88,509 research outputs found
Localization of Macroscopic Object Induced by the Factorization of Internal Adiabatic Motion
To account for the phenomenon of quantum decoherence of a macroscopic object,
such as the localization and disappearance of interference, we invoke the
adiabatic quantum entanglement between its collective states(such as that of
the center-of-mass (C.M)) and its inner states based on our recent
investigation. Under the adiabatic limit that motion of C.M dose not excite the
transition of inner states, it is shown that the wave function of the
macroscopic object can be written as an entangled state with correlation
between adiabatic inner states and quasi-classical motion configurations of the
C.M. Since the adiabatic inner states are factorized with respect to each parts
composing the macroscopic object, this adiabatic separation can induce the
quantum decoherence. This observation thus provides us with a possible solution
to the Schroedinger cat paradoxComment: Revtex4,23 pages,1figur
Quantum Thermalization With Couplings
We study the role of the system-bath coupling for the generalized canonical
thermalization [S. Popescu, et al., Nature Physics 2,754(2006) and S. Goldstein
et al., Phys. Rev. Lett. 96, 050403(2006)] that reduces almost all the pure
states of the "universe" [formed by a system S plus its surrounding heat bath
] to a canonical equilibrium state of S. We present an exactly solvable, but
universal model for this kinematic thermalization with an explicit
consideration about the energy shell deformation due to the interaction between
S and B. By calculating the state numbers of the "universe" and its subsystems
S and B in various deformed energy shells, it is found that, for the
overwhelming majority of the "universe" states (they are entangled at least),
the diagonal canonical typicality remains robust with respect to finite
interactions between S and B. Particularly, the kinematic decoherence is
utilized here to account for the vanishing of the off-diagonal elements of the
reduced density matrix of S. It is pointed out that the non-vanishing
off-diagonal elements due to the finiteness of bath and the stronger
system-bath interaction might offer more novelties of the quantum
thermalization.Comment: 4 pages, 2 figure
Epitaxial graphene on SiC(0001): More than just honeycombs
The potential of graphene to impact the development of the next generation of
electronics has renewed interest in its growth and structure. The
graphitization of hexagonal SiC surfaces provides a viable alternative for the
synthesis of graphene, with wafer-size epitaxial graphene on SiC(0001) now
possible. Despite this recent progress, the exact nature of the graphene-SiC
interface and whether the graphene even has a semiconducting gap remain
controversial. Using scanning tunneling microscopy with functionalized tips and
density functional theory calculations, here we show that the interface is a
warped carbon sheet consisting of three-fold hexagon-pentagon-heptagon
complexes periodically inserted into the honeycomb lattice. These defects
relieve the strain between the graphene layer and the SiC substrate, while
still retaining the three-fold coordination for each carbon atom. Moreover,
these defects break the six-fold symmetry of the honeycomb, thereby naturally
inducing a gap: the calculated band structure of the interface is
semiconducting and there are two localized states near K below the Fermi level,
explaining the photoemission and carbon core-level data. Nonlinear dispersion
and a 33 meV gap are found at the Dirac point for the next layer of graphene,
providing insights into the debate over the origin of the gap in epitaxial
graphene on SiC(0001). These results indicate that the interface of the
epitaxial graphene on SiC(0001) is more than a dead buffer layer, but actively
impacts the physical and electronic properties of the subsequent graphene
layers
An SU(4) Model of High-Temperature Superconductivity and Antiferromagnetism
We present an SU(4) model of high-temperature superconductivity having many
similarities to dynamical symmetries known to play an important role in
microscopic nuclear structure physics and in elementary particle physics.
Analytical solutions in three dynamical symmetry limits of this model are
found: an SO(4) limit associated with antiferromagnetic order; an SU(2) X SO(3)
limit that may be interpreted as a d-wave pairing condensate; and an SO(5)
limit that may be interpreted as a doorway state between the antiferromagnetic
order and the superconducting order. The model suggests a phase diagram in
qualitative agreement with that observed in the cuprate superconductors. The
relationship between the present model and the SO(5) unification of
superconductivity and antiferromagnetic order proposed by Zhang is discussed.Comment: A long paper extended from the early version cond-mat/9903150;
accepted by Phys. Rev.
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