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Nanotubes boost battery performance

Carbon nanotubes could make ideal electrodes for lithium-ion batteries, boosting their power output by up to ten-fold compared with conventional devices, claim a group of researchers at Massachusetts Institute of Technology who have demonstrated the technique. They say that it will enable manufacturers to shrink batteries for portable applications such as ultra-light mobile phones and wearable electronics. In the longer term it could lead to high-performance batteries for larger applications such as hybrid electric cars and industrial machinery.

Lithium-ion batteries consist of two electrodes, the anode (which is negative) and the cathode (positive), separated by an electrolyte – a conducting material through which charged ions can move easily. During cell discharge, the positively charged lithium ions travel across the electrolyte to the cathode, so producing an electric current. When the batteries are recharged, an external current forces the ions to move in the opposite direction so that they can be stored at the anode.

These batteries are routinely used in portable electronics but their power output and charge-storage capacity still remain far below those of electrochemical capacitors. Batteries, however, have several advantages over capacitors, not least that they can store more charge and have a much lower rate of self-discharge.

A simple swap

Now, Yang Shao-Horn of the Massachusetts Institute of Technology (MIT) and colleagues have discovered a way to increase power output in these devices. They replace one of the electrodes in lithium-ion batteries by one made from multiwalled carbon nanotubes, which are tiny rolled up sheets of carbon atoms. The power output of the improved devices is now on a par with electrochemical capacitors at 100 kW kg^–1, but their “gravimetric energy” (the amount of charge they can store) is up to ten-fold higher.

The new CNT electrodes can “grab” and store larger amounts of lithium charge than conventional electrodes, which have been made from many chemicals over the years including iodine and copper sulfide. For example, there are numerous oxygen groups that can undergo redox (oxidation or reduction) reactions on the surface of the CNTs. The CNT electrodes are also very stable. The researchers found that the material performed just as well even after 1000 cycles of charging and discharging.

A super battery

Shao-Horn’s team made the new electrodes using a layer-by-layer fabrication technique in which a base material, such as ITO glass or metal foil, is dipped into solutions containing carbon nanotubes. The nanotubes are made negatively or positively charged, for the electrodes, by treating, or “functionalizing”, them with simple organic compounds, such as carboxyl (COOH) and amine (NH₂) groups. These CNT layers are placed alternately on a surface and bind strongly together because the positively charged tubes attract the negatively charged ones, to make stable and robust films after a simple heat treatment.

Bridging the technology

“We now hope to make thicker electrodes – up to 50 µm across – with the same performance characteristics,” Shao-Horn told physicsworld.com. The electrodes made so far are only a few microns in size, which limits their use to small, portable, applications.

Yury Gogotsi of Drexel University, also in the US, who was not involved in the work, believes that there are many potential applications for these high performing batteries. “Bridging the performance gap between batteries and electrochemical capacitors is an important task, and the MIT group has made an important step in this direction,” he says.

“There is still much work to do though. The data presented in this new work may only be valid for relatively thin films and individual electrodes with no packaging and it may be completely different for a real-world battery with its multiple parts and outer container”, he adds.

The results were published in Nature Nanotechnology.

Exoplanet mass calculated directly

Researchers in the Netherlands and in the US are the first to measure directly the mass of a planet orbiting a star other than our Sun. In developing their new technique, they also discovered that this planet, which is approximately the same size as Jupiter but closer to its star, is being tormented by a raging storm.

Previous attempts to gauge the mass of such exoplanets have relied on estimations, where astrophysicists look at the slight “wobble” of a star caused by the gravitational pull of the planet. The extent of this movement can be used to estimate the planet’s mass as a proportion of the stellar mass – which itself is an estimate based on its spectral characteristics and distance from Earth.

Ignas Snellen of Leiden University led a team in developing a more accurate method by focusing on the atmosphere of an exoplanet. They demonstrate the technique on HD 209458b, a well known “hot Jupiter” some 150 light-years from Earth. Because this planet sweeps between Earth and its host star, every three and a half days, it changes the star’s chemical spectrograph as recorded on Earth. By comparing the star’s spectrograph before and during a transit the researchers can calculate the chemical content of the planetary atmosphere.

Doppler shift

Using the Very Large Telescope (VLT) in Chile, fitted with the CRIRES spectrograph, Snellen’s team was able to hone in on the planet’s carbon-monoxide (CO) signal, which was predicted to produce many spectral lines over these wavelengths. They were able to detect a small Doppler shift in the CO gas. From this they could calculate that the planet is orbiting its star at a velocity of 140 km s^–1.

