58,907 research outputs found
Correlation functions, Bell's inequalities and the fundamental conservation laws
I derive the correlation function for a general theory of two-valued spin
variables that satisfy the fundamental conservation law of angular momentum.
The unique theory-independent correlation function is identical to the quantum
mechanical correlation function. I prove that any theory of correlations of
such discrete variables satisfying the fundamental conservation law of angular
momentum violates the Bell's inequalities. Taken together with the Bell's
theorem, this result has far reaching implications. No theory satisfying
Einstein locality, reality in the EPR-Bell sense, and the validity of the
conservation law can be constructed. Therefore, all local hidden variable
theories are incompatible with fundamental symmetries and conservation laws.
Bell's inequalities can be obeyed only by violating a conservation law. The
implications for experiments on Bell's inequalities are obvious. The result
provides new insight regarding entanglement, and its measures.Comment: LaTeX, 12pt, 11 pages, 2 figure
Modelling for research on chemical control of mammals in New Zealand
Development of predictive formulae or qualitative statements about the probable outcome of control campaigns entails knowledge of bait quality and distribution, behaviour, vagaries of weather at the time of the control campaign, and other factors which govern the probability that the target animals will accept bait. This paper collates experience in recognising, estimating and using some of these variables for predicting the outcome of large-scale poisoning, and discusses possible approaches to the solution of some hard-core problems
Spin dynamics in a superconductor / ferromagnet proximity system
The ferromagnetic resonance of thin sputtered Ni80Fe20 films grown on Nb is
measured. By varying the temperature and thickness of the Nb the role of the
superconductivity on the whole ferromagnetic layer in these heterostructures is
explored. The change in the spin transport properties below the superconducting
transition of the Nb is found to manifest itself in the Ni80Fe20 layer by a
sharpening in the resonance of the ferromagnet, or a decrease in the effective
Gilbert damping co-efficient. This dynamic proximity effect is in contrast to
low frequency studies in these systems, where the effect of the superconductor
is confined to a small region in the ferromagnet. We interpret this in terms of
the spin pumping model.Comment: 4 pages, 4 figures, to be submitted for publicatio
Sudden Critical Current Drops Induced in S/F Structures
In the search for new physical properties of S/F structures, we have found
that the superconductor critical current can be controlled by the domain state
of the neighboring ferromagnet. The superconductor is a thin wire of thickness
d_{s} ~ 2 xi_{S}. Nb/Co and Nb/Py (Permalloy Ni_{80}Fe_{20}) bilayer structures
were grown with a significant magnetic anisotropy. Critical current
measurements of Nb/Co structures with ferromagnet thickness d_{F} > 30nm show
sudden drops in two very defined steps when the measurements are made along the
hard axes direction (i.e. current track parallel to hard anisotropy axes
direction). These drops disappear when they are made along the easy axis
direction or when the ferromagnet thickness is below 30nm. The drops are
accompanied by vortex flux flow. In addition magnetorestistance measurements
close to Tc show a sharp increase near saturation fields of the ferromagnet.
Similar results are reproduced in Nb/Py bilayer structure with the ferromagnet
thickness d_{F} ~ 50nm along the easy anisotropy axes. These results are
explained as being due to spontaneous vortex formation and flow induced by
Bloch domain walls of the ferromagnet underneath. We argue these Bloch domain
walls produce a 2D vortex-antivortex lattice structure.Comment: 6 pages, 6 figure
Loophole-free Bell test based on local precertification of photon's presence
A loophole-free violation of Bell inequalities is of fundamental importance
for demonstrating quantum nonlocality and long-distance device-independent
secure communication. However, transmission losses represent a fundamental
limitation for photonic loophole-free Bell tests. A local precertification of
the presence of the photons immediately before the local measurements may solve
this problem. We show that local precertification is feasible by integrating
three current technologies: (i) enhanced single-photon down-conversion to
locally create a flag photon, (ii) nanowire-based superconducting single-photon
detectors for a fast flag detection, and (iii) superconducting transition-edge
sensors to close the detection loophole. We carry out a precise space-time
analysis of the proposed scheme, showing its viability and feasibility.Comment: REVTeX4, 7 Pages, 1 figur
Constructing N-qubit entanglement monotones from anti-linear operators
We present a method to construct entanglement measures for pure states of
multipartite qubit systems. The key element of our approach is an antilinear
operator that we call {\em comb} in reference to the {\em hairy-ball theorem}.
For qubits (or spin 1/2) the combs are automatically invariant under
SL(2,\CC). This implies that the {\em filters} obtained from the combs are
entanglement monotones by construction. We give alternative formulae for the
concurrence and the 3-tangle as expectation values of certain antilinear
operators. As an application we discuss inequivalent types of genuine
four-qubit entanglement.Comment: 5 pages, revtex4; more detailed illustration of the metho
A Topos Foundation for Theories of Physics: IV. Categories of Systems
This paper is the fourth in a series whose goal is to develop a fundamentally
new way of building theories of physics. The motivation comes from a desire to
address certain deep issues that arise in the quantum theory of gravity. Our
basic contention is that constructing a theory of physics is equivalent to
finding a representation in a topos of a certain formal language that is
attached to the system. Classical physics arises when the topos is the category
of sets. Other types of theory employ a different topos. The previous papers in
this series are concerned with implementing this programme for a single system.
In the present paper, we turn to considering a collection of systems: in
particular, we are interested in the relation between the topos representation
for a composite system, and the representations for its constituents. We also
study this problem for the disjoint sum of two systems. Our approach to these
matters is to construct a category of systems and to find a topos
representation of the entire category.Comment: 38 pages, no figure
Characterizing the nonlocal correlations of particles that never interacted
Quantum systems that have never interacted can become nonlocally correlated
through a process called entanglement swapping. To characterize nonlocality in
this context, we introduce local models where quantum systems that are
initially uncorrelated are described by uncorrelated local variables. While a
pair of maximally entangled qubits prepared in the usual way (i.e., emitted
from a common source) requires a visibility close to 70% to violate a Bell
inequality, we show that an entangled pair generated through entanglement
swapping will already violate a Bell inequality for visibilities as low as 50%
under our assumption.Comment: 5 pages, 2 figure
Research on gravitational mass sensors Quarterly progress report no. 1, 15 Oct. 1964 - 14 Jan. 1965
Lunar orbiter and deep space probe gravitational sensor for determining mass distribution of moon and asteroid
Pair plasma cushions in the hole-boring scenario
Pulses from a 10 PW laser are predicted to produce large numbers of
gamma-rays and electron-positron pairs on hitting a solid target. However, a
pair plasma, if it accumulates in front of the target, may partially shield it
from the pulse. Using stationary, one-dimensional solutions of the two-fluid
(electron-positron) and Maxwell equations, including a classical radiation
reaction term, we examine this effect in the hole-boring scenario. We find the
collective effects of a pair plasma "cushion" substantially reduce the
reflectivity, converting the absorbed flux into high-energy gamma-rays. There
is also a modest increase in the laser intensity needed to achieve threshold
for a non-linear pair cascade.Comment: 17 pages, 5 figures. Accepted for publication in Plasma Physics and
Controlled Fusion. Typos corrected, reference update
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