36 research outputs found
Entanglement in a Time-Dependent Coupled XY Spin Chain in an External Magnetic Field
We consider an infinite one dimensional anisotropic XY spin chain with a
nearest neighbor time-dependent Heisenberg coupling J(t) between the spins in
presence of a time-dependent magnetic field h(t). We discuss a general solution
for the system and present an exact solution for particular choice of J and h
of practical interest. We investigate the dynamics of entanglement for
different degrees of anisotropy of the system and at both zero and finite
temperatures. We find that the time evolution of entanglement in the system
show non-ergodic and critical behavior at zero and finite temperatures and
different degrees of anisotropy. The asymptotic behavior of entanglement at the
infinite time limit at zero temperature and constant J and h depends only the
parameter lambda=J/h rather than the individual values of J and h for all
degrees of anisotropy but changes for nonzero temperature. Furthermore, the
asymptotic behavior is very sensitive to the initial values of J and h and for
particular choices we may create finite asymptotic entanglement regardless of
the final values of J and h. The persistence of quantum effects in the system
as it evolves and as the temperature is raised is studied by monitoring the
entanglement. We find that the quantum effects dominates within certain regions
of the kT-lambda space that vary significantly depending on the degree of the
anisotropy of the system. Particularly, the quantum effects in the Ising model
case persists in the vicinity of both its critical phase transition point and
zero temperature as it evolves in time. Moreover, the interplay between the
different system parameters to tune and control the entanglement evolution is
explored.Comment: 33 pages, 17 figures; v3: Grammar errors and typos corrected, Figure
17(b) update
Nuclear-induced time evolution of entanglement of two-electron spins in anisotropically coupled quantum dot
We study the time evolution of entanglement of two spins in anisotropically
coupled quantum dot interacting with the unpolarized nuclear spins environment.
We assume that the exchange coupling strength in the z-direction is
different from the lateral one . We observe that the entanglement decays
as a result of the coupling to the nuclear environment and reaches a saturation
value, which depends on the value of the exchange interaction difference between the two spins and the strength of the applied external
magnetic field. We find that the entanglement exhibits a critical behavior
controlled by the competition between the exchange interaction and the
external magnetic field. The entanglement shows a quasi-symmetric behavior
above and below a critical value of the exchange interaction. It becomes more
symmetric as the external magnetic field increases. The entanglement reaches a
large saturation value, close to unity, when the exchange interaction is far
above or below its critical value and a small one as it closely approaches the
critical value. Furthermore, we find that the decay rate profile of
entanglement is linear when the exchange interaction is much higher or lower
than the critical value but converts to a power law and finally to a Gaussian
as the critical value is approached from both directions. The dynamics of
entanglement is found to be independent of the exchange interaction for
isotropically coupled quantum dot.Comment: 24 pages and 7 figures. v3: major change
Radiation pattern of two identical emitters driven by a Laguerre-Gaussian beam: An atom nanoantenna
We study the directional properties of a radiation field emitted by a
geometrically small system composed of two identical two-level emitters located
at short distances and driven by an optical vortex beam, a Laguerre-Gaussian
beam which possesses a structured phase and amplitude. We find that the system
may operate as a nanoantenna for controlled and tunable directional emission.
Polar diagrams of the radiation intensity are presented showing that a constant
phase or amplitude difference at the positions of the emitters plays an
essential role in the directivity of the emission. We find that the radiation
patterns may differ dramatically for different phase and amplitude differences
at the positions of the emitters. As a result the system may operate as a two-
or one-sided nanoantenna. In particular, a two-sided highly focused directional
emission can be achieved when the emitters experience the same amplitude and a
constant phase difference of the driving field. We find a general directional
property of the emitted field that when the phase differences at the positions
of the emitters equal an even multiple of \pi/4, the system behaves as a
two-sided antenna. When the phase difference equals an odd multiple of \pi/4,
the system behaves as an one-sided antenna. The case when the emitters
experience the same phase but different amplitudes of the driving field is also
considered and it is found that the effect of different amplitudes is to cause
the system to behave as a uni-directional antenna radiating along the
interatomic axis.Comment: published versio
Solitary wave solutions of the Vakhnenko–Parkes equation
In this paper, two solitary wave solutions are obtained for the Vakhnenko–Parkes equation with power law nonlinearity by the ansatz method. Both topological as well as non-topological solitary wave solutions are obtained. The parameter regimes, for the existence of solitary waves, are identified during the derivation of the solution
Sleep disorders and its effect on community
The main aim of this paper is to analysis the effect of sleep disorders on the community. This study is quantitative. The questionnaire was designed and distributed among the student in school in the city of Riyadh high and intermediate school. The sample of this study consist 100 students. The researcher visited a school in the city of Riyadh high and intermediate school sections and that on December 10 to 11 to measure the impact of sleep disorders through a questionnaire that measures the effects of lack of sleep and then make them aware of the benefits of sleep and harm of lack of sleep from the physical and psychological effects, and it gave a lecture educate the students and then distribute them brochure contain the benefits and harmful effects of sleep. SPSS 21 was used to analysis that data. The results of the study indicated that lack of sleep limits a person's ability to think and solve the problem effectively, which means that people who wake up for a long time influence them to learn at an effective level. Lack of sleep affects the ability of thinking and can limit your ability to accurately interpret events, which can be difficult to respond correctly to situations in which effective decision-making is intelligent. The lack of sleep, even for one night can lead to swelling of the eyes and turn the skin into pale skin. Keywords: Sleep disorders, community
Optimization of antireflection coating design using pc1d simulation for c − si solar cell application
Minimizing the photon losses by depositing an anti-reflection layer can increase the conversion efficiency of the solar cells. In this paper, the impact of anti-reflection coating (ARC) for enhancing the efficiency of silicon solar cells is presented. Initially, the refractive indices and reflectance of various ARC materials were computed numerically using the OPAL2 calculator. After which, the reflectance of SiO2, TiO2, SiNx with different refractive indices (n) were used for analyzing the performance of a silicon solar cells coated with these materials using PC1D simulator. SiNx and TiO2 as single-layer anti-reflection coating (SLARC) yielded a short circuit current density (Jsc ) of 38.4 mA/cm2 and 38.09 mA/cm2 respectively. Highest efficiency of 20.7% was obtained for the SiNx ARC layer with n = 2.15. With Double-layer anti-reflection coating (DLARC), the Jsc improved by ∼0.5 mA/cm2 for SiO2 /SiNx layer and hence the efficiency by 0.3%. Blue loss reduces significantly for the DLARC compared with SLARC and hence increase in Jsc by 1 mA/cm2 is observed. The Jsc values obtained is in good agreement with the reflectance values of the ARC layers. The solar cell with DLARC obtained from the study showed that improved conversion efficiency of 21.1% is obtained. Finally, it is essential to understand that the key parameters identified in this simulation study concerning the DLARC fabrication will make experimental validation faster and cheaper