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Electrons’ magnetic interactions isolated at long last

A measurement of the extremely weak magnetic interaction between two single electrons has been carried out by an international team of physicists. Using experimental techniques first developed for quantum-information and ion-trapping technologies, the team made its measurement despite the presence of magnetic noise, which is a million times stronger than the signal it was seeking. Apart from measuring magnetism at the shortest length scale thus far, the researchers say that their technique could be applied to other measurement scenarios where noise is a dominant factor, such as for quantum-error corrections.

Since the 1920s, researchers have known that the electron possesses an intrinsic angular momentum and an associated magnetic moment – known as its spin magnetic moment. Essentially, each electron acts like a tiny, indivisible magnetic dipole that is affected by magnetic fields. Although researchers have accurately measured the magnetic field of an individual electron, the magnetic interactions between two electrons have proved much more difficult to observe. When two electrons are separated by a very small distance (atomic-scale separations), the magnetic interactions are at their strongest and should be easy to measure. However, in this scenario Pauli’s exclusion principle and Coulomb electrical repulsion dominate the interactions between the electrons, drowning out the magnetic interaction. While these two effects weaken as the electrons move further apart, so does the magnetic interaction, which is then almost completely obscured by ambient magnetic noise.

Isolated interactions

One way of coping with this noise is to completely isolate the electrons from the environment – a technique that is often employed in quantum-information processing. This is the concept that Shlomi Kotler, from the Weizmann Institute of Science, Israel, and colleagues adopted to make their exquisite measurements. Indeed, Kotler says that the team’s measurement was performed at a scale “which is quite exotic – two microns. It is the size of an E. coli bacteria”, meaning that “the most dominant process is not of force between the electrons but of noise”. He further explains that the main tool used by the team to make its measurement was that of “decoherence-free subspaces” – a quantum-computing technique where a system is completely decoupled from its environment to protect information.

Kotler likens the difficulty of this measurement to trying to measure the size of a pea floating in the ocean, with huge waves of noise moving it erratically, across a distance of kilometres. While it would initially seem impossible to make the measurement (thanks to the pea’s constant movement), the trick would be to float alongside the pea. In that case, a wave would have the same effect on the pea and the observer, so that the effect of the waves would be inconsequential. In the researchers’ experiment, one electron is trying to sense the magnetic field of the other. “But that field is riding on top of magnetic noise in the lab, which is a million times bigger,” says Kolter. “The only way to make this measurement possible is to place the two electrons on an equal footing with respect to the ambient magnetic noise. This way, magnetic noise becomes irrelevant.”

Photograph of the experimental set-up, including the trap
Ions inside: Set-up of the experiment. In the middle, a linear Paul trap, designed to trap the charged particles, is viewed through the vacuum-chamber window. Laser beams passing through the side windows are used to manipulate the electron magnets with high precision, allowing for entanglement generation during the 15 seconds of the experiment. (Courtesy: Yoni Dallal)

To do so, the team uses two strontium (88Sr+ ) ions, in a vacuum chamber at a fixed distance of 2 μm from one another, held using a Paul ion trap. Each ion has a single ground-state, spin-1/2 valence electron and no nuclear spin. Using lasers tuned to the atomic transition of the ions, the team manipulated the electrons and prepared them in an initial state where the north pole of one electron is facing the north pole of the other. Like a regular bar magnet, the like poles repel each other and would rotate, thereby interacting. But as the magnets in this case are electrons, quantum effects come into play and the electrons become entangled in what Kolter describes as “both a north–north and south–south facing state”.

Elongated entanglement

Even more surprising is that this naturally created entanglement lasts for 15 s – a surprisingly long time for a system to remain in a coherent, quantum state. After that time, the researchers use laser pulses to detect “whether their north poles are facing or anti-facing each other”. By varying the separation between the two ions, they were able to measure the strength of the magnetic interaction as a function of distance – confirming the expected inverse-cubic (1/d3) dependence of the interaction.

