Recent Noteworthy Physics Papers

[ZapperZ]

J.R. Williams et al., "Unconventional Josephson Effect in Hybrid Superconductor-Topological Insulator Devices", Phys. Rev. Lett. 109, 056803 (2012)

Abstract: We report on transport properties of Josephson junctions in hybrid superconducting-topological insulator devices, which show two striking departures from the common Josephson junction behavior: a characteristic energy that scales inversely with the width of the junction, and a low characteristic magnetic field for suppressing supercurrent. To explain these effects, we propose a phenomenological model which expands on the existing theory for topological insulator Josephson junctions.

Also see a review of this work at APS Physics where you will have a free download to the paper.

Zz.

 

[ZapperZ]

J. Yin et al., "Quantum teleportation and entanglement distribution over 100-kilometre free-space channels" Nature v.488, p.185 (2012).

Abstract: Transferring an unknown quantum state over arbitrary distances is essential for large-scale quantum communication and distributed quantum networks. It can be achieved with the help of long-distance quantum teleportation1, 2 and entanglement distribution. The latter is also important for fundamental tests of the laws of quantum mechanics3, 4. Although quantum teleportation5, 6 and entanglement distribution7, 8, 9 over moderate distances have been realized using optical fibre links, the huge photon loss and decoherence in fibres necessitate the use of quantum repeaters10 for larger distances. However, the practical realization of quantum repeaters remains experimentally challenging11. Free-space channels, first used for quantum key distribution12, 13, offer a more promising approach because photon loss and decoherence are almost negligible in the atmosphere. Furthermore, by using satellites, ultra-long-distance quantum communication and tests of quantum foundations could be achieved on a global scale. Previous experiments have achieved free-space distribution of entangled photon pairs over distances of 600 metres (ref. 14) and 13 kilometres (ref. 15), and transfer of triggered single photons over a 144-kilometre one-link free-space channel16. Most recently, following a modified scheme17, free-space quantum teleportation over 16 kilometres was demonstrated18 with a single pair of entangled photons. Here we report quantum teleportation of independent qubits over a 97-kilometre one-link free-space channel with multi-photon entanglement. An average fidelity of 80.4 ± 0.9 per cent is achieved for six distinct states. Furthermore, we demonstrate entanglement distribution over a two-link channel, in which the entangled photons are separated by 101.8 kilometres. Violation of the Clauser–Horne–Shimony–Holt inequality4 is observed without the locality loophole. Besides being of fundamental interest, our results represent an important step towards a global quantum network. Moreover, the high-frequency and high-accuracy acquiring, pointing and tracking technique developed in our experiment can be directly used for future satellite-based quantum communication and large-scale tests of quantum foundations.

Zz.

 

[frogjg2003]

J. M. Hill and B. J. Cox, "Einstein's special relativity beyond the speed of light" Proc. R. Soc. A published ahead of print October 3, 2012, (2012)

Abstract: We propose here two new transformations between inertial frames that apply for relative velocities greater than the speed of light, and that are complementary to the Lorentz transformation, giving rise to the Einstein special theory of relativity that applies to relative velocities less than the speed of light. The new transformations arise from the same mathematical framework as the Lorentz transformation, displaying singular behaviour when the relative velocity approaches the speed of light and generating the same addition law for velocities, but, most importantly, do not involve the need to introduce imaginary masses or complicated physics to provide well-defined expressions. Making use of the dependence on relative velocity of the Lorentz transformation, the paper provides an elementary derivation of the new transformations between inertial frames for relative velocities v in excess of the speed of light c, and further we suggest two possible criteria from which one might infer one set of transformations as physically more likely than the other. If the energy–momentum equations are to be invariant under the new transformations, then the mass and energy are given, respectively, by the formulae m=(p_\infty/c)[(v/c)^2-1]^{-1/2} and \mathcal{E}=mc^2 where p_\infty denotes the limiting momentum for infinite relative velocity. If, however, the requirement of invariance is removed, then we may propose new mass and energy equations, and an example having finite non-zero mass in the limit of infinite relative velocity is given. In this highly controversial topic, our particular purpose is not to enter into the merits of existing theories, but rather to present a succinct and carefully reasoned account of a new aspect of Einstein's theory of special relativity, which properly allows for faster than light motion.

I'll post the full citation when it officially gets published.

 

[ZapperZ]

K. Borozdin et al., "Cosmic Ray Radiography of the Damaged Cores of the Fukushima Reactors" Phys. Rev. Lett. 109, 152501 (2012).

Abstract: The passage of muons through matter is dominated by the Coulomb interaction with electrons and nuclei. The interaction with the electrons leads to continuous energy loss and stopping of the muons. The interaction with nuclei leads to angle “diffusion.” Two muon-imaging methods that use flux attenuation and multiple Coulomb scattering of cosmic-ray muons are being studied as tools for diagnosing the damaged cores of the Fukushima reactors. Here, we compare these two methods. We conclude that the scattering method can provide detailed information about the core. Attenuation has low contrast and little sensitivity to the core.

Review of this work can be found here. You may also obtain a free copy of the paper at that link since it is published under a Creative Commons license.

Zz.

 

[ZapperZ]

C. Zu et al.,“State-Independent Experimental Test of Quantum Contextuality in an Indivisible System” Phys. Rev. Lett. 109, 150401 (2012).

Abstract: We report the first state-independent experimental test of quantum contextuality on a single photonic qutrit (three-dimensional system), based on a recent theoretical proposal [ Phys. Rev. Lett. 108 030402 (2012)]. Our experiment spotlights quantum contextuality in its most basic form, in a way that is independent of either the state or the tensor product structure of the system.

Read a review of this work here. The link also provides a free copy of the actual paper.

Zz.

 

[Cthugha]

Paula Mellado, Andres Concha, and L. Mahadevan,“Macroscopic Magnetic Frustration” Phys. Rev. Lett. 109, 257203 (2012).

