7,125 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
Mode-Locked Two-Photon States
The concept of mode locking in laser is applied to a two-photon state with
frequency entanglement. Cavity enhanced parametric down-conversion is found to
produce exactly such a state. The mode-locked two-photon state exhibits a
comb-like correlation function. An unbalanced Hong-Ou-Mandel type
interferometer is used to measure the correlation function. A revival of the
typical interference dip is observed. We will discuss schemes for engineering
of quantum states in time domain.Comment: 4 pages, 5 figure
Photon bunching in parametric down-conversion with continuous wave excitation
The first direct measurement of photon bunching (g2 correlation function) in
one output arm of a spontaneous-parametric-down-conversion source operated with
a continuous pump laser in the single-photon regime is demonstrated. The result
is in agreement with the statistics of a thermal field of the same coherence
length, and shows the feasibility of investigating photon statistics with
compact cw-pumped sources. Implications for entanglement-based quantum
cryptography are discussed.Comment: 7 pages, 4 figures, expanded introduction and experimental details
added. Accepted for publication in Phys.Rev.
PCA and K-Means decipher genome
In this paper, we aim to give a tutorial for undergraduate students studying
statistical methods and/or bioinformatics. The students will learn how data
visualization can help in genomic sequence analysis. Students start with a
fragment of genetic text of a bacterial genome and analyze its structure. By
means of principal component analysis they ``discover'' that the information in
the genome is encoded by non-overlapping triplets. Next, they learn how to find
gene positions. This exercise on PCA and K-Means clustering enables active
study of the basic bioinformatics notions. Appendix 1 contains program listings
that go along with this exercise. Appendix 2 includes 2D PCA plots of triplet
usage in moving frame for a series of bacterial genomes from GC-poor to GC-rich
ones. Animated 3D PCA plots are attached as separate gif files. Topology
(cluster structure) and geometry (mutual positions of clusters) of these plots
depends clearly on GC-content.Comment: 18 pages, with program listings for MatLab, PCA analysis of genomes
and additional animated 3D PCA plot
Retrieval of phase memory in two independent atomic ensembles by Raman process
In spontaneous Raman process in atomic cell at high gain, both the Stokes
field and the accompanying collective atomic excitation (atomic spin wave) are
coherent. We find that, due to the spontaneous nature of the process, the
phases of the Stokes field and the atomic spin wave change randomly from one
realization to another but are anti-correlated. The phases of the atomic
ensembles are read out via another Raman process at a later time, thus
realizing phase memory in atoms. The observation of phase correlation between
the Stokes field and the collective atomic excitations is an important step
towards macroscopic EPR-type entanglement of continuous variables between light
and atoms
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
Resistive damping implementation as a method to improve controllability in stiff ohmic RF-MEMS switches
This paper presents in detail the entire procedure of calculating the bias resistance of an ohmic RF-MEMS switch, controlled under resistive damping (charge drive technique). In case of a very stiff device, like the North Eastern University switch, the actuation control under resistive damping is the only way to achieve controllability. Due to the short switching time as well as the high actuation voltage, it is not practical to apply a tailored control pulse (voltage drive control technique). Implementing a bias resistor of 33 MΩ in series with the voltage source, the impact velocity of the cantilever has been reduced 80 % (13.2 from 65.9 cm/s), eliminating bouncing and high initial impact force during the pull-down phase. However, this results in an affordable cost of switching time increase from 2.38 to 4.34 Όs. During the release phase the amplitude of bouncing has also been reduced 34 % (174 from 255 nm), providing significant improvement in both switching operation phases of the switch. © 2013 Springer-Verlag Berlin Heidelberg
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
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