Kolter told physicsworld.com that while the result itself was not surprising – current theories say that magnetism behaves similarly at all scales – it was how long the electrons were entangled for that was unexpected. “Our main surprise was the coherence – the fact that the electrons behaved quantum-mechanically for a ‘human-scale duration’ (15 s and more) and that the tiny forces of magnetism are still strong enough to entangle the two particles over this time. In many respects this is unprecedented.” Conventionally, quantum mechanics is thought to work for tiny systems at short time scales. The team’s system was rather large – 2 µm and so, almost macroscopic – and it still preserved the quantum-mechanical property of entanglement for an extremely long time.

Kolter points out that, nearly 20 years ago, quantum-computation experiments adapted advanced spectroscopic tools to generate entanglement between massive particles, and spectroscopy has been a driving force in experimental quantum computing ever since. Now, Kolter’s research has turned this around by using quantum-computing tools to “do a very sensitive spectroscopy experiment. We believe that this trend will continue to be fruitful in the near future”, he says. Beyond validating the behaviour of the magnetic force at the micron scale, the team’s system could be used to set a bound on “anomalous spin forces” that might come into play beyond Standard Model physics. But it could also be generalized and applied to other scenarios, such as for quantum-error correction protocols.

The research was published in Nature.

A network analysis of the FIFA World Cup

(Courtesy: Paolo Cintia and Luca Pappalardo)
(Courtesy: Paolo Cintia and Luca Pappalardo)

By James Dacey

The FIFA World Cup is under way in Brazil as the national teams from 32 nations battle it out on the pitch for the most prestigious prize in football. It is also an exciting month for football fans across the world as everyone suddenly becomes an expert on the game. Offices, bars and cafes around the world echo with the sound of post-match analysis.

This post-match dissection has now been taken to another level by a pair of computer scientists at the University of Pisa in Italy. At the request of Physics World, Paolo Cintia and Luca Pappalardo have carried out a network analysis of the opening match of the tournament, which saw the hosts Brazil defeat Croatia by three goals to one. Cintia and Pappalardo have viewed the match as if it were an evolving network where players represent nodes that interact by passing the ball to each other along “edges”.

(more…)

Women Rock Science author bags new student-science award

Hadiza Mohammed being presented with the inaugural IOP Student Science Publication Award last night.

The photo above shows me presenting the inaugural Student Science Publication Award, sponsored by the Institute of Physics and IOP Publishing, which publishes Physics World, to Hadiza Mohammed of the online magazine Women Rock Science. She is a working civil engineer currently doing a Master’s in advanced environmental and energy studies.

The award, which was launched this year, recognizes student journalists who produce a regular science publication and seeks in part to nurture the next generation of science writers. It forms part of the annual awards given by the Association of British Science Writers and was presented at a reception held at the Royal Society in London as the culmination of this year’s UK Conference of Science Journalists.

(more…)

Good scientists and honest people

In early 1948, less than three years after the end of the Second World War in Europe, Werner Heisenberg – the Nobel laureate and physicist leader of the failed German atomic bomb project – was invited to the UK as part of an attempt to repair relations between British and German physicists. While in Oxford, Heisenberg spent some time at the house of Francis (formerly Franz) Simon, a low-temperature physicist and one of the many German-Jewish scientists who had left Germany for the UK soon after Hitler came to power in 1933.

Like almost all German Jews, Simon had lost numerous members of his family, not to mention some scientist colleagues, in Nazi death camps. He had also worked enthusiastically in the British “Tube Alloys” programme to build an atomic bomb, and is credited with suggesting, in 1940, the basic process of separating fissionable uranium-235 from the more stable uranium-238 via gaseous diffusion of uranium hexafluoride through a porous barrier. (Initially, his wife’s kitchen sieve, hammered flat, served as the barrier.) This technique was subsequently adopted by the American-led Manhattan Project and further developed between 1942 and 1945, with some advice from Simon during his visits to the US.

