Page 1489 – Physics World

Home » Page 1489

To Svalbard in search of little green men

Svalbard Credit: NASA

By James Dacey

Where do we come from? Are we alone? Where are we going? They’re certainly not shying away from the big questions here at the AAAS conference in San Diego. This morning we were celebrating 50 Years of Astrobiology, which is basically the study of the origin and evolution of life on Earth and the search for signs of extraterrestrial life. The research is about as multidisciplinary as you can get drawing on expertise from astronomy, physics, biology, chemistry, geology, and the planetary sciences at the very least.

As interesting as those big questions are, however, I’m usually left frustrated by the vagueness of the actual research. The scientists seem to be staring hard at images and spectra from planets in search of signs of habitable conditions like on Earth, but they don’t really seem to know what they’re looking for. “We can’t say exactly what the conditions necessary for life are. We don’t know whether extraterrestrial life would have evolved in the same way. We don’t really know where to look,” they say.

Well this morning I was pleased to encounter one astro-scientist who seemed a lot less defeatist and was taking a much more down to Earth approach to the search for extraterrestrial life. Pamela Conrad, a planetary scientist at NASA’s Jet Propulsion Laboratory, spends her days surveying desolate places on Earth in search of key indicators of habitability. In essence, she goes out into the field and assesses the large-scale physics and chemistry of a remote location before moving in to see whether the site can support life.

In her talk she described one adventure that took her to the remote archipelago of Svalbard, located between mainland Norway and the North Pole. After extensive surveying, Conrad came to conclude that a range of factors including temperatures, light, and even the steepness of slopes had an influence over which parts of the land could support life. One interesting factor is the type of underlying geology – dolerite, an igneous rock, is a good place for life on Svalbard because it can warm up easily then contain heat over time.

And this research is more than speculative because the findings could be used in NASA’s Mars Science Laboratory (MSL) mission, which is due to launch in 2011. Once the craft has landed, a NASA rover will collect samples to see whether the planet could have supported life at some point in its history. It is important, therefore, to choose a site that at least has a fighting chance of being habitable – that is assuming we want to find those little green men!

To prevent another 'climategate', researchers need to embrace social media

Scientists discuss the needer for greater transparency in climate research

By James Dacey

Those scientists involved were careless and, to prevent this happening again, the research community needs to deal with the threat posed by new types of media. These were the conclusions of Harvard climate scientist James McCarthy when describing two recent climate scandals, which were both fuelled by viral activity in the blogosphere. McCarthy was talking today at the annual meeting of the American association for the Advancement of Science (AAAS), which is taking place in San Diego, California.

Since that email scandal broke back in November, bloggers across the globe have chipped with strong criticisms of the scientists at the University of East Anglia (UEA) in the UK. You will remember that leaked emails revealed the researchers to have “sexed-up” certain aspects of their climate data to fit a general warming trend. Then, in January, came another blow to climate science when it came to light that the Intergovernmental Panel on Climate Change (IPCC) had included in their latest scientific report a near baseless claim that the central and eastern Himalayas could disappear by 2035.

McCarthy, who previously served as co-chair of an IPCC Working Group, strongly emphasized that these were two isolated incidents, with have no impact on the strong scientific consensus over climate change. However, he also recognises that the climate science community could have done more to deal with the allegations before the issues blew-up into fully-blown scandals. He feels that one way to do this is for researchers to start using social media themselves – which includes blogs, Facebook and Twitter – to disseminate research with the public. “I can tell you, a lot of groups are trying to think about creative ways of entering into the discussion,” he said.

The connected worlds of Japanese art and electromagnetism

Boy Viewing Mount Fuji, Katsushika Hokusa

By James Dacey

At their foundations, physics and art are connected by form. This was the underlying message of a talk by Jack Leibowitz, a condensed matter researcher at the Catholic University of America. He was speaking today at the annual meeting of the American Association for the Advancement of Science (AAAS), which I’m currently at in San Diego, California.

Leibowitz draws an unlikely comparison between the electromagnetic equations of James Clark Maxwell and the Boy Viewing Mount Fuji, a painting by Katsushika Hokusa. The Japanese artist is perhaps better known for his work The Great Wave off Kanagawa, which decorates the living room of just about every student flat in the land.

