12,939 research outputs found
The New SI and the Fundamental Constants of Nature
The launch in 2019 of the new international system of units is an opportunity
to highlight the key role that the fundamental laws of physics and chemistry
play in our lives and in all the processes of basic research, industry and
commerce. The main objective of these notes is to present the new SI in an
accessible way for a wide audience. After reviewing the fundamental constants
of nature and its universal laws, the new definitions of SI units are presented
using, as a unifying principle, the discrete nature of energy, matter and
information in these universal laws. The new SI system is here to stay:
although the experimental realizations may change due to technological
improvements, the definitions will remain unaffected. Quantum metrology is
expected to be one of the driving forces to achieve new quantum technologies of
the second generation.
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La puesta en marcha en 2019 del nuevo sistema internacional de unidades es
una oportunidad para resaltar el papel fundamental que las leyes fundamentales
de la F\'{\i}sica y la Qu\'{\i}mica juegan en nuestra vida y en todos los
procesos de la investigaci\'on fundamental, la industria y el comercio. El
principal objetivo de estas notas es presentar el nuevo SI de forma accesible
para una audiencia amplia. Tras repasar las constantes fundamentales de la
naturaleza y sus leyes universales, se presentan las nuevas definiciones de las
unidades SI utilizando como principio unificador la naturaleza discreta de la
energ\'{\i}a, la materia y la informaci\'on en esas leyes universales. El nuevo
sistema SI tiene vocaci\'on de futuro: aunque las realizaciones experimentales
cambien por mejoras tecnol\'gicas, las definiciones permanecer\'an inalteradas.
La Metrolog\'{\i}a cu\'antica est\'a llamada a ser uno de las fuerzas motrices
para conseguir nuevas tecnolog\'{\i}as cu\'anticas de segunda generaci\'on.Comment: Revtex file, color figures. English version y en espa\~no
Quantum Renormalization Group for 1 Dimensional Fermion Systems
Inspired by the superblock method of White, we introduce a simple
modification of the standard Renormalization Group (RG) technique for the study
of quantum lattice systems. Our method which takes into account the effect of
Boundary Conditions(BC), may be regarded as a simple way for obtaining first
estimates of many properties of quantum lattice systems. By applying this
method to the 1-dimensional free and interacting fermion system, we obtain the
ground state energy with much higher accuracy than the standard RG. We also
calculate the density-density correlation function in the free-fermion case
which shows good agreement with the exact result.Comment: LaTex file, 1 PS figur
Topological Heat Transport and Symmetry-Protected Boson Currents
The study of non-equilibrium properties in topological systems is of
practical and fundamental importance. Here, we analyze the stationary
properties of a two-dimensional bosonic Hofstadter lattice coupled to two
thermal baths in the quantum open-system formalism. Novel phenomena appear like
chiral edge heat currents that are the out-of-equilibrium counterparts of the
zero-temperature edge currents. They support a new concept of dissipative
symmetry-protection, where a set of discrete symmetries protects topological
heat currents, differing from the symmetry-protection devised in closed systems
and zero-temperature. Remarkably, one of these currents flows opposite to the
decreasing external temperature gradient. As the starting point, we consider
the case of a single external reservoir already showing prominent results like
thermal erasure effects and topological thermal currents. Our results are
experimentally accessible with platforms like photonics systems and optical
lattices.Comment: RevTeX4 file, color figure
Single-Step Distillation Protocol with Generalized Beam Splitters
We develop a distillation protocol for multilevel qubits (qudits) using
generalized beam splitters like in the proposal of Pan et al. for ordinary
qubits. We find an acceleration with respect to the scheme of Bennet et al.
when extended to qudits. It is also possible to distill entangled pairs of
photons carrying orbital angular momenta (OAM) states that conserves the total
angular momenta as those produced in recent experiments.Comment: REVTEX4 file, color figure
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