Recent Noteworthy Physics Papers

[ZapperZ]

I. Ferreras et al., "Necessity of Dark Matter in Modified Newtonian Dynamics within Galactic Scales", Phys. Rev. Lett. v.100, p.031302 (2008).

Abstract: To test modified Newtonian dynamics (MOND) on galactic scales, we study six strong gravitational lensing early-type galaxies from the CASTLES sample. Comparing the total mass (from lensing) with the stellar mass content (from a comparison of photometry and stellar population synthesis), we conclude that strong gravitational lensing on galactic scales requires a significant amount of dark matter, even within MOND. On such scales a 2 eV neutrino cannot explain the excess of matter in contrast with recent claims to explain the lensing data of the bullet cluster. The presence of dark matter is detected in regions with a higher acceleration than the characteristic MOND scale of ~10^-10 m/s^2. This is a serious challenge to MOND unless lensing is qualitatively different [possibly to be developed within a covariant, such as Tensor-Vector-Scalar (TeVeS), theory]

With the Bullet cluster evidence, and now this, could MOND be in serious trouble now?

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[ZapperZ]

A.J. Leggett, "Realism and the physical world", Rep. Prog. Phys. v.71, p.022001 (2008)

Abstract: I consider the extent to which the applicability of the concept of classical realism is constrained, irrespective of the validity or not of the quantum formalism, by existing experiments both in the EPR–Bell setup, including recent experiments testing 'nonlocal realistic' theories, and in the area of 'macroscopic quantum coherence'. Unless we are willing to sacrifice one or more other intuitively plausible notions such as that of the conventional 'arrow of time', it appears impossible, in either context, to maintain the classical notion of realism.

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[ZapperZ]

A. Caprez et al., "A macroscopic test of the Aharonov-Bohm effect", Phys. Rev. Lett., v99, p.210401 (2007).

Abstract: The Aharonov-Bohm (AB) effect is a purely quantum mechanical effect. The original (classified as Type-I) AB-phase shift exists in experimental conditions where the electromagnetic fields and forces are zero. It is the absence of forces that makes the AB-effect entirely quantum mechanical. Although the AB-phase shift has been demonstrated unambiguously, the absence of forces in Type-I AB-effects has never been shown. Here, we report the observation of the absence of time delays associated with forces of the magnitude needed to explain the AB-phase shift for a macroscopic system.

Also see the http://arxiv.org/abs/0708.2428" .

A Perspective on this work can also be found in March 20, 2008 issue of Nature (Nature, v.452, p.298 (2008)).

Looks like the AB effect is non-local after all!

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[ZapperZ]

A.N. Pasupathy et al., "Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+{delta}", Science v.320, p.196 (2008).

Abstract: Identifying the mechanism of superconductivity in the high-temperature cuprate superconductors is one of the major outstanding problems in physics. We report local measurements of the onset of superconducting pairing in the high–transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+{delta} using a lattice-tracking spectroscopy technique with a scanning tunneling microscope. We can determine the temperature dependence of the pairing energy gaps, the electronic excitations in the absence of pairing, and the effect of the local coupling of electrons to bosonic excitations. Our measurements reveal that the strength of pairing is determined by the unusual electronic excitations of the normal state, suggesting that strong electron-electron interactions rather than low-energy (<0.1 volts) electron-boson interactions are responsible for superconductivity in the cuprates.

A http://www.sciencedaily.com/releases/2008/04/080410140538.htm" can be found on ScienceDaily. So the cuprates may not have a "glue" that is responsible for the superconducting mechanism? Oh my! Phil Anderson might be right after all! :)

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[ZapperZ]

E.V. Linder, "Mapping the cosmological expansion", Rep. Prog. Phys. v.71, p.056901 (2008).

