5,592 research outputs found
Charge and Spin Transport in the One-dimensional Hubbard Model
In this paper we study the charge and spin currents transported by the
elementary excitations of the one-dimensional Hubbard model. The corresponding
current spectra are obtained by both analytic methods and numerical solution of
the Bethe-ansatz equations. For the case of half-filling, we find that the
spin-triplet excitations carry spin but no charge, while charge -spin
triplet excitations carry charge but no spin, and both spin-singlet and charge
-spin-singlet excitations carry neither spin nor charge currents.Comment: 24 pages, 14 figure
Bell's inequality with Dirac particles
We study Bell's inequality using the Bell states constructed from four
component Dirac spinors. Spin operator is related to the Pauli-Lubanski pseudo
vector which is relativistic invariant operator. By using Lorentz
transformation, in both Bell states and spin operator, we obtain an observer
independent Bell's inequality, so that it is maximally violated as long as it
is violated maximally in the rest frame.Comment: 7 pages. arXiv admin note: text overlap with arXiv:quant-ph/0308156
by other author
Generic Bell inequalities for multipartite arbitrary dimensional systems
We present generic Bell inequalities for multipartite multi-dimensional
systems. The inequalities that any local realistic theories must obey are
violated by quantum mechanics for even-dimensional multipartite systems. A
large set of variants are shown to naturally emerge from the generic Bell
inequalities. We discuss particular variants of Bell inequalities, that are
violated for all the systems including odd-dimensional systems.Comment: Accepted in Phys. Rev. Let
Complementarity of Entanglement and Interference
A complementarity relation is shown between the visibility of interference
and bipartite entanglement in a two qubit interferometric system when the
parameters of the quantum operation change for a given input state. The
entanglement measure is a decreasing function of the visibility of
interference. The implications for quantum computation are briefly discussed.Comment: Final version, to appear on IJMPC; minor revision
Should Engineering Students Learn About Human Factors at Universities?
One of the biggest challenges related to the practical implementation of human performance (HP)/human factors (HF) is the lack of awareness among very large and diverse groups of people. These individuals include leaders at all levels of the hierarchy; engineers; health, safety, and environment (HSE) professionals; and front-line employees. Further, most of them may have an engineering or related technical background as discussed in Closing the Gap in Human Factors: Everybody Has a Role To Play
Multipartite positive-partial-transpose inequalities exponentially stronger than local reality inequalities
We show that positivity of {\it every} partial transpose of -partite
quantum states implies new inequalities on Bell correlations which are stronger
than standard Bell inequalities by a factor of . A violation of
the inequality implies the system is in a bipartite distillable entangled
state. It turns out that a family of -qubit bound entangled states proposed
by D\"ur {[Phys. Rev. Lett. {\bf 87}, 230402 (2001)]} violates the inequality
for .Comment: 4 pages, To appear in Phys. Rev.
Hydrodynamic modelling of ejecta shrapnel in the Vela supernova remnant
Many supernova remnants (SNRs) are characterized by a knotty ejecta
structure. The Vela SNR is an excellent example of remnant in which detached
clumps of ejecta are visible as X-ray emitting bullets that have been observed
and studied in great detail. We aim at modelling the evolution of ejecta
shrapnel in the Vela SNR, investigating the role of their initial parameters
(position and density) and addressing the effects of thermal conduction and
radiative losses. We performed a set of 2-D hydrodynamic simulations describing
the evolution of a density inhomogeneity in the ejecta profile. We explored
different initial setups. We found that the final position of the shrapnel is
very sensitive to its initial position within the ejecta, while the dependence
on the initial density contrast is weaker. Our model also shows that moderately
overdense knots can reproduce the detached features observed in the Vela SNR.
Efficient thermal conduction produces detectable effects by determining an
efficient mixing of the ejecta knot with the surrounding medium and shaping a
characteristic elongated morphology in the clump.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Magnetic and superconducting instabilities in the periodic Anderson model: an RPA stud
We study the magnetic and superconducting instabilities of the periodic
Anderson model with infinite Coulomb repulsion U in the random phase
approximation. The Neel temperature and the superconducting critical
temperature are obtained as functions of electronic density (chemical pressure)
and hybridization V (pressure). It is found that close to the region where the
system exhibits magnetic order the critical temperature T_c is much smaller
than the Neel temperature, in qualitative agreement with some T_N/T_c ratios
found for some heavy-fermion materials. In our study, all the magnetic and
superconducting physical behaviour of the system has its origin in the
fluctuating boson fields implementing the infinite on-site Coulomb repulsion
among the f-electrons.Comment: 9 pages, 2 figure
Spatial Localization and Relativistic Transformation of Quantum Spins
The purity of a reduced state for spins that is pure in the rest frame will
most likely appear to degrade because spin and momentum become mixed when
viewed by a moving observer. We show that such a boost-induced decrease in spin
purity observed in a moving reference frame is intrinsically related to the
spatial localization properties of the wave package observed in the rest frame.
Furthermore, we prove that, for any localized pure state with separable spin
and momentum in the rest frame, its reduced density matrix for spins inevitably
appears to be mixed whenever viewed from a moving reference frame.Comment: 5 pages, 1 figur
Nonlocal effects in Fock space
If a physical system contains a single particle, and if two distant detectors
test the presence of linear superpositions of one-particle and vacuum states, a
violation of classical locality can occur. It is due to the creation of a
two-particle component by the detecting process itself.Comment: final version in PRL 74 (1995) 4571; 76 (1996) 2205 (erratum
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