In is talk, Leibowitz gave the standard eulogy about the irresistible simplicity of Maxwell’s equations, but he compared this with the same appreciation of design that rewards the viewer of Hokusai’s great painting. “We see the powerfully rendered apposition of shapes: the peak of Mount Fuji accentuated by placement of the dark cloud right behind it, which takes the eye to the darkest dark and the lightest light,” he said.

This was certainly high-brow stuff! Actually, if I’m being completely honest, the talk fell a little bit flat on the audience here in San Diego. Leibowitz came across as a bit aloof in his presentation style, and the formality appeared to leave the non-specialist audience despondent – not a single question was asked when things were opened up to the floor. It’s a shame because it seems like a really fascinating topic, so, if interested, I would skip the talks and pick Leibowitz’s book – Hidden Harmony: The Connected worlds of Physics and Art.

First ‘heavy-fermion’ material made in 2D

Physicists in Japan have created the first 2D “heavy-fermion” material – providing the best evidence yet that heavy fermions undergo a quantum phase transition. The material was made using molecular beam epitaxy (MBE), which also allowed the researchers to carry out the first systematic study of how the electronic properties of a heavy-fermion material change when it is made into layers just one molecule thick. The results could help physicists to understand why some other layered materials superconduct at relatively high temperatures.

Heavy-fermion materials such as cerium indide (CeIn₃) are so called because their conduction electrons, which are fermions, move as if they are hundreds of times more massive than electrons in conventional metals such as copper. This large “effective mass” arises because the interactions between the electrons are very strong. Similar strong interactions are thought to play an important role in high-temperature superconductors – a class of materials that physicists have struggled to understand for nearly 25 years.

Heavy-fermion materials therefore provide a useful testbed for high-temperature superconductors. Even better, a wide range of heavy-fermion materials with slightly different electronic properties can be made by combining metals such as indium or aluminium with rare-Earth elements like cerium. High-temperature superconductors cannot be easily altered in such systematic ways.

Layered structures

Physicists are particularly keen to understand how heavy fermions behave in materials with layered crystal structures because high-temperature superconductors are also made from 2D layers. In particular, layered heavy-fermion materials would let them test the idea that high-temperature superconductivity is linked to the electrons being confined to 2D crystalline planes.

That link is backed up by the observation that some superconductors exist in states near to a quantum phase transition. Unlike conventional phase transitions, which occur at finite temperatures and are driven by thermal fluctuations, quantum phase transitions occur at absolute zero and are driven by quantum fluctuations, which are more persistent in 2D materials.

Unfortunately, while physicists have had some success in growing 3D heavy-fermion crystals, they had struggled to find materials that contain the desired 2D confinement. Now, however, Yuji Matsuda and colleagues at the University of Kyoto and Nagoya University have borrowed a technique from the semiconductor industry to create the first layered heavy-fermion materials.

Matsuda’s team used molecular beam expitaxy (MBE) to deposit 30 alternating layers of CeIn₃ and lanthanum indide (LaIn₃) on an atomically flat substrate. LaIn₃ is used because it has a similar crystal structure to CeIn₃, but is not a heavy-fermion material. The team made several different structures this way – all with LaIn₃ layers four molecules thick – but with CeIn₃ layers that varied from one to eight molecules thick.

2D versus 3D

The LaIn₃ layers are thick enough that there should be no coupling between electrons in adjacent layers – which means that each CeIn₃ layer should behave as a separate and isolated system. Furthermore, the one-molecule-thick layers should behave as a 2D material, whereas the eight-molecule-thick layers should exhibit 3D behaviour.

The team looked for evidence of a quantum phase transition as the CeIn₃ layers became thinner. Although it is impossible to cool a sample to absolute zero, Matsuda and colleagues were able to chill their structures to 100 mK. They found two tantalizing bits of evidence pointing to a quantum phase transition between magnetic and non-magnetic phases of CeIn₃.

First, the resistivity of the material was found to increase when exposed to a magnetic field. Second, the resistivity of the material shifted from being a quadratic function of temperature for thick CeIn₃ layers to a linear function of temperature for the thinnest layers. Both of these suggest that electrons are scattering from quantum magnetic fluctuations in the CeIn₃ layers.

Missing superconductivity

“This study has shown that a quantum critical point occurs in this heavy-fermion material,” says Suchitra Sebastian of the University of Cambridge in the UK. However, she points out that superconductivity was not seen in this system – something that she hopes will be seen in future MBE experiments.