Abstract: The ability to map the cosmological expansion has developed enormously, spurred by the turning point one decade ago of the discovery of cosmic acceleration. The standard model of cosmology has shifted from a matter dominated, standard gravity, decelerating expansion to the present search for the origin of acceleration in the cosmic expansion. We present a wide ranging review of the tools, challenges and physical interpretations. The tools include direct measures of cosmic scales through Type Ia supernova luminosity distances, and angular distance scales of baryon acoustic oscillation and cosmic microwave background density perturbations, as well as indirect probes such as the effect of cosmic expansion on the growth of matter density fluctuations. Accurate mapping of the expansion requires understanding of systematic uncertainties in both the measurements and the theoretical framework, but the result will give important clues to the nature of the physics behind accelerating expansion and to the fate of the universe.

And excellent review source, especially if you're interested in how various results in cosmology are obtained.

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[ZapperZ]

D. N. Matsukevich et al., "Bell Inequality Violation with Two Remote Atomic Qubits", Phys. Rev. Lett. v.100, p.150404 (2008).

Abstract: We observe violation of a Bell inequality between the quantum states of two remote Yb+ ions separated by a distance of about 1 m with the detection loophole closed. The heralded entanglement of two ions is established via interference and joint detection of two emitted photons, whose polarization is entangled with each ion. The entanglement of remote qubits is also characterized by full quantum state tomography.

Could we be on a clear path for a loophole-free Bell-type experiment? This report certainly is providing a convincing evidence that we are well on our way!

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[ZapperZ]

M.T. Murphy et al. "Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe", Science v. 320, p. 1611 (2008).

Abstract: The Standard Model of particle physics assumes that the so-called fundamental constants are universal and unchanging. Absorption lines arising in molecular clouds along quasar sightlines offer a precise test for variations in the proton-to-electron mass ratio, µ, over cosmological time and distance scales. The inversion transitions of ammonia are particularly sensitive to µ as compared to molecular rotational transitions. Comparing the available ammonia spectra observed toward the quasar B0218+357 with new, high-quality rotational spectra, we present the first detailed measurement of µ with this technique, limiting relative deviations from the laboratory value to |{Delta}µ/µ| < 1.8 x 10–6 (95% confidence level) at approximately half the universe's current age—the strongest astrophysical constraint to date. Higher-quality ammonia observations will reduce both the statistical and systematic uncertainties in these observations.

In other words, even as far back as half of the universe's age, this ratio of the mass of the proton to the mass of electron, hasn't changed up to the accuracy limit of this measurement.

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[ZapperZ]

L. Li et al., "Phase Transitions of Dirac Electrons in Bismuth", Science v.321, p.547 (2008).

Abstract: The Dirac Hamiltonian, which successfully describes relativistic fermions, applies equally well to electrons in solids with linear energy dispersion, for example, in bismuth and graphene. A characteristic of these materials is that a magnetic field less than 10 tesla suffices to force the Dirac electrons into the lowest Landau level, with resultant strong enhancement of the Coulomb interaction energy. Moreover, the Dirac electrons usually come with multiple flavors or valley degeneracy. These ingredients favor transitions to a collective state with novel quantum properties in large field. By using torque magnetometry, we have investigated the magnetization of bismuth to fields of 31 tesla. We report the observation of sharp field-induced phase transitions into a state with striking magnetic anisotropy, consistent with the breaking of the threefold valley degeneracy.

Read a http://www.sciencedaily.com/releases/2008/07/080725152314.htm".

This is another example where relativistic equations need not require some esoteric conditions to be applicable. Some of them can be found in the very material that we use in our electronics.

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[Gokul43201]

Kamimara, Y. et al. "Iron-based superconductor LaO_1-xF_xFeAs (x=0.05-0.12) with Tc=26 K". J. Am. Chem. Soc. 130, 3296 (2008).

Abstract: We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F^- ions at the O^2- site. The transition temperature (Tc) exhibits a trapezoid shape dependence on the F^- content, with the highest Tc of ~26 K at ~11 atom %.

Full paper available here: http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/2008/130/i11/abs/ja800073m.html
For further developments, see:
Science Daily
http://www.natureasia.com/asia-materials/highlight.php?id=222

Related follow up:
Chen, X.H. et al. "Superconductivity at 43 K in SmFeAsO_1-xF_x", Nature 453, 761 (2008).This is a first observation of high Tc behavior outside of cuprate systems.

