
#1
Jul2706, 01:42 PM

Mentor
P: 28,791

The aim of this thread is to highlight recent (as in within the past 3 months) noteworthy physics papers that have been published in peerreviewed journals. Anyone can post here, subject to the guidelines listed below:
1. Papers must be from respected peerreviewed journals. This includes Nature, Science, Physical Review Letters, The Physical Review Journals, European Physical Review, Europhysics Letters, Physics Letters, Applied Physics Letters, and Journal of Applied Physics. 2. Provide the full reference to the paper. If the paper also can be found on the web without requiring subscription (such as on the eprint ArXiv), please provide the url. In any case, the full reference to the paper in the journal must be provided. The format for the reference should be as follows: First Author's Name et al., Journal Name, Volume number, Page/Article number, (Year). 3. Provide the full abstract to the paper. This is not necessary if the paper is also available for free on the web. 4. [Optional] Please write a brief description why you are highlighting this paper, and why it is noteworthy. 5. [Optional] If this paper is also highlighted by other services, such as AIP's Physics News Update or ScienceDaily, please provide the link to those highlights. This can be added later as they are found. 6. This thread is only meant for highlighting the paper, not as a discussion thread. Please create a different thread if you think the paper deserves some discussion or comments. Zz. 



#2
Jul2706, 01:47 PM

P: 306

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




#3
Jul2706, 01:54 PM

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P: 28,791

G. Gabrielse et al., Phys. Rev. Lett., 97, 030802 (2006).
New Determination of the Fine Structure Constant from the Electron g Value and QED Abstract: Quantum electrodynamics (QED) predicts a relationship between the dimensionless magnetic moment of the electron (g) and the fine structure constant ([itex]\alpha[/itex]). A new measurement of g using a oneelectron quantum cyclotron, together with a QED calculation involving 891 eighthorder Feynman diagrams, determine [itex]\alpha^{1}=137.035 999 710 (96) [0.70 ppb]. The uncertainties are 10 times smaller than those of nearest rival methods that include atomrecoil measurements. Comparisons of measured and calculated g test QED most stringently, and set a limit on internal electron structure. Also see: http://www.aip.org/enews/physnews/2006/split/7831.html Two obvious reasons why this paper is noteworth: 1. The most accurate determination of the fine structure constant 2. The amazing agreement with QED predictions that takes into account up to the 8th order corrections. Edit: There is a Perspective article on this paper written by Dan Kleppnner in the latest issue of Science: Science 28 July 2006:Vol. 313. no. 5786, pp. 448  449. Edit2: There is also a review of this work on PhysicsWeb. http://physicsweb.org/articles/news/10/8/1/1 Zz. 



#4
Jul2706, 02:00 PM

PF Gold
P: 4,182

Recent Noteworthy Physics Papers
Light Transport in Cold Atoms in Thermal Decoherence
Labeyrie, G. Physical Review Letters, v. 97, no. 1, 7 July 2006 http://www.citebase.org/abstract?id=...antph/0603153 Not so much because I know exactly what's going on, but it sounds relevent to the recent experiments in which light was stopped. I'm reading it now... 



#5
Jul2706, 02:43 PM

Emeritus
Sci Advisor
PF Gold
P: 11,154

I thought this was nice  a recent breakthrough in Soft Cond Mat, this paper reports on what appears to be the first detailed model of pebble erosion, one with significant predictive capability. I'll defer to PhysicsWeb for their introduction to the paper:
Abstract: Other links : arXiv eprint: http://arxiv.org/PS_cache/condmat/pdf/0607/0607061.pdf PhysicsWeb news report : http://physicsweb.org/articles/news/10/7/7/1 