Abstract: Although geometrical frustration transcends scale, it has primarily been evoked in the micro- and mesoscopic realm to characterize such phases as spin ice, liquids, and glasses and to explain the behavior of such materials as multiferroics, high-temperature superconductors, colloids, and copolymers. Here we introduce a system of macroscopic ferromagnetic rotors arranged in a planar lattice capable of out-of-plane movement that exhibit the characteristic honeycomb spin ice rules studied and seen so far only in its mesoscopic manifestation. We find that a polarized initial state of this system settles into the honeycomb spin ice phase with relaxation on multiple time scales. We explain this relaxation process using a minimal classical mechanical model that includes Coulombic interactions between magnetic charges located at the ends of the magnets and viscous dissipation at the hinges. Our study shows how macroscopic frustration arises in a purely classical setting that is amenable to experiment, easy manipulation, theory, and computation, and shows phenomena that are not visible in their microscopic counterparts.

A review of this work can be found here. This is a very cute experiment. These guys just created a triangular lattice composed of 352 macroscopic magnets and simulated a simplified version of spin ice that way. Also check the supplementary material. It contains a nice video of the magnet system developing towards a steady state. Setting up that experiment must have been lots of fun.

 

[Cthugha]

M. Giustina et al., "Bell violation using entangled photons without the fair-sampling assumption" Nature (2013) doi:10.1038/nature12012. (advance online publication) http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12012.html?WT.ec_id=NATURE-20130418

Abstract: The violation of a Bell inequality is an experimental observation that forces the abandonment of a local realistic viewpoint—namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light1, 2. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble3. To do this, we use the Eberhard form of Bell’s inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms4. Technical improvements of the photon source5, 6 and high-efficiency transition-edge sensors7 were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.

 

[ZapperZ]

A. S. Stodolna et al.,"Hydrogen Atoms under Magnification: Direct Observation of the Nodal Structure of Stark States"

Abstract: To describe the microscopic properties of matter, quantum mechanics uses wave functions, whose structure and time dependence is governed by the Schrödinger equation. In atoms the charge distributions described by the wave function are rarely observed. The hydrogen atom is unique, since it only has one electron and, in a dc electric field, the Stark Hamiltonian is exactly separable in terms of parabolic coordinates (η, ξ, φ). As a result, the microscopic wave function along the ξ coordinate that exists in the vicinity of the atom, and the projection of the continuum wave function measured at a macroscopic distance, share the same nodal structure. In this Letter, we report photoionization microscopy experiments where this nodal structure is directly observed. The experiments provide a validation of theoretical predictions that have been made over the last three decades.

A synopsis of the work can be found here, which also has a link for free access to the actual paper.

Zz.

 

[ZapperZ]

J Heeck, "How Stable is the Photon?", Phys. Rev. Lett. 111, 021801 (2013).

Abstract: Yes, the photon. While a nonzero photon mass has been under experimental and theoretical study for years, the possible implication of a finite photon lifetime lacks discussion. The tight experimental upper bound of the photon mass restricts the kinematically allowed final states of photon decay to the lightest neutrino and/or particles beyond the standard model. We discuss the modifications of the well-measured cosmic microwave background spectrum of free streaming photons due to photon mass and lifetime and obtain model-independent constraints on both parameters—most importantly a lower direct bound of 3 yr on the photon lifetime, should the photon mass be at its conservative upper limit. In that case, the lifetime of microwave photons will be time-dilated by a factor order 10^15.

You may read a synopsis of this work at the APS Physics and report on it at Physics World.

Zz.

 

[korialstasz]

O. Firstenberg et al., "Attractive photons in a quantum nonlinear medium" Nature (2013) doi:10.1038/nature12512. http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12512.html

Abstract: The fundamental properties of light derive from its constituent particles—massless quanta (photons) that do not interact with one another. However, it has long been known that the realization of coherent interactions between individual photons, akin to those associated with conventional massive particles, could enable a wide variety of novel scientific and engineering applications. Here we demonstrate a quantum nonlinear medium inside which individual photons travel as massive particles with strong mutual attraction, such that the propagation of photon pairs is dominated by a two-photon bound state. We achieve this through dispersive coupling of light to strongly interacting atoms in highly excited Rydberg states. We measure the dynamical evolution of the two-photon wavefunction using time-resolved quantum state tomography, and demonstrate a conditional phase shift exceeding one radian, resulting in polarization-entangled photon pairs. Particular applications of this technique include all-optical switching, deterministic photonic quantum logic and the generation of strongly correlated states of light.

 

[ZapperZ]

A. D. Wissner-Gross and C. E. Freer, "Causal Entropic Forces", Phys. Rev. Lett. v.110, p.168702 (2013).

Abstract: Recent advances in fields ranging from cosmology to computer science have hinted at a possible deep connection between intelligence and entropy maximization, but no formal physical relationship between them has yet been established. Here, we explicitly propose a first step toward such a relationship in the form of a causal generalization of entropic forces that we find can cause two defining behaviors of the human “cognitive niche”—tool use and social cooperation—to spontaneously emerge in simple physical systems. Our results suggest a potentially general thermodynamic model of adaptive behavior as a nonequilibrium process in open systems.

Read the synopsis in APS Physics.

Zz.

 

[DennisN]

Andreas Reiserer, Stephan Ritter, Gerhard Rempe
Nondestructive Detection of an Optical Photon
Science DOI: 10.1126/science.1246164 (2013)
http://www.sciencemag.org/content/early/2013/11/13/science.1246164
Paper on arxiv: http://arxiv-web3.library.cornell.edu/abs/1311.3625

Abstract:
All optical detectors to date annihilate photons upon detection, thus excluding repeated measurements. Here, we demonstrate a robust photon detection scheme which does not rely on absorption. Instead, an incoming photon is reflected off an optical resonator containing a single atom prepared in a superposition of two states. The reflection toggles the superposition phase which is then measured to trace the photon. Characterizing the device with faint laser pulses, a single-photon detection efficiency of 74% and a survival probability of 66% is achieved. The efficiency can be further increased by observing the photon repeatedly. The large single-photon nonlinearity of the experiment should enable the development of photonic quantum gates and the preparation of novel quantum states of light.

