Recent Noteworthy Physics Papers

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P.J. Mohr and D.B. Newell, "The physics of fundamental constants", Am. J. Phys. v.78, p.338 (2010).

Abstract: This Resource Letter provides a guide to the literature on the physics of fundamental constants and their values as determined within the International System of Units (SI). Journal articles, books, and websites that provide relevant information are surveyed. Literature on redefining the SI in terms of exact values of fundamental constants is also included.

A very useful paper to have and to keep. Not only does it describe all of the major fundamental constants of our universe that we know of so far, but it also describes how they are measured/determined, AND gives you a boatload of references along with each of these constants.

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M. Rypdal and K. Rypdal, "Testing Hypotheses about Sun-Climate Complexity Linking", Phys. Rev. Lett. v.104, p.128501 (2010).

Abstract: We reexamine observational evidence presented in support of the hypothesis of a sun-climate complexity linking by N. Scafetta and B. J. West, Phys. Rev. Lett. 90, 248701 (2003), which contended that the integrated solar flare index (SFI) and the global temperature anomaly (GTA) both follow Lévy walk statistics with the same waiting-time exponent μ≈2.1. However, their analysis does not account for trends in the signal, cannot deal correctly with infinite variance processes (Lévy flights), and suffers from considering only the second moment. Our analysis shows that properly detrended, the integrated SFI is well described as a Lévy flight, and the integrated GTA as a persistent fractional Brownian motion. These very different stochastic properties of the solar and climate records do not support the hypothesis of a sun-climate complexity linking.

The preprint of the manuscript can be found here. Ars Technica also has a report on this paper.

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S. Pironio et al., "Random numbers certified by Bell’s theorem", Nature v.464, p.1021 (2010).

Abstract: Randomness is a fundamental feature of nature and a valuable resource for applications ranging from cryptography and gambling to numerical simulation of physical and biological systems. Random numbers, however, are difficult to characterize mathematically, and their generation must rely on an unpredictable physical process. Inaccuracies in the theoretical modelling of such processes or failures of the devices, possibly due to adversarial attacks, limit the reliability of random number generators in ways that are difficult to control and detect. Here, inspired by earlier work on non-locality-based and device-independent quantum information processing, we show that the non-local correlations of entangled quantum particles can be used to certify the presence of genuine randomness. It is thereby possible to design a cryptographically secure random number generator that does not require any assumption about the internal working of the device. Such a strong form of randomness generation is impossible classically and possible in quantum systems only if certified by a Bell inequality violation15. We carry out a proof-of-concept demonstration of this proposal in a system of two entangled atoms separated by approximately one metre. The observed Bell inequality violation, featuring near perfect detection efficiency, guarantees that 42 new random numbers are generated with 99 per cent confidence. Our results lay the groundwork for future device-independent quantum information experiments and for addressing fundamental issues raised by the intrinsic randomness of quantum theory.

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T. Hanaguri et al., "Unconventional s-Wave Superconductivity in Fe(Se,Te)", Science v.328, p.474 (2010).

Abstract: The superconducting state is characterized by a pairing of electrons with a superconducting gap on the Fermi surface. In iron-based superconductors, an unconventional pairing state has been argued for theoretically. We used scanning tunneling microscopy on Fe(Se,Te) single crystals to image the quasi-particle scattering interference patterns in the superconducting state. By applying a magnetic field to break the time-reversal symmetry, the relative sign of the superconducting gap can be determined from the magnetic-field dependence of quasi-particle scattering amplitudes. Our results indicate that the sign is reversed between the hole and the electron Fermi-surface pockets (s±-wave), favoring the unconventional pairing mechanism associated with spin fluctuations.

It is an amazing experiment. Not only have they clearly measured the pairing symmetry for the Cooper pairs in this family of superconductors, but they managed to detect the unusual and difficult-to-measure s±-wave symmetry! To my knowledge, this is the first time someone has experimentally determined this symmetry, using STM no less!

There is also a review article on this work written by J.E. Hoffman in the same issue of Science.

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I. Afek et al., "High-NOON States by Mixing Quantum and Classical Light", Science v.328, p.879 (2010).

