3,145 research outputs found
Realisation of Hardy's Thought Experiment
We present an experimental realisation of Hardy's thought experiment [Phys.
Rev. Lett. {\bf 68}, 2981 (1992)], using photons. The experiment consists of a
pair of Mach-Zehnder interferometers that interact through photon bunching at a
beam splitter. A striking contradiction is created between the predictions of
quantum mechanics and local hidden variable based theories. The contradiction
relies on non-maximally entangled position states of two particles.Comment: 5 page
Linked and knotted beams of light, conservation of helicity and the flow of null electromagnetic fields
Maxwell's equations allow for some remarkable solutions consisting of pulsed
beams of light which have linked and knotted field lines. The preservation of
the topological structure of the field lines in these solutions has previously
been ascribed to the fact that the electric and magnetic helicity, a measure of
the degree of linking and knotting between field lines, are conserved. Here we
show that the elegant evolution of the field is due to the stricter condition
that the electric and magnetic fields be everywhere orthogonal. The field lines
then satisfy a `frozen field' condition and evolve as if they were unbreakable
filaments embedded in a fluid. The preservation of the orthogonality of the
electric and magnetic field lines is guaranteed for null, shear-free fields
such as the ones considered here by a theorem of Robinson. We calculate the
flow field of a particular solution and find it to have the form of a Hopf
fibration moving at the speed of light in a direction opposite to the
propagation of the pulsed light beam, a familiar structure in this type of
solution. The difference between smooth evolution of individual field lines and
conservation of electric and magnetic helicity is illustrated by considering a
further example in which the helicities are conserved, but the field lines are
not everywhere orthogonal. The field line configuration at time t=0 corresponds
to a nested family of torus knots but unravels upon evolution
Robust long-distance entanglement and a loophole-free Bell test with ions and photons
Two trapped ions that are kilometers apart can be entangled by the joint
detection of two photons, each coming from one of the ions, in a basis of
entangled states. Such a detection is possible with linear optical elements.
The use of two-photon interference allows entanglement distribution without
interferometric sensitivity to the path length of the photons. The present
method of creating entangled ions also opens up the possibility of a
loophole-free test of Bell's inequalities.Comment: published versio
Separable approximation to two-body matrix elements
Two-body matrix elements of arbitrary local interactions are written as the
sum of separable terms in a way that is well suited for the exchange and
pairing channels present in mean-field calculations. The expansion relies on
the transformation to center of mass and relative coordinate (in the spirit of
Talmi's method) and therefore it is only useful (finite number of expansion
terms) for harmonic oscillator single particle states. The converge of the
expansion with the number of terms retained is studied for a Gaussian two body
interaction. The limit of a contact (delta) force is also considered. Ways to
handle the general case are also discussed.Comment: 10 pages, 5 figures (for high resolution versions of some of the
figures contact the author
Reconfigurable Boolean Logic using Magnetic Single-Electron Transistors
We propose a novel hybrid single-electron device for reprogrammable low-power
logic operations, the magnetic single-electron transistor (MSET). The device
consists of an aluminium single-electron transistors with a GaMnAs magnetic
back-gate. Changing between different logic gate functions is realized by
reorienting the magnetic moments of the magnetic layer which induce a voltage
shift on the Coulomb blockade oscillations of the MSET. We show that we can
arbitrarily reprogram the function of the device from an n-type SET for
in-plane magnetization of the GaMnAs layer to p-type SET for out-of-plane
magnetization orientation. Moreover, we demonstrate a set of reprogrammable
Boolean gates and its logical complement at the single device level. Finally,
we propose two sets of reconfigurable binary gates using combinations of two
MSETs in a pull-down network
Mass Dependence of M3Y-Type Interactions and the Effects of Tensor Correlations
The mass dependence of the M3Y-type effective interactions and the effects of
tensor correlations are examined. Two-body nuclear matrix elements are obtained
by the lowest order constrained variational (LOCV) technique with and without
tensor correlations. We have found that the tensor correlations are important
especially in the triplet-even (TE) and tensor-even (TNE) channels in order to
reproduce the G-matrix elements obtained previously. Then M3Y-type potentials
for inelastic scattering are obtained by fitting our two-body matrix elements
to those of a sum of Yukawa functions for the mass numbers A=24, A=40 and A=90.Comment: 13 pages, 6 table
Real time statistical field theory
We have written a {\it Mathematica} program that calculates the integrand
corresponding to any amplitude in the closed-time-path formulation of real time
statistical field theory. The program is designed so that it can be used by
someone with no previous experience with {\it Mathematica}. It performs the
contractions over the tensor indices that appear in real time statistical field
theory and gives the result in the 1-2, Keldysh or RA basis. We have used the
program to calculate the ward identity for the QED 3-point function, the QED
4-point function for two photons and two fermions, and the QED 5-point function
for three photons and two fermions. In real time statistical field theory,
there are seven 3-point functions, 15 4-point functions and 31 5-point
functions. We produce a table that gives the results for all of these
functions. In addition, we give a simple general expression for the KMS
conditions between -point green functions and vertex functions, in both the
Keldysh and RA basesComment: 25 pages, 12 figure
Low voltage control of ferromagnetism in a semiconductor p-n junction
The concept of low-voltage depletion and accumulation of electron charge in
semiconductors, utilized in field-effect transistors (FETs), is one of the
cornerstones of current information processing technologies. Spintronics which
is based on manipulating the collective state of electron spins in a
ferromagnet provides complementary technologies for reading magnetic bits or
for the solid-state memories. The integration of these two distinct areas of
microelectronics in one physical element, with a potentially major impact on
the power consumption and scalability of future devices, requires to find
efficient means for controlling magnetization electrically. Current induced
magnetization switching phenomena represent a promising step towards this goal,
however, they relay on relatively large current densities. The direct approach
of controlling the magnetization by low-voltage charge depletion effects is
seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets
are separated by many orders of magnitude in their typical carrier
concentrations. Here we demonstrate that this concept is viable by reporting
persistent magnetization switchings induced by short electrical pulses of a few
volts in an all-semiconductor, ferromagnetic p-n junction.Comment: 11 pages, 4 figure
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