Extracts from the Internet

Reactor antineutrino oscillations

New more precisely measured data of RENO experiment on oscillations of electron antineutrinos anti-νe born in atomic reactors are presented. Anti-νe from six reactors were registered during 2200 days using identical near and far detectors and the anti-νe flux variation on the way between them was examined. In the detectors, anti-νe induced inverse beta decay anti-νe+p → e+n on nuclei of hydrocarbon scintillator containing gadolinium Gd impurity. Registered were gamma-ray photons from positron annihilation and from neutron absorption by Gd nuclei by the time-lagged coincidence circuit. The obtained data show a clear periodic dependence on the ratio L/Eν of the anti-νe path L to its energy Eν as it should be under oscillations. Close to Eν ≈ 5 MeV, both detectors show some difference between the registered anti-νe energy spectrum and the calculated one. To explain this discrepancy one should specify the models of neutrino generation in reactors. The values obtained for the neutrino oscillation parameters are as follows: sin2(2θ13)=0,0896 ± 0.0048(stat) ± 0.0047(syst) and |Δ m232|=(2.63 ± 0.14) × 10-3 eV2 (in the case of normal mass hierarchy). Source: Phys. Rev. Lett. 121 201801 (2018)

Optomechanical Bell test

The states of vibrational modes of macroscopic mechanical oscillators quantum-entangled among themselves and with photons have been experimentally obtained over the past few years. S. Groblacher (Delft University of Technology, Netherlands) with colleagues checked for the first time the violation of Bell inequalities for mechanical oscillators consisting of 1010 atoms each and entangled with the radiation field. Two rod-shaped silicon oscillators 10 µm long were located in two interferometer arms. The photons that passed through the rods induced their mechanical vibration. Then repeated laser pulses interacting with the vibrating oscillators were let through the interferometer, which resulted in mixing the frequencies of phonons and reradiated photons. The detectors registered pulses at the outlet from the interferometer, and the correlations between the pulses with upward or downward frequency shifts were examined. The measured correlation coefficient S = 2.174+0.041-0.042 violates the Bell inequality S < 2 at the level of four standard deviations, which refutes the presence of hidden parameters in the quantum-mechanical description of the system. Source: Phys. Rev. Lett. 121 220404 (2018)

Parallel frequency-bin qubits

P. Lougovski (Oak Ridge National Laboratory, USA) and his colleagues realized quantum gates at two parallel frequency-bin entangled qubits in the same optical fiber. The frequency quantum information encoding is rather promising for application in quantum communication and quantum calculations since it is capable of supporting many qubits in a single optical fiber. Difficult is frequency mixing with maintaining a low noise level. In the experiment with electro-optical phase modulators and two-photon frequency combs, a Hong – Ou – Mandel interference was observed with visibility of 97 %. This allowed different independent operations to be performed simultaneously on two qubits encoded at different frequency-bin photons in optical fiber. Source: Optica 5 1455 (2018)

A lens for extreme-UV radiation

Usual lenses of solid materials are inapplicable for focusing light of an extreme-UV range because of a strong light absorption in a substance. In this spectral region, reflecting mirrors and diffraction plates are typically used. L. Drescher (Max Born Institute, Germany) with colleagues constructed a new lens for an extreme-UV range not consisting of solid material but formed by a gas jet. The light crosses orthogonally the jet with a transverse density gradient. Near atomic resonances, photon reemission by helium atoms changes their phases, and summation of phases of the light waves that passed through the jet induces the beam focusing as would be done by a cylindrical lens. Changing the gas density can control the focal length of the gas lens. The light beam of an extreme-UV range was narrowed from the initial width of 2.7 mm to 410 µm. The minimum scale is limited by geometrical and chromatic aberrationand can be diminished through the method modification. The application of a second perpendicular gas jet might narrow the light beam in the other direction. The new lens may appear to be useful, in particular, for observation of structural variations of biomolecules on short time scales. Source: Nature 564 91 (2018)

Cosmological radio recombination lines

Radio-frequency recombination lines in space are due to stimulated transitions between highly excited electron levels of Rydberg atoms. In the rarified cosmic medium, the population of these levels can be rather high. The radio recombination lines have up to now been only observed from the gas in our Galaxy and from near galaxies. K.L. Emig (Leiden Observatory, Netherlands) with colleagues used the telescope - radio interferometer network LOFAR to register for the first time recombination radio lines at a cosmological distance in the spectrum of quasar 3C 190 at z = 1.1946. An array of 13 lines corresponding to transitions with principal quantum numbers n = 266-301 was observed. The radio-frequency lines were revealed with confidence exceeding > 5 σ. Different scenarios of the origin of these lines are possible. They can emerge on both hydrogen and carbon atoms in a dwarf galaxy along the line of sight. The carbon must be found in cold neutral gas clouds and the hydrogen - in hot clouds with a high degree of ionization. The lines may also appear in gas currents from the galactic active nucleus, but this model encounters some difficulties due to a high gas velocity. The observation of recombination radio lines is of importance for clarifying the physical state of the gas in far objects. Source: arXiv:1811.08104 [astro-ph.GA]

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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.

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