Recent Noteworthy Physics Papers

[ZapperZ]

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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[ZapperZ]

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 http://physicsworld.com/cws/article/news/42612" .

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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.

 

[ZapperZ]

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 http://physics.aps.org/articles/v3/48" , and also get a free download of the actual publication.

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[ZapperZ]

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 http://arxiv.org/PS_cache/arxiv/pdf/1005/1005.5230v2.pdf" .

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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.

http://arxiv.org/abs/hep-ph/9604357"

 

[ZapperZ]

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 http://www.sif.it/SIF/resources/public/files/va2009/seidel_0630.pdf" .

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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 http://www.physorg.com/news199009831.html" .

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[ultrafast]

I imagine APS' http://physics.aps.org/" showcases many of these papers.

 

[ZapperZ]

I imagine APS' http://physics.aps.org/" 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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[ZapperZ]

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 http://www.sciencemag.org/cgi/content/abstract/330/6001/211?ijkey=7469109e591af519fde2f5aef4db1ed7c25df273&keytype2=tf_ipsecsha".

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[ZapperZ]

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 http://focus.aps.org/story/v26/st15" .

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[ZapperZ]

L.A. Wray et al., "Observation of topological order in a superconducting doped topological insulator", Nature Physics v.6, p.855 (2010).

Abstract: [1]Experimental observation of topological order in three-dimensional bulk solids has recently led to a flurry of research activity. Unlike the two-dimensional electron gas or quantum Hall systems, three-dimensional topological insulators can harbour superconductivity and magnetism, making it possible to study the interplay between topologically ordered phases and broken-symmetry states. One outcome of this interplay is the possible realization of Majorana fermions—quasiparticles that are their own antiparticles—on topological surfaces, which is of great interest in fundamental physics. Here we present measurements of the bulk and surface electron dynamics in Bi2Se3 doped with copper with a transition temperature Tc up to 3.8 K, observing its topological character for the first time. Our data show that superconductivity occurs in a bulk relativistic quasiparticle regime where an unusual doping mechanism causes the spin-polarized topological surface states to remain well preserved at the Fermi level of the superconductor where Cooper pairing takes place. These results suggest that the electron dynamics in superconducting Bi2Se3 are suitable for trapping non-Abelian Majorana fermions. Details of our observations constitute important clues for developing a general theory of topological superconductivity in doped topological insulators.[/i]

A review of this paper http://news.softpedia.com/news/Split-Personality-Material-Found-at-Princeton-164508.shtml".

It won't be surprising if the Majorana fermions are first found in such a condensed matter system.

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[ZapperZ]

D.J. Toms, "Quantum gravitational contributions to quantum electrodynamics", Nature v.468, p.56 (2010).

Abstract: Quantum electrodynamics describes the interactions of electrons and photons. Electric charge (the gauge coupling constant) is energy dependent, and there is a previous claim that charge is affected by gravity (described by general relativity) with the implication that the charge is reduced at high energies. However, that claim has been very controversial and the matter has not been settled. Here I report an analysis (free from the earlier controversies) demonstrating that quantum gravity corrections to quantum electrodynamics have a quadratic energy dependence that result in the electric charge vanishing at high energies, a result known as asymptotic freedom.

A review of this work http://www.nature.com/news/2010/101103/full/news.2010.580.html" (link open for free only for a limited time).

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[Kurdt]

D.J. Toms, "Quantum gravitational contributions to quantum electrodynamics", Nature v.468, p.56 (2010).

Abstract: Quantum electrodynamics describes the interactions of electrons and photons. Electric charge (the gauge coupling constant) is energy dependent, and there is a previous claim that charge is affected by gravity (described by general relativity) with the implication that the charge is reduced at high energies. However, that claim has been very controversial and the matter has not been settled. Here I report an analysis (free from the earlier controversies) demonstrating that quantum gravity corrections to quantum electrodynamics have a quadratic energy dependence that result in the electric charge vanishing at high energies, a result known as asymptotic freedom.

A review of this work http://www.nature.com/news/2010/101103/full/news.2010.580.html" (link open for free only for a limited time).

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The pre-print is on arXiv at the following link:

http://arxiv.org/abs/1010.0793

 

[Cthugha]

R. Ahuja et al., "Relativity and the Lead-Acid Battery", Phys. Rev. Lett. v.106, p.018301 (2011).

Abstract: The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7–1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.