Instead, the resistance of the thin layers is very large, which Matsuda and colleagues believe is related to the diffusion of lanthanum (La) atoms into the CeIn₃ layers. These impurities would scatter the electron pairs needed for superconductivity. This problem could be alleviated by using a spacing material other than LaIn₃.

The study is described in Science 327 980.

Tracing nuclear dust

Image courtesy: The American Physical Society

By James Dacey

Any human activity leaves behind dust, and, if we look closely at this dust, it will always provide a clue to the activity that produced it. This is the idea of nuclear forensic scientist, Klaus Lützenkirchen, who draws an analogy between crime scene investigation and the need to monitor global nuclear activities in a more scientific fashion. Lützenkirchen was speaking today at the annual conference of the American Association for the Advancement of Science (the “triple A-S”), which kicked-off today in San Diego, California.

Earlier in the day, Vice President Joe Biden had addressed this same issue during a speech at the White House, and the American Physical Society (APS) has just released a report, Technical Steps to Support Nuclear Downsizing.

Lützenkirchen, who is head of the nuclear safeguards and security unit at the European Commission Joint Research Centre (JRC), admits that his analogy does break down somewhat as nuclear fingerprints rarely tend to be unique. He proposes, therefore, building a profile of nuclear dust (actual, not figurative, dust), focused on the analysis of chemical, morphological and isotopic qualities. In this way, scientists can collect vital clues to the origins of intercepted nuclear material.

This discussion of international nuclear activities is strongly in keeping with the theme at this year’s AAAS meeting, “Bridging Science and Society”. I’m here in sunny San Diego (yeah, life’s cruel sometimes), so watch this space for more entries from the meeting in the coming days.

Ultracold magnetic atoms bode well for quantum studies

Physicists in the US have for the first time trapped ultracold atoms of dysprosium, the most magnetic element in the periodic table. The breakthrough could open the door to a greater understanding of superfluidity, highly sensitive probes of magnetic fields, and new ways to read and encode quantum information.

Researchers would like to trap as many of the periodic table’s elements as possible, because the unique properties of each allow for different simulations of condensed-matter systems. The typical method involves a magneto-optical trap (MOT), in which a laser causes atoms to temporarily absorb photons and jump into an excited state. These photons give the atoms a push that, combined with the right magnetic field, is directed towards the centre of the group and keeps the atoms cooled and trapped.

Yet some elements have proved easier to trap with MOTs than others. Dysprosium has long been considered to be a difficult candidate because it has so many metastable states close to its ground state. Every time an atom falls into one of these, it would need a separate laser of the correct wavelength to return it to the ground state where the original laser functions. Dysprosium has more than a hundred metastable states, which, researchers assumed, would mean more than a hundred different lasers.

Success with erbium

However, recent research has shown that metastable states do not preclude trapping altogether. In 2006 physicists Jabez McClelland and James Hanssen at the National Institute of Standards and Technology in the US discovered that they could use an MOT to trap erbium – another element with numerous metastable states. It worked because the magnetic field strongly coupled to the magnetic moments of the atoms, thereby keeping them trapped long enough for them to fall back into their ground state of their own accord.

No-one could have predicted before we did the experiment that this would work Benjamin Lev, University of Illinois

It is this work of McClelland and Hanssen that inspired Benjamin Lev and colleagues at the University of Illinois at Urbana-Champaign to try an MOT with dysprosium. “No-one could have predicted before we did the experiment that this would work – and work so well,” says Lev. “Theories of dysprosium structure – and data on its structure, like metastable lifetime – were just too poor to provide a predictor.”

In the Illinois group’s system, dysprosium is first heated to 1250 °C so that it expands through a pinhole, creating an atomic beam. Four lasers then slow the beam down until it is at near rest and glides into a high-vacuum chamber. Finally the application of six laser beams and a magnetic field forms the MOT and cools the atoms – of which there are almost a billion – to between 10 and 1000 microKelvin.

‘A clear breakthrough’

Peter van der Straten of Utrecht University in the Netherlands calls the system “a clear breakthrough in the world of laser cooling and trapping”. However, he is unsure of the additional benefits of dysprosium over erbium or chromium, which also have strong magnetic moments and which are therefore attractive for simulations of superfluid states. Indeed, chromium has even been cooled into a Bose–Einstein condensate (BEC), which is a prerequisite for such simulations. “It is to be expected that [Lev’s group] will try to go that way quickly, and, because they have a large number of atoms, they are very likely to succeed,” he adds. “However, the story of chromium has shown that the path to BEC is not simple due to the strong interactions, and that many hurdles have to be taken before victory is achieved.”