Abstract: Precision measurements can be brought to their ultimate limit by harnessing the principles of quantum mechanics. In optics, multiphoton entangled states, known as NOON states, can be used to obtain high-precision phase measurements, becoming more and more advantageous as the number of photons grows. We generated "high-NOON" states (N = 5) by multiphoton interference of quantum down-converted light with a classical coherent state in an approach that is inherently scalable. Super-resolving phase measurements with up to five entangled photons were produced with a visibility higher than that obtainable using classical light only.

Read a perspective article on this work in the same issue of Science. A summary of this work can also be found on the PhysicsWorld website.

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Cthugha

C. L. Salter et al., "An entangled-light-emitting diode", Nature v.465, p.594 (2010).

Abstract: A quantum computer based on optical processes requires a source of entangled photons that can be delivered efficiently on demand. Such a source has now been developed: it involves a compact light-emitting diode with an embedded quantum dot that can be driven electrically to generate entangled photon pairs.

I already heard Mark Stevenson give a talk on this topic at QD 2010 and it was pretty obvious that it would just be a matter of time until we see the results in one of the big two journals. The realization of a semiconductor based, electrically pumped entangled photon source is one huge step to take entangled photons out of the lab and into the "real world", including commercial usage.

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J.T. Stewart et al., "Verification of Universal Relations in a Strongly Interacting Fermi Gas", Phys. Rev. Lett. 104, 235301 (2010).

Abstract: Many-body fermion systems are important in many branches of physics, including condensed matter, nuclear, and now cold atom physics. In many cases, the interactions between fermions can be approximated by a contact interaction. A recent theoretical advance in the study of these systems is the derivation of a number of exact universal relations that are predicted to be valid for all interaction strengths, temperatures, and spin compositions. These equations, referred to as the Tan relations, relate a microscopic quantity, namely, the amplitude of the high-momentum tail of the fermion momentum distribution, to the thermodynamics of the many-body system. In this work, we provide experimental verification of the Tan relations in a strongly interacting gas of fermionic atoms by measuring both the microscopic and macroscopic quantities in the same system.

You may read the Viewpoint article on this work here, and also get a free download of the actual publication.

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J.-P. Bocquet et al. "Limits on Light-Speed Anisotropies from Compton Scattering of High-Energy Electrons", Phys. Rev. Lett. v.104, p.241601 (2010).

Abstract: The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the European Synchrotron Radiation Facility’s GRAAL facility constrains such anisotropies representing the first nonthreshold collision-kinematics study of Lorentz violation. When interpreted within the minimal standard-model extension, this result yields the two-sided limit of 1.6×10^-14 at 95% confidence level on a combination of the parity-violating photon and electron coefficients (κ˜o+)YZ, (κ˜o+)ZX, cTX, and cTY. This new constraint provides an improvement over previous bounds by 1 order of magnitude.

The ArXiv version can be found here.

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*Count Iblis*

T. Goldman, Neutrino Oscillations and Energy-Momentum Conservation, Mod. Phys. Lett. A25, 479 (2010).

Abstract:

A description of neutrino oscillation phenomena is presented which is based on relativistic quantum mechanics and includes both entangled state and source dependent aspects, unlike both of the conventional approaches which use either equal energies or equal momenta for the different neutrino mass eigenstates. To second order in the neutrino masses, the standard result is recovered thus showing an absence of source dependence to this order. The time dependence of the wavefunction is found to be crucial to recovering the conventional result. An ambiguity appears at fourth order in the neutrino masses which generally leads to source dependence, but the standard formula can be promoted to this order by a plausible convention.

Preprint version.

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T. van Zoest et al., "Bose-Einstein Condensation in Microgravity", Science v.328, p.1540 (2010).

Abstract: Albert Einstein’s insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.

Also see the Perspective article on this paper in the same issue of Science.

A presentation viewgraphs by one of the authors can be found here.

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ZapperZ

U. Sinha et al., "Ruling Out Multi-Order Interference in Quantum Mechanics, Science v.329, p.418 (2010).

Abstract:Quantum mechanics and gravitation are two pillars of modern physics. Despite their success in describing the physical world around us, they seem to be incompatible theories. There are suggestions that one of these theories must be generalized to achieve unification. For example, Born’s rule—one of the axioms of quantum mechanics—could be violated. Born’s rule predicts that quantum interference, as shown by a double-slit diffraction experiment, occurs from pairs of paths. A generalized version of quantum mechanics might allow multipath (i.e., higher-order) interference, thus leading to a deviation from the theory. We performed a three-slit experiment with photons and bounded the magnitude of three-path interference to less than 10^–2 of the expected two-path interference, thus ruling out third- and higher-order interference and providing a bound on the accuracy of Born’s rule. Our experiment is consistent with the postulate both in semiclassical and quantum regimes.