 

[Gokul43201]

L.W. Martin, et al., "Electric field control of ferromagnetism using a magnetoelectric multiferroic," Nature Mater. 7, 478 (2008)

Abstract: Multiferroics are of interest for memory and logic device applications, as the coupling between ferroelectric and magnetic properties enables the dynamic interaction between these order parameters. Here, we report an approach to control and switch local ferromagnetism with an electric field using multiferroics. We use two types of electromagnetic coupling phenomenon that are manifested in heterostructures consisting of a ferromagnet in intimate contact with the multiferroic BiFeO3. The first is an internal, magnetoelectric coupling between antiferromagnetism and ferroelectricity in the BiFeO3 film that leads to electric-field control of the antiferromagnetic order. The second is based on exchange interactions at the interface between a ferromagnet (Co_0.9Fe_0.1) and the antiferromagnet. We have discovered a one-to-one mapping of the ferroelectric and ferromagnetic domains, mediated by the colinear coupling between the magnetization in the ferromagnet and the projection of the antiferromagnetic order in the multiferroic. Our preliminary experiments reveal the possibility to locally control ferromagnetism with an electric field.

Full text and summary available here: http://www-als.lbl.gov/als/science/sci_archive/171magnetism.html

For a review on multiferroics, see: Ying-Hao Chu et al, "Controlling magnetism with multiferroics", Materials Today 10, 16 (2007) http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6X1J-4PND5YK-S&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_userid=10&md5=0a7fb2548257eb459e194e1903854b23

The ability to control ferromagnetism using electric fields has huge potential in the area of GMR based memory storage devices.

 

[ZapperZ]

D. Salart et al., "Testing the speed of 'spooky action at a distance'", Nature v.454, p.861 (2008).

Abstract: Correlations are generally described by one of two mechanisms: either a first event influences a second one by sending information encoded in bosons or other physical carriers, or the correlated events have some common causes in their shared history. Quantum physics predicts an entirely different kind of cause for some correlations, named entanglement. This reveals itself in correlations that violate Bell inequalities (implying that they cannot be described by common causes) between space-like separated events (implying that they cannot be described by classical communication). Many Bell tests have been performed, and loopholes related to locality and detection have been closed in several independent experiments. It is still possible that a first event could influence a second, but the speed of this hypothetical influence (Einstein's 'spooky action at a distance') would need to be defined in some universal privileged reference frame and be greater than the speed of light. Here we put stringent experimental bounds on the speed of all such hypothetical influences. We performed a Bell test over more than 24 hours between two villages separated by 18 km and approximately east–west oriented, with the source located precisely in the middle. We continuously observed two-photon interferences well above the Bell inequality threshold. Taking advantage of the Earth's rotation, the configuration of our experiment allowed us to determine, for any hypothetically privileged frame, a lower bound for the speed of the influence. For example, if such a privileged reference frame exists and is such that the Earth's speed in this frame is less than 10-3 times that of the speed of light, then the speed of the influence would have to exceed that of light by at least four orders of magnitude.

Also read the News and Views article in the same issue.

Edit: http://physicsworld.com/cws/article/news/35404" can also be found at PhysicsWorld.

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[sygrup]

just want to say I fully AGREE! :!)

yes yes ))

 

[ZapperZ]

C.G. Camara et al. "Correlation between nanosecond X-ray flashes and stick–slip friction in peeling tape", Nature v.455, p.1089 (2008).

Abstract: Relative motion between two contacting surfaces can produce visible light, called triboluminescence. This concentration of diffuse mechanical energy into electromagnetic radiation has previously been observed to extend even to X-ray energies. Here we report that peeling common adhesive tape in a moderate vacuum produces radio and visible emission along with nanosecond, 100-mW X-ray pulses that are correlated with stick–slip peeling events. For the observed 15-keV peak in X-ray energy, various models give a competing picture of the discharge process, with the length of the gap between the separating faces of the tape being 30 or 300 mum at the moment of emission. The intensity of X-ray triboluminescence allowed us to use it as a source for X-ray imaging. The limits on energies and flash widths that can be achieved are beyond current theories of tribology.