With relative ease, Snellen’s team was then able to calculate the masses of both star and planet using Newton’s law of gravitation, knowing also the velocity of the host star due to its orbit round the centre of mass of the system. “This is exactly the same method used to calculate the mass of binary star systems, except one of the bodies here is an exoplanet,” says Snellen.

Obtaining more accurate values for exoplanet masses could enable researchers to glean more information about the nature of exoplanets. “The mass is one of the most important parameters of the planet. It is by measuring the mass, together with other properties such as orbital period and eccentricity and radius, that we learn what exoplanets are made of, and how they form and evolve,” says Susan Aigrain, an exoplanet researcher at the University of Oxford in the UK.

A raging storm

The second result of this research is the discovery of an intense wind at high altitudes in the planet’s atmosphere. The researchers see that during the planet’s transit in front of the star, the whole CO signal is blue-shifted with respect to the velocity of the star, suggesting that the atmosphere is moving towards us. This observation fits with the prediction that hot gases from the planet’s day side flowing towards its cooler night side.

“Exoplanet atmospheres will be among the richest topics to explore over many years to come. Some examples of what we want to learn more about include cloud formation and weather in exoplanet atmospheres,” says Markus Janson, another exoplanet researcher at the University of Toronto.

The researchers intend to develop their research by building a more detailed profile of this exoplanet’s atmosphere. They have already secured a further 155 hours’ operational time on the VLT to be spread over the next two years.

Snellen hopes that in the longer term, his group’s technique could be used to investigate more Earth-like planets, which are significantly smaller and therefore more difficult to observe. “From looking at our own planet we can see that life has a very large influence on the composition of the atmosphere, especially with the presence of oxygen and ozone,” he says.

This research is published in this week’s Nature.

Quantum states controlled in silicon

A new method controlling quantum states in silicon has been developed by an international team of physicists using giant “Rydberg atoms” created by doping the material with phosphorous impurities. The technique could be used to control quantum-computing devices made from silicon, while the solid-state Rydberg atoms themselves could provide physicists with a new tool for studying quantum mechanics.

Computers based on quantum-mechanical concepts such as entanglement could, in principle, out perform conventional computers on certain tasks. Although the scientific literature is full of schemes for quantum computers, physicists are yet to build practical devices capable of sustained quantum computations. However, some physicists believe that silicon-based devices could be the way forward.

The reason for their optimism is that nanometre-sized components can be made from ultrapure crystalline silicon – essential for minimizing unwanted noise that can destroy quantum information. Indeed, researchers have already shown that quantum bits (or qubits) of information can be stored for long periods of time in the spin states of impurity atoms in silicon. The snag, though, is that it has proved tricky to make these atoms interact and so process quantum information.

Superposition of states

Ben Murdin at the University of Surrey, researchers at University College London, the FOM Institute for Plasma Physics in the Netherlands and Heriot Watt University in Edinburgh have now shown that phosphorus-doped silicon could offer a way forward. The team used a commercially grown silicon crystal, which comes doped with a precise amount of phosphorus to boost its electron density. Each phosphorus atom has one more valence electron than silicon and so is like a giant hydrogen atom with a positive core and an electron in an orbital about 30 lattice spacings in diameter.

But unlike a conventional Rydberg atom, which is in a high-energy state, the impurity is normally in its lowest energy (ground) state. The team begin by putting each impurity atom into a combination of the ground and first excited states using a terahertz pulse from the FELIX free-electron laser in the Netherlands. In such a superposition of states an observer cannot know which state the impurity is in until a measurement is made – much like Schrödinger’s famous cat.

Slipping out of phase

The superposition state oscillates at a specific frequency that is defined in part by the magnetic moments of the neighbouring silicon atoms. Because there are several isotopes of silicon in the crystal the magnetic environment of each impurity is slightly different, which causes the oscillations of the impurities to slip out of phase with each other.

The team then fired a second terahertz pulse at the sample, which adjusted the relative phases of the impurities so that they all oscillated in unison. This resulted in a flash of light – called a “photon echo”. However, the photon echo occurs only if the impurities are in an superposition state. So by adjusting the delay between the two pulses and measuring the intensity of the echo, the team was able to deduce that the state lasted for about 160 ps.

Optical control

While this might seem like a short time, Murdin points out that it is nevertheless long enough to use the impurity to control neighbouring qubits. He believes that this could be done by placing spin-qubit impurities near Rydberg impurities such that their electron orbitals overlap. This would allow the qubits to be controlled using photons, which could help to reduce noise.