In short, Simon was well acquainted with the difficulty of building an atomic bomb, and was under no illusions about what Hitler would have done with one if Heisenberg’s project had succeeded. As such, the conversation that took place between Simon and Heisenberg during the latter’s visit to Oxford must have been little short of surreal.

We know about this conversation because of a fascinating letter Simon wrote afterwards – a letter that is unfamiliar to biographers of Heisenberg, and is reproduced, apparently for the first time, in Nuclear Dawn, Kenneth McRae’s biography of Simon. The letter was written as a report to Simon’s colleague and friend Michael Perrin, a deputy director of Tube Alloys who had played a key role in corralling the chief German nuclear scientists at Farm Hall, Cambridgeshire, in mid-1945. During their enforced stay at the hall, British intelligence secretly recorded their revelatory private conversations – including Heisenberg’s incredulous and discombobulated reaction to a BBC radio report about the atomic bombing of Hiroshima on 6 August.

By the time he visited Oxford, however, Heisenberg’s attitude had changed. “Heisenberg claims that German scientists had no other wish than to prevent Hitler from getting the bomb,” Simon reported in his letter to Perrin. According to Heisenberg, he added, “They knew about everything, including the fast neutron reaction and the possibility of using plutonium, but all their actions were determined by their aim to mislead Hitler and the ‘high ups’ about the possibilities of a bomb. [Heisenberg] said that if he had gone to Hitler at the beginning of the war and told him what he knew, then he was quite sure that Germany could have developed the atomic bomb just like the Allies!”

When Simon openly doubted this account – without giving away his inside knowledge of the Farm Hall recordings – Heisenberg insisted on its truth. Simon’s analysis of the situation is astute: “I am quite sure that Heisenberg, like many other Germans, is a strictly honest person in his private life,” he wrote, “but as soon as the greater glory of the ‘fatherland’ is involved – and perhaps also his glory as a scientist – it is quite a different matter. Whether he now deliberately tells these falsehoods I cannot say. It is quite possible that … he has so persuaded himself that this picture is correct that he now seriously believes in it.”

Although Nuclear Dawn is the first book to include this letter, it is not the first biography of Simon. In 1966, 10 years after his premature death, Simon’s former secretary at Oxford’s Clarendon Laboratory, Nancy Arms, published a brief but exceptionally vivid portrait of him called A Prophet in Two Countries. Arms had the full support of Simon’s widow Lotte, who gave her access to his extensive personal papers (including his wartime diaries while advising the Manhattan Project), and Richard Rhodes drew on Arms’ account in his classic history The Making of the Atomic Bomb. Nuclear Dawn is similarly well informed: the author, McRae, is Lotte’s son-in-law, and he quotes from Simon’s diaries in great detail.

McRae is a retired political scientist, rather than a historian of science or a biographer. Accordingly, the strongest parts of his book are the sections about politics, especially those dealing with Simon’s dedicated but abortive attempts to encourage the British occupation authorities to de-Nazify German academe after 1945. Heisenberg’s arrogance and self-deception were, in Simon’s view, tolerable because of his brilliance, but he abhorred the retrograde reappointment of mediocre scientists known to have behaved opportunistically (or worse) before and during the war. In objecting to a proposal to invite an openly Nazi physicist, Eduard Justi, to the UK at the same time as Heisenberg, Simon argued to an unconvinced Nevill Mott: “What the world needs now are not so much good scientists – there are plenty of them – as honest people.” Simon always refused to accept the idea that science and politics belong in separate realms, which was the main excuse of his former German physics colleagues for their passivity in the Third Reich – as discussed in Philip Ball’s recent history Serving the Reich (see our review).