This is a good demonstration that there are devices used every day - like the lead-acid battery, which are still not understood ab-initio today and much more complex than one might imagine. In this case relativistic effects become important. Also, the concluding sentence of the paper: "Finally, we note that cars start due to relativity." is one of the funniest paper endings I have read recently.

 

[teopze]

R. Ahuja et al., "Relativity and the Lead-Acid Battery", Phys. Rev. Lett. v.106, p.018301 (2011).

Abstract: The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7–1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.

This is a good demonstration that there are devices used every day - like the lead-acid battery, which are still not understood ab-initio today and much more complex than one might imagine. In this case relativistic effects become important. Also, the concluding sentence of the paper: "Finally, we note that cars start due to relativity." is one of the funniest paper endings I have read recently.

I'm glad you like the ending :)

Although we did expect relativity to have some impact on the EMF of the lead-acid battery it was a surprise to find out that relativity accounts for such a major part of the voltage. Thanks for posting the paper on Physics Forums. All the best. PZE

 

[ZapperZ]

That certainly is a very catchy ending! :)

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[ZapperZ]

D. Fausti et al., "Light-Induced Superconductivity in a Stripe-Ordered Cuprate", Science v.331, p.189 (2011).

Abstract: One of the most intriguing features of some high-temperature cuprate superconductors is the interplay between one-dimensional “striped” spin order and charge order, and superconductivity. We used mid-infrared femtosecond pulses to transform one such stripe-ordered compound, nonsuperconducting $La_{1.675}Eu_{0.2}Sr_{0.125}CuO_4$, into a transient three-dimensional superconductor. The emergence of coherent interlayer transport was evidenced by the prompt appearance of a Josephson plasma resonance in the c-axis optical properties. An upper limit for the time scale needed to form the superconducting phase is estimated to be 1 to 2 picoseconds, which is significantly faster than expected. This places stringent new constraints on our understanding of stripe order and its relation to superconductivity.

News report of it can be found here:

http://www.theengineer.co.uk/news/light-turns-insulator-into-a-superconductor/1006901.article

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[ZapperZ]

R. Ahuja et al., "Relativity and the Lead-Acid Battery", Phys. Rev. Lett. v.106, p.018301 (2011).

Abstract: The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7–1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.

This is a good demonstration that there are devices used every day - like the lead-acid battery, which are still not understood ab-initio today and much more complex than one might imagine. In this case relativistic effects become important. Also, the concluding sentence of the paper: "Finally, we note that cars start due to relativity." is one of the funniest paper endings I have read recently.

I'm glad you like the ending :)

Although we did expect relativity to have some impact on the EMF of the lead-acid battery it was a surprise to find out that relativity accounts for such a major part of the voltage. Thanks for posting the paper on Physics Forums. All the best. PZE

That certainly is a very catchy ending! :)

Zz.

In case people missed it, there's a very nice review of this work in the http://focus.aps.org/story/v27/st2" section.

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[ZapperZ]

S. Mark et al., "Fully Electrical Read-Write Device Out of a Ferromagnetic Semiconductor", Phys. Rev. Lett. v.106, p.057204 (2011).

Abstract: We report the realization of a read-write device out of the ferromagnetic semiconductor (Ga,Mn)As as the first step to a fundamentally new information processing paradigm. Writing the magnetic state is achieved by current-induced switching and readout of the state is done by the means of the tunneling anisotropic magnetoresistance effect. This 1 bit demonstrator device can be used to design an electrically programmable memory and logic device.

See accompanying http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.057204" , which also gives you access to obtain the paper.

BTW, if you encounter people who think that physics doesn't produce anything with real applications, show this!

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[piareround]

Ok I know most people post really recent physics papers. However, this paper was done in 2006 and, as a college student myself, I think is a great teaching reasource to help student in understand angular momentum in quantum mechanics.

"Integer Versus Half-Integer Angular Momentum", Am. J. Phys, 74, 191-192 (2006).

