to SrCu2_2(BO3_3)2_2 when this material is doped in future.Comment: 4 pages, 3 figure

    Non-centrosymmetric superconductors on honeycomb lattice

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    We study non-centrosymmetric topological superconductivity in correlated doped quantum spin-Hall insulators (QSHI) on honeycomb lattice without inversion symmetry where the intrinsic (Kane-Mele) and Rashba spin-orbit couplings can in general exist. We explore the generic topologically non-trivial superconducting phase diagram of the model system. Over a certain parameter space, the parity-mixing superconducting state with co-existing spin-singlet dd+idid and spin-triplet pp+ipip-wave pairing is found. On a zigzag nanoribbon, the parity-mixing superconducting state shows co-existing helical and chiral Majorana fermions at edges. Relevance of our results for experiments is discussed.Comment: 11 pages, 8 figure

    Strain induced superconducting pair-density-wave states in graphene

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    Graphene is known to be non-superconducting. However, surprising superconductivity is recently discovered in a flat-band in a twisted bi-layer graphene. Here we show that superconductivity can be more easily realized in topological flat-bands induced by strain in graphene through periodic ripples. Specifically, it is shown that by including correlation effects, the chiral d-wave superconductivity can be stabilized under strain even for slightly doped graphene. The chiral d-wave superconductivity generally coexists with charge density waves (CDW) and pair density waves (PDW) of the same period. Remarkably, a pure PDW state with doubled period that coexists with the CDW state is found to emerge at a finite temperature region under reasonable strain strength. The emergent PDW state is shown to be superconducting with non-vanishing superfluid density, and it realizes the long searched superconducting states with non-vanishing center of mass momentum for Cooper pairs.Comment: 7 pages, 5 figures, to appear in Phys. Rev.

    Modeling network technology deployment rates with different network models

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    To understand the factors that encourage the deployment of a new networking technology, we must be able to model how such technology gets deployed. We investigate how network structure influences deployment with a simple deployment model and different network models through computer simulations. The results indicate that a realistic model of networking technology deployment should take network structure into account.Comment: 14 pages, 9 figure