Extracts from the Internet

CP invariance violation in neutrino oscillations

In the T2K experiment, a combined analysis of muon neutrino νμ and antineutrino anti-νμ oscillations was performed, and the obtained difference in the rate of their oscillations testified to the CP violation in the lepton sector. The νμ and anti-νμ beams were generated at the J-PARC acceleration complex (Japan) and were registered by the near detector and the far detector, Super-Kamiokande, at a distance of 295 km. The data were obtained on both the disappearance of νμ and anti-νμ and the appearance of electronic νe and anti-νe in the beams. Within the time of observation, the far detector registered 32 νe and 135 νμ in the original νμ beam and 4 anti-νe and 66 anti-νμ in the anti-νμ beam. These data imply that the phase δCP responsible for CP violation covers the range of (−3.13,−0.39). The observational data are best fitted in the case of direct mass hierarchy when δCP=−1.791, which is close to the maximum CP violation value. Given this, the hypothesized CP conservation, when δCP=0 or π, is excluded to a 90 % confidence. In the T2K experiment, Russian researchers from INR RAS are taking part. Source: Phys. Rev. Lett. 118 151801 (2017)

Quantum communication without particle transmission

R.H. Dicke pointed out in 1981 that quantum mechanics admits information exchange without transmission of physical particles. A modified method was proposed by M.S. Zubairy (Texas A&M University, USA) and his colleagues in 2013. In their approach, the information is coded by the sender through a change of the interferometer configuration and the recipient receives the message by analyzing the passage of auxiliary particles through the interferometer. An array of interferometers was considered, and it was proposed to perform measurements using the quantum Zeno effect so that the number of transmitted physical particles tend to zero with increasing number of interferometers. Y. Cao (the University of Science and Technology of China) et al. were the first to realize a similar scheme in their experiment. Two Michelson – Morley interferometers were used through which particles passed many times. The recipient of information applied photons from a single-photon source as test particles and the sender used a liquid-crystal modulator to open and close the additional interferometer arm linking him with the sender of information. Even if photons have not passed through this arm, its presence in itself influenced the interference pattern observed by the recipient of the information. Thus, the information transmission proceeded without transmission of particles. The method was illustrated by a monochromic image of 100×100 pixels with transmission precision of 87 %. Source: PNAS 114 4920 (2017)

Self-testing of a quantum system

The possibility of self-testing of devices operating with quantum information to estimate correctness of their work from the correlation of classical output signals for certain input signals without knowledge of the device inner workings. The result of self-testing can be obtained, for example, by verifying the violation of Bell type inequalities. In recent years self-testing has been demonstrated for several simple systems, but the general situation remained unclear. The researchers from the California Institute of Technology (USA) and the National University of Singapore A. Coladangelo, K.T. Goh and V. Scarani studied this question theoretically as applied to bipartite systems consisting of two coupled qubits. They received an affirmative answer by proving the theorem ondevice self-testing by output correlations — self-testing of such systems was shown to be actually possible. Source: Nature Communications 8 15485 (2017)

Quantum processor for solution of a system of linear equations

Many computational problems will be solved exponentially faster on quantum than on classical computers. The quantum solution of linear equations has already been demonstrated on photon qubits and qubits based on atomic nuclei. Y. Zheng (the Institute of Physics, Chinese Academy of Sciences) with colleagues did it for the first time using solid-state superconducting qubits. Josephson junctions made of aluminum on a sapphire substrate formed Xmon-qubits (a type of transmon qubits). The computer “processor” consisted of four such qubits, and the whole device included 15 one- and two-qubit logic cells. A system of two linear equations was solved using the quantum algorithm proposed by A. Harrow, A. Hassidim and S. Lloyd. The quantum fidelity of the calculations restricted by decoherence and errors in the cells was 0.837. The superconducting quantum schemes are a promising approach for creation of scalable quantum computers that can be extended by increasing the number of qubits. Source: Phys. Rev. Lett. 118 210504 (2017)

Burst of gravitational waves GW170104

LIGO interferometer registered a burst of gravitational waves GW170104 which became the third among the reliably registered ones. Its registration confirms the conclusion that a new window for observations — gravitational waves — appeared in astronomy. The burst came from the distance of 880 Mpc, where two black holes of masses 31M and 19M merged to form a black hole of mass 49M. The signal-to-noise ratio for this even is equal to 13. From the burst characteristics it was found that the angular momentum of at least one of the black holes before coalescence was not directed along the orbital angular momentum of the binary system, which evidences in favor of the model of formation of a pair of black holes in a star cluster. Immediately after the gravitational burst registration a search for signals coincident with it began on 30 ground-based and space telescopes from radio to gamma-ray electromagnetic wave ranges and a search was undertaken for neutrino signals, but no accompanying signals were revealed. No deviations from the predictions of General Relativity were registered in the characteristics of the observed gravitational-wave signal, and the absence of visible signal dispersion gave the restriction on the graviton mass mg < 7.7×10−23 eV / s2. Source: Phys. Rev. Lett. 118 221101 (2017)

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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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