 

[ZapperZ]

P. San-Jose et al, "Electron-Induced Rippling in Graphene", Phys. Rev. Lett. v.106, p.045502 (2011).

Abstract: We show that the interaction between flexural phonons, when corrected by the exchange of electron-hole excitations, may drive the graphene sheet into a quantum critical point characterized by the vanishing of the bending rigidity of the membrane. Ripples arise then due to spontaneous symmetry breaking, following a mechanism similar to that responsible for the condensation of the Higgs field in relativistic field theories, and leading to a zero-temperature buckling transition in which the order parameter is given by the square of the gradient of the flexural phonon field.

In other words, they think we can find hints of the Higgs field in graphene! http://physicsworld.com/cws/article/news/44994" .

This is why condensed matter systems, such as the recently discovered topological insulators, are so interesting and important, and another example where condensed matter physics contributes to fundamental physics.

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[ZapperZ]

A. O. Sushkov et al., "Observation of the thermal Casimir force", Nature Physics doi:10.1038/nphys1909.

Abstract: Quantum theory predicts the existence of the Casimir force between macroscopic bodies, a force arising from the zero-point energy of electromagnetic field modes around them. A thermal Casimir force, due to thermal rather than quantum fluctuations of the electromagnetic field at finite temperature, was theoretically predicted long ago. Here we report the experimental observation of the thermal Casimir force between two gold plates. We measured the attractive force between a flat and a spherical plate for separations between 0.7 μm and 7 μm. An electrostatic force caused by potential patches on the plates’ surfaces is included in the analysis. Previous measurements of the quantum-fluctuation-induced force have been unable to clearly settle the question of whether the correct low-frequency form of the dielectric constant dispersion for calculating Casimir forces is the Drude model or the plasma model. Our experimental results are in excellent agreement (reduced χ2 of 1.04) with the Casimir force calculated using the Drude model, including the T=300 K thermal force, which dominates over the quantum fluctuation-induced force at separations greater than 3 μm. The plasma model result is excluded in the measured separation range.

See a review of this work at http://physicsworld.com/cws/article/news/45048" .

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[Cthugha]

S. S. Hodgman et al., "Direct Measurement of Long-Range Third-Order Coherence in Bose-Einstein Condensates", Science v.331, p.1046 (2011).

Abstract: A major advance in understanding the behavior of light was to describe the coherence of a light source by using correlation functions that define the spatio-temporal relationship between pairs and larger groups of photons. Correlations are also a fundamental property of matter. We performed simultaneous measurement of the second- and third-order correlation functions for atoms. Atom bunching in the arrival time for pairs and triplets of thermal atoms just above the Bose-Einstein condensation (BEC) temperature was observed. At lower temperatures, we demonstrated conclusively the long-range coherence of the BEC for correlation functions to third order, which supports the prediction that like coherent light, a BEC possesses long-range coherence to all orders.

 

[ZapperZ]

F. L. Pratt et al., "Magnetic and non-magnetic phases of a quantum spin liquid", Nature v.471, p.612 (2011).

Abstract: A quantum spin-liquid phase is an intriguing possibility for a system of strongly interacting magnetic units in which the usual magnetically ordered ground state is avoided owing to strong quantum fluctuations. It was first predicted theoretically for a triangular-lattice model with antiferromagnetically coupled S = 1/2 spins1. Recently, materials have become available showing persuasive experimental evidence for such a state2. Although many studies show that the ideal triangular lattice of S = 1/2 Heisenberg spins actually orders magnetically into a three-sublattice, non-collinear 120° arrangement, quantum fluctuations significantly reduce the size of the ordered moment3. This residual ordering can be completely suppressed when higher-order ring-exchange magnetic interactions are significant, as found in nearly metallic Mott insulators4. The layered molecular system κ-(BEDT-TTF)2Cu2(CN)3 is a Mott insulator with an almost isotropic, triangular magnetic lattice of spin-1/2 BEDT-TTF dimers5 that provides a prime example of a spin liquid formed in this way6, 7, 8, 9, 10, 11. Despite a high-temperature exchange coupling, J, of 250 K (ref. 6), no obvious signature of conventional magnetic ordering is seen down to 20 mK (refs 7, 8). Here we show, using muon spin rotation, that applying a small magnetic field to this system produces a quantum phase transition between the spin-liquid phase and an antiferromagnetic phase with a strongly suppressed moment. This can be described as Bose–Einstein condensation of spin excitations with an extremely small spin gap. At higher fields, a second transition is found that suggests a threshold for deconfinement of the spin excitations. Our studies reveal the low-temperature magnetic phase diagram and enable us to measure characteristic critical properties. We compare our results closely with current theoretical models, and this gives some further insight into the nature of the spin-liquid phase.

