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physicsworld.comFrontiersIn briefElement 117 createdScientists in Russia and the US have created a newelement with 117 protons by firing calcium-48ions at a target of berkelium-249. Although nuclearphysicists had previously synthesized a total of27 elements heavier than uranium, element 117had remained elusive because the target materialneeded to produce it – berkelium-249 – is sodifficult to make. The researchers managed,however, to produce 22 mg of it by intense neutronirradiation over two years, which they then firedcalcium-48 ions at over a 150 day period. The newelement is the most neutron-rich isotope yetproduced, but its half-life of 78 ms is 87 timeslonger than a previously discovered isotopecontaining one neutron less. This supports the ideathat neutron-rich superheavy nuclei could beextremely stable (Phys. Rev. Lett. at press).Gravitational waves within sightFluctuations in the curvature of space–time knownas gravitational waves could be discovered within ayear of current detectors being upgraded, providedthat the detectors focus their search on emissionsfrom binary black holes. That is the view ofastrophysicists in Poland, who believe there aresignificantly more of these astrophysical systemsthan was previously thought. After analysing datafrom the Sloan Digital Survey, the researchersfound that 50% of stars in a sample of 300 000galaxies have a lower “metallicity” than the Sun,which makes them much more likely to formblack-hole binaries as they lose less mass at theend of their lives. Upgrades to the LIGO and VIRGOexperiments, to be completed by 2015, should givethem the sensitivity to detect these gravitationalwaves “within the first year of operation”, claim theresearchers (arXiv:1004.0386).Wonder material steals the lightResearchers at IBM have made the firstphotodetector from graphene – a sheet of carbonjust one atom thick. Photodetectors convert opticalsignals into electrical current and they are widelyused in communications and sensing. Theresearchers needed to overcome a rare flaw ingraphene: the electrons and holes in the bulk ofthe material recombine too quickly, which leavesno free electrons to carry current. They applied aninternal electric field via palladium or titaniumelectrodes that are on top of multilayered orsingle-layered graphene, which separates theelectrons and holes. The graphene photodetectorcan detect optical data at rates of 10 Gbit s –1 ; thiscompares well with optical networks made of othermaterials, such as group III–V semiconductors(Nature Photonics 10.1038/nphoton.2010.40).Read these articles in full and sign up for freee-mail news alerts at physicsworld.com4Strange quark weighs in preciselyElementary stuff “Strange” quarks are the heaviest ofthe three light quarks.A collaboration of particle physicists inEurope and North America has calculatedthe mass of strange quarks to an accuracy ofbetter than 2% – beating previous results bya factor of 10. This is the first time that themass of one of the lighter quarks has beenconstrained to such accuracy and could helpexperimentalists to scrutinize the StandardModel of particle physics.It is notoriously difficult to determine themass of quarks because these elementaryparticles never exist in isolation – instead thestrong force constrains them into boundstates called hadrons, such as the proton andthe neutron. The picture is complicated be -cause a large portion of the hadron mass isbelieved to belong to the strong force itself,mediated by particles known as gluons, andthe exact nature of gluon–quark interactionsis poorly understood. Theorists thereforehave to combine measurements of hadronI spy quantum behaviourPhysicists in the US have observed quantumbehaviour in a macroscopic object largeenough to be seen with the naked eye – a thindisc-shaped mechanical resonator measuringabout 6.25 mm × 6.25 mm and consisting ofaround a trillion atoms. In making their ob -servations, Andrew Cleland and colleaguesat the University of California, Santa Barbara(UCSB) have exploited one of the fundamentalprinciples of quantum mechanics –objects being in two states at the same time.To achieve these “superposition states”,an object needs to be cooled down to itsquantum ground state, at which point theamplitude of its vibrations is reduced to closeto zero. Until now, such states have onlybeen induced in objects up to the atomicscale and some larger molecules, such as“buckyballs”, which are made up of 60 carbonatoms. However, the temperature towhich an object needs to be cooled in orderChristine Daviesbehaviour with calculations based on quantumchromodynamics (QCD), the theory ofthe strong force, to define the mass of singlequarks. Refinements to this theory over theyears have enabled physicists to calculate themass of the heavier three quarks – the top,bottom and charm – to an accuracy of 99%.Unfortunately, it is has been much more difficultto make accurate predictions for themass of the three lighter quarks – the up,down and strange – so reference tables stillcontain errors of up to 30%.Christine Davies at the University of Glas -gow and colleagues in the High PrecisionQCD Collaboration have, however, takena different approach, known as “latticeQCD”. The technique, which requires theuse of supercomputers, enables theorists toconfine the highly nonlinear strong interactionby defining quarks as nodes on a gridand gluons as the connecting lines. Davies’team adapts lattice QCD to calculate a ratioof the mass of the charm quark to the massof the strange quark. As the charm mass iswell known, the researchers can estimate thestrange quark mass to be 92.4 ± 2.5 MeV/c 2(arXiv:0910.3102v2).The result will be of particular interest toresearchers at CERN’s LHCb experiment,who, by studying mesons made of bottomquarks, are trying to recreate conditions fromshortly after the Big Bang. “This is all part ofpinning down the Stan dard Model and askinghow nature can tell the difference be -tween matter and antimatter,” says Davies.to reach its ground state is proportional to itsfrequency. As the aluminium-based “quantumdrum” used in the UCSB experimentresonates at about six billion vibrations persecond, it could reach this resonation stateat “just” 0.1 K. “A regular tuning fork, forexample, would need to be cooled by an -other factor of a million to reach the samestate,” says Cleland.The team measured the quantum state ofthe resonator by connecting it electrically toa superconducting quantum bit, or “qubit”,that was used to excite a single phonon in theresonator. This excitation was then transferredmany times between the resonatorand qubit to enable the researchers to createa superposition state in the resonator wherean excitation and a lack of excitation existedsimultaneously. When the researchers meas -ured the state, via the qubit, the resonatorhad to “choose” which state it was in (Nature464 697). The experiment could enable re -searchers to study the boundaries betweenthe quantum and classical worlds.Physics World May 2010