24,065 research outputs found
Measurement in control and discrimination of entangled pairs under self-distortion
Quantum correlations and entanglement are fundamental resources for quantum
information and quantum communication processes. Developments in these fields
normally assume these resources stable and not susceptible of distortion. That
is not always the case, Heisenberg interactions between qubits can produce
distortion on entangled pairs generated for engineering purposes (e. g. for
quantum computation or quantum cryptography). Experimental work shows how to
produce entangled spin qubits in quantum dots and electron gases, so its
identification and control are crucial for later applications. The presence of
parasite magnetic fields modifies the expected properties and behavior for
which the pair was intended. Quantum measurement and control help to
discriminate the original state in order to correct it or, just to try of
reconstruct it using some procedures which do not alter their quantum nature.
Two different kinds of quantum entangled pairs driven by a Heisenberg
Hamiltonian with an additional inhomogeneous magnetic field which becoming
self-distorted, can be reconstructed without previous discrimination by adding
an external magnetic field, with fidelity close to 1 (with respect to the
original state, but without discrimination). After, each state can be more
efficiently discriminated. The aim of this work is to show how combining both
processes, first reconstruction without discrimination and after discrimination
with adequate non-local measurements, it's possible a) improve the
discrimination, and b) reprepare faithfully the original states. The complete
process gives fidelities better than 0.9. In the meanwhile, some results about
a class of equivalence for the required measurements were found. This property
lets us select the adequate measurement in order to ease the repreparation
after of discrimination, without loss of entanglement.Comment: 6 figure
Cotunneling theory of inelastic STM spin spectroscopy
We propose cotunneling as the microscopic mechanism that makes possible
inelastic electron spectroscopy of magnetic atoms in surfaces for a wide range
of systems, including single magnetic adatoms, molecules and molecular stacks.
We describe electronic transport between the scanning tip and the conducting
surface through the magnetic system (MS) with a generalized Anderson model,
without making use of effective spin models. Transport and spin dynamics are
described with an effective cotunneling Hamiltonian in which the correlations
in the magnetic system are calculated exactly and the coupling to the
electrodes is included up to second order in the tip-MS and MS-substrate. In
the adequate limit our approach is equivalent to the phenomenological Kondo
exchange model that successfully describe the experiments . We apply our method
to study in detail inelastic transport in two systems, stacks of Cobalt
Phthalocyanines and a single Mn atom on CuN. Our method accounts both, for
the large contribution of the inelastic spin exchange events to the conductance
and the observed conductance asymmetry.Comment: 12 pages, 6 figure
Network-wide assessment of 4D trajectory adjustments using an agent-based model
This paper presents results from the SESAR ER3 Domino project. It focuses on an ECAC-wide assessment of two 4D-adjustment mechanisms, implemented separately and conjointly. These reflect flight behaviour en-route and at-gate, optimising given (cost) objective functions. New metrics designed to capture network effects are used to analyse the results of a microscopic, agent based model. The results show that some implementations of the mechanisms allow the protection of the network from ‘domino’ effects. Airlines focusing on costs may trigger additional side-effects on passengers, displaying, in some instances, clear trade-offs between passenger- and flight-centric metrics
Generating sequences and Poincar\'e series for a finite set of plane divisorial valuations
Let be a finite set of divisorial valuations centered at a 2-dimensional
regular local ring . In this paper we study its structure by means of the
semigroup of values, , and the multi-index graded algebra defined by ,
\gr_V R. We prove that is finitely generated and we compute its minimal
set of generators following the study of reduced curve singularities. Moreover,
we prove a unique decomposition theorem for the elements of the semigroup.
The comparison between valuations in , the approximation of a reduced
plane curve singularity by families of sets of divisorial
valuations, and the relationship between the value semigroup of and the
semigroups of the sets , allow us to obtain the (finite) minimal
generating sequences for as well as for .
We also analyze the structure of the homogeneous components of \gr_V R. The
study of their dimensions allows us to relate the Poincar\'e series for and
for a general curve of . Since the last series coincides with the
Alexander polynomial of the singularity, we can deduce a formula of A'Campo
type for the Poincar\'e series of . Moreover, the Poincar\'e series of
could be seen as the limit of the series of ,
A minimal model for acoustic forces on Brownian particles
We present a generalization of the inertial coupling (IC) [Usabiaga et al. J.
Comp. Phys. 2013] which permits the resolution of radiation forces on small
particles with arbitrary acoustic contrast factor. The IC method is based on a
Eulerian-Lagrangian approach: particles move in continuum space while the fluid
equations are solved in a regular mesh (here we use the finite volume method).
Thermal fluctuations in the fluid stress, important below the micron scale, are
also taken into account following the Landau-Lifshitz fluid description. Each
particle is described by a minimal cost resolution which consists on a single
small kernel (bell-shaped function) concomitant to the particle. The main role
of the particle kernel is to interpolate fluid properties and spread particle
forces. Here, we extend the kernel functionality to allow for an arbitrary
particle compressibility. The particle-fluid force is obtained from an imposed
no-slip constraint which enforces similar particle and kernel fluid velocities.
This coupling is instantaneous and permits to capture the fast, non-linear
effects underlying the radiation forces on particles. Acoustic forces arise
either because an excess in particle compressibility (monopolar term) or in
mass (dipolar contribution) over the fluid values. Comparison with theoretical
expressions show that the present generalization of the IC method correctly
reproduces both contributions. Due to its low computational cost, the present
method allows for simulations with many particles using a standard Graphical
Processor Unit (GPU)
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