Still, Lev is not deterred. As well as creating a dysprosium BEC, his group is planning to use the system as a quantum-information processor, as a microscope for imaging magnetic materials with high resolution and sensitivity.

The work is described in Phys. Rev. Lett. 104 063001.

Fermi pins down a colossal accelerator

Matter ejected from a supermassive black hole travels several light years before being accelerated to nearly the speed of light. This is the surprising conclusion of an international team of astronomers who used the Fermi Gamma-ray Space Telescope to study radiation from a blazar – a supermassive black hole that fires an intense beam of radiation directly at Earth. The result is at odds with some theories that suggest the acceleration occurs much nearer to the black hole.

Up to a billion times heavier than the Sun, supermassive black holes are mind-boggling entities that dominate the centre of most large galaxies. Many are surrounded by a thin “accretion disc” of matter that swirls into the black hole like water going down a drain. Near the centre of the disc, the matter is so hot that atoms are stripped of electrons to create a rotating plasma that generates huge magnetic fields.

In some supermassive black holes the magnetic field lines pop out of either side of the disk like uncoiling springs, taking jets of matter with them (see figure). If one of the jets happens to point towards Earth, astronomers see a “blazar” – literally, a blaze of radiation at energies all the way up to the highest detectable gamma rays. The radiation is focused into a tight beam by a process called relativistic beaming, which means that it is created in a region of the jet that has been accelerated to about 95% of the speed of light.

Flaring blazar

But exactly what drives this acceleration to near light speed – and exactly where it occurs along the length of the jet – has long been a mystery. Now, however, the Fermi astronomers, and colleagues using several other ground- and space-based instruments, have an answer after studying a 20-day increase in the intensity of gamma rays emitted by blazar 3C 279. They also measured how the polarization of visible light changed during this flare – visible light is polarized because it is produced by electrons orbiting the magnetic field lines in the jets.

They spotted a big change in polarization, which they think occurs as a huge “blob” of ejected material encounters a bend in the jet located at least 10,000 black-hole-radii away – roughly 10 light-years – from the black hole itself. As this polarization rotation occurred exactly at the same time as the flare itself, they conclude that the flare must also be produced by the blob of ejected material. The blazar was therefore produced at a distance that is up to a thousand times further from the centre of the hole than had been predicted by some models.

Concerted coordination of telescopes

Andy Young, an astrophysicist at the University of Bristol in the UK says that the work in an example of what can achieved when astronomers make “a concerted effort to coordinate various observatories”. Young, who was not involved in the 3C 279 analysis, told physicsworld.com that Fermi is currently monitoring a number of different blazars so astronomers can combine observations from a number of flares.

One important goal of such studies is to gain a better understanding of how supermassive black holes grow by accreting matter. Not all black holes eject matter in jets, and understanding why jets occur could provide important insights into the evolution of galaxies and galaxy clusters. This is because the jets are so powerful that they can heat up the gas in vast areas of space, which appears to affect how galaxies grow.

The work is reported in Nature 463 919.

WISE opens its eyes on the sky

Image of stars being born in a cloud of gas and dust. Inset shows the centre of the cloud taken by NASA’s Hubble Space Telescope (credit: NASA)

By Michael Banks

NASA has released the first images taken by its Wide-field Infrared Survey Explorer (WISE space telescope, which launched in mid December.

The seven awe-inspiring images include a star-forming cloud teeming with gas, dust and massive newborn stars (above), a detailed picture of the Andromeda galaxy — the closest large galaxy to the Milky Way — and a comet streaking across the sky.

Costing $320m, WISE is an infrared space telescope that will probe the coolest stars in the universe and the structure of galaxies at four wavelengths between 3 – 25 micrometres. As WISE is designed to detect infra-red radiation from cool objects, the telescope and detectors are chilled to 12 K with liquid helium.

WISE will circle the Earth’s poles at an altitude of 525 km scanning the entire sky one-and-a-half times in nine months where it will also measure the diameters of more than 100 000 asteroids.

Look out for more amazing images soon.

