4,829 research outputs found
Theoretical Simulation of 87Rb Absorption Spectrum in a Thermal Cell
In this paper, we present a theoretical simulation of 87Rb absorption
spectrum in a thermal cm-cell which is adaptive to the experimental
observation. In experiment, the coupling and probe beams are configured to
copropagate but perpendicular polarized, making up to five velocity selective
optical pumping (VSOP) absorption dips able to be identified. A -type
electromagnetically induced transparency (EIT) is also observed for each group
of velocity-selected atoms. The spectrum by only sweeping the probe beam can be
decomposed into a combination of Doppler-broadened background and three VSOP
dips for each group of velocity-selected atoms, companied by an EIT peak. This
proposed theoretical model can be used to simulate the spectrum adaptive to the
experimental observation by non-linear least-square fit method. The fit for
high quality of experimental observation can determine valuable transition
parameters such as decaying rates and coupling beam power accurately
A Bidirectional Adaptive Bandwidth Mean Shift Strategy for Clustering
The bandwidth of a kernel function is a crucial parameter in the mean shift
algorithm. This paper proposes a novel adaptive bandwidth strategy which
contains three main contributions. (1) The differences among different adaptive
bandwidth are analyzed. (2) A new mean shift vector based on bidirectional
adaptive bandwidth is defined, which combines the advantages of different
adaptive bandwidth strategies. (3) A bidirectional adaptive bandwidth mean
shift (BAMS) strategy is proposed to improve the ability to escape from the
local maximum density. Compared with contemporary adaptive bandwidth mean shift
strategies, experiments demonstrate the effectiveness of the proposed strategy.Comment: Accepted by ICIP 201
High Quality of Electromagnetically Induced Transparency Spectroscopy of 87Rb in a Buffer Gas Cell with Magnetic Field
We have studied the phenomenon of electromagnetically induced transparency
(EIT) of 87Rb vapor with a buffer gas in a magnetic field at room temperature.
It is found that the spectral lines caused by the velocity selective optical
pump effects get much weaker and wider when the sample cell mixed with a 5-Torr
N2 gas while the EIT signal kept almost unchanged. A weighted least-square fit
is also developed to remove the Doppler broadening completely. This spectral
method provides a way to measure the Zeeman splitting with high resolution, for
example, the {\Lambda}-type EIT resonance splits into four peaks on the D2 line
of 87Rb in the thermal 2-cm vapor cell with a magnetic field along the electric
field of the linearly polarized coupling laser. The high resolution spectrum
can be used to lock the laser to a given frequency by tuning the magnetic
field.Comment: 6 figure
Super sub-wavelength patterns in photon coincidence detection
High-precision measurements implemented by means of light is desired in all
fields of science. However, light is a wave and Rayleigh criterion gives us a
diffraction limitation in classical optics which restricts to get arbitrary
high resolution. Sub-wavelength interference has a potential application in
lithography to beat the classical Rayleigh limit of resolution. We carefully
study the second-order correlation theory to get the physics behind
sub-wavelength interference in photon coincidence detection. A Young's
double-slit experiment with pseudo-thermal light is carried out to test the
second-order correlation pattern. The result shows that when different scanning
ways of two point detectors are chosen, one can get super sub-wavelength
interference patterns. We then give a theoretical explanation to this
surprising result, and find this explanation is also suitable for the result by
using entangled light. Furthermore, we discuss the limitation of this kind of
super sub-wavelength interference patterns in quantum lithography.Comment: 5 pages, 5 figures, comments are welcom
Modeling Stock Market Based on Genetic Cellular Automata
An artificial stock market is established with the modeling method and ideas
of cellular automata. Cells are used to represent stockholders, who have the
capability of self-teaching and are affected by the investing history of the
neighboring ones. The neighborhood relationship among the stockholders is the
expanded Von Neumann relationship, and the interaction among them is realized
through selection operator and crossover operator. Experiment shows that the
large events are frequent in the fluctuations of the stock price generated by
the artificial stock market when compared with a normal process and the price
returns distribution is a Levy distribution in the central part followed by an
approximately exponential truncation.Comment: 5 pages, 4 figures, to be published in <Int. J. Mod. Phys. B
Control excitation and coherent transfer in a dimer
In this article, the processes of energy absorption and coherent transfer in
a dimer is studied. The dimer includes two two-level pigments --- donor and
acceptor, where donor is assumed being excited by a control pulse in the time
domain. We investigate the dynamics of probability that the acceptor is in the
excited state and the total efficiency of energy absorption and transfer under
different temporal shape of control pulse. Quantum concurrence of the dimer is
also discussed
Probing the topological charge of a vortex beam with dynamic angular double slits
When a vortex beam with the spiral phase structure passes through a dynamic
angular double slits (ADS), the interference pattern changes alternatively
between destructive and constructive at the angular bisector direction of the
ADS due to their phase difference. Based on this property, we experimentally
demonstrate a simple method, which can precisely and efficiently determine the
topological charge of vortex beams. What is more, this scheme allows
determining both the modulus and sign of the topological charge of vortex beams
simultaneously.Comment: 4 pages, 4 figure
Demonstration of quantum permutation algorithm with a single photon ququart
We report an experiment to demonstrate a quantum permutation determining
algorithm with linear optical system. By employing photon polarization and
spatial modes, we realize the quantum ququart states and all the essential
permutation transformations. Compared with the classical case, this work
determines the parity of the permutation in only one step of evaluation and
displays the remarkable speedup of quantum algorithm. This experiment is
accomplished in single photon level and exhibits strong universality in quantum
computation.Comment: Comments are welcom
Characterizing vortex beam with angular-double-slit interference
The Fraunhofer diffraction intensity distribution of Laguerre-Gaussian beam
is studied in an angular-double-slit interferometer. We demonstrate that the
spiral phase structure of vortex light can be clearly revealed in this
interference geometry, and it gives us an efficient way to distinguish
different order of Laguerre-Gaussian beams. This angular-double-slit
interference gives us a better understanding to the nature of orbital angular
momentum and the interpretation of vortex beams interference phenomenon.Comment: 4 pages, 5 figure
Evaluating Laguerre-Gaussian beams with an invariant parameter
We define a new parameter about Laguerre-Gaussian (LG) beams, named
, which is only related to mode indices and . This parameter
is able to both evaluate and distinguish LG beams. The values are
first calculated theoretically and then measured experimentally for several
different LG beams. Another mode quality parameter, value, is also
measured. The comparison between and shows same trend for
the quality of LG mode, while the measurement of is much easier
than .Comment: 3.1 pages, 4 figures, 1 tabl
- …