7,477 research outputs found
Spin correlated interferometry for polarized and unpolarized photons on a beam splitter
Spin interferometry of the 4th order for independent polarized as well as
unpolarized photons arriving simultaneously at a beam splitter and exhibiting
spin correlation while leaving it, is formulated and discussed in the quantum
approach. Beam splitter is recognized as a source of genuine singlet photon
states. Also, typical nonclassical beating between photons taking part in the
interference of the 4th order is given a polarization dependent explanation.Comment: RevTeX, 19 pages, 1 ps figure, author web page at
http://m3k.grad.hr/pavici
Area-Constrained Planar Elastica
We determine the equilibria of a rigid loop in the plane, subject to the
constraints of fixed length and fixed enclosed area. Rigidity is characterized
by an energy functional quadratic in the curvature of the loop. We find that
the area constraint gives rise to equilibria with remarkable geometrical
properties: not only can the Euler-Lagrange equation be integrated to provide a
quadrature for the curvature but, in addition, the embedding itself can be
expressed as a local function of the curvature. The configuration space is
shown to be essentially one-dimensional, with surprisingly rich structure.
Distinct branches of integer-indexed equilibria exhibit self-intersections and
bifurcations -- a gallery of plots is provided to highlight these findings.
Perturbations connecting equilibria are shown to satisfy a first order ODE
which is readily solved. We also obtain analytical expressions for the energy
as a function of the area in some limiting regimes.Comment: 23 pages, several figures. Version 2: New title. Changes in the
introduction, addition of a new section with conclusions. Figure 14 corrected
and one reference added. Version to appear in PR
Large deformation of spherical vesicle studied by perturbation theory and Surface evolver
With tangent angle perturbation approach the axial symmetry deformation of a
spherical vesicle in large under the pressure changes is studied by the
elasticity theory of Helfrich spontaneous curvature model.Three main results in
axial symmetry shape: biconcave shape, peanut shape, and one type of myelin are
obtained. These axial symmetry morphology deformations are in agreement with
those observed in lipsome experiments by dark-field light microscopy [Hotani,
J. Mol. Biol. 178, (1984) 113] and in the red blood cell with two thin
filaments (myelin) observed in living state (see, Bessis, Living Blood Cells
and Their Ultrastructure, Springer-Verlag, 1973). Furthermore, the biconcave
shape and peanut shape can be simulated with the help of a powerful software,
Surface Evolver [Brakke, Exp. Math. 1, 141 (1992) 141], in which the
spontaneous curvature can be easy taken into account.Comment: 16 pages, 6 EPS figures and 2 PS figure
Concise theory of chiral lipid membranes
A theory of chiral lipid membranes is proposed on the basis of a concise free
energy density which includes the contributions of the bending and the surface
tension of membranes, as well as the chirality and orientational variation of
tilting molecules. This theory is consistent with the previous experiments
[J.M. Schnur \textit{et al.}, Science \textbf{264}, 945 (1994); M.S. Spector
\textit{et al.}, Langmuir \textbf{14}, 3493 (1998); Y. Zhao, \textit{et al.},
Proc. Natl. Acad. Sci. USA \textbf{102}, 7438 (2005)] on self-assembled chiral
lipid membranes of DCPC. A torus with the ratio between its two
generated radii larger than is predicted from the Euler-Lagrange
equations. It is found that tubules with helically modulated tilting state are
not admitted by the Euler-Lagrange equations, and that they are less
energetically favorable than helical ripples in tubules. The pitch angles of
helical ripples are theoretically estimated to be about 0 and
35, which are close to the most frequent values 5 and
28 observed in the experiment [N. Mahajan \textit{et al.}, Langmuir
\textbf{22}, 1973 (2006)]. Additionally, the present theory can explain twisted
ribbons of achiral cationic amphiphiles interacting with chiral tartrate
counterions. The ratio between the width and pitch of twisted ribbons is
predicted to be proportional to the relative concentration difference of left-
and right-handed enantiomers in the low relative concentration difference
region, which is in good agreement with the experiment [R. Oda \textit{et al.},
Nature (London) \textbf{399}, 566 (1999)].Comment: 14 pages, 7 figure
Security improvement of using modified coherent state for quantum cryptography
Weak coherent states as a photon source for quantum cryptography have limit
in secure data rate and transmission distance because of the presence of
multi-photon events and loss in transmission line. Two-photon events in a
coherent state can be taken out by a two-photon interference scheme. We
investigate the security issue of utilizing this modified coherent state in
quantum cryptography. A 4 dB improvement in secure data rate or a nearly
two-fold increase in transmission distance over the coherent state are found.
With a recently proposed and improved encoding strategy, further improvement is
possible.Comment: 5 pages, 2 figures, to appear in Physical Review
Specific heats of dilute neon inside long single-walled carbon nanotube and related problems
An elegant formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and the potential of neon (Ne)
inside an infinitely long SWNT is analytically derived out under the condition
of the Lennard-Jones potential between Ne and carbon atoms.
Specific heats of dilute Ne inside long (20, 20) SWNT are calculated at
different temperatures. It is found that Ne exhibits 3-dimensional (3D) gas
behavior at high temperature but behaves as 2D gas at low temperature.
Especially, at ultra low temperature, Ne inside (20, 20) nanotubes behaves as
lattice gas. A coarse method to determine the characteristic temperature
for low density gas in a potential is put forward. If
, we just need to use the classical statistical
mechanics without solving the Shr\"{o}dinger equation to consider the thermal
behavior of gas in the potential. But if , we
must solve the Shr\"{o}dinger equation. For Ne in (20,20) nanotube, we obtain
K.Comment: 14 pages, 7 figure
Quantum Communication with Correlated Nonclassical States
Nonclassical correlations between the quadrature-phase amplitudes of two
spatially separated optical beams are exploited to realize a two-channel
quantum communication experiment with a high degree of immunity to
interception. For this scheme, either channel alone can have an arbitrarily
small signal-to-noise ratio (SNR) for transmission of a coherent ``message''.
However, when the transmitted beams are combined properly upon authorized
detection, the encoded message can in principle be recovered with the original
SNR of the source. An experimental demonstration has achieved a 3.2 dB
improvement in SNR over that possible with correlated classical sources.
Extensions of the protocol to improve its security against eavesdropping are
discussed.Comment: 8 pages and 4 figures (Figure 1; Figures 2a, 2b; Figure 2
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