Murdin told physicsworld.com that his team is now working on a technique to position individual impurities to nanometre accuracy using the tip of a scanning probe microscope. First, they plan to place two phosphorus impurities next to each other and show that the quantum-control system can be used to entangle the two Rydberg atoms.

Jeremy O’Brien of Bristol University says that the possibility of quantum control using such Rydberg atoms is “exciting”. He adds that the work could open up a new area of physics research, comparing it to the emerging field of cavity quantum electrodynamics which grew out of studies of the interactions between light and quantum dots.

The work is reported in Nature 465 1057.

Speedy star points to more massive Milky Way

The fastest star ever seen in the Milky Way’s ancient halo may boost estimates for our galaxy’s mass, say German astronomers. In order for its gravity to hold on to such a speedy star, the Milky Way must have roughly two trillion times more mass than that of the Sun.

The Milky Way boasts hundreds of billions of stars, but most of its mass is in the enormous – and invisible – “dark halo” that engulfs the bright galactic disc to which the Sun belongs. Thus, the Milky Way’s exact mass is unknown, with most estimates ranging from 1 to 2 trillion solar masses.

Now Norbert Przybilla, Alfred Tillich, and Ulrich Heber of Dr Karl Remeis Observatory in Bamberg and Ralf-Dieter Scholz of the Astrophysical Institute in Potsdam argue that the higher figure is probably correct.

Racing towards us

They studied a star called SDSS J1539+0239, which is racing toward us in the constellation Serpens. This is a horizontal-branch star, which means that it is in a more advanced stage of evolution than the Sun. Whereas the Sun generates energy by converting hydrogen into helium, this star converts helium into carbon and oxygen.

The team determined the star’s velocity in 3D by first working out three parameters. The first, and easiest, is the star’s Doppler shift, which reveals how fast the star moves towards Earth. Xiangxiang Xue of the National Astronomical Observatories in China and colleagues reported this two years ago to an accuracy of 2%.

Przybilla’s team then measured the second quantity: the star’s proper motion, which is the apparent movement, year after year, across our line of sight. By looking at the star’s changing position on photographic plates taken in different years, the astronomers determined the proper motion to an accuracy of about 20%.

Distance a difficulty

The third, and most difficult, quantity is the star’s distance, which the astronomers estimate is 39,000 light-years – plus or minus 20%. Together with the proper motion, the distance reveals the speed at which the star moves across our line of sight.

Relative to the galactic centre, the star is racing through space at roughly 694 kilometres a second. That is three times faster than the Sun and about 60 kilometres a second faster than the previous halo star speed record holder. “It was immediately clear that this star must be something special and interesting,” says Przybilla.

Indeed, the only stars faster are “hypervelocity” stars, shot out of the galactic centre by interactions with the Milky Way’s central supermassive black hole. But such stars may no longer be bound to the galaxy, so they don’t constrain its mass. By contrast, the star in Serpens is probably native to the halo. “It is coming towards us,” says Przybilla, “so the probability that it belongs to the Milky Way is very high.”

The star’s high speed means that the Galaxy must have at least 1.8 trillion solar masses or else the star would have escaped the Galaxy’s grasp. This mass estimate agrees with studies of galaxies orbiting the Milky Way, but it is twice as high as the figure that Xue’s team reached after studying Doppler shifts of halo stars.

‘Interesting and important’

“The result is interesting and important,” says Scott Tremaine, an astronomer at the Institute for Advanced Study in Princeton, New Jersey, who was not involved with the work. However, he does have concerns: “Most of the reason they’re getting this very high velocity for the star is because of the component across the line of sight,” he says. And that is where the greatest uncertainty lies.

Fortunately, help is on the way. In 2012, the European Space Agency will launch Gaia, a satellite to measure precise motions and distances for a billion stars, including the one in Serpens. Says Przybilla: “Gaia will be a revolution in our view of the nearby universe.”

The astronomers will report their work in The Astrophysical Journal and a preprint appears at arXiv: 1005.5026.

Glimpsing the birth of a distant star

Courtesy: A Marston (ESTEC/ESA) et al., JPL, Caltech, NASA

By James Dacey

Our telescopes have delivered so many incredible snapshots of the universe that there is a danger of us becoming a bit blasé about new images.

Not so with this one. This image of a future star as it is been born out of a cloud of gas and dust reminds us of just how beautiful the universe can be.

With the rather less inspiring name of L1448-IRS2E, it is located around 800 light-years away in the Perseus star-forming region, and was captured by the Submillimeter Array in Hawaii and the Spitzer Space Telescope.

It could well be the youngest known star, though it is still too dim to be classified as a true protostar by astronomers.