Review of this work can be found at PhysOrg and PhysicsWorld.

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ultrafast

I imagine APS' Physics site showcases many of these papers.

ZapperZ

Quote by ultrafast

I imagine APS' Physics site showcases many of these papers.

That site highlights only papers published in the APS journals (Physical Review family), since they provide free access to those papers.

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ZapperZ

E. Haller et al., "Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons", Nature v.466, p.597 (2010).

Abstract: Quantum many-body systems can have phase transitions even at zero temperature; fluctuations arising from Heisenberg’s uncertainty principle, as opposed to thermal effects, drive the system from one phase to another. Typically, during the transition the relative strength of two competing terms in the system’s Hamiltonian changes across a finite critical value. A well-known example is the Mott–Hubbard quantum phase transition from a superfluid to an insulating phase, which has been observed for weakly interacting bosonic atomic gases. However, for strongly interacting quantum systems confined to lower-dimensional geometry, a novel type of quantum phase transition may be induced and driven by an arbitrarily weak perturbation to the Hamiltonian. Here we observe such an effect—the sine–Gordon quantum phase transition from a superfluid Luttinger liquid to a Mott insulator, —in a one-dimensional quantum gas of bosonic caesium atoms with tunable interactions. For sufficiently strong interactions, the transition is induced by adding an arbitrarily weak optical lattice commensurate with the atomic granularity, which leads to immediate pinning of the atoms. We map out the phase diagram and find that our measurements in the strongly interacting regime agree well with a quantum field description based on the exactly solvable sine–Gordon model. We trace the phase boundary all the way to the weakly interacting regime, where we find good agreement with the predictions of the one-dimensional Bose–Hubbard model. Our results open up the experimental study of quantum phase transitions, criticality and transport phenomena beyond Hubbard-type models in the context of ultracold gases.

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J. Leach et al., "Quantum Correlations in Optical Angle–Orbital Angular Momentum Variables", Science v.329, p.662 (2010).

Abstract: Entanglement of the properties of two separated particles constitutes a fundamental signature of quantum mechanics and is a key resource for quantum information science. We demonstrate strong Einstein, Podolsky, and Rosen correlations between the angular position and orbital angular momentum of two photons created by the nonlinear optical process of spontaneous parametric down-conversion. The discrete nature of orbital angular momentum and the continuous but periodic nature of angular position give rise to a special sort of entanglement between these two variables. The resulting correlations are found to be an order of magnitude stronger than those allowed by the uncertainty principle for independent (nonentangled) particles. Our results suggest that angular position and orbital angular momentum may find important applications in quantum information science.

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ZapperZ

O. Ben-David et al., "The Dynamics of the Onset of Frictional Slip", Science v.330, p.211 (2010).

Abstract: The way in which a frictional interface fails is critical to our fundamental understanding of failure processes in fields ranging from engineering to the study of earthquakes. Frictional motion is initiated by rupture fronts that propagate within the thin interface that separates two sheared bodies. By measuring the shear and normal stresses along the interface, together with the subsequent rapid real-contact-area dynamics, we find that the ratio of shear stress to normal stress can locally far exceed the static-friction coefficient without precipitating slip. Moreover, different modes of rupture selected by the system correspond to distinct regimes of the local stress ratio. These results indicate the key role of nonuniformity to frictional stability and dynamics with implications for the prediction, selection, and arrest of different modes of earthquakes.

We get frequent questions on the origin of friction and when things start to slip. This shows that even on something that we know at the "macroscopic" level, there's still a lot to learn at the microscopic scale.

Edit: The Science webpage has a tag that says "FREE Full Text" for this paper. I don't know if you get to see this paper for free, but here's the link to it.

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I. Altfeder et al., "Vacuum Phonon Tunneling", Phys. Rev. Lett. v.105, p.166101 (2010).

Abstract: Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

A Physical Review Focus article of this work can be found here.

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ultrafast	I imagine APS' Physics site showcases many of these papers.