This thing has been getting a lot of popular media coverage because the simple act of peeling an ordinary scotch tape in moderate vacuum can actually generate a small amount of short x-ray burst.

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[mn4j]

Event-by-Event Simulation of Einstein-Podolsky-Rosen-Bohm Experiments:

http://www.springerlink.com/content/p28v88867w7213mu/ Open Access
http://arxiv.org/pdf/0712.3693

Abstract We construct an event-based computer simulation model of the Einstein-Podolsky-Rosen-Bohm experiments with photons. The algorithm is a one-to-one copy of the data gathering and analysis procedures used in real laboratory experiments. We consider two types of experiments, those with a source emitting photons with opposite but otherwise unpredictable polarization and those with a source emitting photons with fixed polarization. In the simulation, the choice of the direction of polarization measurement for each detection event is arbitrary. We use three different procedures to identify pairs of photons and compute the frequency of coincidences by analyzing experimental data and simulation data. The model strictly satisfies Einstein’s criteria of local causality, does not rely on any concept of quantum theory and reproduces the results of quantum theory for both types of experiments. We give a rigorous proof that the probabilistic description of the simulation model yields the quantum theoretical expressions for the single- and two-particle expectation values.​

 

[ZapperZ]

A. Fragner et al. "Resolving Vacuum Fluctuations in an Electrical Circuit by Measuring the Lamb Shift", Science v.322, p.1357 (2008).

Abstract: Quantum theory predicts that empty space is not truly empty. Even in the absence of any particles or radiation, in pure vacuum, virtual particles are constantly created and annihilated. In an electromagnetic field, the presence of virtual photons manifests itself as a small renormalization of the energy of a quantum system, known as the Lamb shift. We present an experimental observation of the Lamb shift in a solid-state system. The strong dispersive coupling of a superconducting electronic circuit acting as a quantum bit (qubit) to the vacuum field in a transmission-line resonator leads to measurable Lamb shifts of up to 1.4% of the qubit transition frequency. The qubit is also observed to couple more strongly to the vacuum field than to a single photon inside the cavity, an effect that is explained by taking into account the limited anharmonicity of the higher excited qubit states.

An amazing feat to detect a Lamb shift in a many-body system such an a superconducting electronic circuit.

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[ZapperZ]

J. S. Lundeen and A. M. Steinberg, "Experimental Joint Weak Measurement on a Photon Pair as a Probe of Hardy's Paradox", Phys. Rev. Lett. 102, 020404 (2009).

Abstract: It has been proposed that the ability to perform joint weak measurements on postselected systems would allow us to study quantum paradoxes. These measurements can investigate the history of those particles that contribute to the paradoxical outcome. Here we experimentally perform weak measurements of joint (i.e., nonlocal) observables. In an implementation of Hardy's paradox, we weakly measure the locations of two photons, the subject of the conflicting statements behind the paradox. Remarkably, the resulting weak probabilities verify all of these statements but, at the same time, resolve the paradox.

This experiment appears to be the confirmation and resolution of the Hardy's paradox.

A news article on this http://exchangemagazine.com/morningpost/2009/week3/Friday/0116014.htm" .

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[ZapperZ]

A. Cabello et al., "Proposed Bell Experiment with Genuine Energy-Time Entanglement", Phys. Rev. Lett. v.102, p.040401 (2009).

Abstract: Franson's Bell experiment with energy-time entanglement [Phys. Rev. Lett. 62, 2205 (1989)] does not rule out all local hidden variable models. This defect can be exploited to compromise the security of Bell inequality-based quantum cryptography. We introduce a novel Bell experiment using genuine energy-time entanglement, based on a novel interferometer, which rules out all local hidden variable models. The scheme is feasible with actual technology.

