31,344 research outputs found
Discrete and finite Genral Relativity
We develop the General Theory of Relativity in a formalism with extended
causality that describes physical interaction through discrete, transversal and
localized pointlike fields. The homogeneous field equations are then solved for
a finite, singularity-free, point-like field that we associate to a ``classical
graviton". The standard Einstein's continuous formalism is retrieved by means
of an averaging process, and its continuous solutions are determined by the
chosen imposed symetry. The Schwarzschild metric is obtained by the imposition
of spherical symmetry on the averaged field.Comment: Modified conform the version to appear in Classical and Quantum
Gravit
Correlated electrons systems on the Apollonian network
Strongly correlated electrons on an Apollonian network are studied using the
Hubbard model. Ground-state and thermodynamic properties, including specific
heat, magnetic susceptibility, spin-spin correlation function, double occupancy
and one-electron transfer, are evaluated applying direct diagonalization and
quantum Monte Carlo. The results support several types of magnetic behavior. In
the strong-coupling limit, the quantum anisotropic spin 1/2 Heisenberg model is
used and the phase diagram is discussed using the renormalization group method.
For ferromagnetic coupling, we always observe the existence of long-range
order. For antiferromagnetic coupling, we find a paramagnetic phase for all
finite temperatures.Comment: 7 pages, 8 figure
Pairwise thermal entanglement in Ising-XYZ diamond chain structure in an external magnetic field
Quantum entanglement is one of the most fascinating types of correlation that
can be shared only among quantum systems. The Heisenberg chain is one of the
simplest quantum chains which exhibits a reach entanglement feature, due to the
Heisenberg interaction is quantum coupling in the spin system. The two
particles were coupled trough XYZ coupling or simply called as two-qubit XYZ
spin, which are the responsible for the emergence of thermal entanglement.
These two-qubit operators are bonded to two nodal Ising spins, and this process
is repeated infinitely resulting in a diamond chain structure. We will discuss
two-qubit thermal entanglement effect on Ising-XYZ diamond chain structure. The
concurrence could be obtained straightforwardly in terms of two-qubit density
operator elements, using this result, we study the thermal entanglement, as
well as the threshold temperature where entangled state vanishes. The present
model displays a quite unusual concurrence behavior, such as, the boundary of
two entangled regions becomes a disentangled region, this is intrinsically
related to the XY-anisotropy in the Heisenberg coupling. Despite a similar
property had been found for only two-qubit, here we show in the case of a
diamond chain structure, which reasonably represents real materials.Comment: 6 pages, 7 figure
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