9,881 research outputs found
Efficient sharing of a continuous-variable quantum secret
We propose an efficient scheme for sharing a continuous variable quantum
secret using passive optical interferometry and squeezers: this efficiency is
achieved by showing that a maximum of two squeezers is required to replicate
the secret state, and we obtain the cheapest configuration in terms of total
squeezing cost. Squeezing is a cost for the dealer of the secret as well as for
the receivers, and we quantify limitations to the fidelity of the replicated
secret state in terms of the squeezing employed by the dealer.Comment: 7 pages, 3 figure
Current and current fluctuations in quantum shuttles
We review the properties of electron shuttles, i.e. nanoelectromechanical
devices that transport electrons one-by-one by utilizing a combination of
electronic and mechanical degrees of freedom. We focus on the extreme quantum
limit, where the mechanical motion is quantized. We introduce the main
theoretical tools needed for the analysis, e.g. generalized master equations
and Wigner functions, and we outline the methods how the resulting large
numerical problems can be handled. Illustrative results are given for current,
noise, and full counting statistics for a number of model systems. Throughout
the review we focus on the physics behind the various approximations, and some
simple examples are given to illustrate the theoretical concepts. We also
comment on the experimental situation.Comment: Minireview; technical level aimed at general audience, based on an
invited talk at "Transport Phenomena in Micro and Nanodevices", October 17-21
Kona, Hawai
An omnidirectional retroreflector based on the transmutation of dielectric singularities
In the field of transformation optics, metamaterials mimic the effect of
coordinate transformations on electromagnetic waves, creating the illusion that
the waves are propagating through a virtual space. Transforming space by
appropriately designed materials makes devices possible that have been deemed
impossible. In particular, transformation optics has led to the demonstration
of invisibility cloaking for microwaves, surface plasmons and infrared light.
Here we report the achievement of another "impossible task". We implement, for
microwaves, a device that would normally require a dielectric singularity, an
infinity in the refractive index. We transmute a singularity in virtual space
into a mere topological defect in a real metamaterial. In particular, we
demonstrate an omnidirectional retroreflector, a device for faithfully
reflecting images and for creating high visibility, from all directions. Our
method is robust, potentially broadband and similar techniques could be applied
for visible light
No approximate complex fermion coherent states
Whereas boson coherent states with complex parametrization provide an
elegant, and intuitive representation, there is no counterpart for fermions
using complex parametrization. However, a complex parametrization provides a
valuable way to describe amplitude and phase of a coherent beam. Thus we pose
the question of whether a fermionic beam can be described, even approximately,
by a complex-parametrized coherent state and define, in a natural way,
approximate complex-parametrized fermion coherent states. Then we identify four
appealing properties of boson coherent states (eigenstate of annihilation
operator, displaced vacuum state, preservation of product states under linear
coupling, and factorization of correlators) and show that these approximate
complex fermion coherent states fail all four criteria. The inapplicability of
complex parametrization supports the use of Grassman algebras as an appropriate
alternative.Comment: Argumentation made cleare
George Champlain Sibley: Shady Dealings on the Early Frontier
Danisi offers an analysis of Sibley’s time as assistant factor at Fort Bellefontaine under factor Rodolphe Tillier, a man of strong political connections and elastic ethics. Tillier fired Sibley, Danisi argues, because he discovered and revealed Tillier’s shady business dealings while a government official; ultimately, Sibley was exonerated and even promoted to factor of the newly formed Fort Osage
Hoyle state and rotational features in Carbon-12 within a no-core shell model framework
By using only a fraction of the model space extended beyond current no-core
shell-model limits and a schematic effective many-nucleon interaction, we gain
additional insight within a symmetry-guided shell-model framework, into the
many-body dynamics that gives rise to the ground state rotational band together
with phenomena tied to alpha-clustering substructures in the low-lying states
in C-12, and in particular, the challenging Hoyle state and its first 2+
excitation. For these states, we offer a novel perspective emerging out of
no-core shell-model considerations, including a discussion of associated
nuclear shapes and matter radii. This, in turn, provides guidance for ab initio
shell models by informing key features of nuclear structure and the
interaction.Comment: 5 pages, 4 figure
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