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Flash Physics: Antiprotonic helium passes symmetry test, Parkes radio telescope kicks off alien search, Nanobionic spinach detects explosions

Antiprotonic helium passes latest symmetry test

Masaki Hori at the Max Planck Institute for Quantum Optics in Garching, Germany, and members of the CERN-based ASACUSA collaboration have made the most precise measurement ever of the antiproton/electron mass ratio. This was done by studying antiprotonic helium, which is an exotic atom comprising an antiproton, an electron and a helium nucleus. The team cooled about two-billion antiprotonic helium atoms to about 1.6 K. Then it measured the energies of 13 different atomic transitions using laser spectroscopy. The experiments revealed that the antiproton/electron mass ratio was identical to the proton/electron mass ratio to better than one part in one billion. If nature obeys charge, parity and time-reversal (CPT) symmetry, then these two mass ratios should be identical. Any discrepancy would therefore be of great interest to physicists because it could provide a glimpse of physics beyond the Standard Model of particle physics. The measurement is reported in Science.

Australian radio telescope kicks off alien search

The Parkes radio telescope in New South Wales, Australia, has begun its observation run as part of the Breakthrough Listen initiative – the $100m search for intelligent life beyond Earth, launched in 2015 by entrepreneur Yuri Milner and Stephen Hawking. Together with the Green Bank Telescope and the Automated Planet Finder at Lick Observatory in the US, and the newly built Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China, the observatories will spend the next decade studying exoplanets for any signs of developed life with technologies similar to our own. The Parkes telescope has access to the Southern Hemisphere sky, which the Breakthrough scientists deem as “rich with targets”, including the centre of our Milky Way galaxy, large swaths of the galactic plane, and other galaxies in the nearby universe. “The addition of Parkes is an important milestone,” says Milner. “These major instruments are the ears of planet Earth, and now they are listening for signs of other civilizations.” The Australian telescope’s first observation as part of the Breakthrough programme took place yesterday and it studied the newly discovered rocky exoplanet orbiting the nearest star to the Sun, Proxima Centauri.

Nanobionic spinach leaves could detect explosions

Nanobionic spinach plants — Spinach sensor: researchers embedded carbon nanotubes into spinach leaves. (Courtesy: M H Wong)

Plant leaves embedded with carbon nanotubes (CNTs) could be used to detect chemical explosives, thanks to new work done by researchers at the Massachusetts Institute of Technology in the US, who have transformed a plant into a living sensor that wirelessly relays this information to a handheld device like a smartphone. The technique for engineering electronics into plants, known as “nanobionics” is a new and upcoming field of research that could have a variety of applications – for example, it could be used in agriculture to improve crop yields and margins. The MIT team, led by Michael Strano, wrapped single-walled CNTs (that fluoresce in the near-infrared spectrum) in a polymer that is sensitive to molecules in certain explosives. If the molecules bind to the polymer, the fluorescence of the CNT changes and the signal can be picked up by an infrared camera to indicate the presence and the amount of explosive present. Read more about the research at nanotechweb.org.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on spotting spin-spirals in a quantum liquid.

Atom assembler makes defect-free arrays

Researchers at the Institut d’Optique Graduate School at the CNRS and Université Paris-Saclay in France have developed a new way to rearrange cold atoms one-by-one in fully ordered arrays. Their technique could be used to simulate quantum systems using neutral atoms held in 2D arrays of optical traps.

Optical traps – or tweezers – work by trapping atoms, molecules or small transparent objects near the focus of a laser beam. The technique allows particles to be picked up and moved using just light. They have played crucial roles in manipulating viruses and proteins for medical research and have also been used for assembling tiny nanomachines. Holding cold atoms in arrays of optical traps has also proven very useful to physicists because the arrays can simulate the quantum physics of solid materials. However, creating such arrays of atoms remains a challenge.

Order from disorder

Now, Thierry Lahaye and colleagues have overcome an important shortcoming of optical traps that makes it difficult to use the technique to assemble perfect arrays of single cold atoms.

