902 research outputs found
Maximal entanglement of squeezed vacuum states via swapping with number-phase measurement
We propose a method to refine entanglement via swapping from a pair of
squeezed vacuum states by performing the Bell measurement of number sum and
phase difference. The resultant states are maximally entangled by adjusting the
two squeezing parameters to the same value. We then describe the teleportation
of number states by using the entangled states prepared in this way.Comment: 4 pages, 1 PS figure, RevTe
Practical quantum repeaters with linear optics and double-photon guns
We show how to create practical, efficient, quantum repeaters, employing
double-photon guns, for long-distance optical quantum communication. The guns
create polarization-entangled photon pairs on demand. One such source might be
a semiconducter quantum dot, which has the distinct advantage over parametric
down-conversion that the probability of creating a photon pair is close to one,
while the probability of creating multiple pairs vanishes. The swapping and
purifying components are implemented by polarizing beam splitters and
probabilistic optical CNOT gates.Comment: 4 pages, 4 figures ReVTe
Teleportation-based number state manipulation with number sum measurement
We examine various manipulations of photon number states which can be
implemented by teleportation technique with number sum measurement. The
preparations of the Einstein-Podolsky-Rosen resources as well as the number sum
measurement resulting in projection to certain Bell state may be done
conditionally with linear optical elements, i.e., beam splitters, phase
shifters and zero-one-photon detectors. Squeezed vacuum states are used as
primary entanglement resource, while single-photon sources are not required.Comment: 9 pages, 4 figures, Misprints are corrected. 3 figures for number sum
measurement are added. Discussion on manipulations are expanded. Calculations
for success probabilities are added. Fig.4 is adde
Glass Transition of Hard Sphere Systems: Molecular Dynamics and Density Functional Theory
The glass transition of a hard sphere system is investigated within the
framework of the density functional theory (DFT). Molecular dynamics (MD)
simulations are performed to study dynamical behavior of the system on the one
hand and to provide the data to produce the density field for the DFT on the
other hand. Energy landscape analysis based on the DFT shows that there appears
a metastable (local) free energy minimum representing an amorphous state as the
density is increased. This state turns out to become stable, compared with the
uniform liquid, at some density, around which we also observe sharp slowing
down of the relaxation in MD simulations.Comment: 5 pages, 5 figure
STATIONARY SOLUTIONS IN BRANS-DICKE STOCHASTIC INFLATIONARY COSMOLOGY
In Brans-Dicke theory the Universe becomes divided after inflation into many
exponentially large domains with different values of the effective
gravitational constant. Such a process can be described by diffusion equations
for the probability of finding a certain value of the inflaton and dilaton
fields in a physical volume of the Universe. For a typical chaotic inflation
potential, the solutions for the probability distribution never become
stationary but grow forever towards larger values of the fields. We show here
that a non-minimal conformal coupling of the inflaton to the curvature scalar,
as well as radiative corrections to the effective potential, may provide a
dynamical cutoff and generate stationary solutions. We also analyze the
possibility of large nonperturbative jumps of the fluctuating inflaton scalar
field, which was recently revealed in the context of the Einstein theory. We
find that in the Brans--Dicke theory the amplitude of such jumps is strongly
suppressed.Comment: 19 pages, LaTe
Stripe order at low temperatures in La{2-x}Sr{x}NiO4 for 1/3 < x < 1/2
Stripe order in La{2-x}Sr{x}NiO4 beyond x = 1/3 was studied with neutron
scattering technique. At low temperatures, all the samples exhibit hole stripe
order. Incommensurability \epsilon of the stripe order is approximately linear
in the hole concentration n_h = x + 2\delta up to x = 1/2, where \delta denotes
the off-stoichiometry of oxygen atoms. The charge and spin ordering
temperatures exhibit maxima at n_h = 1/3, and both decrease beyond n_h > 1/3.
For 1/3 < n_h < 1/2, the stripe ordering consists of the mixture of the
\epsilon = 1/3 stripe order and the n_h = 1/2 charge/spin order.Comment: REVTeX, 4 pages, 4 figure
Demonstration of Feed-Forward Control for Linear Optics Quantum Computation
One of the main requirements in linear optics quantum computing is the
ability to perform single-qubit operations that are controlled by classical
information fed forward from the output of single photon detectors. These
operations correspond to pre-determined combinations of phase corrections and
bit-flips that are applied to the post-selected output modes of
non-deterministic quantum logic devices. Corrections of this kind are required
in order to obtain the correct logical output for certain detection events, and
their use can increase the overall success probability of the devices. In this
paper, we report on the experimental demonstration of the use of this type of
feed-forward system to increase the probability of success of a simple
non-deterministic quantum logic operation from approximately 1/4 to 1/2. This
logic operation involves the use of one target qubit and one ancilla qubit
which, in this experiment, are derived from a parametric down-conversion photon
pair. Classical information describing the detection of the ancilla photon is
fed-forward in real-time and used to alter the quantum state of the output
photon. A fiber optic delay line is used to store the output photon until a
polarization-dependent phase shift can be applied using a high speed Pockels
cell
Generation of entangled states of two atoms inside a leaky cavity
An in-depth theoretical study is carried out to examine the
quasi-deterministic entanglement of two atoms inside a leaky cavity. Two
-type three-level atoms, initially in their ground states, may become
maximally entangled through the interaction with a single photon. By working
out an exact analytic solution, we show that the probability of success depends
crucially on the spectral function of the injected photon. With a cavity
photon, one can generate a maximally entangled state with a certain probability
that is always less than 50%. However, for an injected photon with a narrower
spectral width, this probability can be significantly increased. In particular,
we discover situations in which entanglement can be achieved in a single trial
with an almost unit probability
Interface and electronic characterization of thin epitaxial Co3O4 films
The interface and electronic structure of thin (~20-74 nm) Co3O4(110)
epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl2O4(110)
single crystal substrates have been investigated by means of real and
reciprocal space techniques. As-grown film surfaces are found to be relatively
disordered and exhibit an oblique low energy electron diffraction (LEED)
pattern associated with the O-rich CoO2 bulk termination of the (110) surface.
Interface and bulk film structure are found to improve significantly with
post-growth annealing at 820 K in air and display sharp rectangular LEED
patterns, suggesting a surface stoichiometry of the alternative Co2O2 bulk
termination of the (110) surface. Non-contact atomic force microscopy
demonstrates the presence of wide terraces separated by atomic steps in the
annealed films that are not present in the as-grown structures; the step height
of ~ 2.7 A corresponds to two atomic layers and confirms a single termination
for the annealed films, consistent with the LEED results. A model of the (1 *
1) surfaces that allows for compensation of the polar surfaces is presented.Comment: 8 pages, 7 figure
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