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| Issue 4, 2024 |
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Extracts from the Internet | ||
Search for quantum gravity effects in neutrino observations1 December 2022The theory of quantum gravity, aimed at unifying the gravitational field with other fundamental interactions, has not yet been completely formulated [1, 2], but a search for its possible experimental manifestations has already begun. One of the promising areas is the search for cosmological neutrinos coming from far galaxies. The space-time fluctuations described by quantum operators of different dimensions could induce noticeable anomalies in neutrino oscillations during their pass. Thus, neutrinos are a giant interferometer of cosmological scale. The IceCube telescope has recently reached, for the first time in its statistics, the range of parameters, making obvious a contribution of dimension-6 operators in cosmological neutrino oscillations [3]. The IceCube contains an array of photomultipliers at depths of 1450-2450 m in Antarctic ice thatare scanning the volume of 1 km3. The interaction between neutrinos of different flavors (electronic, muon, and tau-neutrino) and atoms generate fluxes of secondary particles whose properties are indicative of neutrino flavor. Numerous events have been detected with neutrino energies over 60 TeV with different flavors. These observations were compared with the results of numerical simulation of neutrino spectra that appeared in astrophysical sources and experienced oscillations. Quantum gravity effects in neutrino oscillations have not been revealed to date, but the negative result allowed obtaining new limits on the theory’s parameters. [1] Gorelik G E Phys. Usp. 48 1039 (2005); UFN 175 1093 (2005) [2] Kazakov D I Phys. Usp. 62 364 (2019); UFN 189 387 (2019) [3] Abbasi R et al. Nature Physics 18 1287 (2022) Tripartite quantum correlations1 December 2022Verification of basicelements of quantum mechanics remains one of the topical subjects of research, especially in connection with new directions in quantum technologies. In quantum mechanics, along with entangled quantum states of two particles (bipartite-entangles states), also possible are quantum correlations of three particles (tripartite-entangled states) that have no classical analogues. A theoretical analysis has shown that tripartite correlations cannot be reduced to several bipartite ones. H. Cao (University of Science and Technology of China) and their co-authors obtained a new, more rigorous criterion for verification of this statement [4]. The criterion resembling Bell inequalities can be applied to different modifications of quantum mechanics. H. Cao with colleagues performed an experiment, where such a verification was successfully realized.The experiment involved laser radiation photons in Greenberger–Horne–Zeilinger states. Tripartite correlationswere shown with 26.3 σ confidence not to be reduced to hidden variables or to a combination of so-called “exotic bipartite correlations” but are a fundamental form of quantum correlations. Laser technologies similar to those used in this experiment find wide application in quantum communication devices and in quantum calculations (see, e.g., [5-7]). [4] Cao H et al. Phys. Rev. Lett. 129 150402 (2022) [5] Khabarova K Yu, Zalivako I V, Kolachevsky N N Phys. Usp. 65(12) (2022); UFN 182 1305 (2022) [6] Sukachev D D Phys. Usp. 64 1021 (2021); UFN 191 1077 (2021) [7] Zheltikov A M, Scully M O Phys. Usp. 63 698 (2020); UFN 190 749 (2020) Electron optics in graphene1 December 2022The linear form of the dispersion relation for electrons in graphene monolayer allows control of the electron motion by methods similar to those of classical optics. In particular, it has been demonstrated earlier that electron fluxes passing through p-n junction in graphene can be collimated with the Klein tunneling effect and can undergo refraction in the course of Veselago lensing in a substance with negative dielectric permittivity and magnetic permeability [8]. However, the collimation and focusing efficiency remained low. The latter, in particular, obstructed realization of controlled quantum interference of electrons. X. Zhang (University of Minnesota, USA) and their co-authors designed a new architecture of a bipolar graphene microcavity, in which one can solve the above-mentioned problems through graphene deformation and certain electrostatic potentials [9].A combination of these effects creates several consecutiveVeselago lensing processes. Thus, electrons were localized, and the general collimation efficiency heightened. This method may prove to be useful in design of new optical devices realizing controlled quantum interference. Forgraphene electronics, see [10, 11]. [8] Veselago V G Sov. Phys. Usp. 10 509 (1968); UFN 92 517 (1967) [9] Zhang X et al. Nature Communications 13 6711 (2022) [10] Ratnikov P V, Silin A P Phys. Usp. 61 1139 (2018); UFN 188 1249 (2018) [11] Antonova I V Phys. Usp. 65 567 (2022); UFN 192 609 (2022) Hydrated ions1 December 2022A proton in water forms a hydroxonium ion H3O+, and water molecules draw up around it in a certain way with formation, in particular, of Zundel H5O2+ and Eigen cations H9O4+ (called after the scientists who investigated them). The properties of these cations are important for the process of proton diffusion in water according to the Grotthuss mechanism describing proton jumps through a hydrogen bond network that considerably increase the diffusion coefficient. In several experiments, the IR spectrum of these cations in the gas phase of water was measured. However, a complete understanding of the spectrum formation mechanisms, including the reason for the great difference between the Eigen and Zundel cation spectra, has not been reached because of complexity of multidimensional quantum dynamics of complex ions. M. Schroder (Heidelberg University, Germany) and his co-authors performed new theoretical calculations providing insight into the indicated effects [12]. The linear absorption spectrum of cations was successfully simulated for the first time using full-dimensional (33-dimensional) quantum-dynamical simulations allowing for correlations between low-frequency large-amplitude displacements, extension of O–H bonds, and other factors. Analysis has shown that the dynamic subunit formed by two water molecules and a proton is the smallest structure reproducing the spectra and anharmonic cation modes. The difference in the spectra is explained by different effectson this subunit of the environmental conditions in different cations. [12] Schröder M et al. Nature Communications 13 6170 (2022) An unusual ring-like radio source1 December 2022Machine learning algorithms allow discovering astronomical objects with extraordinary properties, which remained unnoticed in giant catalogues in the course of their customary processing. In particular, the set of Astronomaly algorithms showed up to the best advantage in the search for optical transients and galaxies with unique morphology. M. Lochner (University of the Western Cape and South African Astronomical Observatory) and their co-authors applied Astronomaly to process theMeerKAT Galaxy Cluster Legacy Survey (MGCLS) including ≈ 720 000 radio sources [13]. The survey was drawn up mainly with the help of MeerKAT radio telescope located inSAR – the prototype of SKA class telescopes 1 km2 in area. A unique ring-like radio source 75 kpc in size with luminosity of 1025 W Hz−1 comparable to the luminosity of powerful radio galaxies was discovered byAstronomaly in Abell 209 galactic cluster. The source is located near the galaxy at redshift z=0.55, surrounded by a diffuse envelope. Close to it are structures resembling radio jets and radio blades. The ring-like object may have resulted from the action of a shock wave after termination of the active star formation in the galaxy. It could also have been formed by matterejected from a powerful radio galaxy orfrom a pair of merging supermassive black holes. However, the existing models cannot provide an exhaustive explanation of the observed source structure. This source remotely resembles the radio circles discovered recently by ASKAP radio interferometer, whose origin now remains unclear. [13] Lochner M et al., arXiv:2211.02062 [astro-ph.GA] |
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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