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| Issue 12, 2024 |
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Extracts from the Internet | ||
A new particle: Zc(3900)1 July 2013Belle collaboration (KEKB accelerator, Japan) è BessIII (electron--positron collider in Beijing, China) independently obtained evidence of having produced a particle Zc(3900) that has an electric charge and presumably consists of four quarks: c, anti-c, u and anti-d. In both experiments, the object of study was the structure of charmonium-like resonance Y(4260) in the intermediate states of the reaction e+e- → π+π-J/ψ. On the charmonium-like states, see the review in the Phys. Usp. 53 219 (2010). The particle Y(4260) was first identified in 2005; it is assumed that it includes an additional gluon on top of the gluons that connect ñ and anti-c quarks. An additional resonance peak about 46 MeV wide was observed at 3.9 GeV; it was interpreted as a four-quark state Zc(3900) with a mass of about 3.9 GeV. On the whole, 466 events of creation of Zc(3900) were observed in the two experiments. As an alternative model, it is proposed that the Zc(3900) may consist of a loosely-coupled pair of two-quark D-mesons. Sources: Phys. Rev. Lett. 110 252001 (2013), Phys. Rev. Lett. 110 252002 (2013) Quantum computing: solving a system of linear equations1 July 2013X.-D. Cai (The Chinese University of Science and Technology in Hefei, China) with colleagues were able to solve a set of two linear equations with two unknowns, Ax=b, using a simple quantum computer. To be precise, they measured the anticipated value of the quantum operator corresponding to the solution. A.W. Harrow, A. Hassidim and S. Lloyd have theoretically shown in 2009 that the quantum algorithm for solving a set of linear equations with N unknowns will consume time ∼ ln N while the duration of the classical calculations is ∼ N. In other words, the quantum computer should be able to exponentially speed up the solution of such problems. In the new experiment, the operation of the quantum algorithm was demonstrated by using four quantum bits, or qubits (for which photons were used), and a set of logic cells based on beam splitters (mirrors and prisms) operated first to calculate the inverse 2×2 matrix A-1 and then to conduct the matrix multiplication which yielded the solution. The quality of the calculations (their fidelity) was from 0.825 to 0.993 but the application of more sophisticated single-photon sources and detectors may in the future improve this parameter. Source: Phys. Rev. Lett. 110 230501 (2013) The “photoionization microscopy” of the hydrogen atom1 July 2013In their experiment, A.S. Stodolna (Institute of Atomic and Molecular Physics, The Netherlands) and her colleagues implemented the method of visualization of the electron wave function in a hydrogen atom which was proposed theoretically by Yu.N. Demkov, V.D. Kondratovich and V.N. Ostrovskii (JETP Lett. 34 403 (1981)). The method is based on the fact that in photoionization of an atom in a uniform electric field, the possible trajectories of emitted electrons may again intersect at a great distance from the atom while preserving quantum coherence and creating a scaled-up intreference pattern representing the distribution of the electron density in the atom. Irradiation by laser pulses produced several hundreds of thousands of acts of ionization in hydrogen atoms in static electric field, in which atoms were transformed to the excited quasibound Stark states. The emitted electrons were detected on a flat screen perpendicular to the electric field which created the effect of an electrostatic lens with magnification of about 20,000. This experiment investigated both the resonant and the non-resonant photoexcitation. In the first of these cases, the process was the tunneling of electrons across a maximum on the potential curve; the screen showed an interference pattern in the form of concentric rings corresponding to 0, 1, 2 or 3 nodes of the electron wave function in the atom. Source: Phys. Rev. Lett. 110 213001 (2013) Imaging of currents on the surface of a topological insulator1 July 2013Stanford University researchers were able to record electrical currents flowing along the surface of a topological insulator by detecting the magnetic field of these currents with the superconducting detector (SQUID). Topological insulators are special in that only the surface of these materials retains high conductivity while in the bulk they become insulators. This property has been previously observed in experiments but there was no successful direct recording of currents on the surface. To conduct this new experiment, a highly sensitive SQUID was constructed in order to measure the magnetic field with spatial resolution of a few microns. A specimen of mercury telluride shaped into an elongated parallelepiped was manufactured, with a quantum-wall like structure. Electric current passed through the sample along the longer edges, perpendicularly to the electric field. The measurements showed that in conditions of low electric field, with the bulk of the specimen conducting, the magnetic lines of force covered the entire sample. However, with electric field continuing to increase, the magnetic field lines separated and surrounded two faces separately. This corresponded to the transition of the sample to the state of a topological insulator, with only two faces remaining conducting. Source: Nature Materials, Published online 16 June 2013 Magnetar 1E 2259+586 has abruptly slowed its rate of revolution1 July 2013R.F. Archibald (McGill University, Canada) et al. discovered, using the the X-ray telescope of the Swift space observatory, found in April 2012 that the magnetar 1E 2259+586 (the neutron star with very strong magnetic field) has suddenly slowed down its rate of rovolution (in comparison with the gradual decrease of the period T typical of pulsars). Observations of several dozens of jumpwise accelerations in the rotation of radio pulsar were reported in the past. These accelerations (known as glitches) were interpreted as produced by angular momentum exchange between the differentially rotating layers of the neutron star, that is, the solid crust and the internal neutron fluid, producing cracks in the crust. No acceptable interpretation of the slow-down (named as antiglitch) of the magnetar 1E 2259+586 has been found yet and may even require reconsideration of the structural models of the neutron star. The antiglitch may be explained both by internal mechanisms, and by external causes, such as plasma ejections. The April 2012 antiglitch was accompanied with a burst of hard x-ray emission recorded by the Enrico Fermi Space Telescope. A second, less intense, change in the pulsar frequency occurred in August 2012; owing to the poorly understood value of dT/dt it could be interpreted either as second antiglitch or as a glitch. The second event was not accompanied by signals in the radio or x-ray range, which contradicts the plasma ejection hypothesis. Source: Nature 497 591 (2013) |
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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