435 research outputs found
Robustness of Entanglement as a Resource
The robustness of multipartite entanglement of systems undergoing decoherence
is of central importance to the area of quantum information. Its
characterization depends however on the measure used to quantify entanglement
and on how one partitions the system. Here we show that the unambiguous
assessment of the robustness of multipartite entanglement is obtained by
considering the loss of functionality in terms of two communication tasks,
namely the splitting of information between many parties and the teleportation
of states.Comment: 11 pages, 5 figure
Scaling laws for the decay of multiqubit entanglement
We investigate the decay of entanglement of generalized N-particle
Greenberger-Horne-Zeilinger (GHZ) states interacting with independent
reservoirs. Scaling laws for the decay of entanglement and for its finite-time
extinction (sudden death) are derived for different types of reservoirs. The
latter is found to increase with the number of particles. However, entanglement
becomes arbitrarily small, and therefore useless as a resource, much before it
completely disappears, around a time which is inversely proportional to the
number of particles. We also show that the decay of multi-particle GHZ states
can generate bound entangled states.Comment: Minor mistakes correcte
A Novel Approach to Study Highly Correlated Nanostructures: The Logarithmic Discretization Embedded Cluster Approximation
This work proposes a new approach to study transport properties of highly
correlated local structures. The method, dubbed the Logarithmic Discretization
Embedded Cluster Approximation (LDECA), consists of diagonalizing a finite
cluster containing the many-body terms of the Hamiltonian and embedding it into
the rest of the system, combined with Wilson's idea of a logarithmic
discretization of the representation of the Hamiltonian. The physics associated
with both one embedded dot and a double-dot side-coupled to leads is discussed
in detail. In the former case, the results perfectly agree with Bethe ansatz
data, while in the latter, the physics obtained is framed in the conceptual
background of a two-stage Kondo problem. A many-body formalism provides a solid
theoretical foundation to the method. We argue that LDECA is well suited to
study complicated problems such as transport through molecules or quantum dot
structures with complex ground states.Comment: 17 pages, 13 figure
Effect of topology on the transport properties of two interacting dots
The transport properties of a system of two interacting dots, one of them
directly connected to the leads constituting a side-coupled configuration
(SCD), are studied in the weak and strong tunnel-coupling limits. The
conductance behavior of the SCD structure has new and richer physics than the
better studied system of two dots aligned with the leads (ACD). In the weak
coupling regime and in the case of one electron per dot, the ACD configuration
gives rise to two mostly independent Kondo states. In the SCD topology, the
inserted dot is in a Kondo state while the side-connected one presents Coulomb
blockade properties. Moreover, the dot spins change their behavior, from an
antiferromagnetic coupling to a ferromagnetic correlation, as a consequence of
the interaction with the conduction electrons. The system is governed by the
Kondo effect related to the dot that is embedded into the leads. The role of
the side-connected dot is to introduce, when at resonance, a new path for the
electrons to go through giving rise to the interferences responsible for the
suppression of the conductance. These results depend on the values of the
intra-dot Coulomb interactions. In the case where the many-body interaction is
restricted to the side-connected dot, its Kondo correlation is responsible for
the scattering of the conduction electrons giving rise to the conductance
suppression
Kondo resonance effect on persistent currents through a quantum dot in a mesoscopic ring
The persistent current through a quantum dot inserted in a mesoscopic ring of
length L is studied. A cluster representing the dot and its vicinity is exactly
diagonalized and embedded into the rest of the ring. The Kondo resonance
provides a new channel for the current to flow. It is shown that due to scaling
properties, the persistent current at the Kondo regime is enhanced relative to
the current flowing either when the dot is at resonance or along a perfect ring
of same length. In the Kondo regime the current scales as , unlike
the scaling of a perfect ring. We discuss the possibility of detection
of the Kondo effect by means of a persistent current measurement.Comment: 11 pages, 3 Postscript figure
Laplacian growth with separately controlled noise and anisotropy
Conformal mapping models are used to study competition of noise and
anisotropy in Laplacian growth. For that, a new family of models is introduced
with the noise level and directional anisotropy controlled independently.
Fractalization is observed in both anisotropic growth and the growth with
varying noise. Fractal dimension is determined from cluster size scaling with
its area. For isotropic growth we find d = 1.7, both at high and low noise. For
anisotropic growth with reduced noise the dimension can be as low as d = 1.5
and apparently is not universal. Also, we study fluctuations of particle areas
and observe, in agreement with previous studies, that exceptionally large
particles may appear during the growth, leading to pathologically irregular
clusters. This difficulty is circumvented by using an acceptance window for
particle areas.Comment: 13 pages, 15 figure
Test of quantum nonlocality for cavity fields
There have been studies on formation of quantum-nonlocal states in spatially
separate two cavities. We suggest a nonlocal test for the field prepared in the
two cavities. We couple classical driving fields with the cavities where a
nonlocal state is prepared. Two independent two-level atoms are then sent
through respective cavities to interact off-resonantly with the cavity fields.
The atomic states are measured after the interaction. Bell's inequality can be
tested by the joint probabilities of two-level atoms being in their excited or
ground states. We find that quantum nonlocality can also be tested using a
single atom sequentially interacting with the two cavities. Potential
experimental errors are also considered. We show that with the present
experimental condition of 5% error in the atomic velocity distribution, the
violation of Bell's inequality can be measured.Comment: 14pages, 2figures. accepted to Phys. Rev.
Tetrapotassium diantimony(III) tin(IV) tetradecafluoride
The title compound, K4Sb2SnF14, is built from anionic layers, with an overall composition of [Sb2SnF14]4− extending parallel to the ac plane, and K+ cations. The layers are made up from vertex-sharing centrosymmetric SnF6 octahedra and Sb2F12 dimers. The Sn—F distances are in the range 1.9581 (14)–1.9611 (17) Å. The Sb polyhedra contain three short terminal Sb—F bonds [1.9380 (14)–2.0696 (15) Å], one short bridging bond [2.0609 (17) Å], one bridging bond of medium length [2.7516 (15) Å], and two longer bridging bonds [3.0471 (18) and 3.117 (2) Å]. The K+ ions are coordinated by F atoms with coordination numbers 10 and 8, and K—F bond lengths are in the range 2.6235 (16)–3.122 (2) Å
Trends in Sexual Behavior and Sexually Transmitted Infections After Initiating Human Immunodeficiency Virus Pre-Exposure Prophylaxis in Men Who Have Sex with Men from Amsterdam, the Netherlands:A Longitudinal Exposure-Matched Study
- …