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Issue 12, 2024
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Extracts from the Internet


Oscillations D0-àíòè-D0

The LHCb experiment being carried out on the Large Hadron Collider (and involving some Russian researchers) recorded flipping (oscillations) of the D0- meson (quark composition: c-anti-u) into its antiparticle anti-D0 predicted by the Standard model. These oscillations are caused by neutral weak currents through charm mixing. Similar oscillations of K0-, B0 and D0s mesons were already observed in the past. Oscillations D0-anti-D0 were also observed earlier in the joint data array of BaBar, Belle and CDF but their statistical significance was low. In the new experiment LHCb, the type of particle (D0 or anti-D0) was first detected from the presence of π+ in the decays D*+ → D0π+ and from the ratio of the rates R of the Cabibbo-favored decay D0 → K-π+ to Cabibbo-suppressed decay D0 → K+π-. Note that the same products of the decay K+π- were produced in the oscillations D0-anti-D0 followed by the decays anti-D0 → K+π-. The measured form of R as a function of time confirms the fact of the oscillations D0-àíòè-D0, while the hypothesis of their absence (of R=const) is excluded at the confidence level 9.1 σ. Source: Phys. Rev. Lett. 110 101802 (2013)

Calculating unknown eigenvalues with a quantum algorithm

Until recently, quantum calculations were carried out in quantum bits, i.e. qubits, but the devices for read-out of the results (the measurements) had to be specially configured using known classical (non-quantum ) solutions of the same problems. A team of researchers from the Universities of Bristol (United Kingdom) and Queensland (Australia) have implemented an experiment of a new type, without simplifying the circuits of quantum read-out, with the result of quantum computation not known in advance. The phase of the states of photon polarization was determined iteratively (using the phase estimation algorithm). The method of finding the phase φ in the eigenstate of the unitary operator Uψ=ei2πφψ is widely used in quantum algorithms and makes it possible to exponentially speed up calculations in comparison with the classical case. Eigenstates for the polarization of photons transmitted through splitters were constructed, and consecutive bits were calculated in the binary phase representation in the measurement chain, beginning with less significant bits which were later used to improve the knowledge of the more significant ones. Quantum computing without an answer already known are an important step on the way to creating practical quantum computers. Source: Nature Photonics 7 223 (2013)

Collapse of wave function in graphene

Y. Wang et al. (University of California and Berkeley National Laboratory, USA) used clusters of calcium ions in the lattice of graphene to implement an analog of the effect of collapse of electron's wave function in the vicinity of a superheavy nucleus; this effect was predicted by I.Ya. Pomeranchuk and Ya.A. Smorodinskii (J. Phys. USSR 9 97 (1945)) but so far remained unobserved. According to QED calculations (see the review by Ya.B. Zeldovich and V.S. Popov, Sov. Phys. Usp. 14 673 (1972)), the atom becomes unstable when its charge Z increases above Z>Zc ≈ 170. The wave function of the electron collapses: the electron falls onto the nucleus, resulting in creation and ejection of positrons. Using a scanning tunneling microscope, clusters of about 5 nm in diameter were formed of pairs of ions (calcium dimers) in the lattice of graphene, up to five dimers in each cluster. The dimers were formed spontaneously under heating and then moved by a microscope needle into clusters. The same microscope was used to monitor the electron cloud; it was also used to measure the spectrum dI/dV at different distances from the cluster. Electrons in graphene have high interaction constant and relativistic-type dispersion curve, which creates favorable conditions for wave function collapse already at cluster charge Zc ≈ 1. The interaction between an electron and a cluster of 3-5 dimers indeed resulted in wave function collapse, which manifested itself in the formation of a resonance state of electrons with energy below the Dirac point at distances greater than 10 nm from clusters. In accordance with the prediction in the version with individual nuclei, electron vacancies — holes — were ejected instead of positrons in the experiment with graphene. The results of the experiment are in good agreement with the theoretical calculations of wavefunction collapse. Alternative explanations, such as multiple scattering of electrons between dimers, are incapable of reproducing the observed pattern. Source: Science, online publication of March 7, 2013

Polymer capacitor

Researchers at Nanyang Technological University (Singapore) created a prototype capacitor with polymer insulator between plates, whose characteristics are much better than those of conventional capacitors; they can find important appolications in microelectronics. Polymer capacitors were used previously as well but had a serious drawback: low field of electric breakdown due to defects in polymer structure which led to destruction of the insulator. Singaporean researchers synthesized a new multilayer dielectric with breakdown threshold much higher than is typical of ordinary capacitors. The dielectric is based on chemically, thermally and electrically very stable polymer. Source: physicsworld.com

Black hole with large angular momentum

It has been established using x-ray space telescopes NuStar and XMM-Newton that the supermassive black hole at the center of the galaxy NGC 1365 has angular momentum L close to the maximum allowed by general relativity. This result was obtained by recording the variable x-ray emission reflected from the inner region of the accretion disk around the black hole. The faster the rotation of the black hole, the smaller the radius of the inner part of the disk, which produces a very specific modification of the emission spectrum. The interaction of radiation with the gas along the line of sight can also distort the spectrum, so it was necessary to separate this contribution from relativistic effects. This problem has been solved by G. Risaliti (at the Arcetri Observatory in Florence) and his colleagues with a telescope NuStar whose working wavelength range from 3 to 80 keV is somewhat higher than in other x-ray telescopes. Observations in the high energy segment of the x-ray spectrum made it possible to identify unambiguously the effect of broadening of the iron line and the excess of Compton radiation as produced by the gravitational field of the black hole. These measurements gave the parameter of the angular momentum of the black hole as a=Lc/(GM2)≥0.84, against the maximum possible a=1. The black hole could obtain this large angular momentum either during its formation or at a later stage, under strongly nonspherical accretion of matter, or in merging with other black holes. Source: Nature 494 449 (2013)

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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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