412 research outputs found
On the Energy Transfer Performance of Mechanical Nanoresonators Coupled with Electromagnetic Fields
We study the energy transfer performance in electrically and magnetically
coupled mechanical nanoresonators. Using the resonant scattering theory, we
show that magnetically coupled resonators can achieve the same energy transfer
performance as for their electrically coupled counterparts, or even outperform
them within the scale of interest. Magnetic and electric coupling are compared
in the Nanotube Radio, a realistic example of a nano-scale mechanical
resonator. The energy transfer performance is also discussed for a newly
proposed bio-nanoresonator composed of a magnetosomes coated with a net of
protein fibers.Comment: 9 Pages, 3 Figure
Polariton Condensation and Lasing
The similarities and differences between polariton condensation in
microcavities and standard lasing in a semiconductor cavity structure are
reviewed. The recent experiments on "photon condensation" are also reviewed.Comment: 23 pages, 6 figures; Based on the book chapter in Exciton Polaritons
in Microcavities, (Springer Series in Solid State Sciences vol. 172), V.
Timofeev and D. Sanvitto, eds., (Springer, 2012
Uncovering the overlapping community structure of complex networks in nature and society
Many complex systems in nature and society can be described in terms of
networks capturing the intricate web of connections among the units they are
made of. A key question is how to interpret the global organization of such
networks as the coexistence of their structural subunits (communities)
associated with more highly interconnected parts. Identifying these a priori
unknown building blocks (such as functionally related proteins, industrial
sectors and groups of people) is crucial to the understanding of the structural
and functional properties of networks. The existing deterministic methods used
for large networks find separated communities, whereas most of the actual
networks are made of highly overlapping cohesive groups of nodes. Here we
introduce an approach to analysing the main statistical features of the
interwoven sets of overlapping communities that makes a step towards uncovering
the modular structure of complex systems. After defining a set of new
characteristic quantities for the statistics of communities, we apply an
efficient technique for exploring overlapping communities on a large scale. We
find that overlaps are significant, and the distributions we introduce reveal
universal features of networks. Our studies of collaboration, word-association
and protein interaction graphs show that the web of communities has non-trivial
correlations and specific scaling properties.Comment: The free academic research software, CFinder, used for the
publication is available at the website of the publication:
http://angel.elte.hu/clusterin
Parameters of Pseudo-Random Quantum Circuits
Pseudorandom circuits generate quantum states and unitary operators which are
approximately distributed according to the unitarily invariant Haar measure. We
explore how several design parameters affect the efficiency of pseudo-random
circuits, with the goal of identifying relevant trade-offs and optimizing
convergence. The parameters we explore include the choice of single- and
two-qubit gates, the topology of the underlying physical qubit architecture,
the probabilistic application of two-qubit gates, as well as circuit size,
initialization, and the effect of control constraints. Building on the
equivalence between pseudo-random circuits and approximate -designs, a
Markov matrix approach is employed to analyze asymptotic convergence properties
of pseudo-random second-order moments to a 2-design. Quantitative results on
the convergence rate as a function of the circuit size are presented for qubit
topologies with a sufficient degree of symmetry. Our results may be
theoretically and practically useful to optimize the efficiency of random state
and operator generation.Comment: 17 pages, 14 figures, 2 Appendice
Fabrication and operation of a two-dimensional ion-trap lattice on a high-voltage microchip
Microfabricated ion traps are a major advancement towards scalable quantum computing with trapped ions. The development of more versatile ion-trap designs, in which tailored arrays of ions are positioned in two dimensions above a microfabricated surface, will lead to applications in fields as varied as quantum simulation, metrology and atomâion interactions. Current surface ion traps often have low trap depths and high heating rates, because of the size of the voltages that can be applied to them, limiting the fidelity of quantum gates. Here we report on a fabrication process that allows for the application of very high voltages to microfabricated devices in general and use this advance to fabricate a two-dimensional ion-trap lattice on a microchip. Our microfabricated architecture allows for reliable trapping of two-dimensional ion lattices, long ion lifetimes, rudimentary shuttling between lattice sites and the ability to deterministically introduce defects into the ion lattice
The Naming Game in Social Networks: Community Formation and Consensus Engineering
We study the dynamics of the Naming Game [Baronchelli et al., (2006) J. Stat.
Mech.: Theory Exp. P06014] in empirical social networks. This stylized
agent-based model captures essential features of agreement dynamics in a
network of autonomous agents, corresponding to the development of shared
classification schemes in a network of artificial agents or opinion spreading
and social dynamics in social networks. Our study focuses on the impact that
communities in the underlying social graphs have on the outcome of the
agreement process. We find that networks with strong community structure hinder
the system from reaching global agreement; the evolution of the Naming Game in
these networks maintains clusters of coexisting opinions indefinitely. Further,
we investigate agent-based network strategies to facilitate convergence to
global consensus.Comment: The original publication is available at
http://www.springerlink.com/content/70370l311m1u0ng3
Shape-resonant superconductivity in nanofilms: from weak to strong coupling
Ultrathin superconductors of different materials are becoming a powerful
platform to find mechanisms for enhancement of superconductivity, exploiting
shape resonances in different superconducting properties. Here we evaluate the
superconducting gap and its spatial profile, the multiple gap components, and
the chemical potential, of generic superconducting nanofilms, considering the
pairing attraction and its energy scale as tunable parameters, from weak to
strong coupling, at fixed electron density. Superconducting properties are
evaluated at mean field level as a function of the thickness of the nanofilm,
in order to characterize the shape resonances in the superconducting gap. We
find that the most pronounced shape resonances are generated for weakly coupled
superconductors, while approaching the strong coupling regime the shape
resonances are rounded by a mixing of the subbands due to the large energy gaps
extending over large energy scales. Finally, we find that the spatial profile,
transverse to the nanofilm, of the superconducting gap acquires a flat behavior
in the shape resonance region, indicating that a robust and uniform multigap
superconducting state can arise at resonance.Comment: 7 pages, 4 figures. Submitted to the Proceedings of the Superstripes
2016 conferenc
Autism as a disorder of neural information processing: directions for research and targets for therapy
The broad variation in phenotypes and severities within autism spectrum disorders suggests the involvement of multiple predisposing factors, interacting in complex ways with normal developmental courses and gradients. Identification of these factors, and the common developmental path into which theyfeed, is hampered bythe large degrees of convergence from causal factors to altered brain development, and divergence from abnormal brain development into altered cognition and behaviour. Genetic, neurochemical, neuroimaging and behavioural findings on autism, as well as studies of normal development and of genetic syndromes that share symptoms with autism, offer hypotheses as to the nature of causal factors and their possible effects on the structure and dynamics of neural systems. Such alterations in neural properties may in turn perturb activity-dependent development, giving rise to a complex behavioural syndrome many steps removed from the root causes. Animal models based on genetic, neurochemical, neurophysiological, and behavioural manipulations offer the possibility of exploring these developmental processes in detail, as do human studies addressing endophenotypes beyond the diagnosis itself
- âŚ