The discovery and characteristics of L1448-IRS2E are described in a recent paper in the Astrophysical Journal.

Neutrino plot gets thicker

The inside of the MiniBooNE tank (Courtesy: Fermilab Visual Media Services)

By James Dacey

Last week, I reported a result to emerge from the MINOS experiment at Fermilab, which – if confirmed – will add a fascinating new dimension to our understanding of neutrinos. The researchers were looking at a feature known as neutrino oscillation, whereby these elusive particles mysteriously switch identity between the three different flavours of neutrino.

According to all conventional models, the extent to which this process occurs should be the same for neutrinos as it is for antineutrinos. But to their great surprise, the MINOS team discovered that this is not the case. They found that the energy over which this process occurs in muon neutrinos and muon antineutrinos (converting into tau neutrinos and tau antineutrinos, respectively) is different by around 40%.

A MINOS spokesperson, Jenny Thomas of University College London, told me that the audience was “very surprised” by the result when it was presented last week at the Neutrino 2010 conference in Athens, Greece. But the 2 sigma confidence level seems to have restricted the results to causing a minor ripple, not a soaring wave, in the particle-physics community.

Crashing in behind this MINOS announcement, however, is a new result at a fellow Fermilab experiment that will surely add momentum to their findings. Researchers at the MiniBooNe experiment say that they have seen a similar discrepancy but with muon neutrinos – at a lower energy – oscillating into electron neutrinos (and the related process for muon antineutrinos). What’s more, their results are presented to a confidence of 3 sigma.

David Wark, a neutrino physicist at Imperial College, London, says that if either MINOS or MiniBooNE are correct, “it would not be a surprise but an overwhelming shock”. He points out, however, that the experiments take measurements of different oscillations and don’t directly support each other. “In both cases, we need to see more data,” he says.

Fortunately for Wark (or unfortunately, depending on how big that shock is), MINOS and MiniBooNe are both continuing to take data for at least the next couple of years. It will be interesting to see what happens next.

Topological quintet bags Europhysics prize

Five physicists who brought us the quantum spin-Hall effect and topological insulators have been awarded this year’s Europhysics Prize from the European Physical Society’s condensed-matter division. The winners are Shoucheng Zhang of Stanford University; Charles Kane and Eugene Mele of the University of Pennyslvania; and Hartmut Buhmann and Laurens Molenkamp of Würzburg University in Germany.

Since being confirmed experimentally in 2007, the two related phenomena have become major topics of research in solid-state physics with hundreds of papers on the arXiv preprint server covering the subjects. The quintet’s pioneering research could also allow physicists to catch the first glimpse of an elusive particle called the Majorana fermion and lead to noise-resistant quantum computers.

Topological framework

Zhang, Kane and Mele are honoured for their theoretical work on the quantum spin-Hall effect (QSHE), which occurs in certain very thin insulators. It involves spin-up electrons conducting along one edge of the insulator, with spin-down electrons conducting along the opposite edge. The trio’s efforts laid down a theoretical framework for topological insulators – materials that are insulators in the bulk but are good electrical conductors on the surface.

In 2005 Kane and Mele proposed a general theory that predicts which materials are 2D topological insulators. The pair identified graphene – sheets of carbon just one atom thick – as a candidate, although it has not been feasible to establish this experimentally. Working independently, however, Zhang predicted in 2006 that mercury telluride should be a 2D topological insulator. This prediction was confirmed experimentally in 2007 by Buhmann and Molenkamp, the other two winners of this year’s prize.

Joel Moore of the University of California, Berkeley said the award is a “fitting recognition of an exciting discovery that shows the constructive interaction between theoretical predictions and experimental work in condensed matter physics”.

Since extended to 3D

Such materials are called 2D topological insulators because the effect occurs in extremely thin materials where the electrons are confined to two dimensions and the effect is related to the shape (or topology) of the electron wave functions. In 2007 Kane and Mele – and independently Moore, Leon Balents and Rahul Roy – realized that topological insulators can also exist in thicker 3D materials. This was confirmed experimentally in 2008 by Zahid Hasan and colleagues at Princeton University.

Marcel Franz of the University of British Columbia told physicsworld.com that 3D topological insulators “constitute a truly new phase of quantum matter”. “We thought we understood all the aspects of the band theory in solids but these recent developments show that in fact we completely missed some topological aspects that proved to be of fundamental importance,” he added.

Particle and anti-particle

Physicists are particularly keen to see what happens at the interface between a topological insulator and a superconductor. Some physicists believe that such structures could harbour a new type of quasiparticle reminiscent of the “Majorana fermions”, which were predicted in 1937 by the Italian theorist Ettore Majorana but have yet to be seen.