#6
Jul2806, 06:49 AM

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P: 28,791

B. R. Heckel et al., Phys. Rev. Lett., 97, 021603 (2006)
New CPViolation and PreferredFrame Tests with Polarized Electrons Abstract: We used a torsion pendulum containing [itex]~9×10^{22}[/itex] polarized electrons to search for CPviolating interactions between the pendulum's electrons and unpolarized matter in the laboratory's surroundings or the Sun, and to test for preferredframe effects that would precess the electrons about a direction fixed in inertial space. We find [itex]g_P^e g_S^N/(\hbar c) < 1.7 \times10^{36}[/itex] and [itex]g_A^e g_V^N/(\hbar c) < 4.8 \times 10^{56}[/itex] for [itex]\lambda > 1[/itex] AU. Our preferredframe constraints, interpreted in the Kostelecký framework, set an upper limit on the parameter b<= [itex]5.0 \times10^{21}[/itex] eV that should be compared to the benchmark value [itex]m_e^2/M_{Planck} = 2 \times 10^{17}[/itex] eV. This paper is from the same Eric Adelberger group at U. of Washington has has made the measurement of the gravititational constant G up to the sub micron scales. The result of this paper puts even more severe constraints on any preferred frame effects and CPT violation. Zz. 



#7
Jul2806, 08:32 AM

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P: 28,791

Here's something you can show your instructor in your circuit theory class. :)
J. Gabelli et al., Science v.313. p.499 (2006) Violation of Kirchhoff's Laws for a Coherent RC Circuit. Abstract:What is the complex impedance of a fully coherent quantum resistancecapacitance (RC) circuit at gigahertz frequencies in which a resistor and a capacitor are connected in series? While Kirchhoff's laws predict addition of capacitor and resistor impedances, we report on observation of a different behavior. The resistance, here associated with charge relaxation, differs from the usual transport resistance given by the Landauer formula. In particular, for a singlemode conductor, the chargerelaxation resistance is half the resistance quantum, regardless of the transmission of the mode. The new mesoscopic effect reported here is relevant for the dynamical regime of all quantum devices. Of course, the significance of this work is not really to show that Kirchhoff's law doesn't work in this regime, but rather to study the behavior of conduction at the mesoscopic scale. This is important since electronics components are getting to be smaller, and quantum computing and circuits will be relevant in future devices. It is vital to know how such components differ from their classical counterparts. Zz. Edit: They have put this up on ArXiv, so if you don't have access to Science, this is how you can get it: http://arxiv.org/abs/condmat/0610572 



#8
Jul3106, 06:55 AM

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P: 28,791

P. Walther et al., Phys. Rev. Lett., 97, 020501 (2006)
Experimental Entangled Entanglement Abstract: All previous tests of local realism have studied correlations between singleparticle measurements. In the present experiment, we have performed a Bell experiment on three particles in which one of the measurements corresponds to a projection onto a maximally entangled state. We show theoretically and experimentally that correlations between these entangled measurements and singleparticle measurements are too strong for any localrealistic theory and are experimentally exploited to violate a ClauserHorneShimonyHoltBell inequality by more than 5 standard deviations. We refer to this possibility as "entangled entanglement." This is another paper on the EPRtype experiment (or more specifically, the CHSHtype) from the Zeilinger group. This time, they are measuring the joint properties of 2 or more entangled particles. Zz. 



#9
Aug206, 07:06 AM

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P: 28,791

E. Vliegen and F. Merkt, Phys. Rev. Lett. 97, 033002 (2006).
NormalIncidence Electrostatic Rydberg Atom Mirror Abstract: A Rydberg atom mirror has been designed and its operational principle tested experimentally. A supersonic expansion containing H atoms moving with a velocity of 720 m/s initially propagates toward a quadrupolar electrostatic mirror. The H atoms are then photoexcited to n=27 Rydberg states with a positive Stark shift and move in a rapidly increasing electric field. The H atom beam is stopped in 4.8 µs, only 1.9 mm away from the photoexcitation spot, and is then reflected back. The reflection process is monitored by pulsed field ionization and imaging. An interesting paper. They have generated what is essentially an atomic mirror. A further review of this work can be found here: http://focus.aps.org/story/v18/st3 Zz. 



