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Recent Noteworthy Physics Papers

  1. Dec 3, 2017 #201

    ISamson

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    https://www.sciencenews.org/article...7&utm_medium=email&utm_campaign=Editors_Picks

    Arrow of time reversed in quantum experiment.

    Moderators' note:

    Reversing the thermodynamic arrow of time using quantum correlations
    https://arxiv.org/abs/1711.03323
     
    Last edited by a moderator: Dec 3, 2017
  2. Dec 4, 2017 #202

    DrClaude

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  3. Dec 4, 2017 #203

    ZapperZ

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    Please note that, per Post #1, papers being highlighted in this thread should follow the format outlined. This will make it consistent and concise.

    Also note that this thread only highlights a paper, and encourages discussion of it in another thread.

    Zz.
     
  4. Mar 7, 2018 #204

    ZapperZ

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    Z. Papic et. al. "Imaging Anyons with Scanning Tunneling Microscopy" PRX v.8, 0110371 (2018).

    Abstract: Anyons are exotic quasiparticles with fractional charge that can emerge as fundamental excitations of strongly interacting topological quantum phases of matter. Unlike ordinary fermions and bosons, they may obey non-Abelian statistics—a property that would help realize fault-tolerant quantum computation. Non-Abelian anyons have long been predicted to occur in the fractional quantum Hall (FQH) phases that form in two-dimensional electron gases in the presence of a large magnetic field, such as the ν=5/2 FQH state. However, direct experimental evidence of anyons and tests that can distinguish between Abelian and non-Abelian quantum ground states with such excitations have remained elusive. Here, we propose a new experimental approach to directly visualize the structure of interacting electronic states of FQH states with the STM. Our theoretical calculations show how spectroscopy mapping with the STM near individual impurity defects can be used to image fractional statistics in FQH states, identifying unique signatures in such measurements that can distinguish different proposed ground states. The presence of locally trapped anyons should leave distinct signatures in STM spectroscopic maps, and enables a new approach to directly detect—and perhaps ultimately manipulate—these exotic quasiparticles.

    A review of this paper can be found here, and the actual paper itself can be accessed for free here.

    Zz.
     
  5. Mar 20, 2018 #205

    ZapperZ

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    A. Curtis et al., "Micro-scale fusion in dense relativistic nanowire array plasmas", Nature Communications, DOI: 10.1038/s41467-018-03445.

    Abstract: Nuclear fusion is regularly created in spherical plasma compressions driven by multi-kilojoule pulses from the world’s largest lasers. Here we demonstrate a dense fusion environment created by irradiating arrays of deuterated nanostructures with joule-level pulses from a compact ultrafast laser. The irradiation of ordered deuterated polyethylene nanowires arrays with femtosecond pulses of relativistic intensity creates ultra-high energy density plasmas in which deuterons (D) are accelerated up to MeV energies, efficiently driving D–D fusion reactions and ultrafast neutron bursts. We measure up to 2 × 106 fusion neutrons per joule, an increase of about 500 times with respect to flat solid targets, a record yield for joule-level lasers. Moreover, in accordance with simulation predictions, we observe a rapid increase in neutron yield with laser pulse energy. The results will impact nuclear science and high energy density research and can lead to bright ultrafast quasi-monoenergetic neutron point sources for imaging and materials studies.

    This is an open access paper. You may get the full paper here.

    This is astounding because they claim to have achieved fusion using just "joule-level" laser pulses. But before you start dreaming of fusion-powered energy, the intensity level here is envisioned to be suitable as a neutron point source.

    Zz.
     
  6. Apr 9, 2018 #206

    ZapperZ

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    H. Kim et al., "Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal" Science Advances 06 Apr 2018:Vol. 4, no. 4, eaao4513 DOI: 10.1126/sciadv.aao4513 (no full reference as of now).

    Abstract: In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to form either spin-singlet or spin-triplet bound states. The “spin” of a Bloch electron, however, is fixed by the symmetries of the crystal and the atomic orbitals from which it is derived and, in some cases, can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing beyond spin-triplet, with higher spin quasi-particles combining to form quintet or septet pairs. We report evidence of unconventional superconductivity emerging from a spin-3/2 quasi-particle electronic structure in the half-Heusler semimetal YPtBi, a low-carrier density noncentrosymmetric cubic material with a high symmetry that preserves the p-like j = 3/2 manifold in the Bi-based Γ8 band in the presence of strong spin-orbit coupling. With a striking linear temperature dependence of the London penetration depth, the existence of line nodes in the superconducting order parameter Δ is directly explained by a mixed-parity Cooper pairing model with high total angular momentum, consistent with a high-spin fermionic superfluid state. We propose a kp model of the j = 3/2 fermions to explain how a dominant J = 3 septet pairing state is the simplest solution that naturally produces nodes in the mixed even-odd parity gap. Together with the underlying topologically nontrivial band structure, the unconventional pairing in this system represents a truly novel form of superfluidity that has strong potential for leading the development of a new series of topological superconductors.

    The full access to this paper can be obtained here. Not sure if this is an open access paper, or available only for a short time.

    A general review of this paper can be found here.

    So just when you think the phenomenon of superconductivity is done surprising us......

    Zz.
     
  7. Apr 10, 2018 #207

    ZapperZ

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    Another fascinating result from the world of superconductivity, which isn't done in producing more surprises:

    K. Kamiya et al., "Discovery of superconductivity in quasicrystal", Nature Communications v9., Article number: 154 (2018).

    Abstract: Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al–Zn–Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of Tc≅0.05 K. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity.

    You may read the full paper here. A review of this work can be found at PhysicsWorld.

    Zz.
     