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[hiyok]

this is a recent paper addressing the origin of spin glass in hole-doped cuprate superconductors. The author attempts a new mechanism for spin glass that can live with Zhang-Rice singlet states. The paper is located at

J. Phys.: Condens. Matter 21 (2009) 075702

Abstract: To address the incompatibility of Zhang–Rice singlet formation and the observed spin glass behavior, an effective model is proposed for the electronic behavior of cuprate materials. The model includes an antiferromagnetic interaction between the spin of the hole in a Zhang–Rice orbital and the spin of the hole on the corresponding copper site. While in the large interaction limit this recovers the t–J model, in the low energy limit the Zhang–Rice singlets are deformed. It is also shown that such deformation can induce random defect ferromagnetic (FM) bonds between adjacent local spins, an effect herein referred to as unusual double exchange, and then spin glass behavior shall result in the case of localized holes. A derivation of the model is also presented.

 

[ZapperZ]

V. Moshchalkov et al., "Type-1.5 Superconductivity" Phys. Rev. Lett. 102, 117001 (2009)

Abstract: We demonstrate the existence of a novel superconducting state in high quality two-component MgB2 single crystalline superconductors where a unique combination of both type-1 (lambda1/xi1<1/sqrt(2)) and type-2 (lambda2/xi2>1/sqrt(2)) superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances, which stabilizes unconventional stripe- and gossamerlike vortex patterns that we have visualized in this type-1.5 superconductor using Bitter decoration and also reproduced in numerical simulations.

If this is true, they have found a new phase of superconductivity where both Type I and Type II properties resides in the same material (but in different bands).

You may also read a http://physics.aps.org/articles/v2/22" AND, get a free copy of the exact paper.

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[Cthugha]

D. Gross, S.T. Flammia and J. Eisert, "Most Quantum States Are Too Entangled To Be Useful As Computational Resources" Phys. Rev. Lett. 102, 190501 (2009)

Abstract: It is often argued that entanglement is at the root of the speedup for quantum compared to classical computation, and that one needs a sufficient amount of entanglement for this speedup to be manifest. In measurement-based quantum computing, the need for a highly entangled initial state is particularly obvious. Defying this intuition, we show that quantum states can be too entangled to be useful for the purpose of computation, in that high values of the geometric measure of entanglement preclude states from offering a universal quantum computational speedup. We prove that this phenomenon occurs for a dramatic majority of all states: the fraction of useful n-qubit pure states is less than exp(-n2). This work highlights a new aspect of the role entanglement plays for quantum computational speedups.

Quantum computers are still far from realization. Usually fast decoherence and the problem of producing high degrees of entanglement between large numbers of qubits are mentioned as the first big problems, which one thinks of. Now Gross et al. show that most highly entangled quantum states will not provide a significant increase in computational speed compared to classical computers. So it might be necessary in future to identify and understand the few remaining entangled states, which are indeed useful for computation.

There is also an accompanying viewpoint to this article: http://link.aip.org/link/?&l_creator=getabs-normal&l_dir=REV&l_rel=VIEWPOINT&from_key=PRLTAO000102000019190501000001&from_keyType=CVIPS&from_loc=AIP&to_j=PHYSGM&to_v=2&to_p=38&to_loc=APS&to_url=http%3A%2F%2Flink.aps.org%2Fdoi%2F10.1103%2FPhysics.2.38

 

[ZapperZ]

M. Gu et al. "http://arxiv.org/abs/0809.0151" ", Physica D: Nonlinear Phenomena, v.238, p.835 (2009).

Abstract: In 1972, P.W. Anderson suggested that ‘More is Different’, meaning that complex physical systems may exhibit behavior that cannot be understood only in terms of the laws governing their microscopic constituents. We strengthen this claim by proving that many macroscopic observable properties of a simple class of physical systems (the infinite periodic Ising lattice) cannot in general be derived from a microscopic description. This provides evidence that emergent behavior occurs in such systems, and indicates that even if a ‘theory of everything’ governing all microscopic interactions were discovered, the understanding of macroscopic order is likely to require additional insights.

Read the News and Views article on this paper in Nature 459, 332-334 (21 May 2009).

Edit: read the http://arxiv.org/abs/0809.0151" here.