#10
Aug506, 08:13 PM

Emeritus
Sci Advisor
PF Gold
P: 11,154

Zz, would you like to post a few comments on JC Davis' recent Nature paper on tunneling spectroscopy in BSCCO?




#11
Aug506, 09:06 PM

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P: 28,791

Yes, I'm going to once I finish reading it carefully enough. This will be my own review of the paper, especially since they cited two of my papers.
:) Zz. 



#12
Aug706, 07:36 AM

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P: 28,791

As requested by Gokul, here it is:
J. Lee et al., Nature v.442, p.546 (2006) Interplay of electronlattice interactions and superconductivity in [itex]Bi_2Sr_2CaCu_2O_{8+\delta}[/itex] Abstract:Formation of electron pairs is essential to superconductivity. For conventional superconductors, tunnelling spectroscopy has established that pairing is mediated by bosonic modes (phonons); a peak in the second derivative of tunnel current [itex]d^2I/dV^2[/itex] corresponds to each phonon mode. For hightransitiontemperature (highTc) superconductivity, however, no boson mediating electron pairing has been identified. One explanation could be that electron pair formation and related electron–boson interactions are heterogeneous at the atomic scale and therefore challenging to characterize. However, with the latest advances in [itex]d^2I/dV^2[/itex] spectroscopy using scanning tunnelling microscopy, it has become possible to study bosonic modes directly at the atomic scale. Here we report [itex]d^2I/dV^2[/itex] imaging studies of the highTc superconductor [itex]Bi_2Sr_2CaCu_2O_{8+\delta}[/itex]. We find intense disorder of electron–boson interaction energies at the nanometre scale, along with the expected modulations in [itex]d^2I/dV^2[/itex]. Changing the density of holes has minimal effects on both the average mode energies and the modulations, indicating that the bosonic modes are unrelated to electronic or magnetic structure. Instead, the modes appear to be local lattice vibrations, as substitution of [itex]^{18}O[/itex] for [itex]^{16}O[/itex] throughout the material reduces the average mode energy by approximately 6 per cent—the expected effect of this isotope substitution on lattice vibration frequencies. Significantly, the mode energies are always spatially anticorrelated with the superconducting pairinggap energies, suggesting an interplay between these lattice vibration modes and the superconductivity. A review of this paper can be found in both the same issue of Nature, and in Science of the same week. A short overview of it can also be found here: http://physicsweb.org/articles/news/10/8/4/1 And now, my take on this. This work encompasses both areas of my expertise  tunneling and angleresolved photoemission (i.e. check out the reference to the "mode" energy). It also continues the ongoing battle between phonons and magnetic fluctuations as the mechanism for superconductivity in these cuprate compounded. The phonon scenario has gotten a lot of bruises lately with a number of rather interesting experimental results. However, with this paper, they seem to make a comeback  but have they? One of the continuing issues in tunneling spectroscopy in these material is the origin of what is known as the "diphum structure" in practically ALL of highTc tunneling spectroscopy (see the arrows in Fig. 1b of the paper). This is a structure that is at an energy larger than the superconducting gap. A similar structure is seen quite clearly in ARPES measurement, especially at or near the antinodal direction of the crystal momentum space. In conventional superconductors, these structures have been extracted from the tunneling data (the [itex]d^2I/dV^2[/itex] spectrum) using the McMillanRowell inversion and the resulting "modes" matches exactly with the phonon modes for that material. This was one of the most convincing evidence that phonons were responsible for the superconducting mechanism in these materials. Doing this for highTc superconductors isn't that easy. The phonon modes for these materials are still not that wellknown. Furthermore, the material is very complicated. To be able to know of phonons are responsible, you can't just do one measurement  you need to do this for different types of phonon spectra and see if the changes in superconductivity follows that trend. The isotope effect is a good example. This is essentially what is done in this paper. They doped the high Tc superconductor with an isotope of oxygen (doping this family of highTc superconductors with oxygen introduces holes, which are the charge carriers in this "holedoped" superconductors). So doping with O18 means you are introducing a heavier hole as the charge carrier. This changes the phonons spectrum, and in particular, they found that the "mode" energy reduced by the expected amount. [This "mode" energy is roughly the strength of the coupling between the charge carrier (in this case, the holes) and the boson that is the "force carrier". If you believe in phonons as the mechanism, then this boson is a phonon. If you believe in magnetic fluctuations, then this boson could be a spinon or a magnon. This is the QFT description of interactions in this scenario.] So is this a slamdunk evidence for phonons? Nope. There are two issues that are still left dangling: 1. Even by changing the doping oxygen isotope and changing the mode energy, the value of Tc doesn't change! One would expect, as in conventional superconductor, that as one changes the strength of the mode coupling, that Tc would also change. This didn't occur (which is why the isotope effect is still vague in highTc compounds). 2. In performing tunneling experiments in this particular material, the "cleave surface" is not the CuO plane (where it is believed all superconductivity is occuring), but rather the insulating BiO layer. So the charge carrier has to first pass through these insulating barrier. Now, there are many tantalizing evidence that when one dopes this material, not all of the oxygen actually does get doped into the CuO later, but rather some gets into the insulating later. The charge carriers making the tunneling adventure can be affected by such a barrier. So the signature that was seen in this paper cannot rule out the insulating layer as the origin of the effects they witnessed. While this paper certainly gives a strong "straw" to the phonon camps, I still don't see how it can explain a series of other experimental results that it could not be consistent with. This is an ongoing battle that will require other results to settle. Edit: They have uploaded the paper to the eprint ArXiv. You may find it here: http://arxiv.org/abs/condmat/0608149 Zz. 