  8. Apr 26, 2018 #208

    mfb

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    Stabilized entanglement of massive mechanical oscillators
    From the abstract:
    The entanglement was stable for many minutes, a significant improvement over a related experiment from 2011 with a few picoseconds coherence time (Entangled diamonds vibrate together).
     
  9. May 2, 2018 #209

    ZapperZ

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    S.W. Hawking and T. Hertog "A smooth exit from eternal inflation?" J. High Energ. Phys. (2018) 2018: 147. https://doi.org/10.1007/JHEP04(2018)147.

    Abstract: The usual theory of inflation breaks down in eternal inflation. We derive a dual description of eternal inflation in terms of a deformed Euclidean CFT located at the threshold of eternal inflation. The partition function gives the amplitude of different geometries of the threshold surface in the no-boundary state. Its local and global behavior in dual toy models shows that the amplitude is low for surfaces which are not nearly conformal to the round three-sphere and essentially zero for surfaces with negative curvature. Based on this we conjecture that the exit from eternal inflation does not produce an infinite fractal-like multiverse, but is finite and reasonably smooth.

    This, of course, is the last paper written by Hawking while he was alive. The full version of the published paper can be found here. The arXiv version has been online since his death, but it has finally been published.

    Astrophysicist Ethan Siegel has written an earlier explanation of this paper, in case you missed it.

    Zz.
     
  10. May 4, 2018 #210

    Andy Resnick

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    "Characterization of the 1S–2S transition in antihydrogen"
    M. Ahmadi, B. X. R. Alves, J. S. Wurtele Nature volume 557, pages71–75 (2018) doi:10.1038/s41586-018-0017-2


    From the abstract: "We find that the shape of the spectral line agrees very well with that expected for hydrogen and that the resonance frequency agrees with that in hydrogen to about 5 kilohertz out of 2.5 × 1015 hertz. This is consistent with charge–parity–time invariance at a relative precision of 2 × 10−12—two orders of magnitude more precise than the previous determination8—corresponding to an absolute energy sensitivity of 2 × 10−20 GeV."
     
  11. Jun 22, 2018 #211

    ZapperZ

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    T.E. Collett et al., "A precise extragalactic test of General Relativity", Science v.360, p.1342 (2018).

    Abstract: Einstein’s theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens ESO 325-G004 provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, γ. By reconstructing the observed light profile of the lensed arcs and the observed spatially resolved stellar kinematics with a single self-consistent model, we conclude that γ = 0.97 ± 0.09 at 68% confidence. Our result is consistent with the prediction of 1 from General Relativity and provides a strong extragalactic constraint on the weak-field metric of gravity.

    Ethan Siegel has an article describing in greater detail the significance of this result. You may read the full manuscript of the paper here.

    Zz.
     
  12. Jul 5, 2018 #212

    ZapperZ

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    On the heels of the previous post of GR verification at the galactic scale, comes this test of GR's strong equivalence principle involving a neutron star and two white dwarfs.

    A.M. Archibald et al., "Universality of free fall from the orbital motion of a pulsar in a stellar triple system", Nature, 559, p73 (2018).

    Abstract: Einstein’s theory of gravity—the general theory of relativity—is based on the universality of free fall, which specifies that all objects accelerate identically in an external gravitational field. In contrast to almost all alternative theories of gravity, the strong equivalence principle of general relativity requires universality of free fall to apply even to bodies with strong self-gravity. Direct tests of this principle using Solar System bodies are limited by the weak self-gravity of the bodies, and tests using pulsar–white-dwarf binaries have been limited by the weak gravitational pull of the Milky Way. PSR J0337+1715 is a hierarchical system of three stars (a stellar triple system) in which a binary consisting of a millisecond radio pulsar and a white dwarf in a 1.6-day orbit is itself in a 327-day orbit with another white dwarf. This system permits a test that compares how the gravitational pull of the outer white dwarf affects the pulsar, which has strong self-gravity, and the inner white dwarf. Here we report that the accelerations of the pulsar and its nearby white-dwarf companion differ fractionally by no more than 2.6 × 10−6. For a rough comparison, our limit on the strong-field Nordtvedt parameter, which measures violation of the universality of free fall, is a factor of ten smaller than that obtained from (weak-field) Solar System tests and a factor of almost a thousand smaller than that obtained from other strong-field tests.

    The News and Views article on this paper can be found here.

    Zz.
     
  13. Jul 15, 2018 #213

    ZapperZ

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    These are two papers reporting on the same observation, which strengthens its validity.

    The IceCube Collaboration,Fermi-LAT,MAGIC,AGILE,ASAS-SN,HAWC,H.E.S.S.,INTEGRAL,Kanata,Kiso,Kapteyn,Liverpool Telescope,Subaru,Swift/NuSTAR,VERITAS,VLA/17B-403 teams, "Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A" Science 361, 146 (2018).

    Abstract: Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera–electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray–emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

    Full paper can be found here.


    The IceCube Collaboration, "Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert" Science 361, 147 (2018)

    Abstract: A high-energy neutrino event detected by IceCube on 22 September 2017 was coincident in direction and time with a gamma-ray flare from the blazar TXS 0506+056. Prompted by this association, we investigated 9.5 years of IceCube neutrino observations to search for excess emission at the position of the blazar. We found an excess of high-energy neutrino events, with respect to atmospheric backgrounds, at that position between September 2014 and March 2015. Allowing for time-variable flux, this constitutes 3.5σ evidence for neutrino emission from the direction of TXS 0506+056, independent of and prior to the 2017 flaring episode. This suggests that blazars are identifiable sources of the high-energy astrophysical neutrino flux.

    Full paper can be found here.

    These two papers are significant because it adds another "messenger", this time neutrinos, in making astronomical observation. We had light/EM radiation since the beginning of observational astronomy, and we recently added gravitational waves to that. So welcome, neutrinos!

    Zz.
     
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