The weakest aspect of Nuclear Dawn is that it is neither a full-fledged biography nor a full study of the projects to build an atomic bomb in Britain, Germany, Japan, the Soviet Union and the US. Simon’s childhood and youth are virtually omitted, for example, and in a lengthy (if insightful) chapter comparing and contrasting the five national bomb projects, he entirely vanishes from view. A shorter book concentrating only on Simon would have worked better, and could perhaps have told us more about his other achievements, which included a British knighthood (added to the German Iron Cross, First Class he won for gallantry in the First World War) and his role in establishing what would eventually become the world’s most distinguished group in low-temperature physics. As the one-time head of the Clarendon Laboratory, Frederick Lindemann (Lord Cherwell) wrote of Simon in an obituary: “Not only was he supreme in experimental research; he had a clearer and more fundamental understanding of the basis of thermodynamics with statistical mechanics than any man since Einstein.” Despite its gaps, however, Nuclear Dawn is an invaluable source for historians of the Anglo–American atomic bomb project, especially as it concerns the life of a physicist who deserves to be more clearly remembered.

  • 2014 Oxford University Press £35.00hb 284pp

Web life: Excursion Set

So what is this site about?

Excursion Set is a blog written by Richard Easther, a theoretical cosmologist at the University of Auckland, New Zealand. “To a mathematician or an astrophysicist, the phrase ‘excursion set’ is a term of art,” he explains. “But it also suggests a series of adventures, and on my blog I make excursions into cosmology, astrophysics, particle physics, science news and scientific perspectives on everyday life.”

What are some of the topics covered?

As the above explanation suggests, it is common for Easther’s blog posts to begin with one subject and then lead, via a pleasant and logical path, to a different one. A blog post on “The angle of repose”, for example, begins with an account of Easther’s research-related visit to the Yukawa Institute for Theoretical Physics in Kyoto, Japan. Pretty soon, however, he takes an excursion to a nearby temple, and before you know it, he’s into the physics of Zen sand-gardening and the difficulties of maintaining the temple’s beautiful, UNESCO-listed sandcastle. At the end, he concludes that “playing with sand provides work for physicists as well as for gardening monks”. In another post, he declares that “making up stories about the material world seems to be one of the few universal human activities”, and then deftly turns an explanation of his recent work on N-body simulations into a romantic comedy of gravitational attraction.

Anything else?

Bad or over-hyped science reporting is another common theme. Unusually, though, he seems to think this is partly the fault of specialist science bloggers, and not just mainstream journalists. Bloggers and Tweeters are, he notes, “key consumers of the media releases cranked out by Nature and university media people, and come largely from the same demographic as the scientists who complain about pressure to sex [their research] up for Nature. If Nature didn’t exist, would we have needed to invent it?”

Why should I visit?

Easther is a good science communicator, and although his blog isn’t updated all that often (about twice a month on average), he’s had some interesting things to say when big science stories have emerged. In March 2013, for example, he live-blogged the release of data from the Planck team, and earlier this year he was one of many contributors to online discussions of the BICEP2 results. This debate, he points out, is a great example of “open science” in action, with hundreds or even thousands of scientists worldwide scrutinizing the results to determine whether they really constitute evidence for cosmic inflation. And contrary to the idea that nobody would eat sausage if they could see it being made, he argues, “a sausage factory with a window is more likely to be a sausage factory that is spotlessly clean and uses top-quality raw materials”.

Can you give me a sample quote?

From a post about BICEP2 on 17 April: “For theoretical physicists, ambulance chasing involves getting papers out quickly after a major data release. Some ambulance chasers make significant contributions, some are just trying to draw attention to their earlier work, while others are banging out insubstantial papers in the hope that they will be cited by their slower colleagues. But whatever their motives, cosmologists have certainly been busy: the BICEP2 discovery paper has been cited 188 times on arXiv, all in preprints written within a month of the original announcement. I am pretty sure this is a world record, and you can always check the current tally. In fairness, though, cosmologists were so giddy about BICEP2 it wouldn’t have surprised me if someone had stolen an ambulance and driven it in circles, flashing the lights and letting rip with the siren.”