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[ZapperZ]

A. V. Ponomarev et al., "ac-Driven Atomic Quantum Motor", Phys. Rev. Lett. v.102, p.230601 (2009) .

Abstract: We propose an ac-driven quantum motor consisting of two different, interacting ultracold atoms placed into a ring-shaped optical lattice and submerged in a pulsating magnetic field. While the first atom carries a current, the second one serves as a quantum starter. For fixed zero-momentum initial conditions the asymptotic carrier velocity converges to a unique nonzero value. We also demonstrate that this quantum motor performs work against a constant load.

A review of this paper can also be found at the http://sciencenow.sciencemag.org/cgi/content/full/2009/609/1".

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[ZapperZ]

R. Horodecki et al., "Quantum Entanglement", Rev. Mod. Phys. v.81, p865 (2009).

Abstract: From the point of view of quantum information science, entanglement is a resource that can be used to perform tasks that are impossible in a classical world. In a certain sense, the more entanglement we have, the better we can perform those tasks. Thus, one of the main goals in this field has been to identify under which conditions two or more systems are entangled, and how entangled they are. This paper reviews the main criteria to detect entanglement as well as entanglement measures and also discusses the role of entanglement in quantum communication and cryptography.

This is a HUGE, 78-page review of quantum entanglement. We get a lot of frequent questions on this topic, so it is appropriate to post a source that has a wealth of information and references.

The Arxiv version of this paper http://arxiv.org/abs/quant-ph/0702225" .

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[ZapperZ]

M. Karski et al., "Quantum Walk in Position Space with Single Optically Trapped Atoms", Science v.325, p. 174 (2009).

Abstract: The quantum walk is the quantum analog of the well-known random walk, which forms the basis for models and applications in many realms of science. Its properties are markedly different from the classical counterpart and might lead to extensive applications in quantum information science. In our experiment, we implemented a quantum walk on the line with single neutral atoms by deterministically delocalizing them over the sites of a one-dimensional spin-dependent optical lattice. With the use of site-resolved fluorescence imaging, the final wave function is characterized by local quantum state tomography, and its spatial coherence is demonstrated. Our system allows the observation of the quantum-to-classical transition and paves the way for applications, such as quantum cellular automata.

Read the http://sciencenow.sciencemag.org/cgi/content/full/2009/710/2".

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[ZapperZ]

M. Aßmann et. al., "Higher-Order Photon Bunching in a Semiconductor Microcavity", Science v.325, p.297 (2009).

Abstract: Quantum mechanically indistinguishable particles such as photons may show collective behavior. Therefore, an appropriate description of a light field must consider the properties of an assembly of photons instead of independent particles. We have studied multiphoton correlations up to fourth order in the single-mode emission of a semiconductor microcavity in the weak and strong coupling regimes. The counting statistics of single photons were recorded with picosecond time resolution, allowing quantitative measurement of the few-photon bunching inside light pulses. Our results show bunching behavior in the strong coupling case, which vanishes in the weak coupling regime as the cavity starts lasing. In particular, we verify the n factorial prediction for the zero-delay correlation function of n thermal light photons.

The bunching and anti-bunching phenomena are considered to be THE strongest evidence for photons. These have no classical equivalence.

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[ZapperZ]

G. Kirchmair et al., "State-independent experimental test of quantum contextuality", Nature v.460, p.494 (2009).

Abstract: The question of whether quantum phenomena can be explained by classical models with hidden variables is the subject of a long-lasting debate. In 1964, Bell showed that certain types of classical models cannot explain the quantum mechanical predictions for specific states of distant particles, and some types of hidden variable models have been experimentally ruled out. An intuitive feature of classical models is non-contextuality: the property that any measurement has a value independent of other compatible measurements being carried out at the same time. However, a theorem derived by Kochen, Specker and Bell shows that non-contextuality is in conflict with quantum mechanics. The conflict resides in the structure of the theory and is independent of the properties of special states. It has been debated whether the Kochen–Specker theorem could be experimentally tested at al. First tests of quantum contextuality have been proposed only recently, and undertaken with photons and neutrons. But these tests required the generation of special quantum states and left various loopholes open. Here we perform an experiment with trapped ions that demonstrates a state-independent conflict with non-contextuality. The experiment is not subject to the detection loophole and we show that, despite imperfections and possible measurement disturbances, our results cannot be explained in non-contextual terms.