When dealing with cold atoms, explains Lahaye, “there is a problem in that each optical trap is randomly loaded in an array and so only has a 50% probability of being filled with an atom at any one time.” “Now for applications we ideally want a fully loaded array – that is, one in which each trap has a probability of 100% of containing a single atom,” he says, adding, “although researchers have tried to solve this problem in a number of ways before now, none have been so efficient and versatile as the one we have demonstrated in this work.”

Maxwell’s demon

Lahaye and colleagues’ solution to the filling problem is to sort disordered arrays of atoms into ordered ones using optical potentials. The researchers used a spatial light modulator to create arbitrary 2D arrays of up to 100 traps. Each trap has a radius of around 1 μm and the traps were separated by about 3 μm. The traps were loaded randomly with rubidinium-87 atoms with a filling probability of 50%.

The team then used fast-moving optical tweezers to rearrange the atoms in the disordered array into a pre-defined spatial configuration of their choice (see figure). The team likens the process to how a Maxwell’s demon operates. “Although only the entropy associated with the atomic positions in the arrays is removed,” they explain, “the much higher entropy associated with the motion of each atom in each trap remains unaffected.”

The occupation of the array sites was measured by illuminating the system with light and observing the fluorescence of the rubidium atoms using a CCD camera.

Quantum simulations

The researchers say that the technique could be used to simulate a variety of quantum systems including quantum magnets. “We are now trying to perform these types of experiments using our technique and combine our previous work in which we excited trapped atoms to highly excited (Rydberg) states to simulate the quantum Ising model (which describes idealized magnets),” Lahaye explains. “We are also looking into using our atom-by-atom assembler to perform quantum simulations of ‘frustrated’ magnets, by comparing what happens in different array geometries, such as square and triangular lattices.”

The atom-by-atom assembler is described in Science.

A version of this article first appeared on nanotechweb.org

Flash Physics: NASA and FEMA conduct asteroid-impact exercises, tiny lasers for microscopy, NSF reviews its Arecibo and Green Bank funding

“Asteroid-impact emergency-planning” exercises held by NASA and FEMA

“What would we do if we discovered a large asteroid on course to impact Earth?” That was the scenario being discussed at a recent joint meeting – held by NASA and the Federal Emergency Management Agency (FEMA) – in El Segundo, California. The third in a series of meetings, the two agencies aim to develop and design a way to respond in case of an asteroid impact. “It’s not a matter of if – but when – we will deal with such a situation,” says Thomas Zurbuchen, the recently appointed associate administrator for NASA’s science-mission directorate. “But unlike any other time in our history, we now have the ability to respond to an impact threat through continued observations, predictions, response planning and mitigation.” According to the agencies, exercises such as this one allow the planetary-science community to show how it would collect, analyse and share data about a hypothetical asteroid predicted to impact Earth, while giving emergency managers a chance to discuss how that data would be used to prepare and respond to the threat, as well as warn the public. “It is critical to exercise these kinds of low-probability but high-consequence disaster scenarios,” says FEMA administrator Craig Fugate. “By working through our emergency-response plans now, we will be better prepared if and when we need to respond to such an event.” The scenario simulated during this exercise involved a hypothetical possible impact four years from now – a fictitious asteroid imagined to have been recently discovered, with a 2% probability of impact with the Earth on 20 September 2020. While mounting a deflection mission to move the asteroid off its collision course has been previously simulated, this particular exercise was designed so that the time to impact was too short for a deflection mission to be feasible – and so to pose a great future challenge to emergency managers faced with a mass evacuation of large metropolitan areas. You can read more about these planning exercise’s on NASA’s Planetary Defense portal.

Tiny lasers could boost microscopy

A new microscopy technique that uses micron-sized lasers to illuminate objects from within has been created by researchers in the US and Slovenia. Seok Hyun Yun and colleagues at Harvard University, Massachusetts Institute of Technology and the J Stefan institute in Ljubljana have shown that perovskite nanowires (about 5 μm long and 400 nm thick) can be pumped by a green laser so that they emit their own red laser light. They also created a microscopy system that uses a spectrometer to obtain images using only the laser light emitted by the nanowires. The system could be used to create high-resolution images of biological samples by having cells or tissue absorb the nanowires. This is similar to fluorescence microscopy, which involves adding a fluorescent dye to samples – but Yun and colleagues say the nanowires could offer several advantages over fluorescence microscopy, including superior depth resolution. The nanowires are described in Physical Review Letters and could also be engineered to emit different coloured light, depending on their local chemical environments.

