1,717 research outputs found
Selective dynamical decoupling for quantum state transfer
State transfer across discrete quantum networks is one of the elementary
tasks of quantum information processing. Its aim is the faithful placement of
information into a specific position in the network. However, all physical
systems suffer from imperfections, which can severely limit the transfer
fidelity. We present selective dynamical decoupling schemes which are capable
of stabilizing imperfect quantum state transfer protocols on the model of a
bent linear qubit chain. The efficiency of the schemes is tested and verified
in numerical simulations on a number of realistic cases. The simulations
demonstrate that these selective dynamical decoupling schemes are capable of
suppressing unwanted errors in quantum state transfer protocols efficiently.Comment: 20 pages, 9 figure
Nontrivial edge coupling from a Dirichlet network squeezing: the case of a bent waveguide
In distinction to the Neumann case the squeezing limit of a Dirichlet network
leads in the threshold region generically to a quantum graph with disconnected
edges, exceptions may come from threshold resonances. Our main point in this
paper is to show that modifying locally the geometry we can achieve in the
limit a nontrivial coupling between the edges including, in particular, the
class of -type boundary conditions. We work out an illustration of this
claim in the simplest case when a bent waveguide is squeezed.Comment: LaTeX, 16 page
Graph-like asymptotics for the Dirichlet Laplacian in connected tubular domains
We consider the Dirichlet Laplacian in a waveguide of uniform width and
infinite length which is ideally divided into three parts: a "vertex region",
compactly supported and with non zero curvature, and two "edge regions" which
are semi-infinite straight strips. We make the waveguide collapse onto a graph
by squeezing the edge regions to half-lines and the vertex region to a point.
In a setting in which the ratio between the width of the waveguide and the
longitudinal extension of the vertex region goes to zero, we prove the
convergence of the operator to a selfadjoint realization of the Laplacian on a
two edged graph. In the limit operator, the boundary conditions in the vertex
depend on the spectral properties of an effective one dimensional Hamiltonian
associated to the vertex region.Comment: Major revision. Reviewed introduction. Changes in Th. 1, Th. 2, and
Th. 3. Updated references. 23 page
Low Power Superconducting Microwave Applications and Microwave Microscopy
We briefly review some non-accelerator high-frequency applications of
superconductors. These include the use of high-Tc superconductors in front-end
band-pass filters in cellular telephone base stations, the High Temperature
Superconductor Space Experiment, and high-speed digital electronics. We also
present an overview of our work on a novel form of near-field scanning
microscopy at microwave frequencies. This form of microscopy can be used to
investigate the microwave properties of metals and dielectrics on length scales
as small as 1 mm. With this microscope we have demonstrated quantitative
imaging of sheet resistance and topography at microwave frequencies. An
examination of the local microwave response of the surface of a heat-treated
bulk Nb sample is also presented.Comment: 11 pages, including 6 figures. Presented at the Eight Workshop on RF
Superconductivity. To appear in Particle Accelerator
Quantum walk state transfer on a hypercube
We investigate state transfer on a hypercube by means of a quantum walk where
the sender and the receiver vertices are marked by a weighted loops. First, we
analyze search for a single marked vertex, which can be used for state transfer
between arbitrary vertices by switching the weighted loop from the sender to
the receiver after one run-time. Next, state transfer between antipodal
vertices is considered. We show that one can tune the weight of the loop to
achieve state transfer with high fidelity in shorter run-time in comparison to
the state transfer with a switch. Finally, we investigate state transfer
between vertices of arbitrary distance. It is shown that when the distance
between the sender and the receiver is at least 2, the results derived for the
antipodes are well applicable. If the sender and the receiver are direct
neighbours the evolution follows a slightly different course. Nevertheless,
state transfer with high fidelity is achieved in the same run-time
Diffusion processes in thin tubes and their limits on graphs
The present paper is concerned with diffusion processes running on tubular
domains with conditions on nonreaching the boundary, respectively, reflecting
at the boundary, and corresponding processes in the limit where the thin
tubular domains are shrinking to graphs. The methods we use are probabilistic
ones. For shrinking, we use big potentials, respectively, reflection on the
boundary of tubes. We show that there exists a unique limit process, and we
characterize the limit process by a second-order differential generator acting
on functions defined on the limit graph, with Kirchhoff boundary conditions at
the vertices.Comment: Published in at http://dx.doi.org/10.1214/11-AOP667 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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