美国物理学会(APS)电子刊物physics于今天凌晨完成了2013年度最后一期的编辑。第一篇文章是2013年十一大物理学进展(Highlights of the Year)，这些进展的原文全部发表在Phys. Rev. Lett.之上。中国科学院高能所第三代北京谱仪器(BESIII)发现的四夸克物质被列为进展之首。 

为不喜英文者干点体力活如下： 

 Highlights of the Year

Published December 30, 2013|Physics 6, 139 (2013)|DOI: 10.1103/Physics.6.139

Physics looks back at the standout storiesof 2013. http://physics.aps.org/articles/v6/139

As 2013 draws to a close, we look back on the research covered in Physicsthat really made waves in and beyond the physics community. In thinking about whichstories to highlight, we considered a combination of factors: popularity on thewebsite, a clear element of surprise or discovery, or signs that the work couldlead to better technology. On behalf of the Physics staff, we wish everyonean excellent New Year.

– Matteo Rini and Jessica Thomas

Four-Quark Matter

Quarks come in twos and threes—or so nearly every experiment has toldus. This summer, the BESIII Collaboration in China and the Belle Collaboration inJapan reported they had sorted through the debris of high-energy electron-positroncollisions and seen a mysteriousparticle that appeared to contain four quarks. Though other explanations forthe nature of the particle, dubbed Zc(3900), are possible, the “tetraquark”interpretation may be gaining traction: BESIII has since seenaseries of other particles that appear to contain four quarks.

Strangers from Beyond our Solar System

Detector experiments hunting for rare events can go years and never seeanything out of the ordinary. So it was cause for excitement when IceCube, a giantneutrino telescope at the South Pole, reported the detectionof two neutrinos with energies of around 1000 tera-electron-volts (TeV), roughlya billion times more energetic than those arriving from the Sun. Scientists at IceCubehave since further analyzed their data and reported26 more neutrinos with energies above 30 TeV. Researchers will need to observe manymore of the neutrinos before they can be certain of their source, and that may requirea larger detector. But they believe the particles were produced outside of the SolarSystem (experiments haven’t detected neutrinos from so far away since 1987) andmay be carrying information about astrophysical events, like gamma-ray bursts, indistant galaxies.

Dark Matter is Still Obscure

2013 was an eventful year in dark-matter research, with leading searchefforts releasing long-awaited results—though the puzzle of what makes up the darkmatter remains unsolved. In April, the collaboration running the Alpha MagneticSpectrometer aboard the International Space Station reported the observation of an excess of positronsin the cosmic ray flux. This could well originate from the annihilation of dark-matterparticles in space, but data at higher energies are needed to rule out other explanations.Two other Earth-bound experimentsinstead attempted to capture candidate dark-matter particles called WIMPs asthey pass through Earth. The Cryogenic Dark Matter Search (CDMS) experiment at Fermilabin Illinois caused a stir when it announced it had detected a few blips in its scintillatorsthat could potentially be assigned to WIMPs. But the excitement was soon dampenedby the Large Underground Xenon (LUX) experiment in South Dakota. LUX, with nominallymuch better sensitivity, saw no evidence of such dark-matter particles. Both experimentsare now racing to improve their sensitivities and hoping to deliver unequivocaldark-matter signals.

Light Stopped for One Minute

Light travels at 300,000 million km/hour in vacuum, but physicists knowhow to engineer materials that can bring it to a complete halt—an effect that couldbe used in quantum computing to store information carried by photons. A team atthe Technical University of Darmstadt, Germany, managed to stop a beam of light for a record-breakingfull minute. The method exploits a phenomenon called electromagnetically inducedtransparency, in which a control laser can make an opaque medium temporarily transparentand thus able to store light. While one minute is approximately the theoreticallimit achievable in the particular crystal the team used, much longer storage timesmay be in sight: The researchers are now tuning their experiments to work with europium-dopedcrystals, which theoretically allow storage times of several hours.

Telescope Detects Twist in Ancient Cosmic Light

The cosmic microwave background (CMB)—the “afterglow” of the big bang—isour best source of information on the infant Universe. While researchers race tointerpret the all-sky CMB map released in March 2013 by the Planck satellite, oneof the year’s highlights in cosmology came from a terrestrial observation: A collaborationrunning the South Pole Telescope made the first detection of a subtle distortionin the CMB radiation known as B-mode polarization. The observed twisting occursbecause the CMB light rays experience gravitational lensing as they encounter lumpsof matter en route through the Universe to us. The achievement could leadto a map of the distribution of matter in the Universe, including the elusive darkmatter.

