Localization of one-photon state in space and Einstein-Podolsky-Rosen paradox in spontaneous parametric down conversion

An experiment on one-photon state localization in space using a correlation technique in Spontaneous Parametric Down Conversion (SPDC) process is discussed. Results of measurements demonstrate an idea of the Einstein-Podolsky-Rosen (EPR) paradox for coordinate and momentum variables of photon states. Results of the experiment can be explained with the help of an advanced wave technique. The experiment is based on the idea that two-photon states of optical electromagnetic fields arising in the nonlinear process of the spontaneous parametric down conversion (spontaneous parametric light scattering) can be explained by quantum mechanical theory with the help of a single wave function

Dispersion and fidelity in quantum interferometry

We consider Mach-Zehnder and Hong-Ou-Mandel interferometers with nonclassical states of light as input, and study the effect that dispersion inside the interferometer has on the sensitivity of phase measurements. We study in detail a number of different one- and two-photon input states, including Fock, dual Fock, N00N states, and photon pairs from parametric downconversion. Assuming there is a phase shift $\phi_0$ in one arm of the interferometer, we compute the probabilities of measurement outcomes as a function of $\phi_0$, and then compute the Shannon mutual information between $\phi_0$ and the measurements. This provides a means of quantitatively comparing the utility of various input states for determining the phase in the presence of dispersion. In addition, we consider a simplified model of parametric downconversion for which probabilities can be explicitly computed analytically, and which serves as a limiting case of the more realistic downconversion model.Comment: 12 pages, 14 figures. Submitted to Physical Review

Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites

With the perovskite multiferroic RMnO3 (R = Gd, Tb, Dy) as guidance, we argue that the Dzyaloshinskii-Moriya interaction (DMI) provides the microscopic mechanism for the coexistence and strong coupling between ferroelectricity and incommensurate magnetism. We use Monte-Carlo simulations and zero temperature exact calculations to study a model incorporating the double-exchange, superexchange, Jahn-Teller and DMI terms. The phase diagram contains a multiferroic phase between A and E antiferromagnetic phases, in excellent agreement with experiments.Comment: 6 pages, 5 figure

Similarity of organized patterns in driving and basal stresses of Antarctic and Greenland ice sheets beneath extensive areas of basal sliding

The rate of ice transport from the interior of ice sheets to their margins, and hence the rate with which it contributes to sea level, is determined by the balance of driving stress, basal resistance, and ice internal deformation. Using recent high-resolution observations of the Antarctic and Greenland ice sheets, we compute driving stress and ice deformation velocities, inferring basal traction by inverse techniques. The results reveal broad-scale organization in 5–20 km band-like patterns in both the driving and basal shear stresses located in zones with substantial basal sliding. Both ice sheets experience basal sliding over areas substantially larger than previously recognized. The likely cause of the spatial patterns is the development of a band-like structure in the basal shear stress distribution that is the results of pattern-forming instabilities related to subglacial water. The similarity of patterns on the Greenland and Antarctic ice sheets suggests that the flow of ice sheets is controlled by the same fundamental processes operating at their base, which control ice sheet sliding and are highly variable on relatively short spatial and temporal scales, with poor predictability. This has far-reaching implications for understanding of the current and projection of the future ice sheets' evolution

Полярные сияния в каспе и его приполюсной окрестности: исследование отдельного события

Summary We present a case study of the dayside aurora observed simultaneously with optical instruments from the ground and with auroral particle spectrometers aboard the DMSP F16 and F17 satellites. Optical observations were carried out with an all-sky camera at the Polar Geophysical Institute (PGI) observatory Barentsburg on Svalbard. The aurora as a whole moved equatorward in response to negative turning of the IMF Bz component and then the distinct faint rayed arc intensified, moved to the north and faded. Satellite DMSP F17 crossed the cusp twenty minutes after Bz turned southward. Joint analysis of optical and satellite data showed that faint auroral structures are embedded into the cusp precipitations and correspond to the bursts of electron precipitations with energy below 100 eV. The next satellite crossed the camera field-of-view ten minutes later and the data showed that the source of the faded poleward moving rayed arc was located, most probably, on the non-closed magnetic field lines. This finding and the presence of ion-energy dispersion in the DMSP data allows us to make the conclusion that the dayside reconnection may be considered as the reason for this kind of aurora activity. In this study we also estimated the altitude and horizontal scale of auroral rays in the cusp.Исследован редкий случай одновременной регистрации дневных полярных сияний наземной оптической аппаратурой и детектором высыпающихся частиц на спутниках DMSP F16 и F17. Оптические измерения проводились камерой полного обзора неба Полярного геофизического института, установленной в обсерватории Баренцбург на арх. Шпицберген. Следуя развороту вертикальной компоненты межпланетного магнитного поля (Bz-компоненты ММП) в область отрицательных значений, система слабых лучистых дуг сместилась к югу, после чего одна из дуг начала дрейфовать обратно к полюсу и пропала. Спутник DMSP F17 пересек касп спустя двадцать минут после разворота Bz-компоненты. Совместный анализ оптических и спутниковых данных показал, что наблюдаемые слабые лучистые структуры находятся в области каспенных высыпаний и пространственно связаны с всплеском высыпающихся электронов с энергией менее 100 эВ. Следующий спутник DMSP пересек поле  зрения камеры спустя десять минут после первого,  и анализ его данных показал, что эта дуга в момент исчезновения находилась в области разомкнутых силовых линий. Этот результат, дополненный специфической формой протонных высыпаний в данных спутника DMSP, которую традиционно связывают с пересоединением, позволил нам прийти к выводу, что смещавшаяся к полюсу слабая лучистая дуга могла представлять собой ионосферный след только что пересоединившейся магнитной силовой трубки, уносимой солнечным ветром в антисолнечном направлении. Оценена высота и поперечный размер элемента лучистой структуры в каспе

Superconducting joining of melt-textured Y-Ba-Cu-O bulk material

The Tm-Ba-Cu-O solder can be successfully used to produce a superconductive joint between MT-YBCO parts. The peculiarities of solidification, phase formation, structure transformations and electromagnetic properties of MT-YBCO soldered with TmBa2Cu3O7-d are discussed.Comment: PS of 6 pages text and 5 figures, presented at ICMC'2000, Brasi

Two-Photon Entanglement and EPR Experiments Using Type-2 Spontaneous Parametric Down Conversion

Simultaneous entanglement in spin and space-time of a two-photon quantum state generated in type-2 spontaneous parametric down-conversion is demonstrated by the observation of quantum interference with 98% visibility in a simple beam-splitter (Hanburry Brown-Twiss) anticorrelation experiment. The nonlocal cancellation of two-photon probability amplitudes as a result of this double entanglement allows us to demonstrate two different types of Bell's inequality violations in one experimental setup