Entangled clocks could provide accurate world time standard

Plans for a global network of atomic clocks that are synchronized using quantum entanglement have been unveiled by physicists in the US. The resulting universal time standard would be more accurate than is currently possible with individual atomic clocks, and the network could also be used to do a range of fundamental and applied research, such as mapping the Earth’s gravitational field or even testing new theories of gravity. While some of the technologies needed to build the network already exist, other elements still need further development.

Atomic clocks have revolutionized the world in ways that were unimaginable when the first atomic clock was built in 1949. The Global Positioning System (GPS), for example, uses atomic clocks to measure the travel time of signals from four satellites to a GPS receiver almost anywhere on Earth. As clocks have become more accurate, researchers have proposed ever-more-exotic applications such as relativistic geodesy, in which the strength of gravity at various points, and therefore the local density of the Earth, could be mapped by measuring variations in the rates of clocks at different locations. Scientists have also suggested that ultra-accurate atomic clocks placed in outer space could detect gravitational waves.

The ultimate limits on the stability of a single atomic clock are determined by Heisenberg’s uncertainty principle, which limits how precisely a system’s oscillations can be measured. This has been drastically reduced in recent years with the invention of optical lattice clocks containing thousands of particles, allowing the quantum uncertainty to be reduced by averaging. In the new research, Mikhail Lukin’s quantum-optics group at Harvard University has teamed up with Jun Ye’s quantum-metrology group at the National Institute for Standards and Technology (NIST), the JILA Lab and the University of Colorado. Ye’s team holds the current world record for clock accuracy, and now the two groups have come up with a way to make an even better timekeeper by effectively combining several atomic clocks into one.

Entangled super clock

Their plan involves many clocks, all stationed in different countries and connected by both classical and quantum links. In each cycle of the synchronization process, one clock (the “central clock”) sends out one photon from an entangled pair to each of the other clocks, via the quantum link. This allows the clocks to prepare a single, collective entangled state and to transfer this entangled state on to the atoms in the clocks. Each clock then measures this collective entangled state and, after doing so, it uses the classical link to send both its own laser frequency and the phase difference it measures between this laser frequency and the atoms to the central clock. The central clock can then calculate the average phase difference and use it to calculate the correction that needs to be applied to the frequency to bring all the clocks back into phase. The clocks thereby reduce their uncertainty by collectively averaging over all the atoms in all the clocks, effectively behaving as a single, super-accurate atomic clock.

This distributed set-up would provide all the participating parties with access to the ultra-precise time signal at any time, creating a universal time standard. The network would also be more secure against physical attack because, even if one of the systems were disabled, each party could fall back on its own atomic clock. Finally, it might be possible to use changes in the rate of individual clocks to detect gravitational waves or even to test new theories of gravity. “If you have this very good reference, and there is a local node that doesn’t follow this reference, then that’s a signal,” explains Lukin. It could either mean that the clock is not working properly, he says, or it might represent something more fundamental. In principle, one of the clocks could be taken out of the Earth’s gravitational field to make non-local tests of fundamental physics, for example, although the engineering challenges would be severe.

Far-fetched but well-reasoned

Eugene Polzik, a quantum-optics expert whose team at the Niels Bohr Institute in Copenhagen built the first atomic clock containing entangled atoms, describes the proposal as “very interesting and important”. He says, however, that before the scheme can be realized, two main technical hurdles must be overcome. First, scientists must successfully generate the giant quantum state containing far more atoms than has so far been achieved, and second, quantum repeaters will have to be developed to allow entanglement distribution around the world. “We have to dream,” he concludes. “And it’s always good to have a far-fetched proposal, which is backed up by reason, and that’s exactly what this paper is doing.”

The proposal is described in Nature Physics.

From the lab to the marketplace

Many physical scientists at some point in their careers believe they have a brilliant idea for a commercial product based on their research. But there is a world of difference between excitedly sharing that idea with a colleague over a cup of coffee and actually creating a successful product that can slot nicely into a gap in the market. In this pair of video interviews, Physics World meets business professionals involved in the process of commercializing scientific research.

