6,344 research outputs found
Multiparticle Quantum Superposition and Stimulated Entanglement by Parity Selective Amplification of Entangled States
A multiparticle quantum superposition state has been generated by a novel
phase-selective parametric amplifier of an entangled two-photon state. This
realization is expected to open a new field of investigations on the
persistence of the validity of the standard quantum theory for systems of
increasing complexity, in a quasi decoherence-free environment. Because of its
nonlocal structure the new system is expected to play a relevant role in the
modern endeavor on quantum information and in the basic physics of
entanglement.Comment: 13 pages and 3 figure
‘If I climb a wall of ten meters’: capoeira, parkour and the politics of public space among (post)migrant youth in Turin, Italy
Rather than being seen as citizens, the children of immigrants are portrayed as a population to be controlled and contained across Europe. In Italy today, debates about cultural ‘authenticity’ and renewed nationalism accompany waves of moral panic that depict a country under siege by illegal and unwanted immigrants. Specifically in cities, immigrants and their children are imagined and portrayed as alien and out of place. Drawing on fourteen months of ethnographic research in Turin, Italy, with children of immigrants aged between 16 and 21, De Martini Ugolotti and Moyer illustrate how these youth make use of their bodies through capoeira and parkour practices to contest and reappropriate public spaces, thereby challenging dominant visions about what constitutes the public, how it should be used and by whom. They analyse the ‘body in place’ to understand how the children of immigrants navigate unequal spatial relations and challenge dominant regimes of representation, while also attempting to improve their life conditions and reach their personal goals
One-way quantum computation via manipulation of polarization and momentum qubits in two-photon cluster states
Four-qubit cluster states of two photons entangled in polarization and linear
momentum have been used to realize a complete set of single qubit rotations and
the C-NOT gate for equatorial qubits with high values of fidelity. By the
computational equivalence of the two degrees of freedom our result demonstrate
the suitability of two photon cluster states for rapid and efficient one-way
quantum computing.Comment: RevTex4, 4 pages, 3 figure
Active Galactic Nuclei in Groups and Clusters of Galaxies: Detection and Host Morphology
The incidence and properties of Active Galactic Nuclei (AGN) in the field,
groups, and clusters can provide new information about how these objects are
triggered and fueled, similar to how these environments have been employed to
study galaxy evolution. We have obtained new XMM-Newton observations of seven
X-ray selected groups and poor clusters with 0.02 < z < 0.06 for comparison
with previous samples that mostly included rich clusters and optically-selected
groups. Our final sample has ten groups and six clusters in this low-redshift
range (split at a velocity dispersion of km/s). We find that the
X-ray selected AGN fraction increases from in clusters to for the
groups (85% significance), or a factor of two, for AGN above an 0.3-8keV X-ray
luminosity of erg/s hosted by galaxies more luminous than .
The trend is similar, although less significant, for a lower-luminosity host
threshold of mag. For many of the groups in the sample we have also
identified AGN via standard emission-line diagnostics and find that these AGN
are nearly disjoint from the X-ray selected AGN. Because there are substantial
differences in the morphological mix of galaxies between groups and clusters,
we have also measured the AGN fraction for early-type galaxies alone to
determine if the differences are directly due to environment, or indirectly due
to the change in the morphological mix. We find that the AGN fraction in
early-type galaxies is also lower in clusters compared to
for the groups (92% significance), a result consistent with the hypothesis that
the change in AGN fraction is directly connected to environment.Comment: 18 pages, 9 figures; accepted by The Astrophysical Journal; for
higher-resolution versions of some figures, see
http://u.arizona.edu/~tjarnold/Arnold09
Ultraviolet and soft X--ray photon--photon elastic scattering in an electron gas
We have considered the processes which lead to elastic scattering between two
far ultraviolet or X--ray photons while they propagate inside a solid, modeled
as a simple electron gas. The new ingredient, with respect to the standard
theory of photon--photon scattering in vacuum, is the presence of low--energy,
nonrelativistic electron--hole excitations. Owing to the existence of
two--photon vertices, the scattering processes in the metal are predominantly
of second order, as opposed to fourth order for the vacuum case. The main
processes in second order are dominated by exchange of virtual plasmons between
the two photons. For two photons of similar energy , this gives
rise to a cross section rising like up to maximum of around
~cm, and then decreasing like . The maximal cross
section is found for the photon wavevector , the Fermi surface
size, which typically means a photon energy in the keV range.
Possible experiments aimed at checking the existence of these rare but
seemingly measurable elastic photon--photon scattering processes are discussed,
using in particular intense synchrotron sources.Comment: 33 pages, TeX, Version 3.1, S.I.S.S.A. preprint 35/93/C
Input-Output Relations in Optical Cavities: a Simple Point of View
In this work we present a very simple approach to input-output relations in
optical cavities, limiting ourselves to one- and two-photon states of the
field.
After field quantization, we derive the non-unitary transformation between
{\em Inside} and {\em Outside} annihilation and creation operators. Then we
express the most general two-photon state generated by {\em Inside} creation
operators, through base states generated by {\em Outside} creation operators.
After renormalization of coefficients of inside two-photon state, we calculate
the outside photon-number probability distribution in a general case. Finally
we treat with some detail the single mode and symmetrical cavity case.Comment: 34 pages, 5 figures jpg, LaTe
Integrated Distributed Energy Resource Pricing and Control
U.S. policy is to allow owners of distributed resources to effectively and reliably provide their services at scale, and operate harmoniously on an interconnected distribution and transmission grid. Accordingly, regulation, new business models and technology advances over the past decade have led to significant growth rates in distributed energy resources including generation, responsive demand, energy conservation and customer adoption of industrial, commercial and residential energy management systems. The result is that several regions are reaching proposed capacity levels for distributed generation that exceed traditional operating and engineering practices for distribution systems. At the same time, policies advocating wholesale spot prices to customer devices (“prices to devices”) have not adequately considered distribution system reliability impacts or relationship to distributed generation. As such, it is also not clear that current market models or regulations are entirely adequate or appropriate for the several emerging hybrid regional markets, such as California, with millions of distributed energy resources envision by the year 2020
Entanglement and Quantum Superposition of a Macroscopic - Macroscopic system
Two quantum Macro-states and their Macroscopic Quantum Superpositions (MQS)
localized in two far apart, space - like separated sites can be non-locally
correlated by any entangled couple of single-particles having interacted in the
past. This novel Macro - Macro paradigm is investigated on the basis of a
recent study on an entangled Micro-Macro system involving N=10^5 particles.
Crucial experimental issues as the violation of Bell's inequalities by the
Macro - Macro system are considered.Comment: 4 pages, 4 figure
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