 

[Cthugha]

Jörn Dunkel and Stefan Hilbert, "Consistent thermostatistics forbids negative absolute temperatures", Nature Physics, advanced online publication, doi:10.1038/nphys2831 (2013).

Abstract: Over the past 60 years, a considerable number of theories and experiments have claimed the existence of negative absolute temperature in spin systems and ultracold quantum gases. This has led to speculation that ultracold gases may be dark-energy analogues and also suggests the feasibility of heat engines with efficiencies larger than one. Here, we prove that all previous negative temperature claims and their implications are invalid as they arise from the use of an entropy definition that is inconsistent both mathematically and thermodynamically. We show that the underlying conceptual deficiencies can be overcome if one adopts a microcanonical entropy functional originally derived by Gibbs. The resulting thermodynamic framework is self-consistent and implies that absolute temperature remains positive even for systems with a bounded spectrum. In addition, we propose a minimal quantum thermometer that can be implemented with available experimental techniques.

The authors argue that there are important differences between the definitions of entropy given by Gibbs and the approximate one given by Boltzmann. They show that only the Boltzmann version gives a negative absolute temperature as sometimes reported in experiments on nuclear spin systems. The authors then argue that only the Gibbs version of entropy is fully consistent and make it clear that the negative Boltzmann temperature cannot have the meaning of a thermodynamic temperature.

See also the news and views article in the same issue: http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2831.html

 

[Cthugha]

Jianyong Cen, Ping Yuan, and Simin Xue, "Observation of the Optical and Spectral Characteristics of Ball Lightning", Phys. Rev. Lett. v.112, p. 035001 (2014).

Abstract: Ball lightning (BL) has been observed with two slitless spectrographs at a distance of 0.9 km. The BL is generated by a cloud-to-ground lightning strike. It moves horizontally during the luminous duration. The evolution of size, color, and light intensity is reported in detail. The spectral analysis indicates that the radiation from soil elements is present for the entire lifetime of the BL.

Yes, this paper is about the mysterious natural ball lightning and it appears in a quality journal. Looks like this ball lightning was a dirty fellow. The researchers found lots of spectral lines you would expect from the elements present in the soil. Also see this focus article, which summarizes the paper.

 

[Amok]

M. W. Ray, E. Ruokokoski, S. Kandel, M. Möttönen & D. S. Hall,"Observation of Dirac monopoles in a synthetic magnetic field", Nature 505, 657-660 (2014),
doi:10.1038/nature12954

Magnetic monopoles—particles that behave as isolated north or south magnetic poles—have been the subject of speculation since the first detailed observations of magnetism several hundred years ago1. Numerous theoretical investigations and hitherto unsuccessful experimental searches2 have followed Dirac’s 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field3. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge3, 4. Although analogues of magnetic monopoles have been found in exotic spin ices5, 6 and other systems7, 8, 9, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10, 11, 12, 13). Here we demonstrate the controlled creation14 of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose–Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.


Haven't been active in these forums for a while, but a colleague brought this paper to my attention and I felt like sharing to see if it might interest someone :D

 

[ZapperZ]

M. W. Ray, E. Ruokokoski, S. Kandel, M. Möttönen & D. S. Hall,"Observation of Dirac monopoles in a synthetic magnetic field", Nature 505, 657-660 (2014),
doi:10.1038/nature12954

Magnetic monopoles—particles that behave as isolated north or south magnetic poles—have been the subject of speculation since the first detailed observations of magnetism several hundred years ago1. Numerous theoretical investigations and hitherto unsuccessful experimental searches2 have followed Dirac’s 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field3. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge3, 4. Although analogues of magnetic monopoles have been found in exotic spin ices5, 6 and other systems7, 8, 9, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10, 11, 12, 13). Here we demonstrate the controlled creation14 of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose–Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.


Haven't been active in these forums for a while, but a colleague brought this paper to my attention and I felt like sharing to see if it might interest someone :D

A review of this paper can be found at PhysicsWorld:

http://physicsworld.com/cws/article/news/2014/jan/30/magnetic-monopoles-seen-in-the-lab

Note that both this, and the earlier claim of magnetic monopole physics observation in spin-ice, are both condensed matter systems. This is just another example where the so-called "applied" field of physics is actually providing insight on fundamental physics.

Zz.

 

[ZapperZ]

Y-C. Lee, M-H. Hsieh, S.T. Flammia, and R-K. Lee "Local PT Symmetry Violates the No-Signaling Principle", Phys. Rev. Lett. 112, 130404 (2014).

Abstract: Bender et al. [Phys. Rev. Lett. 80, 5243 (1998)] have developed PT-symmetric quantum theory as an extension of quantum theory to non-Hermitian Hamiltonians. We show that when this model has a local PT symmetry acting on composite systems, it violates the nonsignaling principle of relativity. Since the case of global PT symmetry is known to reduce to standard quantum mechanics A. Mostafazadeh [J. Math. Phys. 43, 205 (2001)], this shows that the PT-symmetric theory is either a trivial extension or likely false as a fundamental theory.

A review of this can be found at APS Physics.

Zz.

 

[ZapperZ]

T. Grover, et al., "Emergent Space-Time Supersymmetry at the Boundary of a Topological Phase" Science v.344, p.280 (2014).

Abstract: In contrast to ordinary symmetries, supersymmetry (SUSY) interchanges bosons and fermions. Originally proposed as a symmetry of our universe, it still awaits experimental verification. Here, we theoretically show that SUSY emerges naturally in condensed matter systems known as topological superconductors. We argue that the quantum phase transitions at the boundary of topological superconductors in both two and three dimensions display SUSY when probed at long distances and times. Experimental consequences include exact relations between quantities measured in disparate experiments and, in some cases, exact knowledge of the universal critical exponents. The topological surface states themselves may be interpreted as arising from spontaneously broken SUSY, indicating a deep relation between topological phases and SUSY.

