224 research outputs found
Spin quadrupoletronics: moving spin anisotropy around
We show that spin anisotropy can be transferred to an isotropic system by
transport of spin quadrupole moment. We derive the quadrupole moment current
and continuity equation and study a high-spin valve structure consisting of two
ferromagnets coupled to a quantum dot probing an impurity spin. The quadrupole
back-action on their coupled spin results in spin torques and anisotropic spin
relaxation which do not follow from standard spin current considerations. We
demonstrate the detection of the impurity spin by charge transport and its
manipulation by electric fields.Comment: v2 updated arXiv reference [6
Notions of Infinity in Quantum Physics
In this article we will review some notions of infiniteness that appear in
Hilbert space operators and operator algebras. These include proper
infiniteness, Murray von Neumann's classification into type I and type III
factors and the class of F{/o} lner C*-algebras that capture some aspects of
amenability. We will also mention how these notions reappear in the description
of certain mathematical aspects of quantum mechanics, quantum field theory and
the theory of superselection sectors. We also show that the algebra of the
canonical anti-commutation relations (CAR-algebra) is in the class of F{/o}
lner C*-algebras.Comment: 11 page
Twisted duality of the CAR-Algebra
We give a complete proof of the twisted duality property M(q)'= Z M(q^\perp)
Z* of the (self-dual) CAR-Algebra in any Fock representation. The proof is
based on the natural Halmos decomposition of the (reference) Hilbert space when
two suitable closed subspaces have been distinguished. We use modular theory
and techniques developed by Kato concerning pairs of projections in some
essential steps of the proof.
As a byproduct of the proof we obtain an explicit and simple formula for the
graph of the modular operator. This formula can be also applied to fermionic
free nets, hence giving a formula of the modular operator for any double cone.Comment: 32 pages, Latex2e, to appear in Journal of Mathematical Physic
Semicausal operations are semilocalizable
We prove a conjecture by DiVincenzo, which in the terminology of Preskill et
al. [quant-ph/0102043] states that ``semicausal operations are
semilocalizable''. That is, we show that any operation on the combined system
of Alice and Bob, which does not allow Bob to send messages to Alice, can be
represented as an operation by Alice, transmitting a quantum particle to Bob,
and a local operation by Bob. The proof is based on the uniqueness of the
Stinespring representation for a completely positive map. We sketch some of the
problems in transferring these concepts to the context of relativistic quantum
field theory.Comment: 4 pages, 1 figure, revte
Dynamics of charged fluids and 1/L perturbation expansions
Some features of the calculation of fluid dynamo systems in
magnetohydrodynamics are studied. In the coupled set of the ordinary linear
differential equations for the spherically symmetric dynamos, the
problem represented by the presence of the mixed (Robin) boundary conditions is
addressed and a new treatment for it is proposed. The perturbation formalism of
large expansions is shown applicable and its main technical steps are
outlined.Comment: 16 p
Relativity and the low energy nd Ay puzzle
We solve the Faddeev equation in an exactly Poincare invariant formulation of
the three-nucleon problem. The dynamical input is a relativistic
nucleon-nucleon interaction that is exactly on-shell equivalent to the high
precision CDBonn NN interaction. S-matrix cluster properties dictate how the
two-body dynamics is embedded in the three-nucleon mass operator. We find that
for neutron laboratory energies above 20 MeV relativistic effects on Ay are
negligible. For energies below 20 MeV dynamical effects lower the nucleon
analyzing power maximum slightly by 2% and Wigner rotations lower it further up
to 10 % increasing thus disagreement between data and theory. This indicates
that three-nucleon forces must provide an even larger increase of the Ay
maximum than expected up to now.Comment: 29 pages, 2 ps figure
Entanglement, Haag-duality and type properties of infinite quantum spin chains
We consider an infinite spin chain as a bipartite system consisting of the
left and right half-chain and analyze entanglement properties of pure states
with respect to this splitting. In this context we show that the amount of
entanglement contained in a given state is deeply related to the von Neumann
type of the observable algebras associated to the half-chains. Only the type I
case belongs to the usual entanglement theory which deals with density
operators on tensor product Hilbert spaces, and only in this situation
separable normal states exist. In all other cases the corresponding state is
infinitely entangled in the sense that one copy of the system in such a state
is sufficient to distill an infinite amount of maximally entangled qubit pairs.
We apply this results to the critical XY model and show that its unique ground
state provides a particular example for this type of entanglement.Comment: LaTeX2e, 34 pages, 1 figure (pstricks
An Algebraic Jost-Schroer Theorem for Massive Theories
We consider a purely massive local relativistic quantum theory specified by a
family of von Neumann algebras indexed by the space-time regions. We assume
that, affiliated with the algebras associated to wedge regions, there are
operators which create only single particle states from the vacuum (so-called
polarization-free generators) and are well-behaved under the space-time
translations. Strengthening a result of Borchers, Buchholz and Schroer, we show
that then the theory is unitarily equivalent to that of a free field for the
corresponding particle type. We admit particles with any spin and localization
of the charge in space-like cones, thereby covering the case of
string-localized covariant quantum fields.Comment: 21 pages. The second (and crucial) hypothesis of the theorem has been
relaxed and clarified, thanks to the stimulus of an anonymous referee. (The
polarization-free generators associated with wedge regions, which always
exist, are assumed to be temperate.
Local adsorption geometry of acetylene on Si(100)(2×1)
Using C 1s scanned-energy-mode photoelectron diffraction the local adsorption geometry of acetylene on the Si(100)(2x1) surface has been determined and the results are compared with those of a similar study of ethylene adsorption on this surface. Both molecules bond to the surface along the Si-Si dimers with the C-C bonds parallel to the surface such that the C atoms are in off-atop sites relative to the Si dimer atoms. In both cases the Si-Si bond length (2.36±0.21 Å for ethylene and 2.44±0.58 Å for acetylene) is compatible only with the dimer remaining intact after adsorption and not with the Si-Si distance of an ideally terminated undimerized Si(100) surface (3.84 Å)
Reconstructing Bohr's Reply to EPR in Algebraic Quantum Theory
Halvorson and Clifton have given a mathematical reconstruction of Bohr's
reply to Einstein, Podolsky and Rosen (EPR), and argued that this reply is
dictated by the two requirements of classicality and objectivity for the
description of experimental data, by proving consistency between their
objectivity requirement and a contextualized version of the EPR reality
criterion which had been introduced by Howard in his earlier analysis of Bohr's
reply. In the present paper, we generalize the above consistency theorem, with
a rather elementary proof, to a general formulation of EPR states applicable to
both non-relativistic quantum mechanics and algebraic quantum field theory; and
we clarify the elements of reality in EPR states in terms of Bohr's
requirements of classicality and objectivity, in a general formulation of
algebraic quantum theory.Comment: 13 pages, Late
- …