Image of the Andromeda galaxy taken by NASA’s WISE craft (credit: NASA)

Gravity’s effect on time confirmed

Physicists in the US and Germany have used two fundamental tenets of quantum mechanics to perform a high-precision test of Einstein’s general theory of relativity. The researchers exploited wave-particle duality and superposition within an atom interferometer to prove that an effect known as gravitational redshift – the slowing down of time near a massive body – holds true to a precision of seven parts in a billion. The result is important in the search for a theory of quantum gravity and could have significant practical implications, such as improving the accuracy of global positioning systems.

Gravitational redshift follows on from the equivalence principle that underlies general relativity. The equivalence principle states that the local effects of gravity are the same as those of being in an accelerated frame of reference. So the downward force felt by someone in a lift could be equally due to an upward acceleration of the lift or to gravity. Pulses of light sent upwards from a clock on the lift floor will be Doppler shifted, or redshifted, when the lift is accelerating upwards, meaning that this clock will appear to tick more slowly when its flashes are compared at the ceiling of the lift to another clock. Because there is no way to tell gravity and acceleration apart, the same will hold true in a gravitational field; in other words the greater the gravitational pull experienced by a clock, or the closer it is to a massive body, the more slowly it will tick.

Confirmation of this effect supports the idea that gravity is a manifestation of space–time curvature because the flow of time is no longer constant throughout the universe but varies according to the distribution of massive bodies. Reinforcing the idea of space–time curvature is important when distinguishing between different theories of quantum gravity because there are some versions of string theory in which matter can respond to something other than the geometry of space–time.

Universality of freefall

Gravitational redshift, however, as a manifestation of local position invariance (the idea that the outcome of any non-gravitational experiment is independent of where and when in the universe it is carried out) is the least well confirmed of the three types of experiment that support the equivalence principle. The other two, the universality of freefall and local Lorentz invariance, have been verified with precisions of 10^–13 or better, whereas gravitational redshift had previously been confirmed only to a precision of 7 × 10^–5. This was achieved in 1976 by recording the difference in elapsed time as measured by two atomic clocks – one on the surface of the Earth and the other sent up to an altitude of 10,000 km in a rocket.

This kind of redshift measurement is limited by the degree of gravitational pull provided by the Earth’s mass. The new research, carried out by Holger Müller of the University of California Berkeley, Achim Peters of Humboldt University in Berlin and Steven Chu, previously at Berkeley but now US secretary of energy, is limited in the same way but manages to dramatically increase precision thanks to an ultrafine clock provided by quantum mechanics.

In 1997 Peters used laser trapping techniques developed by Chu to capture caesium atoms and cool them to a few millionths of a degree above absolute zero (in order to reduce their velocity as much as possible), and then used a vertical laser beam to impart an upward kick to the atoms in order to measure gravitational freefall.

Now, Chu and Müller have re-interpreted the results of that experiment to give a measurement of the gravitational redshift.

In the experiment each of the atoms was exposed to three laser pulses. The first pulse placed the atom into a superposition of two equally probable states – either leaving it alone to decelerate and then fall back down to Earth under gravity’s pull or giving it an extra kick so that it reached a greater height before descending. A second pulse was then applied at just the right moment so as to push the atom in the second state back faster toward Earth, causing the two superposition states to meet on the way down. At this point the third pulse measured the interference between these two states brought about by the atom’s existence as a wave, the idea being that any difference in gravitational redshift as experienced by the two states existing at difference heights above the Earth’s surface would be manifest as a change in the relative phase of the two states.

Enormous frequency

The virtue of this approach is the extremely high frequency of a caesium atom’s de Broglie wave – some 3 × 10²⁵ Hz. Although during the 0.3 s of freefall the matter waves on the higher trajectory experienced an elapsed time of just 2 × 10^–20 s more than the waves on the lower trajectory did, the enormous frequency of their oscillation, combined with the ability to measure amplitude differences of just one part in 1000, meant that the researchers were able to confirm gravitational redshift to a precision of 7 × 10^–9.

As Müller puts it, “If the time of freefall was extended to the age of the universe – 14 billion years – the time difference between the upper and lower routes would be a mere one thousandth of a second, and the accuracy of the measurement would be 60 ps, the time it takes for light to travel about a centimetre.”

This extreme precision could become useful as global positioning systems become ever more accurate. As Müller points out, to determine the position of an object on the ground to millimetre accuracy the atomic clocks on GPS satellites would need to operate with a precision of 10^–17, a figure in fact achieved recently by a clock developed at the National Institute of Standards and Technology in the US (see “New optical clock breaks accuracy record”). But at the satellites’ altitude of 20,000 km, such clocks will experience a speeding up of time of about one part in 10¹⁰ thanks to gravitational redshift. Recovering the precision of 10^–17 would therefore require knowing the redshift effect to a precision of 10^–7.