This is another example where a so-called "applied" field of physics (condensed matter) is providing insight into fundamental physics. Condensed matter systems had already discovered analogs of Majorana fermions and magnetic monopoles.

Zz.

 

[Cthugha]

T. Peng, et al., "Delayed-Choice Quantum Eraser with Thermal Light" Phys. Rev. Lett. 112, 180401 (2014).

Abstract: We report a random delayed-choice quantum eraser experiment. In a Young’s double-slit interferometer, the which-slit information is learned from the photon-number fluctuation correlation of thermal light. The reappeared interference indicates that the which-slit information of a photon, or wave packet, can be “erased” by a second photon or wave packet, even after the annihilation of the first. Different from an entangled photon pair, the jointly measured two photons, or wave packets, are just two randomly distributed and randomly created photons of a thermal source that fall into the coincidence time window. The experimental observation can be explained as a nonlocal interference phenomenon in which a random photon or wave packet pair, interferes with the pair itself at distance.

The delayed choice quantum eraser is a topic which comes up quite often in this forum. It is frequently seen that people tend to assume strange things like "changing the past" in order to explain the experiment. Here is a completely classical version of the experiment using just classical light which shows that there is absolutely nothing mystical going on and everything can be explained in terms of standard physics.

 

[Andy Resnick]

G. B. Lemos, V. Borish, G. D. Cole, S. Ramelow, R. Lapkiewicz, and A. Zeilinger, "Quantum imaging with undetected photons," Nature 512, 409-412 (2014).

"Information is central to quantum mechanics. In particular, quantum interference occurs only if there exists no information to distinguish between the superposed states. The mere possibility of obtaining information that could distinguish between overlapping states inhibits quantum interference1, 2. Here we introduce and experimentally demonstrate a quantum imaging concept based on induced coherence without induced emission3, 4. Our experiment uses two separate down-conversion nonlinear crystals (numbered NL1 and NL2), each illuminated by the same pump laser, creating one pair of photons (denoted idler and signal). If the photon pair is created in NL1, one photon (the idler) passes through the object to be imaged and is overlapped with the idler amplitude created in NL2, its source thus being undefined. Interference of the signal amplitudes coming from the two crystals then reveals the image of the object. The photons that pass through the imaged object (idler photons from NL1) are never detected, while we obtain images exclusively with the signal photons (from NL1 and NL2), which do not interact with the object. Our experiment is fundamentally different from previous quantum imaging techniques, such as interaction-free imaging5 or ghost imaging6, 7, 8, 9, because now the photons used to illuminate the object do not have to be detected at all and no coincidence detection is necessary. This enables the probe wavelength to be chosen in a range for which suitable detectors are not available. To illustrate this, we show images of objects that are either opaque or invisible to the detected photons. Our experiment is a prototype in quantum information—knowledge can be extracted by, and about, a photon that is never detected."

The last few sentences of the abstract are particularly intriguing.

 

[DennisN]

The last few sentences of the abstract are particularly intriguing.

Yes, thanks for the info!
I add links here to the paper mentioned above:
Arxiv link: Quantum Imaging with Undetected Photons: http://arxiv.org/abs/1401.4318
Gabriela B. Lemos, Victoria Borish, Garrett D. Cole, Sven Ramelow, Radek Lapkiewicz, Anton Zeilinger (Submitted on 17 Jan 2014 (v1), last revised 27 Jan 2014 (this version, v2))
Nature link: http://www.nature.com/nature/journal/v512/n7515/full/nature13586.html

 

[ZapperZ]

C. Robens et al., "Ideal Negative Measurements in Quantum Walks Disprove Theories Based on Classical Trajectories" Phys. Rev. X 5, 011003 (2015).

Abstract: We report on a stringent test of the nonclassicality of the motion of a massive quantum particle, which propagates on a discrete lattice. Measuring temporal correlations of the position of single atoms performing a quantum walk, we observe a 6σ violation of the Leggett-Garg inequality. Our results rigorously excludes (i.e., falsifies) any explanation of quantum transport based on classical, well-defined trajectories. We use so-called ideal negative measurements—an essential requisite for any genuine Leggett-Garg test—to acquire information about the atom’s position, yet avoiding any direct interaction with it. The interaction-free measurement is based on a novel atom transport system, which allows us to directly probe the absence rather than the presence of atoms at a chosen lattice site. Beyond the fundamental aspect of this test, we demonstrate the application of the Leggett-Garg correlation function as a witness of quantum superposition. Here, we employ the witness to discriminate different types of walks spanning from merely classical to wholly quantum dynamics.

Don't miss a very interesting review of this work here. That link also provides a link to a free copy to the paper.

Zz.

 

[ZapperZ]

L. Tao et al., "Silicene field-effect transistors operating at room temperature", Nature Nanotechnology http://dx.doi.org/10.1038/NNANO.2014.325[/URL] (2015).