In this first interview, venture capitalist Stan Reiss explains what people in his profession do. Reiss, who works for the international firm Matrix Partners, talks about how spin-off companies can seek financial investment from a range of different sources, including venture capitalists and angel investors. He also discusses the types of things he is personally looking for when deciding whether to invest in a science-based spin-off.

“Not all markets are big, not all inventions are equally useful,” he says. “If you’re going to take that kind of risk, particularly in a physics-based thing that has a lot of technical risk in it, then that risk only makes sense if the upside is commensurate.”

Later in the interview, Reiss explains what business professionals mean when they talk about the “valley of death”, a phase all spin-offs must navigate in the early stages of product development. “That is a situation where you’ve gotten off the ground, you’ve built the team, and the results are not yet there in order for you to be commercial,” he says. “In physics-based start-ups that happens very, very frequently because physics is hard and commercializing physics can take a very long time.”

In the second interview we meet Leon Sandler, who works at the MIT Deshpande Center for Technological Innovation. Sandler explains how the centre was founded at the Massachusetts Institute of Technology (MIT) in order to support the commercialization of technology developed at the university. He talks about the types of innovation it nurtures and the different forms of support that it can provide. “What we’re doing here at MIT is really taking science from the lab and trying to build those enabling technologies that the Amazons, the Microsofts, the Apples and the Googles will actually use later,” he says.

Sandler explains that it is essential for spin-offs to possess a range of skills and knowledge. “You generally want more than one person. Someone who understands business, who understands finance, who understands marketing. A technical person who not only understands what the technology can do, but really has the engineering skills to build something, to produce it. And the fundamental thing in a company is that you need good people and leadership,” he says.

You can find out more the process of commercializing research in the field of materials science via the TMR+ blog. It is published by IOP Publishing, which also publishes Physics World.

Qubits team up to detect errors

For the tiny units of quantum information known as qubits, teamwork pays off. So say researchers based in Austria and Spain, who have stitched together a record seven qubits in a way that enables detection of errors in any of the individual qubits.

Qubits, like the classical bits in today’s computers, have two possible states – up or down, for example. Unlike classical bits, however, qubits can also be in a superposition of both up and down simultaneously. Individual qubits can then be quantum-mechanically entangled with one another, such that they share a single superposed state. Using these capabilities, quantum computers promise to someday perform ultrafast computations to quickly solve certain problems, such as factoring large numbers and searching huge databases.

Fragile states

But quantum-computer developers must first overcome a major challenge: quantum states are fragile and easily shattered by interactions with the environment. These interactions lead to errors, such as a physical qubit flipping its state or becoming out of phase with its neighbours. Therefore, to preserve quantum states long enough to perform useful algorithms, scientists need to join physical qubits into information-processing units called “logical qubits” that can detect and correct errors in their individual components. Researchers have entangled up to five qubits in ways that allowed detection of bit-flip and phase-flip errors separately, but nobody has demonstrated a scheme that can detect both kinds of errors at once. For a fully error-correcting logical qubit, theory predicts that at least seven entangled physical qubits are needed.

Seeking to make such a logical qubit, the research team, led by Rainer Blatt of the University of Innsbruck in Austria, confined seven calcium ions in a trap with electric fields. The ions were lined up like beads on a string and were cooled to near absolute zero. At this temperature, two of the ions’ electronic energy levels can function as qubit states. The scientists then entangled the qubits and created errors by flipping the state, the phase or both the state and phase of one qubit at a time using lasers. Because of how the qubits were entangled, the researchers could tell which qubit had an error and what kind of error it was by measuring light fluorescing from the trapped ions.

It’s alive!

To actually correct errors, the team will need to incorporate into its set-up at least one additional qubit to “read out” errors occurring in the other qubits. To scale up towards a working quantum computer, scientists will also need to develop methods of trapping ions not just in lines but in 2D grids. These steps, while challenging, are “definitely on the agenda”, says Blatt. He says his team’s achievement is “the first decisive step…towards what I call keeping a qubit alive”.