Müller hopes to further improve the precision of the redshift measurements by increasing the distance between the two superposition states of the caesium atoms. The distance achieved in the current research was a mere 0.1 mm, but, he says, by increasing this to 1 m it should be possible to detect gravitational waves, miniscule ripples in the fabric of space–time predicted by general relativity but never before observed.

The work is described in Nature 463 926.

Physicists watch chemistry in slow motion

Physicists in the US have observed chemical reactions taking place at such low temperatures that they are dominated by quantum effects, rather than thermal collisions. The researchers showed that diatomic molecules containing potassium and rubidium are much less likely to react with each other, when cooled to just 500 nK, if they are all prepared in the same quantum state. As well as providing important information about the quantum nature of chemical reactions, the technique could also be used to extend the lifetimes of ultracold gases by reducing the rates at which their constituent atoms and molecules react.

Although quantum mechanics lies at the heart of every chemical reaction, it is not easy to work out how the initial quantum states of the reactants affect the rate of reaction. This is because most of what we know about chemistry is based on observations at tens or hundreds of kelvin, where thermal fluctuations cause atoms and molecules to enter reactions in a wide range of initial quantum states.

One way of getting round this problem is to cool the atoms or molecules to near absolute zero to remove the effects of thermal fluctuations. In this case, the quantum states of the reactants can be fixed at the start of the experiment – and will endure until the reaction occurs. With common molecules such as ammonia, however, physicists have only managed to cool reactants to hundreds of millikelvin – which is not cold enough to fix the initial sates.

Cold enough

But by cooling potassium-rubidium (KrB) molecules to just a few hundred nanokelvin, Jun Ye, Deborah Jin and colleagues at the National Institute of Standards and Technology (NIST) in Colorado and Maryland have been able to observe the effects of specific initial states on how reactions proceed.

The team created the KrB molecules by exposing an ultracold mixture of potassium and rubidium atoms to a magnetic field gradient, which causes the atoms to bind together. The bond between the atoms is further strengthened by exposing the atoms to laser light. By adjusting the way the molecules are prepared, Ye and colleagues could either put all the molecules in the same low-energy quantum state or create a mixture of molecules in two different low-energy states.

When a collision occurs, the molecules can react to form Rb₂ and K₂ – and the energy released causes both to be ejected from the trap. The rate at which the KRb atoms react can therefore be determining by measuring the number of trapped molecules as a function of time. With the gas held at a chilly 500 nK, the KRb molecules were found to collide much more slowly than molecules in a typical chemical reaction.

Tunnelling molecules

KRb molecules are fermions – they have half-integer spin – which means that two molecules will avoid each other if they are both in the same quantum state. Indeed, two identical molecules only react if they first quantum-mechanically tunnel through this effective energy barrier. However, when the molecules are in two different states, this barrier does not exist and the reaction was seen to occur up to 100 times faster.

The researchers then took a closer look at reaction rates for molecules in the same quantum state. By repeating their measurements at several temperatures between 200 and 900 nK, they found that the rate increased as a function of temperature. This confirms that the limiting factor for the reaction is quantum mechanical tunnelling – once the molecules get beyond this barrier, the reaction proceeds rapidly.

New chemical reactions

“For the first time, we can explore how quantum-mechanical rules, as they are applied to the whole composite molecules, propel a chemical reaction,” explains Ye. He adds that the team’s findings could lead to the design of new chemical reactions and provide scientists with new ways of controlling chemical reactions.

A more immediate consequence of the experiment, according to Jeremy Hutson of Durham University in the UK, is that it could help physicists to reduce the rate of unwanted reactions in trapped ultracold gases. Such reactions place severe limits on the types of atoms and molecules that can be trapped – and overcoming these limits could allow simulate a wider range of quantum phenomena that is possible today.

Indeed, Ye told physicsworld.com that the team is now developing new approaches to suppress reactions. “We will use these precisely engineered molecular systems for quantum simulations of condensed matter systems, for example, and explore new phases of matter and quantum phase transitions,” says Ye.

The work is described in Science 327 853.

Browse articles by content type

To Svalbard in search of little green men

To prevent another 'climategate', researchers need to embrace social media

The connected worlds of Japanese art and electromagnetism