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

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Luttinger liquids are discussed.Comment: This paper has been withdrawn by the author as it has been combined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

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,
$\propto |\omega-\mu_F|^r$ ($0<r<1$) 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

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

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,
$k$, becomes independent of the angles of $k$-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

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

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

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 $T_c$
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 SrCu$_2$(BO$_3$)$_2$
when this material is doped in future.Comment: 4 pages, 3 figure

### Non-centrosymmetric superconductors on honeycomb lattice

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 $d$+$id$ and spin-triplet $p$+$ip$-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

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

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

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