Abstract: [i]Free-standing silicene, a silicon analogue of graphene, has a buckled honeycomb lattice[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref1[/URL] and, because of its Dirac bandstructure[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref2[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref3[/URL] combined with its sensitive surface, offers the potential for a widely tunable two-dimensional monolayer, where external fields and interface interactions can be exploited to influence fundamental properties such as bandgap[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref4[/URL] and band character[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref5[/URL] for future nanoelectronic devices[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref6[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref7[/URL]. The quantum spin Hall effect[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref3[/URL], chiral superconductivity[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref8[/URL], giant magnetoresistance[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref9[/URL] and various exotic field-dependent states[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref7[/URL] have been predicted in monolayer silicene. Despite recent progress regarding the epitaxial synthesis of silicene[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref8[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref9[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref10[/URL] and investigation of its electronic properties[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref11[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref13[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref14[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref15[/URL], to date there has been no report of experimental silicene devices because of its air stability issue[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref16[/URL]. Here, we report a silicene field-effect transistor, corroborating theoretical expectations regarding its ambipolar Dirac charge transport[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref17[/URL], with a measured room-temperature mobility of ∼100 cm2 V–1 s–1 attributed to acoustic phonon-limited transport[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref18[/URL] and grain boundary scattering. These results are enabled by a growth–transfer–fabrication process that we have devised—silicene encapsulated delamination with native electrodes. This approach addresses a major challenge for material preservation of silicene during transfer and device fabrication and is applicable to other air-sensitive two-dimensional materials such as germanene[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref2[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref3[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref4[/URL] and phosphorene[URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref19[/URL], [URL]http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.325.html#ref20[/URL]. Silicene's allotropic affinity with bulk silicon and its low-temperature synthesis compared with graphene or alternative two-dimensional semiconductors suggest a more direct integration with ubiquitous semiconductor technology.[/i]

This is the first proof-of-principle demonstration of a transistor made with this material. Read a [URL='http://www.nature.com/news/graphene-s-cousin-silicene-makes-transistor-debut-1.16839']review of this work here[/URL].

Zz.

 

[at94official]

G. Gabrielse et al., Phys. Rev. Lett., 97, 030802 (2006).

New Determination of the Fine Structure Constant from the Electron g Value and QED
Also see: http://www.aip.org/enews/physnews/2006/split/783-1.html

Uhmm . . . ZZ it Seems like the link is not working anymore. :(

 

[ZapperZ]

X-L. Wang et al. "Quantum teleportation of multiple degrees of freedom of a single photon" Nature 518, 516 (2015).

Abstract: Quantum teleportationhttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref1 provides a ‘disembodied’ way to transfer quantum states from one object to another at a distant location, assisted by previously shared entangled states and a classical communication channel. As well as being of fundamental interest, teleportation has been recognized as an important element in long-distance quantum communicationhttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref2, distributed quantum networkshttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref3 and measurement-based quantum computationhttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref4, http://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref5. There have been numerous demonstrations of teleportation in different physical systems such as photonshttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref6, http://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref7, http://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref8, atomshttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref9, ionshttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref10, http://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref11, electronshttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref12 and superconducting circuitshttp://www.nature.com/nature/journal/v518/n7540/full/nature14246.html#ref13. All the previous experiments were limited to the teleportation of one degree of freedom only. However, a single quantum particle can naturally possesses various degrees of freedom—internal and external—and with coherent coupling among them. A fundamental open challenge is to teleport multiple degrees of freedom simultaneously, which is necessary to describe a quantum particle fully and, therefore, to teleport it intact. Here we demonstrate quantum teleportation of the composite quantum states of a single photon encoded in both spin and orbital angular momentum. We use photon pairs entangled in both degrees of freedom (that is, hyper-entangled) as the quantum channel for teleportation, and develop a method to project and discriminate hyper-entangled Bell states by exploiting probabilistic quantum non-demolition measurement, which can be extended to more degrees of freedom. We verify the teleportation for both spin–orbit product states and hybrid entangled states, and achieve a teleportation fidelity ranging from 0.57 to 0.68, above the classical limit. Our work is a step towards the teleportation of more complex quantum systems, and demonstrates an increase in our technical control of scalable quantum technologies.

See a review of this work at PhysicsWorld. Strangely enough, there is also free access to the actual paper, as of now (not sure if this is part of Nature's open access paper, or if this is available only for a limited time). So get it while you can!

Zz.

 

[Andy Resnick]

A. G. Manning et. al., "Wheeler's delayed-choice gedanken experiment with a single atom" Nature Physics (2015) doi:10.1038/nphys3343

Abstract:
The wave–particle dual nature of light and matter and the fact that the choice of measurement determines which one of these two seemingly incompatible behaviours we observe are examples of the counterintuitive features of quantum mechanics. They are illustrated by Wheeler’s famous ‘delayed-choice’ experimenthttp://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3343.html#ref1, recently demonstrated in a single-photon experimenthttp://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3343.html#ref2. Here, we use a single ultracold metastable helium atom in a Mach–Zehnder interferometer to create an atomic analogue of Wheeler’s original proposal. Our experiment confirms Bohr’s view that it does not make sense to ascribe the wave or particle behaviour to a massive particle before the measurement takes placehttp://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3343.html#ref1. This result is encouraging for current work towards entanglement and Bell’s theorem tests in macroscopic systems of massive particleshttp://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3343.html#ref3.

A delayed-choice experiment using massive particles.

 

[ZapperZ]

Wait I'm confused what is this about can you guys please explain

Did you read the very FIRST post in this thread?

Zz.

 

[ZapperZ]

No I'm new to this

Then you should always read the first page of any thread.

Zz.

 

[mfb]

We shouldn't forget the pentaquarks:

Observation of J/ψp Resonances Consistent with Pentaquark States in Λ⁰_b → J/ψK⁻p Decays
R. Aaij et al. (LHCb Collaboration)
Phys. Rev. Lett. 115, 072001

 

[DennisN]

What's the matter with antimatter? Well...