Blatt’s team also performed computational operations on its logical qubit by using lasers to change the states of individual qubits in a controlled way. The researchers showed that they could reliably perform most operations without destroying the qubits’ delicate entangled superpositions. By adding additional qubits to their scheme, the scientists think they can perform all of the operations needed for quantum algorithms.

The achievement “is an interesting and important step” towards a working quantum computer, says John Martinis, a physicist at the University of California, Santa Barbara, who was not involved in the work. He points out that the new study confirms theoretical predictions of how quantum error correction should work. “People expected it to be correct, but it’s really nice to have them directly demonstrate that.” He also applauds Blatt’s team for creating the first logical qubit from seven physical qubits. In April Martinis’s team reported entangling five superconducting qubits and performing nearly error-free operations on them. His team is now working on a similar experiment with more qubits. “We obviously have to catch up now,” he says.

The research is published in Science.

Shutdown of nuclear-waste site threatens neutrino lab

An explosion and a series of radioactive leaks have forced the closure of the Waste Isolation Pilot Plant (WIPP), which is located in a salt mine near Carlsbad, New Mexico, US. The incident has put a temporary halt to the Enriched Xenon Observatory-200 (EXO-200) particle-physics experiment. Installed at WIPP in 2007, the experiment seeks to answer whether neutrinos are Majorana particles – entities that are their own antiparticles. Principal investigator Giorgio Gratta, a Stanford University physicist, hopes to restart operations in early autumn. But for now, he says, “the experiment is closed off”.

WIPP, which holds low- and medium-level radioactive waste, has provided an effective working environment for EXO-200. The experiment is installed 665 m below ground, where it is shielded from cosmic rays, while the salt in the mine produces much less background radioactivity than other types of rock. But February’s explosion and leakage, which occurred nine days after a truck caught fire inside the facility, left no choice but to close the plant to prevent more radioactive material from reaching the surface.

Suspicious drums

Authorities have sealed off the areas containing suspect drums of waste, and are changing the above-ground filters that received material during the fire, explosion and release of radiation. They are also investigating the cause of the explosion, so far without a conclusive result. “We have no finalized timetable for when we’ll resume waste-disposal operations,” says WIPP spokesperson Ben Williams.

EXO-200, which had been undergoing an upgrade, is one of the most sensitive experiments to search for neutrinoless double β decay. Conventional double β decay occurs when two neutrons in an unstable nucleus become protons with the ejection of two electrons and two antineutrinos from the nucleus. EXO-200 was the first experiment to observe this behaviour in xenon. In the neutrinoless form, which has yet to be observed, the electrons alone carry away all the energy from the reaction – and theory indicates that this is possible only if the neutrinos are their own antiparticles.

Postponed upgrade

EXO-200’s first two years of operation revealed no sign of the reaction, according to results reported last week (“EXO-200 narrows its search for Majorana neutrinos”). The now-postponed upgrade, which involves improving the detector and upgrading the electronics, is intended to improve the experiment’s sensitivity by a factor of three. The team is also designing a larger and more sensitive experiment that will have to be located more deeply underground and on a more stable foundation than WIPP’s salt mine. A possible location for that experiment is the SNOLAB underground lab in Ontario, Canada.

Gratta hopes, however, that his team will be allowed back into the plant early this month. “The tentative schedule has us restarting in early fall,” he says. “If we couldn’t get underground for a year we would lose interest and concentrate on the design of the new experiment. But I see no evidence we have to worry about that.”

Science on ice: photographing physicists in Antarctica

It is my search for adrenaline and adventure that led me to Antarctica. As a photographer who specializes in taking scientific and industrial images, I have travelled to many locations around the world that are often dangerous and hard to reach. Often, I’m obliged to wear specific clothing and equipment that protect me from the environment I am in, and for me this difficulty and danger are a large part of the attraction of my job.