Also see a review of this work in the News and Views section of the same issue of Nature on page 587.

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[harrylin]

Hans De Raedt et al: "Extended Boole-Bell inequalities applicable to quantum theory"
J. Comp. Theor. Nanosci. Vol. 8, No.6, p.1011, (2011)
http://www.ingentaconnect.com/content/asp/jctn/2011/00000008/00000006/art00013

Full text also in http://arxiv.org/abs/0901.2546

Abstract:
We address the basic meaning of apparent contradictions of quantum theory and probability frameworks as expressed by Bell's inequalities. We show that these contradictions have their origin in the incomplete considerations of the premises of the derivation of the inequalities. A careful consideration of past work, including that of Boole and Vorob'ev, has lead us to the formulation of extended Boole-Bell inequalities that are binding for both classical and quantum models. The Einstein-Podolsky-Rosen-Bohm gedanken experiment and a macroscopic quantum coherence experiment proposed by Leggett and Garg are both shown to obey the extended Boole-Bell inequalities. These examples as well as additional discussions also provide reasons for apparent violations of these inequalities.

This paper challenges Bell's Theorem about reality and locality. Discussion thread:
https://www.physicsforums.com/showthread.php?t=499002

 

[ZapperZ]

J.J. Hudson et al., "Improved measurement of the shape of the electron", Nature v.473, p. 493 (2011).

Abstract: The electron is predicted to be slightly aspheric1, with a distortion characterized by the electric dipole moment (EDM), de. No experiment has ever detected this deviation. The standard model of particle physics predicts that de is far too small to detect2, being some eleven orders of magnitude smaller than the current experimental sensitivity. However, many extensions to the standard model naturally predict much larger values of de that should be detectable3. This makes the search for the electron EDM a powerful way to search for new physics and constrain the possible extensions. In particular, the popular idea that new supersymmetric particles may exist at masses of a few hundred GeV/c2 (where c is the speed of light) is difficult to reconcile with the absence of an electron EDM at the present limit of sensitivity2, 4. The size of the EDM is also intimately related to the question of why the Universe has so little antimatter. If the reason is that some undiscovered particle interaction5 breaks the symmetry between matter and antimatter, this should result in a measurable EDM in most models of particle physics2. Here we use cold polar molecules to measure the electron EDM at the highest level of precision reported so far, providing a constraint on any possible new interactions. We obtain de = (−2.4 ± 5.7stat ± 1.5syst) × 10−28e cm, where e is the charge on the electron, which sets a new upper limit of |de| < 10.5 × 10−28e cm with 90 per cent confidence. This result, consistent with zero, indicates that the electron is spherical at this improved level of precision. Our measurement of atto-electronvolt energy shifts in a molecule probes new physics at the tera-electronvolt energy scale2.

Read the News reports at (open for a limited time)

http://www.nature.com/nature/journal/v473/n7348/full/nature10104.html

A News and Views on this work written by A. Leanhardt can also also be found in the same Nature issue.

The PhysicsWorld report on this work can be found here (you may need to register to view this later on):

http://physicsworld.com/cws/article/news/46085

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[ZapperZ]

S. Kocsis et al.,"Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer", Science v.332, p.1170 (2011).

Abstract: A consequence of the quantum mechanical uncertainty principle is that one may not discuss the path or “trajectory” that a quantum particle takes, because any measurement of position irrevocably disturbs the momentum, and vice versa. Using weak measurements, however, it is possible to operationally define a set of trajectories for an ensemble of quantum particles. We sent single photons emitted by a quantum dot through a double-slit interferometer and reconstructed these trajectories by performing a weak measurement of the photon momentum, postselected according to the result of a strong measurement of photon position in a series of planes. The results provide an observationally grounded description of the propagation of subensembles of quantum particles in a two-slit interferometer.

Press release on this work http://www.physorg.com/news/2011-06-quantum-physics-photons-two-slit-interferometer.html" .

Astounding piece of work and the use of the weak measurement technique. This is another example where one has to understand the non-commutative operator principle of the "First Quantization" to be able to comprehend what they are doing.