NSF reviewing its funding for Arecibo and Green Bank observatories

Arecibo Observatory (left) and Green Bank Observatory — Funding woes: Arecibo (left) is located in Puerto Rico, and until the recent completion of China’s Five-hundred-meter Aperture Spherical Telescope (FAST), it long held the title of the world’s largest telescope with its 305 m dish. Green Bank is located in West Virginia within the National Radio Quiet Zone and has the world’s largest fully steerable telescope. (Courtesy: Arecibo Observatory and National Radio Astronomy Observatory)

The National Science Foundation in the US is currently in the process of determining its future level of funding for a bunch of astronomical facilities, mainly the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia, US. In reviews carried out over the past decade or longer, both observatories were identified as candidates for funding reductions, largely due to budget constraints that force the NSF to be able to fund other facilities that are thought of as more integral to achieving current astronomy and space-science goals. The NSF is currently carrying out an Environmental Impact Statement (EIS) process to decide both observatories’ fate, before they choose to either make no changes, ramp down funding or “potentially mothball or deconstruct each”. The process began in May for Arecibo and in October for Green Bank, before a final decision will be reached within the next year and a half. Despite various recommendations for reduced funding for Arecibo, Patrick Taylor, group lead for planetary radar at Arecibo, has warned the NSF that “any level of divestment by the NSF of Arecibo, without replacement of that funding from some source, will endanger the NASA-supported work that we do, which is also congressionally mandated, of tracking and characterizing potentially hazardous asteroids.”

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story.

Probing the quantum nature of water

By James Dacey in Beijing on Friday 4 November

After enjoying clear blue skies for the first couple of days of my visit to Beijing, the breeze has disappeared and the smog has taken its hold. One local scientist told me this latest wave is due to pollution from factories south-west of the city, but others have told me it is difficult to pinpoint a particular source. Facemasks are being worn by every other person in the streets, but fortunately I’ve been sheltered by the walls and ceilings of Peking University (PKU).

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Scientific facilities hit by Brazilian budget woes

Two major scientific facilities being built in Brazil are facing delays after failing to receive any the funds allocated to them for 2016. The Sirius synchrotron light source and the Brazilian Multipurpose Research Reactor (RMB) have both been hit by federal budget cuts caused by the recent economic slowdown in the country. Any further funding delays could lead to both facilities being put back a number of years.

Sirius, costing $290m, is being built at the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas, some 100 km north-west of São Paulo, and is expected to begin operation in 2018. As a fourth-generation synchrotron light source, it will generate coherent, high-brightness X-rays that scientists will use to study the structure and properties of materials in unprecedented detail.

Critical point

LNLS director Antônio José Roque da Silva says that officials at the synchrotron have not received the money they were promised for 2016 and are still using 2015 funds. Cash for 2016 was expected to be $87.4m, but that has now been cut to $57.7m by the National Congress of Brazil. “Even though this budget is well below our needs, at this moment the critical point is whether we will in fact receive the funds,” says da Silva.

He says it is critical that funding is maintained to allow officials to order equipment. “To keep the planned activities, it is indispensable to receive funds allocated for this year and have the assurance that no new cuts will threaten the $116m [allocated] for 2017,” warns da Silva. “Otherwise it won’t be possible to meet the schedule.” da Silva adds that even if this funding is received, Sirius will still require an additional $76m to make sure it is open by 2018.

Waiting game

The RMB, meanwhile, is located at Iperó, about 130 km east of São Paulo. Costing $500m, the reactor was expected to open this year. By generating radioisotopes, it promises to ensure Brazil does not depend on other countries for supplying radioisotopes for diagnosing and treating cancer. The RMB will also be used for neutron scattering and will carry out irradiation testing for nuclear fuels and materials.

