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| Issue 11, 2024 |
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Extracts from the Internet | ||
Search for neutrinoless double beta decay1 May 2022CUORE collaboration presented new results of the search for neutrinoless double beta (0νββ) decay of 130Te nuclei [1]. This type of decay has not yet been observed in experiments [2, 3]. It is possible provided that neutrino is a Majorana particle, that is, its own antiparticle. The CUORE experiment is being carried out in the underground tunnel in the Gran Sasso National Laboratory (Italy), where a unique refrigerating unit is holding ≈1.5 tons of material at a temperature of ≈10 mK for several years. The calorimeter for the search of decays is a 742-kg array of 998 130Te cubic crystals provided with germanium thermistors. A considerable thickness of ground screens the detector from the hadron component of cosmic rays decreasing a hundred times the muon flux, and protection from a local gamma-ray emission is partially made of low-background lead found at the sunken ancient Roman ship. Although 0νββ decays themselves have not been discovered, it was established that the 0νββ half-decay time is over 2.2 × 1025 years, which is today the best constraint for 130Te. From this there follows in turn a restriction on the effective Majorana mass <90-305 meV of neutrino, where the range of values is due to uncertainties in the theoretical calculations. The method of cooling large volumes of substance to ultralow temperatures and the way of detector screening from the background elaborated for the CUORE experiment may prove to be useful, in particular, for designing quantum computers based on superconducting elements. [1] Adams D Q et al. Nature 604 53 (2022) [2] Barabash A S Phys. Usp. 57 482 (2014); UFN 184 5240 (2014) [3] Simkovic F Phys. Usp. 64 1238 (2021); UFN 191 1307 (2021) Propensity rules1 May 2022As distinct from the selection rule strictly limiting the final states of nuclear and atomic processes, less rigorous propensity rules exist that only point to more probable channels. One of them is the rule of conservation of a hyperfine spin state (sums of spins and projections of spins) under three-particle recombination. This rule has already been confirmed in experiments with an ultracold gas of molecule-forming 87Rb atoms. To verify this rule under other conditions, S. Haze (University of Ulm, Germany) and their co-authors examined a similar process of three-particle recombination in a 85Rb atom gas whose properties differ considerably from the corresponding properties of 87Rb [4]. In particular, the rate of three-particle recombination of 85Rb is higher than that for 87Rb by four orders of magnitude. Nevertheless, the propensity rules were experimentally found also to hold for 85Rb in the examined binding energy range from zero to 13 GHz × h. [4] Haze S et al. Phys. Rev. Lett. 128 133401 (2022) Verification of quantum contextuality without loopholes1 May 2022Verification of the basic elements of quantum mechanics, in particular, those concerning the absence of hidden parameters (the Bell test) requires the absence of so-called loopholes, which might imitate quantum effects by classical ones in view of imperfection of measurement methods. A supplement to the Bell theorem is the Bell – Kochen – Specker theorem on quantum contextuality stating that the result of quantum measurement does not exist before the measurement itself but depends on other accompanying measurements (on the context). Possible loopholes in verification of this theorem are sharpness loophole, detection loophole, and compatibility loophole. Experiments with simultaneous exclusion of the first two loopholes have already been performed before. In the new experiment, P. Wang (Tsinghua University and Beijing Academy of Quantum Information Sciences, China) and their co-authors verified the Bell – Kochen – Specker theorem for the case when all the three loopholes were excluded [5]. The electron transitions in entrapped 171Yb+ and 138Ba+ ions were examined through fluorescence observation. Each ion was observed separately by an individual photomultiplier. Measurements show the maximal 100-% photon registration efficiency and an over 98-% repeatability, which excluded two loopholes. The use of different ions with different sets of levels also allowed exclusion of the compatibility loophole. The experiment confirmed the Bell – Kochen – Specker theorem in agreement with the standard Copenhagen interpretation of quantum mechanics. For essential questions of quantum mechanics, see [6]. [5] Wang P et al. Science Advances 8 (2022) [6] Belinsky A V Phys. Usp. 63 1256 (2020); UFN 190 1335 (2020) Dark quantum states in a waveguide1 May 2022G. Kirchmair and his colleagues (Institute for Quantum Optics and Quantum Informatics, Austria) performed an experiment investigating generation and transfer of “dark” quantum states of an electromagnetic field between transmon qubits in a microwave waveguide [7]. Qubits play the role of artificial atoms, in which transitions can be accompanied by photon emission. Along with ordinary “bright” states compatible with the eigenmodes of oscillations in the waveguide, “dark” states were also excited that had a very weak coupling with the waveguide because of a certain electric field symmetry. Collective “dark” states have already been obtained in earlier experiments, but coherent control over them was impossible. Two pairs of qubits were placed in a waveguide with a rectangular cross section, at a halfwave distance between the pairs. Qubits in each pair had capacitive coupling. The qubit states were controlled by additional electrodes on the side surface of the waveguide. The coherence time of the obtained dark states was 0.6 ms, which exceeded by three orders of magnitude the coherence time of bright states owing to good insulation of dark states from the waveguide modes liable to relaxation. Dark states are interesting in that they form a separate subspace of states in which quantum calculations with a long coherence time can be made, and at the same time a way of coherent control over such states exists, which was realized in the new experiments. [7] Zanner M et al. Nature Physics (2022) Record far galaxies1 May 2022By the present day, a lot of galaxies have been discovered at redshifts z≈9-11, whose stars had at that epoch the age of ≈300-500 years and therefore must have been born still earlier – at z≈14-15. On this basis, Y. Harikane (University of Tokyo, Japan and University College London, Great Britain) and their co-authors made attempts to seek galaxies at z≈12-16 in the COSMOS and SXDS archive databases in the near IR band [8]. These bases rested on observations by different telescopes of celestial regions with a total area of 2.3 square degrees. The method of Lyman-break selection of objects related to absorption in neutral hydrogen was applied, as well as the photometric color selection criterion. Two bright galaxies were revealed, called HD1 and HD2, at redshifts z≈12-16.5 and z≈12-13. These galaxies had a high UV luminosity and star formation rate, by 1.5-2 orders of magnitudes higher than that of our Galaxy, although they are much smaller in size. A spectroscopic method was used to determine the redshift more accurately. The ALMA radio telescopes discovered with a 3.8 σ confidence the oxygen [OIII] line in HD1, whose shift corresponds to z=13.27, which agrees with the photometric estimate. A spectroscopic confirmation has not yet been obtained for HD2, and the best fitting in photometry gives z=12.3. It is not excluded that the high luminosity of HD1 is partly due to accretion of matter to a supermassive black hole in its center. Another candidate, HD3, has not passed all the selection criteria, but photometry gives for it z≈14.6. The space telescope “James Webb” is expected to allow in the near future a detailed examination of early galaxies at large z. [8] Harikane Y et al. arXiv:2112.09141 [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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