Robustness of spatial Penning trap modes against environment-assisted entanglement

The separability of the spatial modes of a charged particle in a Penning trap in the presence of an environment is studied by means of the positive partial transpose (PPT) criterion. Assuming a weak Markovian environment, described by linear Lindblad operators, our results strongly suggest that the environmental coupling of the axial and cyclotron degrees of freedom does not lead to entanglement at experimentally realistic temperatures. We therefore argue that, apart from unavoidable decoherence, the presence of such an environment does not alter the effectiveness of recently suggested quantum information protocols in Penning traps, which are based on the combination of a spatial mode with the spin of the particle.Comment: 11 pages, 2 figure

Monitoring of downloads of Belgorod State University (Russia) scientists' publications by scientists from other countries

The article presents a review on the functioning of the ResearchGate network and the growth of its popularity both from the literary data and from the experiments in the Google Scholar search engine. It describes a unique weekly monitoring experiments of downloads of Belgorod State University (Russia) scientists' publications by scientists from other countries (starting on 11.01.2015 through 20.12.2015), and it is shown that scientists from the United States (about 10,000 downloads in 2015) and China (about 6,000 downloads in 2015) are most interested in these publication

Motion and homogenization of vortices in anisotropic Type II superconductors

The motion of vortices in an anisotropic superconductor is considered. For a system of well-separated vortices, each vortex is found to obey a law of motion analogous to the local induction approximation, in which velocity of the vortex depends upon the local curvature and orientation. A system of closely packed vortices is then considered, and a mean field model is formulated in which the individual vortex lines are replaced by a vortex density

Optical absorption of non-interacting tight-binding electrons in a Peierls-distorted chain at half band-filling

In this first of three articles on the optical absorption of electrons in half-filled Peierls-distorted chains we present analytical results for non-interacting tight-binding electrons. We carefully derive explicit expressions for the current operator, the dipole transition matrix elements, and the optical absorption for electrons with a cosine dispersion relation of band width $W$ and dimerization parameter $\delta$. New correction (``$\eta$''-)terms to the current operator are identified. A broad band-to-band transition is found in the frequency range $W\delta < \omega < W$ whose shape is determined by the joint density of states for the upper and lower Peierls subbands and the strong momentum dependence of the transition matrix elements.Comment: 17 pages REVTEX 3.0, 2 postscript figures; hardcopy versions before May 96 are obsolete; accepted for publication in The Philosophical Magazine

Monitoramento de downloads de publicações de cientistas da Universidade Estadual de Belgorod (Rússia) por cientistas de outros países

The article presents a review on the functioning of the ResearchGate network and the growth of its popularity both from the literary data and from the experiments in the Google Scholar search engine. It describes a unique weekly monitoring experiments of downloads of Belgorod State University (Russia) scientists' publications by scientists from other countries (starting on 11.01.2015 through 20.12.2015), and it is shown that scientists from the United States (about 10,000 downloads in 2015) and China (about 6,000 downloads in 2015) are most interested in these publications. As a result we see very uneven inverse-square distribution of Belgorod State University publications by countries of the world. The total number of countries appeared to be 91.El artículo presenta una revisión sobre el funcionamiento de la red ResearchGate y el crecimiento de su popularidad tanto a partir de los datos literarios como de los experimentos en el motor de búsqueda Google Scholar. Describe experimentos únicos de monitoreo semanales de descargas de publicaciones de científicos de la Universidad Estatal de Belgorod (Rusia) por científicos de otros países (desde el 11.01.2015 hasta el 20.12.2015), y se muestra que científicos de los Estados Unidos (aproximadamente 10.000 descargas) en 2015) y China (aproximadamente 6.000 descargas en 2015) están más interesados en estas publicaciones. Como resultado, vemos una distribución muy desigual de casillas inversas de las publicaciones de la Universidad Estatal de Belgorod por países del mundo. El número total de países parecía ser 91.O artigo apresenta uma revisão do funcionamento da rede ResearchGate e o crescimento de sua popularidade a partir de dados literários e de experimentos no mecanismo de busca do Google Scholar. Somente experimentos descrito descarga monitoramento publicações semanais de cientistas da Universidade Estadual de Belgorod (Rússia) por cientistas de outros países (a partir de 2015/11/01 a 2015/12/20), e mostra que os cientistas dos Estados Unidos (aproximadamente 10.000 downloads) em 2015) e China (aproximadamente 6.000 downloads em 2015) estão mais interessados nessas publicações.&nbsp; Como resultado, vemos uma distribuição muito desigu al de quadrados inversos das publicações da Universidade Estatal de Belgorod por países do mundo. O número total de países parecia ser de 91

Gauge covariances and nonlinear optical responses

The formalism of the reduced density matrix is pursued in both length and velocity gauges of the perturbation to the crystal Hamiltonian. The covariant derivative is introduced as a convenient representation of the position operator. This allow us to write compact expressions for the reduced density matrix in any order of the perturbation which simplifies the calculations of nonlinear optical responses; as an example, we compute the first and third order contributions of the monolayer graphene. Expressions obtained in both gauges share the same formal structure, allowing a comparison of the effects of truncation to a finite set of bands. This truncation breaks the equivalence between the two approaches: its proper implementation can be done directly in the expressions derived in the length gauge, but require a revision of the equations of motion of the reduced density matrix in the velocity gauge.The work of G.B.V. and D.J.P. is supported by Fundação para a Ciência e Tecnologia (FCT) under the Grants No. PD/BI/129220/2017 and No. PD/BD/135019/2017, respectively. N.M.R.P. acknowledges funding from the European Commission within the project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. No. 696656) and the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing Grant No. UID/FIS/04650/2013.info:eu-repo/semantics/publishedVersio