While cash has been spent obtaining the necessary permits for the RMB, including an environmental licence, officials are still waiting for the release of funds to begin construction. RMB’s budget was supposed to be $47.6m from 2014 to 2016, but only $10.6m has so far been allocated. “The prediction was that the reactor would be ready this year, but, in this saga of precarious disbursements and insufficient funds, our time frame will have to be extended,” says RMB technical co-ordinator José Perotta, who is research director at the National Nuclear Energy Commission.

Brazil’s Ministry of Science, Technology, Innovation and Communications maintains that funds for 2016 for Sirius and RMB are “secure”. The ministry says that the cash for next year has been included in the country’s annual budget, although it has yet to be approved by the country’s national congress.

Robots at arXiv, physicist runs for US president, Einstein emojis galore

Preprint pioneer: Paul Ginsparg in 2002, long before *arXiv* received 10,000 papers per month. (Courtesy: MacArthur Foundation)

By Hamish Johnston

Last month the arXiv preprint server received more than 10,000 papers – the first time in the history of the physics paper depository. While arXiv papers are not peer reviewed, they are checked to ensure that they are “of interest, relevance and value” to the scientific community – which arXiv promises to do within 24 h of submission. So how do they do it? Surely someone doesn’t read every word of every paper? The answer can be found in “What counts as science?”, which appears in Nautilus. arXiv was set up in 1991 by the physicist Paul Ginsparg, who explains how the service uses machine learning to sort the wheat from the chaff – something that has attracted controversy.

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Flash Physics: Space telescope passes milestone, quantum-cryptography record broken, making gold nanostructures

Space telescope passes mirror milestone

The giant mirror at the heart of the James Webb Space Telescope (JWST) has been subjected to the first of many rigorous tests before the mission launches in 2018. The mirror is 6.5 m in diameter and has passed a “centre-of curvature test” of its optical properties at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The tests were done using interferometry to look for tiny imperfections in the shape of the mirror. The mirror will now undergo a large number of mechanical tests that will see it subjected to violent vibrations similar to those it will experience during launch. Then a second centre-of-curvature test will be done. “This is the only test of the entire mirror where we can use the same equipment during a before-and-after test,” explains NASA’s Ritva Keski-Kuha, adding: “This test will show if there are any changes or damages to the optical system.”

Quantum keys distributed over 404 km fibre

A new distance record of 404 km for quantum-key distribution (QKD) on an optical fibre has been achieved by Jian-Wei Pan of the University of Science and Technology of China and colleagues at a number of Chinese universities and research labs. QKD involves two agents – Alice and Bob – exchanging a cryptography key that must be kept secret from an eavesdropper, Eve. This is done by using a quantum-information protocol, which reveals whether Eve has measured information exchanged by Alice and Bob. The team implemented a version of QKD called measurement-device-independent quantum-key distribution (MDIQKD), which was first proposed in 2012 and involves sending out decoy pulses to stop Eve from using loopholes in the original QKD formulation. MDIQKD was performed by encoding quantum information in infrared photos and sending them over 404 km of ultra-low-loss optical fibre. The protocol was also implemented over 311 km of standard optical fibre. As well as doubling the previous record of 200 km, Pan and colleagues were also able to increase the speed of running MDIQKD by a factor of 200 – something that is important for practical implementations of quantum cryptography. The research is described in Physical Review Letters.

Gold 3D nanostructures made using new technique

Schematic of the deposition technique — The 3D nanostructures are made by combining molecular beams of a gold-containing organic compound (left) with water (right) in the presence of an electron beam (centre). (Courtesy: Vienna University of Technology)

Tiny 3D gold structures just a few hundred nanometres in size have been created by using a new technique developed by researchers at the Vienna University of Technology in Austria. Gold nanostructures have unique optical and electronic properties that make them potentially useful for a range of applications from biological sensing to optoelectronics. However, existing techniques for creating the 3D nanostructures are expensive and time consuming. Now, Heinz Wanzenböck and colleagues have used a technique called focused-electron-beam-induced deposition (FEBID) to create 3D nanostructures on a germanium substrate. This involves firing an electron beam and two molecular beams at the substrate. One molecular beam is an organic compound containing gold and the other is simply water. Energy from the electron beam liberates the gold from the organic molecules and the water enhances oxidation, which improves the quality of the 3D gold nanostructures. Whereas previous deposition methods created 3D structures that only contained 30% gold atoms (and 70% carbon), this latest technique achieved 91% gold. The method is described in Scientific Reports.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on funding problems in Brazil.