But my trip to Antarctica was one of my most exciting yet. After months of research, meetings and logistical planning, in October last year I set off on a photographic project to document research supported by the Italian Science Foundation in the Antarctic. My destination was the Italian Mario Zucchelli Station, at Terra Nova Bay on the Ross Sea, and later the French–Italian Concordia Research Station, situated 1200 km inland on the Antarctic Plateau at an elevation of 3233 m.

Two photos: a man in bulky cold-weather clothing including goggles and cloth over his mouth; a glacier with sky and sun behind
On reflection (Left) The environment in Antarctica requires specific clothing and equipment, but also provides an opportunity to see views free from atmospheric pollution. (Right) After taking a few images, Enrico Sacchetti realized that glaciers in the Antarctic are not purely white, but contain many shades of blue. This is because a glacier absorbs more of the red wavelengths entering it than it does of the blue. (Courtesy: Enrico Sacchetti/PNRA)

Getting there was a feat in itself– a 30-hour journey to Christchurch, New Zealand with about 50 kilos of baggage – followed, after a 36-hour stopover, by another 8-hour flight to Antarctica on-board a noisy C-130 military plane. I factored in the stay in New Zealand as I did not want to risk arriving on the ice so tired that I could not be immediately active.

As soon as I stepped off the C-130, the alien nature of Antarctica was truly jolting. I feasted on infinite views of the ice, which gave me an incredible feeling of isolation; I could taste the air, which was bitingly cold at –22.5 °C. But, as a photographer, what struck me most was the quality of the light. Almost completely absent of atmospheric pollution, the air was crystal clear. Following the researchers on planes, helicopters and snowmobiles to remote sites gave me a unique perspective of Antarctica and its scientific adventurers; I felt privileged to visit these places that almost no-one has seen before.

Wide snowy landscape with two snowmobiles ridden by figures dressed in red
Adventures in Antarctica Enrico Sacchetti followed researchers to remote sites via snowmobiles. (Courtesy: Enrico Sacchetti/PNRA)

At Terra Nova Bay I photographed glaciers as well as scientists collecting silverfish egg samples, before travelling inland to Dome C – one of several summits of the flat Antarctic Plateau, and the site of Concordia Station. The transparency of the atmosphere here makes the station well suited to astronomy – stars can be observed even while the Sun is at an elevation of 38°. Experiments located here include the International Robotic Antarctic Infrared Telescope (IRAIT), which is used to study cool stellar objects in our galaxy in the infrared range, and the Antarctic Search for Transiting Exoplanets (ASTEP) 400 optical telescope, designed to identify exoplanets that are transiting their stars. Off-site there is also part of the Super Dual Auroral Radar Network (SuperDARN) – an international radar network for studying the upper atmosphere and ionosphere.

Two photos: a group of people in red snow suits hold a drone overhead as another figure digs the snow; a lone figure in red holds a weather balloon aloft
Up and down (Left) Scientists from the Italian Science Council institutes ISMAR and ISSIA drill a hole in the 2 m thick ice in Terra Nova Bay for capturing silverfish egg samples. (Right) Evening launch of a meteorological balloon into the upper atmosphere above Concordia Research Station. (Courtesy: Enrico Sacchetti/PNRA)

To my surprise, the photographic equipment held up perfectly in temperatures of –48.9 °C. I’m certain that the low humidity was a major factor. After all, Antarctica is one of the driest places on Earth – the Antarctic Plateau being the world’s largest desert.

Although I faced cold weather and high winds, these hardships did not take anything away from the experience of being surrounded by vast natural beauty and enveloped by such pure light. In fact, the inherent difficulties of the White Continent made me appreciate each and every image I shot.

Row of large aerials in snowy landscape
Wintry web Part of the Super Dual Auroral Radar Network, installed in 2013 near Concordia Research Station. (Courtesy: Enrico Sacchetti/PNRA)
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