655 research outputs found
Two-Color Bright Squeezed Vacuum
In a strongly pumped non-degenerate traveling-wave OPA, we produce two-color
squeezed vacuum with up to millions of photons per pulse. Our approach to
registering this macroscopic quantum state is direct detection of a large
number of transverse and longitudinal modes, which is achieved by making the
detection time and area much larger than the coherence time and area,
respectively. Using this approach, we obtain a record value of twin-beam
squeezing for direct detection of bright squeezed vacuum. This makes direct
detection of macroscopic squeezed vacuum a practical tool for quantum
information applications.Comment: 4 pages, 4 figure
Polarization-Entangled Light Pulses of 10^5 Photons
We experimentally demonstrate polarization entanglement for squeezed vacuum
pulses containing more than 10^5 photons. We also study photon-number
entanglement by calculating the Schmidt number and measuring its operational
counterpart. Theoretically, our pulses are the more entangled the brighter they
are. This promises important applications in quantum technologies, especially
photonic quantum gates and quantum memories.Comment: 8 pages, 6 figure
High-visibility multi-photon interference of Hanbury Brown - Twiss type for classical light
Difference-phase (or Hanbury Brown - Twiss type) intensity interference of
classical light is considered in higher orders in the intensity. It is shown
that, while the visibility of sum-phase (NOON-type) interference for classical
sources drops with the order of interference, the visibility of
difference-phase interference has opposite behavior. For three-photon and
four-photon interference of two coherent sources, the visibility can be as high
as 81.8% and 94.4%, respectively. High-visibility three-photon and four-photon
interference of space-time and polarization types has been observed in
experiment, for both coherent and pseudo-thermal light.Comment: 11 pages, 9 figure
Reconstructing Images from Projections Using the Maximum-Entropy Method. Numerical Simulations of Low-Aspect Astrotomography
The reconstruction of images from a small number of projections using the
maximum-entropy method (MEM) with the Shannon entropy is considered. MEM
provides higher-quality image reconstruction for sources with extended
components than the Hogbom CLEAN method, which is also used in low-aspect
astrotomography. The quality of image reconstruction for sources with mixed
structure containing bright, compact features embedded in a comparatively weak,
extended base can be further improved using a difference-mapping method, which
requires a generalization of MEM for the reconstruction of sign-variable
functions.We draw conclusions based on the results of numerical simulations for
a number of model radio sources with various morphologies.Comment: 11 pages, 9 figure
Possibility of local pair existence in optimally doped SmFeAsO(1-x) in pseudogap regime
We report the analysis of pseudogap Delta* derived from resistivity
experiments in FeAs-based superconductor SmFeAsO(0.85), having a critical
temperature T_c = 55 K. Rather specific dependence Delta*(T) with two
representative temperatures followed by a minimum at about 120 K was observed.
Below T_s = 147 K, corresponding to the structural transition in SmFeAsO,
Delta*(T) decreases linearly down to the temperature T_AFM = 133 K. This last
peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of
Fe spins. It is believed that the found behavior can be explained in terms of
Machida, Nokura, and Matsubara (MNM) theory developed for the AFM
superconductors.Comment: 5 pages, 2 figure
Development of the activity of gifted schoolchildren in mastering geometric con-cepts in figurative structures
Background: The relevance of developing mental activity for mastering geometric concepts relates to the change in paradigmatic foundations taking place in modern education. Such a change is associated with the recognition of a schoolchild as a subject of educational and cognitive activity, the initiator of own activity. Objective: The authors attempted to describe a model of a didactic system for developing active usage of geometric concepts in the process of teaching geometry to mathematically gifted schoolchildren in 10-11 grades. The authors also used the GeoGebra dynamic system as a component of the electronic educational environment (EEE). The objective is achieved by characterizing the architecture of the system model, which evokes active usage of geometric concepts within schoolchildren in learning situations; substantiating psychodidactic conditions for the effective development of this activity using the GeoGebra dynamic system; and defining levels, criteria, and indicators of development. Methods: A specially organized educational activity in EEE and a developed system of tasks within the framework of the elective course “Problems of solid geometry and computer graphics” for 10-11 graders represent a didactic means of developing the activities related to figurative-spatial methods of information coding. Findings: The authors described a didactic system model for mastering geometric concepts in figurative structures in the process of teaching geometry to 10-11 graders using the GeoGebra dynamic system. Conclusions: Fostering schoolchildren’ mastering geometric concepts in figurative structures occurs under the direct influence of teaching. However, this process is complex and internally contradictory. The structure of this kind of activity contains actions of different nature
- …