5,547 research outputs found
Neighbours of Einstein's Equations: Connections and Curvatures
Once the action for Einstein's equations is rewritten as a functional of an
SO(3,C) connection and a conformal factor of the metric, it admits a family of
``neighbours'' having the same number of degrees of freedom and a precisely
defined metric tensor. This paper analyzes the relation between the Riemann
tensor of that metric and the curvature tensor of the SO(3) connection. The
relation is in general very complicated. The Einstein case is distinguished by
the fact that two natural SO(3) metrics on the GL(3) fibers coincide. In the
general case the theory is bimetric on the fibers.Comment: 16 pages, LaTe
Manifest Duality in Born-Infeld Theory
Born-Infeld theory is formulated using an infinite set of gauge fields, along
the lines of McClain, Wu and Yu. In this formulation electromagnetic duality is
generated by a fully local functional. The resulting consistency problems are
analyzed and the formulation is shown to be consistent.Comment: 15 pages, Late
Causal structure and degenerate phase boundaries
Timelike and null hypersurfaces in the degenerate space-times in the Ashtekar
theory are defined in the light of the degenerate causal structure proposed by
Matschull. Using the new definition of null hypersufaces, the conjecture that
the "phase boundary" separating the degenerate space-time region from the
non-degenerate one in Ashtekar's gravity is always null is proved under certain
circumstances.Comment: 13 pages, Revte
Ancilla-assisted sequential approximation of nonlocal unitary operations
We consider the recently proposed "no-go" theorem of Lamata et al [Phys. Rev.
Lett. 101, 180506 (2008)] on the impossibility of sequential implementation of
global unitary operations with the aid of an itinerant ancillary system and
view the claim within the language of Kraus representation. By virtue of an
extremely useful tool for analyzing entanglement properties of quantum
operations, namely, operator-Schmidt decomposition, we provide alternative
proof to the "no-go" theorem and also study the role of initial correlations
between the qubits and ancilla in sequential preparation of unitary entanglers.
Despite the negative response from the "no-go" theorem, we demonstrate
explicitly how the matrix-product operator(MPO) formalism provides a flexible
structure to develop protocols for sequential implementation of such entanglers
with an optimal fidelity. The proposed numerical technique, that we call
variational matrix-product operator (VMPO), offers a computationally efficient
tool for characterizing the "globalness" and entangling capabilities of
nonlocal unitary operations.Comment: Slightly improved version as published in Phys. Rev.
Organic field-testing of compounds to control apple scab (Venturia inaequalis) in combination with alleyway cover crops
To find new potential fungicides acceptable to organic production preventing apple scab (Venturia inaequalis) infections on leaf and fruits during primary apple scab infection period.
The trials were carried out in combination with different cover crop treatments in single-tree plots. The formerly resistant variety ‘Delorina’ on rootstock M9, planted 1995 at a planting distance of 3.3 m x 1.6 m, unfertilized and with mechanical weed cleaning in the tree row, were used. The experimental orchard is located at Research Centre Aarslev (100 27´ E, 550 18´N)
Low energy dynamics of spinor condensates
We present a derivation of the low energy Lagrangian governing the dynamics
of the spin degrees of freedom in a spinor Bose condensate, for any phase in
which the average magnetization vanishes. This includes all phases found within
mean-field treatments except for the ferromagnet, for which the low energy
dynamics has been discussed previously. The Lagrangian takes the form of a
sigma model for the rotation matrix describing the local orientation of the
spin state of the gas
Understanding contextualised rational action - author's response
Understanding contextualised rational action - author's respons
Quark-Gluon Jet Differences at LEP
A new method to identify the gluon jet in 3-jet ``{\bf Y}'' decays of
is presented. The method is based on differences in particle multiplicity
between quark jets and gluon jets, and is more effective than tagging by
leptonic decay. An experimental test of the method and its application to a
study of the ``string effect'' are proposed. Various jet-finding schemes for
3-jet events are compared.Comment: 11 pages, LaTeX, 4 PostScript figures availble from the author
([email protected]), MSUTH-92-0
Phase transitions for random states and a semi-circle law for the partial transpose
For a system of N identical particles in a random pure state, there is a
threshold k_0 = k_0(N) ~ N/5 such that two subsystems of k particles each
typically share entanglement if k > k_0, and typically do not share
entanglement if k < k_0. By "random" we mean here "uniformly distributed on the
sphere of the corresponding Hilbert space." The analogous phase transition for
the positive partial transpose (PPT) property can be described even more
precisely. For example, for N qubits the two subsystems of size k are typically
in a PPT state if k
k_1. Since, for a given state of the entire system, the induced state of a
subsystem is given by the partial trace, the above facts can be rephrased as
properties of random induced states. An important step in the analysis depends
on identifying the asymptotic spectral density of the partial transposes of
such random induced states, a result which is interesting in its own right.Comment: 5 pages, 2 figures. This short note contains a high-level overview of
two long and technical papers, arXiv:1011.0275 and arXiv:1106.2264. Version
2: unchanged results, editorial changes, added reference, close to the
published articl
Entanglement requirements for implementing bipartite unitary operations
We prove, using a new method based on map-state duality, lower bounds on
entanglement resources needed to deterministically implement a bipartite
unitary using separable (SEP) operations, which include LOCC (local operations
and classical communication) as a particular case. It is known that the Schmidt
rank of an entangled pure state resource cannot be less than the Schmidt rank
of the unitary. We prove that if these ranks are equal the resource must be
uniformly (maximally) entangled: equal nonzero Schmidt coefficients. Higher
rank resources can have less entanglement: we have found numerical examples of
Schmidt rank 2 unitaries which can be deterministically implemented, by either
SEP or LOCC, using an entangled resource of two qutrits with less than one ebit
of entanglement.Comment: 7 pages Revte
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