S. Ulmer et al., High-precision comparison of the antiproton-to-proton charge-to-mass ratio, Nature 524, 196–199 (13 August 2015) doi:10.1038/nature14861
Paper available for free here: http://www.nature.com/nature/journal/v524/n7564/full/nature14861.html

Abstract:
Invariance under the charge, parity, time-reversal (CPT) transformation is one of the fundamental symmetries of the standard model of particle physics. This CPT invariance implies that the fundamental properties of antiparticles and their matter-conjugates are identical, apart from signs. There is a deep link between CPT invariance and Lorentz symmetry—that is, the laws of nature seem to be invariant under the symmetry transformation of spacetime—although it is model dependent. A number of high-precision CPT and Lorentz invariance tests—using a co-magnetometer, a torsion pendulum and a maser, among others—have been performed, but only a few direct high-precision CPT tests that compare the fundamental properties of matter and antimatter are available. Here we report high-precision cyclotron frequency comparisons of a single antiproton and a negatively charged hydrogen ion (H⁻) carried out in a Penning trap system. From 13,000 frequency measurements we compare the charge-to-mass ratio for the antiproton

to that for the proton

and obtain

. The measurements were performed at cyclotron frequencies of 29.6 megahertz, so our result shows that the CPT theorem holds at the atto-electronvolt scale. Our precision of 69 parts per trillion exceeds the energy resolution of previous antiproton-to-proton mass comparisons as well as the respective figure of merit of the standard model extension by a factor of four. In addition, we give a limit on sidereal variations in the measured ratio of <720 parts per trillion. By following the arguments of ref. 11, our result can be interpreted as a stringent test of the weak equivalence principle of general relativity using baryonic antimatter, and it sets a new limit on the gravitational anomaly parameter of

< 8.7 × 10⁻⁷.

 

[DennisN]

And another paper published yesterday by the ALICE (A Large Ion Collider Experiment) team, concerning antimatter and CPT invariance...

ALICE Collaboration, Precision measurement of the mass difference between light nuclei and anti-nuclei, Nature Physics (2015), doi:10.1038/nphys3432
Paper available for free here: http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3432.html

Abstract:
The measurement of the mass differences for systems bound by the strong force has reached a very high precision with protons and anti-protons. The extension of such measurement from (anti-)baryons to (anti-)nuclei allows one to probe any difference in the interactions between nucleons and anti-nucleons encoded in the (anti-)nuclei masses. This force is a remnant of the underlying strong interaction among quarks and gluons and can be described by effective theories, but cannot yet be directly derived from quantum chromodynamics. Here we report a measurement of the difference between the ratios of the mass and charge of deuterons (d) and anti-deuterons (http://www.nature.com/nphys/journal/vaop/ncurrent/images/nphys3432-m1.gif), and ³He and http://www.nature.com/nphys/journal/vaop/ncurrent/images/nphys3432-m2.gif nuclei carried out with the ALICE (A Large Ion Collider Experiment) detector in Pb–Pb collisions at a centre-of-mass energy per nucleon pair of 2.76 TeV. Our direct measurement of the mass-over-charge differences confirms CPT invariance to an unprecedented precision in the sector of light nuclei. This fundamental symmetry of nature, which exchanges particles with anti-particles, implies that all physics laws are the same under the simultaneous reversal of charge(s) (charge conjugation C), reflection of spatial coordinates (parity transformation P) and time inversion (T).

 

[DennisN]

More life for the electrons...

M. Agostini et al. (Borexino Collaboration), Test of Electric Charge Conservation with Borexino
Phys. Rev. Lett. 115, 231802 – Published 3 December 2015
On arxiv: http://arxiv.org/abs/1509.01223

Abstract:
Borexino is a liquid scintillation detector located deep underground at the Laboratori Nazionali del Gran Sasso (LNGS, Italy). Thanks to the unmatched radio purity of the scintillator, and to the well understood detector response at low energy, a new limit on the stability of the electron for decay into a neutrino and a single monoenergetic photon was obtained. This new bound, τ ≥ 6.6 × 10²⁸ yr at 90% C.L., is 2 orders of magnitude better than the previous limit.

An APS synopsis is here: Synopsis: Still Waiting For Electron Decay

 

[DennisN]

B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)
Observation of Gravitational Waves from a Binary Black Hole Merger
Phys. Rev. Lett. 116, 061102 – Published 11 February 2016

Abstract:
On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10⁻²¹. It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410+160−180Mpc corresponding to a redshift z=0.09+0.03−0.04. In the source frame, the initial black hole masses are 36+5−4M⊙ and 29+4−4M⊙, and the final black hole mass is 62+4−4M⊙, with 3.0+0.5−0.5M⊙c2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

Article on APS: Viewpoint: The First Sounds of Merging Black Holes

 

[ZapperZ]

R. Pohl et al., "Laser spectroscopy of muonic deuterium" Science v.353, p.669 (2016).

Abstract: The deuteron is the simplest compound nucleus, composed of one proton and one neutron. Deuteron properties such as the root-mean-square charge radius rd and the polarizability serve as important benchmarks for understanding the nuclear forces and structure. Muonic deuterium μd is the exotic atom formed by a deuteron and a negative muon μ–. We measured three 2S-2P transitions in μd and obtain rd =

fm, which is 2.7 times more accurate but 7.5σ smaller than the CODATA-2010 value rd =

fm. The μd value is also 3.5σ smaller than the rd value from electronic deuterium spectroscopy. The smaller rd, when combined with the electronic isotope shift, yields a “small” proton radius rp, similar to the one from muonic hydrogen, amplifying the proton radius puzzle.

There is an article on Ars Technica that describes this proton radius problem in a greater detail.

Zz.

 

[ZapperZ]

A. Hamo et al., "Electron attraction mediated by Coulomb repulsion" Nature v.535, p.395 (2016).

Abstract: One of the defining properties of electrons is their mutual Coulomb repulsion. However, in solids this basic property may change; for example, in superconductors, the coupling of electrons to lattice vibrations makes the electrons attract one another, leading to the formation of bound pairs. Fifty years ago it was proposedhttp://www.nature.com/nature/journal/v535/n7612/full/nature18639.html#ref1 that electrons can be made attractive even when all of the degrees of freedom in the solid are electronic, by exploiting their repulsion from other electrons. This attraction mechanism, termed ‘excitonic’, promised to achieve stronger and more exotic superconductivity. Yet, despite an extensive search, experimental evidence for excitonic attraction has yet to be found. Here we demonstrate this attraction by constructing, from the bottom up, the fundamental building blockhttp://www.nature.com/nature/journal/v535/n7612/full/nature18639.html#ref8 of the excitonic mechanism. Our experiments are based on quantum devices made from pristine carbon nanotubes, combined with cryogenic precision manipulation. Using this platform, we demonstrate that two electrons can be made to attract each other using an independent electronic system as the ‘glue’ that mediates attraction. Owing to its tunability, our system offers insights into the underlying physics, such as the dependence of the emergent attraction on the underlying repulsion, and the origin of the pairing energy. We also demonstrate transport signatures of excitonic pairing. This experimental demonstration of excitonic pairing paves the way for the design of exotic states of matter.