Cosmic-ray showers create more muons than expected

Significantly more muons appear to be created in cosmic-ray showers than are predicted by models based on data from the Large Hadron Collider (LHC) at CERN. That’s the conclusion of physicists at the Pierre Auger Observatory in Argentina, whose measurements agree with previous hints at a “muon excess” that first emerged more than 15 years ago. The muon excess could mean that the strong interaction is different at collision energies greater than those currently achieved at the LHC.

The Pierre Auger Observatory is an array of 1660 water-filled tanks spread out over an area of 3000 km². It detects muons created from the decay of low-energy pions in the shower of particles created when a cosmic-ray proton interacts with the atmosphere. Most of these fast-moving muons survive the journey to the ground, where they can be spotted from the Cherenkov light they emit as they travel through the water in the tanks. Four telescopes are also used to spot the fluorescent light in the atmosphere created by the cascade.

Showers that are seen both in the Cherenkov detectors and the telescopes – known as “hybrid events – provide a wealth of information about how the showers occur. The telescope data provide a good measure of how much energy is deposited in a shower, whereas the Cherenkov data tells physicists about how hadrons (such as pions) are created in showers.

Avoiding electrons and positrons

Physicists on the Pierre Auger collaboration have used interaction data gleaned from proton–proton collisions at the LHC to predict how many muons, on average, should be produced by a shower of a given energy. While the cosmic-ray collisions of interest are about 10 times more energetic than LHC collisions, physicists have been able to use LHC data to create models that describe how the muons are produced in the shower, as well as how electrons and positrons are produced. Understanding electron and positron production is important because the Cherenkov detectors also detect these particles and cannot distinguish them from the muons of interest.

The detection rates of muons and electrons/positrons in the Cherenkov detector are a function of where in the sky the showers occur. Events that happen directly overhead a detector will be dominated by electrons and positrons, whereas those arriving from more than 37° from vertical will deposit more muons in the detector. The Pierre Auger data analysed in this latest study contain 411 hybrid events – collected over nine years – that span 0–60°. By looking at the numbers of muons and electrons/positrons detected as a function of shower energy and arrival angle, the team was able to test its LHC-inspired models.

While the numbers of electrons and positrons they detected agreed very well with their models, the muons were wide off the mark. They found that about 33% more muons were detected than predicted by the “EPOS-LHC” model and about 61% more were detected than predicted by the “QGSJet-II-04” model.

Firmer ground

This is not the first time an excess of muons has been spotted. In 2000, physicists working on the HiRes MIA array in Utah detected more muons than expected. Last year, a study of muons from showers nearly horizontal to Pierre Auger detectors also registered more muons than expected. However, this latest study puts the muon excess “on firmer ground”, according to Thomas Gaisser of the University of Delaware, because it involves both Cherenkov and telescope observations.

The research is described in Physical Review Letters, and writing in a commentary piece that accompanies the paper, Gaisser (who is not a member of the Pierre Auger team) highlights two possible explanations for the excess. One is that more collision energy than predicted by the models is going into the production of baryon–antibaryon pairs. The other possibility, according to Gaisser, is that the physics of the strong interaction is different at cosmic-ray collision energies than it is for LHC collisions. However, he points out that further measurements at the Pierre Auger Observatory will be needed to shed further light on the mysterious excess of muons.