If this work holds up, it might possibly be the first indication that there's something to the Bohm-de Broglie picture of quantum mechanics.

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[ZapperZ]

On the heels of the measurement of the average trajectory taken in a double-slit experiment using the weak measurement technique, along comes another report on a fundamental measurement in QM, also using the weak measurement. This time, they made a "direct" measurement of the QM wavefunction itself!

J.S. Lundeen et al., "Direct measurement of the quantum wavefunction" Nature v.474, p.188 (2011).

Abstract: The wavefunction is the complex distribution used to completely describe a quantum system, and is central to quantum theory. But despite its fundamental role, it is typically introduced as an abstract element of the theory with no explicit definition. Rather, physicists come to a working understanding of the wavefunction through its use to calculate measurement outcome probabilities by way of the Born rule. At present, the wavefunction is determined through tomographic methods which estimate the wavefunction most consistent with a diverse collection of measurements. The indirectness of these methods compounds the problem of defining the wavefunction. Here we show that the wavefunction can be measured directly by the sequential measurement of two complementary variables of the system. The crux of our method is that the first measurement is performed in a gentle way through weak measurement so as not to invalidate the second. The result is that the real and imaginary components of the wavefunction appear directly on our measurement apparatus. We give an experimental example by directly measuring the transverse spatial wavefunction of a single photon, a task not previously realized by any method. We show that the concept is universal, being applicable to other degrees of freedom of the photon, such as polarization or frequency, and to other quantum systems—for example, electron spins, SQUIDs (superconducting quantum interference devices) and trapped ions. Consequently, this method gives the wavefunction a straightforward and general definition in terms of a specific set of experimental operations. We expect it to expand the range of quantum systems that can be characterized and to initiate new avenues in fundamental quantum theory.

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S. Zhang et al., "Optical Precursor of a Single Photon" Phys. Rev. Lett. v.106, p.243602 (2011).

Abstract: We report the direct observation of optical precursors of heralded single photons with step- and square-modulated wave packets passing through cold atoms. Using electromagnetically induced transparency and the slow-light effect, we separate the single-photon precursor, which always travels at the speed of light in vacuum, from its delayed main wave packet. In the two-level superluminal medium, our result suggests that the causality holds for a single photon.

Single photons http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.243602" in vacuum!

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R. Lapkiewicz et al., "Experimental non-classicality of an indivisible quantum system, Nature v.474, p.490 (2011).

Abstract: In contrast to classical physics, quantum theory demands that not all properties can be simultaneously well defined; the Heisenberg uncertainty principle is a manifestation of this fact. Alternatives have been explored—notably theories relying on joint probability distributions or non-contextual hidden-variable models, in which the properties of a system are defined independently of their own measurement and any other measurements that are made. Various deep theoretical results imply that such theories are in conflict with quantum mechanics. Simpler cases demonstrating this conflict have been found and tested experimentally with pairs of quantum bits (qubits). Recently, an inequality satisfied by non-contextual hidden-variable models and violated by quantum mechanics for all states of two qubits was introduced and tested experimentally. A single three-state system (a qutrit) is the simplest system in which such a contradiction is possible; moreover, the contradiction cannot result from entanglement between subsystems, because such a three-state system is indivisible. Here we report an experiment with single photonic qutrits which provides evidence that no joint probability distribution describing the outcomes of all possible measurements—and, therefore, no non-contextual theory—can exist. Specifically, we observe a violation of the Bell-type inequality found by Klyachko, Can, Binicioğlu and Shumovsky. Our results illustrate a deep incompatibility between quantum mechanics and classical physics that cannot in any way result from entanglement.

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P. Adamson et al., "First Direct Observation of Muon Antineutrino Disappearance", Phys. Rev. Lett. v.107, p.021801 (2011).

Abstract: This Letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for ν̅ μ production, accumulating an exposure of 1.71×1020 protons on target. In the Far Detector, 97 charged current ν̅ μ events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at 6.3σ. The best fit to oscillation yields |Δm̅2|=[3.36-0.40+0.46(stat)±0.06(syst)]×10-3  eV2, sin⁡2(2θ̅ )=0.86-0.12+0.11(stat)±0.01(syst). The MINOS νμ and ν̅ μ measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters.

You may read a review of this at the http://physics.aps.org/articles/v4/54" and also obtain a free download of the actual paper.

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