#13
Aug806, 02:23 PM

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P: 28,791

I. R. Hooper et al., Phys. Rev. Lett. 97, 053902 (2006).
Making Tunnel Barriers (Including Metals) Transparent Abstract: The classical "brick wall," which may, according to quantum mechanics, leak via tunneling, is here shown to be completely transparent when appropriate impedance matching media are placed both in front of and behind the "wall." Optical experiments involving beyondcriticalangletunnel barriers in the frustrated total internal reflection scheme which mimic quantum mechanical systems provide convincing proof of this remarkable effect. The same mechanism also allows vastly enhanced transmission through unstructured thin metal films without the need for surface wave excitation. A very good review of this paper can be found here: http://focus.aps.org/story/v18/st4 Zz. 



#14
Aug1206, 06:49 AM

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P: 28,791

This time, there are two independent papers published at the same time in the same issue of PRL, both arriving at the same result/conclusion.
Paper 1 K. Beloy et al., Phys. Rev. Lett. 97, 040801 (2006). HighAccuracy Calculation of the Blackbody Radiation Shift in the [itex]^{133}[/itex]Cs Primary Frequency Standard. Abstract: The blackbody radiation (BBR) shift is an important systematic correction for the atomic frequency standards realizing the SI unit of time. Presently, there is controversy over the value of the BBR shift for the primary [itex]^{133}[/itex]Cs standard. At room temperatures, the values from various groups differ at the 3×10[itex]^{15}[/itex] level, while modern clocks are aiming at 10[itex]^{16}[/itex] accuracies. We carry out highprecision relativistic manybody calculations of the BBR shift. For the BBR coefficient beta at T=300 K, we obtain [itex]\beta[/itex] = (1.710±0.006)×10[itex]^{14}[/itex], implying 6×10[itex]^{17}[/itex] fractional uncertainty. While in accord with the most accurate measurement, our 0.35% accurate value is in a substantial (10%) disagreement with recent semiempirical calculations. We identify an oversight in those calculations. Paper 2 E. J. Angstmann et al., Phys. Rev. Lett. 97, 040802 (2006). Frequency Shift of the Cesium Clock Transition due to Blackbody Radiation Abstract: We perform ab initio calculations of the frequency shift induced by a static electric field on the cesium clock hyperfine transition. The calculations are used to find the frequency shifts due to blackbody radiation. Our result [[itex]\delta\nu/E^2[/itex] = 2.26(2)×10[itex]^{10 }[/itex]Hz/(V/m)[itex]^2[/itex]] is in good agreement with early measurements and ab initio calculations performed in other groups. We present arguments against recent claims that the actual value of the effect might be smaller. The difference (~10%) between ab initio and semiempirical calculations is due to the contribution of the continuum spectrum in the sum over intermediate states. These two papers presented a more precise calculation of the hyperfine transition in Cs, which makes the atomic clock more precise as well. They also have explained the 10% discrepency in earlier calculations of this transition. A summary of both papers can be found here: http://physicsweb.org/articles/news/10/8/9/1 Zz 