Flash Physics: LHC smashes luminosity record, gender bias in astronomy, calculating axion masses

LHC smashes luminosity record

CERN’s Large Hadron Collider (LHC) has surpassed its luminosity goals for 2016, delivering 40 inverse femtobarns against a target of 25. For 2016, the LHC was expected to reach a peak luminosity of 10³⁴ cm^–2 s ^–1, but by the end of the run it was regularly operating 30% above that. The LHC also spent about 60% of its operational time delivering stable beams against a target of 50%. “I can’t overstate the significance of this, because the total number of collisions we deliver to the experiments – the integrated luminosity – determines the capacity they have to carry out the great research that they do,” says Frédérick Bordry, CERN director for accelerators and technology. Now that proton–proton collisions are complete for this year, the LHC will begin a two-week programme colliding lead-ions with protons at energies of 5.02 TeV and 8.16 TeV, respectively. This is the first time the LHC has performed lead-proton collisions since 2013.

Study charts decades of gender bias in astronomy citations

Astronomy papers with women as the first author have received 10% fewer citations than comparable papers with male first authors over the past 65 years. That is one conclusion of a study by Neven Caplar, Sandro Tacchella and Simon Birrer at ETH Zurich in Switzerland, which looked at more than 200,000 papers covering published in 1950–2015. While the difference between male and female citations fell between 1950 and 1990, the disparity has remained at about 6% since 1990. Women first authors also wrote 19% fewer papers than males in the seven years following their first paper. The trio also found that the number of papers with a female first author increased from 5% in the 1960s to 25% today. Writing in a preprint on arXiv, the trio also found that prestigious journals such as Science and Nature had the slowest increases in numbers of female-authored papers over the 65 year period.

Supercomputer nails down axion-mass range

Set of images showing the distribution of the dark matter in the universe — This set of images shows the distribution of the dark matter obtained from a previous numerical simulation carried out by the Virgo Consortium. The distribution was calculated for when the universe was about three-billion years old. The left panel displays the continuous distribution of dark-matter particles. The central panel provides a simplified view of the complex network of dark-matter structure according to the so-called halo model. The right panel highlights the dark-matter halos (shown in yellow) that represent the most efficient cosmic sites for the formation of galaxies. (Courtesy: Virgo Consortium/Alexandre Amblard/ESA)

In yet another attempt to nail down the elusive nature of dark matter, a European team of researchers has used a supercomputer to develop a profile of the yet-to-be-detected entity that appears to pervade the universe. Physicists led by Zoltan Fodor of the University of Wuppertal have predicted the masses of dark-matter candidates called axions using the JUQUEEN (Blue Gene/Q) supercomputer at the Forschungszentrum Jülich research institute in Germany. These hypothetical particles are promising dark-matter candidates that are not described by the Standard Model of particle physics but are predicted by an extension to quantum chromodynamics (QCD). Axions are thought to have exceedingly small masses and could, in theory, be detected directly. “However, to find this kind of evidence it would be extremely helpful to know what kind of mass we are looking for,” says team-member Andreas Ringwald at DESY in Hamburg. “Otherwise the search could take decades, because one would have to scan far too large a range.” The team’s simulations showed that if axions exist, they should have a mass of 50–1500 meV, making them up to 10 billion times lighter than electrons. This would require every cubic centimetre of the universe to contain on average 10 million such ultra-lightweight particles. “The results we are presenting will probably lead to a race to discover these particles,” says Fodor. The team says that within the next few years, it should be possible to either confirm or rule out the existence of axions experimentally. The simulations are described in Nature.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on the puzzling excess of atmospheric muons.

Science elevator pitches in Beijing

[brightcove videoID=ref:phw.live/2016-11-02-China-blackhole/1 playerID=106573614001 height=330 width=500]

By James Dacey in Beijing

Could you provide a short entertaining presentation of your research to a non-specialist audience, leaving them feeling both enlightened and inspired? How about trying to do it in a non-native tongue? That’s what several Chinese researchers did on Wednesday evening at the Science Slam event at the European Delegation headquarters in Beijing. The event was part of a day-long communications training workshop aimed at researchers who want to communicate their research to the general public and improve their ability to apply for research grants.

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Flash Physics: Antiprotonic helium passes symmetry test, Parkes radio telescope kicks off alien search, Nanobionic spinach detects explosions

Antiprotonic helium passes latest symmetry test

Australian radio telescope kicks off alien search

Nanobionic spinach leaves could detect explosions