Lasers of Sound

Sound waves and light have much in common, and many concepts from optics,from invisibility cloaks to lasers, have influenced acoustics. In March 2013, aresearch team at NTT Basic Research Laboratories, Japan, demonstrated the first entirely acoustic analogof a laser. The researchers used a “nanodrum” to excite acoustic vibrations(phonons), which they then amplified through stimulated emission to deliver spectrallypure sound waves with a frequency of around 1.7 megahertz. When the team reportedtheir work in March, they weren’t yet able to extract waves from the device. Butrecently, the group has demonstrated phonon waveguides that, in analogy to opticalfibers, could be coupled to the phonon laser to transfer and use the generated acousticwaves. Phonon lasers might one day deliver directional and coherent sound beams,which could be used for imaging or communication applications.

Microscope Spies on Hydrogen

Open any first-year quantum mechanics book and you’ll probably find asketch of hydrogen’s spherical, dumbbell, and clover-shaped electron orbitals. Butuntil this year, researchers couldn’t claim to have actually observed these electronclouds experimentally. To take a peek, researchers at the FOM Institute for Atomicand Molecular Physics, Netherlands, and collaborators designed a “quantum microscope” that ionizedhydrogen atoms with light and then used an electrostatic lens to create an interferencepattern of the escaping electrons. The researchers used the interference image toreconstruct the original electron orbitals.

Facilities in a Box

This year, scientists found new ways to offer some of the capabilitiesof large and expensive facilities in setups that could be housed in individual labs.With equipment that should ultimately fit onto a tabletop, researchers at Los AlamosNational Laboratory, New Mexico, produceda beam of neutrons intense and focused enough to image defects in materials.Possible applications of the mini neutron source, which uses the interaction betweena powerful laser and a solid target to generate the neutrons, include testing neutronsensors and analyzing the effects of radiation damage on materials. In a similareffort, two teams, one led by researchers at Stanford University, California, andthe other a collaboration between researchers at the Max Planck Institute of QuantumOptics and Friedrich Alexander University Erlangen-Nuremberg, both in Germany, presentedan important step toward making cheaper and more compact x-ray sources. The twoteams showed they could accelerateelectrons with nanoscale optical gratings that are much smaller than the radio-frequencytechnology used at particle accelerators. In future work, the teams want to showthe devices can generate higher fields and a greater flux of electrons.

Majorana Fermions Annihilate in Nanowires

Physicists have long been searching for signs of Majorana fermions, whichare neutral fermions that are their own antiparticles. Evidence for a fundamentalparticle that is also a Majorana fermion is inconclusive (see 19 September 2013Synopsis),but condensed matter physicists have shown early evidence that collective states(quasiparticles) in certain superconducting devices can have an analogous behavior.This year, researchers at the University of Illinois at Urbana-Champaign generatedtwo of the quasiparticles at either end of a nanowire connected to superconductingleads and then used a magnetic field to cause the states to annihilate,as expected when a particle meets its antiparticle. Finding examples of Majoranastates in solids could be a route to making quantum computers that are more resistantto noise.

A Year of Quantum Victories—But No Quantum Computer Yet

Do we have quantum computers, and are they better than conventional ones?The Canadian company D-Wave Systems reported that they had successfully tackled a hard-to-solveproblem on their putative quantum computer. But many scientists would arguethere is no evidence that the device, made of ～100 superconducting elements, can be called a quantum computer or thatit outperforms classical computers. While quantum computing may still be some yearsin the future, in 2013 researchers reported a number of victories against obstaclesto quantum information and communication protocols. In quantum cryptography, codemakers regained the upper hand against code breakers, when two independent researchteams demonstrated a new encryptionmethod that may provide the ultimate security against hackers. Two other reportsshowed how entanglement, the essential ingredient that gives quantum technologiesan advantage over classical methods, can be protected from noise and dissipation.A team at the Massachusetts Institute of Technology, Cambridge, showed that in asecure quantum communication channel,the benefits of entanglement can beharnessed even after its breakup induced by noise. And researchers at the FreeUniversity of Berlin, Germany, the Niels Bohr Institute, Denmark, and the TechnicalUniversity of Munich, Germany, suggested that, thanks to a technique called quantumillumination, dissipative processescan be put to use to engineer more robust quantum states.

What’s Inside a Black hole?

In 2012, a group of physicists at the University of California, SantaBarbara, proposed that an observer falling into a black hole would be destroyedby a firewall at the event horizon. If such a firewall existed, they argued, itwould solve certain inconsistencies in black hole theory, but the idea sparked aheated debate among theoretical physicists: firewalls violate Einstein’s well-establishedequivalence principle, which says that an observer can’t distinguish between inertialmotion and free fall and therefore shouldn’t be able to tell if he has passed theevent horizon. This year, two of the original firewall proponents, have rekindledthe debate. The authors developed a theoretical model to describe the interior ofthe black hole, suggesting an in-fallingobserver would encounter a sea of quanta of arbitrarily high energy, i.e., a “wallof fire.”

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