#15
Aug1306, 09:09 AM

Emeritus
Sci Advisor
PF Gold
P: 11,154

LongLived Bloch Oscillations with Bosonic Sr Atoms and Application to Gravity Measurement at the Micrometer Scale
Abstract: We report on the observation of Bloch oscillations on the unprecedented time scale of several seconds. The experiment is carried out with ultracold bosonic ^{88}Sr atoms loaded into a vertical optical standing wave. The negligible atomatom elastic cross section and zero angular momentum in the ground state makes ^{88}Sr an almost ideal Bose gas, insensitive to typical mechanisms of decoherence due to thermalization and external stray fields. The small size of the system enables precision measurements of forces at micrometer scale. This is a challenge in physics for studies of surfaces, Casimir effects, and searches for deviations from Newtonian gravity predicted by theories beyond the standard model. URL: Ferrari, et al, Phys. Rev. Lett. 97, 060402 (2006) Link to eprint: http://www.lens.unifi.it/tinogroup/Sr/doc/0605018.pdf 



#16
Aug2906, 05:41 AM

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P: 28,791

S. Sasaki et al. Superfluidity of Grain Boundaries and Supersolid Behavior, Science v.313, p.1098 (2006)
Abstract: When two communicating vessels are filled to a different height with liquid, the two levels equilibrate because the liquid can flow. We have looked for such equilibration with solid [itex]^4[/itex]He. For crystals with no grain boundaries, we see no flow of mass, whereas for crystals containing several grain boundaries, we detect a mass flow. Our results suggest that the transport of mass is due to the superfluidity of grain boundaries. This is another example on why, when something is published, we need to give it some time to be digested and tested by independent groups to verify that the discovery, or the result, is valid. A report earlier regarding the discovery of "superfluidity" in solid He appears to be due to superfluid flow in the grain boundaries, i.e. it wasn't a supersolid. Zz. 



#17
Sep1206, 06:48 AM

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P: 28,791

M. Steffen et al. Measurement of the Entanglement of Two Superconducting Qubits via State Tomography, Science v.313,p.1423 (2006)
Abstract: Demonstration of quantum entanglement, a key resource in quantum computation arising from a nonclassical correlation of states, requires complete measurement of all states in varying bases. By using simultaneous measurement and state tomography, we demonstrated entanglement between two solidstate qubits. Single qubit operations and capacitive coupling between two superconducting phase qubits were used to generate a Belltype state. Full twoqubit tomography yielded a density matrix showing an entangled state with fidelity up to 87%. Our results demonstrate a high degree of unitary control of the system, indicating that larger implementations are within reach. A review of this paper can be found here: http://physicsweb.org/articles/news/10/9/3/1 Besides the obvious importance to quantum computing, this work is significance because I believe this is the first time the tomography methodology has been applied to characterize the quantum state. Zz. 



#18
Sep1206, 06:57 AM

P: 530




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