Also see the News and Views article on this paper in the same issue of Nature.

So now we have two types of "glue" that can cause electrons to attraction each other in a solid. The phononic source that forms Cooper pairs in conventional superconductors, and now the excitonic glue that essentially is due to other electrons and charges in the material. This channel has been searched for for a long time, since William Little first proposed it in 1964.

Zz.

 

[ZapperZ]

L. F. Pašteka et al., "Relativistic Coupled Cluster Calculations with Variational Quantum Electrodynamics Resolve the Discrepancy between Experiment and Theory Concerning the Electron Affinity and Ionization Potential of Gold", Phys. Rev. Lett. 118, 023002 (2017).

Abstract: The first ionization potential (IP) and electron affinity (EA) of the gold atom have been determined to an unprecedented accuracy using relativistic coupled cluster calculations up to the pentuple excitation level including the Breit and QED contributions. We reach meV accuracy (with respect to the experimental values) by carefully accounting for all individual contributions beyond the standard relativistic coupled cluster approach. Thus, we are able to resolve the long-standing discrepancy between experimental and theoretical IP and EA of gold.

A review of this work can be found at the APS Physics page.

Zz.

 

[Andy Resnick]

Precise measurements of antimatter systems might cast light on why the Universe is dominated by matter. The observation of a transition in an antihydrogen atom heralds the next wave of high-precision antimatter studies.

Observation of the 1S–2S transition in trapped antihydrogen M. Ahmadi,et. al. Nature 541, 506–510 (26 January 2017) doi:10.1038/nature21040

Abstract: The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S–2S transition by Hänsch1 to a precision of a few parts in 1015. Recent technological advances have allowed us to focus on antihydrogen—the antimatter equivalent of hydrogen. The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today’s Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S–2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 × 10⁻¹⁰.

 

[ZapperZ]

J. Handsteiner et al., "Cosmic Bell Test: Measurement Settings from Milky Way Stars", Phys. Rev. Lett. v.118, p.060401 (2017).

Abstract: Bell’s theorem states that some predictions of quantum mechanics cannot be reproduced by a local-realist theory. That conflict is expressed by Bell’s inequality, which is usually derived under the assumption that there are no statistical correlations between the choices of measurement settings and anything else that can causally affect the measurement outcomes. In previous experiments, this “freedom of choice” was addressed by ensuring that selection of measurement settings via conventional “quantum random number generators” was spacelike separated from the entangled particle creation. This, however, left open the possibility that an unknown cause affected both the setting choices and measurement outcomes as recently as mere microseconds before each experimental trial. Here we report on a new experimental test of Bell’s inequality that, for the first time, uses distant astronomical sources as “cosmic setting generators.” In our tests with polarization-entangled photons, measurement settings were chosen using real-time observations of Milky Way stars while simultaneously ensuring locality. Assuming fair sampling for all detected photons, and that each stellar photon’s color was set at emission, we observe statistically significant ≳7.31σ and ≳11.93σ violations of Bell’s inequality with estimated p values of ≲1.8×10⁻¹³ and ≲4.0×10⁻³³, respectively, thereby pushing back by ∼600  years the most recent time by which any local-realist influences could have engineered the observed Bell violation.

Read the synopsis of this paper here. This paper can also be obtained for free under the Creative Commons License.

Zz.

 

[JoePhysics]

Mikhail Lemeshko, "Quasiparticle Approach to Molecules Interacting with Quantum Solvents", Phys. Rev. Lett. v.118, p.095301, (2017).

arXiv pre-print here.

Abstract: Understanding the behavior of molecules interacting with superfluid helium represents a formidable challenge and, in general, requires approaches relying on large-scale numerical simulations. Here, we demonstrate that experimental data collected over the last 20 years provide evidence that molecules immersed in superfluid helium form recently predicted angulon quasiparticles [Phys. Rev. Lett. 114, 203001 (2015)]. Most important, casting the many-body problem in terms of angulons amounts to a drastic simplification and yields effective molecular moments of inertia as straightforward analytic solutions of a simple microscopic Hamiltonian. The outcome of the angulon theory is in good agreement with experiment for a broad range of molecular impurities, from heavy to medium-mass to light species. These results pave the way to understanding molecular rotation in liquid and crystalline phases in terms of the angulon quasiparticle.

Also featured on phys.org.

 

[ZapperZ]

G. Rubino et al., "Experimental verification of an indefinite causal order", Sci. Adv., 3, e1602589 (2017).

Abstract: Investigating the role of causal order in quantum mechanics has recently revealed that the causal relations of events may not be a priori well defined in quantum theory. Although this has triggered a growing interest on the theoretical side, creating processes without a causal order is an experimental task. We report the first decisive demonstration of a process with an indefinite causal order. To do this, we quantify how incompatible our setup is with a definite causal order by measuring a “causal witness.” This mathematical object incorporates a series of measurements that are designed to yield a certain outcome only if the process under examination is not consistent with any well-defined causal order. In our experiment, we perform a measurement in a superposition of causal orders—without destroying the coherence—to acquire information both inside and outside of a “causally nonordered process.” Using this information, we experimentally determine a causal witness, demonstrating by almost 7 SDs that the experimentally implemented process does not have a definite causal order.

You may get the full paper here while it is available for free on Sci. Adv. Press release can be found here.

Zz.