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[ZapperZ]

Y. Jompol et al., "Probing Spin-Charge Separation in a Tomonaga-Luttinger Liquid, Science v.325 p.597 (2009).

Abstract: In a one-dimensional (1D) system of interacting electrons, excitations of spin and charge travel at different speeds, according to the theory of a Tomonaga-Luttinger liquid (TLL) at low energies. However, the clear observation of this spin-charge separation is an ongoing challenge experimentally. We have fabricated an electrostatically gated 1D system in which we observe spin-charge separation and also the predicted power-law suppression of tunneling into the 1D system. The spin-charge separation persists even beyond the low-energy regime where the TLL approximation should hold. TLL effects should therefore also be important in similar, but shorter, electrostatically gated wires, where interaction effects are being studied extensively worldwide.

Just imagine - a charge carrier (say an electron), somehow behaves as if it's spin and its charge have been fractionalized, and thus, move differently. This is what spin-charge separation is. It is one of those fundamental phenomena in condensed matter physics that isn't observed anywhere else, but is something that could potentially be a fundamental principle in the physics of elementary particles.

Previous experiments have shown signatures of such spin-charge separation. It has been shown that the charge and thermal currents in 1D organic conductors violate the Wiedemann-Franz law, an indication of a possible spin-charge separation. The charge current had a different dispersion than the thermal currents, something you don't find in a standard Solid State Physics text.

In this new experiment, a different type of experiment was done - tunneling into a 1D system. There appears to be clear signatures of the spin-charge separation in the tunneling currents that were observed.

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[ZapperZ]

S. S. Hodgman et al., "Metastable Helium: A New Determination of the Longest Atomic Excited-State Lifetime", Phys. Rev. Lett. v.103, p.053002 (2009).

Abstract: Exited atoms may relax to the ground state by radiative decay, a process which is usually very fast (of order nanoseconds). However, quantum-mechanical selection rules can prevent such rapid decay, in which case these “metastable” states can have lifetimes of order seconds or longer. In this Letter, we determine experimentally the lifetime of the longest-lived neutral atomic state—the first excited state of helium (the 2 ^3S_1 metastable state)—to the highest accuracy yet measured. We use laser cooling and magnetic trapping to isolate a cloud of metastable helium (He*) atoms from their surrounding environment, and measure the decay rate to the ground 1 ^1S_0 state via extreme ultraviolet (XUV) photon emission. This is the first measurement using a virtually unperturbed ensemble of isolated helium atoms, and yields a value of 7870(510) seconds, in excellent agreement with the predictions of quantum electrodynamic theory.

Whoa! That's more than 2 hours!

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[ZapperZ]

Z. Bern et al., "Ultraviolet Behavior of N=8 Supergravity at Four Loops", Phys. Rev. Lett. 103, 081301 (2009).

Abstract: We describe the construction of the complete four-loop four-particle amplitude of N=8 supergravity. The amplitude is ultraviolet finite, not only in four dimensions, but in five dimensions as well. The observed extra cancellations provide additional nontrivial evidence that N=8 supergravity in four dimensions may be ultraviolet finite to all orders of perturbation theory.

Read a review of this work AND get http://physics.aps.org/articles/v2/70" .

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[ZapperZ]

L. Maccone "Quantum Solution to the Arrow-of-Time Dilemma", Phys. Rev. Lett. 103, 080401 (2009).

Abstract: The arrow-of-time dilemma states that the laws of physics are invariant for time inversion, whereas the familiar phenomena we see everyday are not (i.e., entropy increases). I show that, within a quantum mechanical framework, all phenomena which leave a trail of information behind (and hence can be studied by physics) are those where entropy necessarily increases or remains constant. All phenomena where the entropy decreases must not leave any information of their having happened. This situation is completely indistinguishable from their not having happened at all. In the light of this observation, the second law of thermodynamics is reduced to a mere tautology: physics cannot study those processes where entropy has decreased, even if they were commonplace.

Read the Focus article on this paper here:

http://focus.aps.org/story/v24/st7

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