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Issue 4, 2024
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Extracts from the Internet


Neutrino oscillations in T2K experiment

The first events of transformation (oscillations) of muon neutrinos into electron neutrinos in the T2K experiment (Japan) were recorded in 2011 by comparing the composition of a beam of muon neutrinos close to its emergence point from the Tokai accelerator and at a distance of 295 km in the Super-Kamiokande detector. By this moment, already 28 events have been observed, with the recording confidence of the oscillations having reached 7.5 σ. It is important that the T2K is the emergence-type experiment for beam neutrinos. As a rule, experiments identifying the emergence of particles are more unequivocal than those in which a lack of particles is declared. The νμ → νe oscillations are closely related to the violation of the CP-invariance in weak interactions and it is expected that as statistical data keep accumulating, it will be possible to study the CP-violation in the lepton sector with respect to neutrino oscillations. Several events of a different type of oscillations (νμ → ντ) have been observed recently in the OPERA experiment (Italy). Some Russian researchers take active part in both the T2K and OPERA experiments. Source: http://t2k-experiment.org

The photon analogue of the Schrodinger cat

A.I. Lvovsky (Calgary University, Calgary, Canada and Russian Quantum center at Skolkovo) and his colleagues succeeded in generating an experimental entangled state of a single photon and a microscopic ensemble of more than 108 photons that way, this created them a photon analogue of the “Schrodinger cat”. The quantum entanglement between the micro- and macro-objects has already been implemented in a number of systems, such as atomic ensembles; however, it has been generated for the first time in the case of photon systems. The experiment started with a pair of photons in entangled states generated by creating parametric down-conversion. One of the photons of the pair was then subjected to a multiple amplification by shifting in the phase space. The measurements were carried out using quantum tomography, while the inverse shifting made it possible to check that quantum coherence has not been violated. Owing to the quantum entanglement, the state of a single photon affected the state of the entire large system which could be created in a superposition of states which would differ by tens of thousands in the number of photons. Source: Nature Physics 9 541 (2013)

Controlled skyrmions

Skyrmions are stable spin structures that carry a topological charge; they were theoretically suggested in 1962 in T. Skyrma's field model and by now have been observed already in several distinct systems. Researchers at the applied physics institute of the Hamburg university in Germany succeeded for the first time to selectively create or eliminate individual skyrmions by using local application of spin-polarized current created by scanning tunneling microscope, on ultrathin magnetic films composed of a PdFe bilayer on the surface of an Iridium crystal. Metastable topological configurations with energies close to the energy barrier were observed in the vicinity of the magnetic field 1-1.4 T of the metastable topological configurations, close in energy but separated by an energy barrier. The potential of the tunnel microscope (on the order of 0.1-1 V) caused reversible transitions across the barrier between energy levels and, correspondingly, the formation or disappearance of skyrmions. The reversibility of transitions signifies that in this mode skyrmions are readily controlled in order to record and store information in this manner, several skyrmions have been created successively and independently at a local spot of the film, after which they appear to have been deleted. Skyrmions were recorded on the basis of characteristic features of changes in the current through the tunnel. Each skyrmion, in whose region the magnetic moment completed 1 full rotation, covered roughly 270 surface atoms of the field in area. The experiment was carried out at low temperature (≤8 K) when, as a result of the probability of transition between topological states due to thermal fluctuations was low. The promise in the practical application of skyrmions is based, among other things, on their magnetic state being more stable than with ordinary magnetic domains. Source: Science 341 636 (2013)

Rotational Doppler effect

Researchers at the Glasgow and Strathclyde universities (Great Britain) succeeded in experimentally measuring for the first time a method of measuring the rate of angular rotation of bodies on the basis of their interaction with the light beam whose photons possess orbital angular momentum. If the angular size of the rotating body is small, then the ordinary Doppler effect required to measure the velocities of parts of the body is small, so that the Doppler effect for the measurement of body parts becomes inapplicable; however, twistedlight is quite suitable for this purpose. What is created in the beam reflected from the rotating body is a shift in frequency, proportional to the product of the body rotation frequency and orbital angular momentum of the photons. In the experiment set up by M.P.J. Lavery et al, a rotating piece of aluminum foil was irradiated by a semiconducting laser with angular momenta ± 18h/2π with equal in magnitude but oppositely directed angular momenta created by programmed space modulators. The rotation axis was parallel to the line of sight but reflection was in fact occurring at slightly different small angles because of some unevenness of the surface. As could be expected, the reflected light in the two beams gained frequency shifts of opposite signs: red and blue shifts. The experiment recorded beats created in the interference of these beams, so the rate of rotation of the disc could be calculated from the characteristic of beating. The results obtained at different rotation speeds were found to be in agreement with the theoretical calculations of this particular effect. Source: Science 341 537 (2013)

B-mode of polarization of microwave background radiation

For the first time the B-mode of polarization of the microwave background (relict) radiation, connected to the vortex component of the polarization tensor has been detected using the 10-m radio-telescope South Pole Telescope located in the Antarctica at the southern pole. The relict polarization component can be generated by its scattering on nonuniformities of matrix plasma (gravity waves) at the recombination epoch, or also be produced as a result of gravitational lensing of radiation at cosmological density fluctuations. The vortex-less mode has already been observed by the interferometer telescope DASI in 2002. These new data obtained during the first season of working with polarization-sensitive bolometric receivers of the South Pole Telescope were recorded reliably for the first time as the b-mode. The calculation of 4-point correlation functions for l ≥ 150 multiples showed that the measured b-mode correlates at the 7.7 σ with the matter distribution map obtained in the Hershel IK scan, as well as with e-mode measurements. As we know from other observations, IK scans give reliable representation of the gravitational potential, which is in fact responsible for gravitational lensing and for the transformation of the e-mode to the b-mode of polarization occurring in the process. Very reliable information has been obtained at the early stages of evolution of the universe, including the inflation stage in the future, when caused by relict gravitational waves. The obtained South Pole Telescope data are a background for which a search of polarization signals due to gravitational waves could be carried out. Source: arXiv:1307.5830 [astro-ph.CO]

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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

It is compiled from a multitude of Internet sources.
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