 

[ZapperZ]

D. Akimov et al., "Observation of coherent elastic neutrino-nucleus scattering" Science 10.1126/science.aao0990 (2017).

Abstract: The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross-section is the largest by far of all low-energy neutrino couplings. This mode of interaction provides new opportunities to study neutrino properties, and leads to a miniaturization of detector size, with potential technological applications. We observe this process at a 6.7-sigma confidence level, using a low-background, 14.6-kg CsI[Na] scintillator exposed to the neutrino emissions from the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the Standard Model for this process, are observed in high signal-to-background conditions. Improved constraints on non-standard neutrino interactions with quarks are derived from this initial dataset.

As of now, you may get the full copy of the paper at the Science website.

Zz.

 

[ZapperZ]

M. Ahmadi, et. al., "Observation of the hyperfine spectrum of antihydrogen" Nature v.548, p.66 (2017).

Abstract: The observation of hyperfine structure in atomic hydrogen by Rabi and co-workers1, 2, 3 and the measurement4 of the zero-field ground-state splitting at the level of seven parts in 10¹³ are important achievements of mid-twentieth-century physics. The work that led to these achievements also provided the first evidence for the anomalous magnetic moment of the electron5, 6, 7, 8, inspired Schwinger’s relativistic theory of quantum electrodynamics9, 10 and gave rise to the hydrogen maser11, which is a critical component of modern navigation, geo-positioning and very-long-baseline interferometry systems. Research at the Antiproton Decelerator at CERN by the ALPHA collaboration extends these enquiries into the antimatter sector. Recently, tools have been developed that enable studies of the hyperfine structure of antihydrogen12—the antimatter counterpart of hydrogen. The goal of such studies is to search for any differences that might exist between this archetypal pair of atoms, and thereby to test the fundamental principles on which quantum field theory is constructed. Magnetic trapping of antihydrogen atoms13, 14 provides a means of studying them by combining electromagnetic interaction with detection techniques that are unique to antimatter12, 15. Here we report the results of a microwave spectroscopy experiment in which we probe the response of antihydrogen over a controlled range of frequencies. The data reveal clear and distinct signatures of two allowed transitions, from which we obtain a direct, magnetic-field-independent measurement of the hyperfine splitting. From a set of trials involving 194 detected atoms, we determine a splitting of 1,420.4 ± 0.5 megahertz, consistent with expectations for atomic hydrogen at the level of four parts in 10⁴. This observation of the detailed behaviour of a quantum transition in an atom of antihydrogen exemplifies tests of fundamental symmetries such as charge–parity–time in antimatter, and the techniques developed here will enable more-precise such tests.

The paper is open access. You may read the entire paper at the Nature website. An overview of the result can be found here.

Zz.

 

[ISamson]

Why just a thread? Wouldn't this make a good category?

I agree. This thread would really make a great category.

 

[mfb]

What is a category?

Individual papers can always get discussed in separate threads in their corresponding subforums.

 

[Amrator]

The Pierre Auger Collaboration et al., Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 10¹⁸ eV, Science, Vol. 357, pp. 1266-1270, (2017)

Abstract: Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using 3 × 10⁴ cosmic rays with energies above 8 × 10¹⁸ electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 km² sr year, we determined the existence of anisotropy in arrival directions. The anisotropy, detected at more than a 5.2σ level of significance, can be described by a dipole with an amplitude of

percent toward right ascension α_d = 100 ± 10 degrees and declination δ_d =

degrees. That direction indicates an extragalactic origin for these ultrahigh-energy particles.

Science website (requires subscribtion): http://science.sciencemag.org/content/357/6357/1266/tab-article-info

arXiv: https://arxiv.org/abs/1709.07321

 

[ZapperZ]

The Pierre Auger Collaboration
Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 10¹⁸ eV
Science 22 Sep. 2017
DOI: 10.1126/science.aan4338

Abstract: Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using 3 × 104 cosmic rays with energies above 8 × 1018 electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 km2 sr year, we determined the existence of anisotropy in arrival directions. The anisotropy, detected at more than a 5.2σ level of significance, can be described by a dipole with an amplitude of View attachment 211636 percent toward right ascension αd = 100 ± 10 degrees and declination δd = View attachment 211637 degrees. That direction indicates an extragalactic origin for these ultrahigh-energy particles.

You should try to follow the format outlined in the first post to be consistent, in case the link doesn’t work in the future.

Zz.

 

[Amrator]

You should try to follow the format outlined in the first post to be consistent, in case the link doesn’t work in the future.

Zz.

Oops, I apologize. I will fix it.

 

[ZapperZ]

W.B. Cairncross et al., "Precision Measurement of the Electron’s Electric Dipole Moment Using Trapped Molecular Ions", Phys. Rev. Lett. v.119, p.153001 (2017).

Abstract: We describe the first precision measurement of the electron’s electric dipole moment (d_e) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on ¹⁸⁰Hf¹⁹F⁺ in its metastable ³Δ₁ electronic state, we obtain d_e=(0.9±7.7stat±1.7syst)×10⁻²⁹  e cm, resulting in an upper bound of |d_e|<1.3×10⁻²⁸  e cm (90% confidence). Our result provides independent confirmation of the current upper bound of |d_e|<9.4×10⁻²⁹  e cm [J. Baron et al., New J. Phys. 19, 073029 (2017)], and offers the potential to improve on this limit in the near future.

Read the Physics Viewpoint article here.

We get frequent posts about people questioning the validity of "point particle" within QED. These types of experiments that try to look for the existence of the electric dipole moment are strongly consistent with this point particle picture. So any question on its validity must address the fact that all of these increasingly-precise measurements are not finding any internal structure within an electron.

Zz.

 

[mfb]

We get frequent posts about people questioning the validity of "point particle" within QED. These types of experiments that try to look for the existence of the electric dipole moment are strongly consistent with this point particle picture. So any question on its validity must address the fact that all of these increasingly-precise measurements are not finding any internal structure within an electron.

The g-2 experiments are very convincing in that aspect as well.

Muon g-2 started taking data a few months ago.

 

[Qamerash]

A nice topic, i'll continue to focus on that