Majorana fermions are electron-like particles that are their own anti-particles. They are neither fermions nor bosons, and instead obey non-Abelian statistics. The quantum states of such particles are expected to be highly resistant to perturbations by environmental noise, making them ideal candidates for quantum computers.

Neutrino surprise emerges from MINOS

Researchers at Fermilab’s MINOS experiment have announced a surprise result that could point to a fundamental difference between neutrinos and their anti particles. The findings, if confirmed by further experimental runs, may help physicists to explore some of the elemental differences between matter and anti-matter.

The MINOS experiment is designed to test the theory that neutrinos can change between types in a process known as neutrino “oscillation”. When this idea was first muted in the 1950s it was controversial because it implies that neutrinos have mass, a feature that contradicts the Standard Model of particle physics. However, the theory has been supported by subsequent experiments, which have found the Sun to be producing fewer electron neutrinos than had been expected. It is also backed-up by an apparent shortfall in muon neutrinos produced by cosmic rays interacting in the Earth’s atmosphere.

It would not just demolish any particular model, it would require revision of the whole way we do particle physics. David Wark, Imperial College

The MINOS experiment was set up to study neutrino oscillation by making the first high precision measurements of a controlled beam of neutrinos produced within a particle accelerator environment. Each experimental run begins at Fermilab near Chicago where a target is bombarded with energetic protons to produce a beam of neutrinos, called the NuMI beam. This is fired through the Earth towards the Soudan mine in Minnesota, some 735 km away. Deep in the mine, the neutrinos interact with the MINOS detector, which consists of a large iron calorimeter in the presence of a magnetic field. MINOS is designed to make highly precise measurements of the energy spectrum of muons, which arise from interactions with the Fermilab neutrinos.

Dips and troughs

Where troughs appear in this energy spectrum, it is an indication that a number of muon neutrinos have oscillated into the less energetic tau neutrinos, which cannot be recorded in the detector. The energy range over which this dip appears can reveal information about the difference between the masses of the two neutrino types. A dip appearing at higher energies corresponds to a larger difference between the masses of the two different types of neutrino. When it began operations in 2006, the MINOS team were initially probing for the mass difference between muon neutrinos and tau neutrinos. After recording firing 7 x 10²⁰ protons at the Fermilab target, they arrived at a result of 2.35 x 10^-3eV², which represents the square of the difference between the mass eigenstates (Δm²) of the two different types of neutrino.

However, more recently the MINOS team has switched its attention to antineutrinos, and the Fermilab NuMI beam was altered to produce a beam of muon antineutrinos. The detector in the Soudan mine operates in the same way except muon antineutrinos produce positively-charged muons rather than negative. Neutrino models suggest that antineutrinos should also oscillate between types, where Δm2 should correspond to the same value as their neutrino counterparts.

To their surprise, however, the MINOS team has recorded a Δm² value of 3.35 x 10^-3eV² between muon antineutrinos and tau antineutrinos, which is larger than their neutrino result by approximately 40%. The neutrino value and the antineutrino value are inconsistent at a confidence level of 90–95%, which corresponds to a statistical significance of approximately 2 sigma. “While the neutrinos and antineutrinos do behave differently on their journey through the Earth, the Standard Model predicts the effect is immeasurably small in the MINOS experiment,” says Jenny Thomas, a spokesperson for the MINOS team based at University College London.

Out of the blue

Thomas says that the result has come “completely out of the blue”, but she warns that the particle physics community generally expects a statistical significance of 3 or 4 sigma before they start to take serious notice of a result. “Clearly, more antineutrino running is essential to clarify whether this effect is just due to a statistical fluctuation,” she adds.

The NuMI beam line

David Wark, a neutrino physicist at Imperial College, London, shares a similar view. “[The uncertainty] isn’t a concern in the sense that it doesn’t show that they did anything wrong, it just shows that there is not enough data to make a strong conclusion.” Wark points out that if there is a difference in the oscillations of neutrinos and anti-neutrinos, this would have an enormous impact on both the Standard Model and local relativistic quantum field theory. “It would not just demolish any particular model, it would require revision of the whole way we do particle physics.”

The MINOS team will continue to take measurements of anti neutrino mass difference, with the current run coming to an end shortly, and the next one getting underway in September. “If the effect does prove to be real, then we could be looking at a 3 sigma significance by February 2012,” says Thomas.

The results were presented earlier this week at the Neutrino 2010 conference in Athens, Greece.

Condensate created in freefall

A Bose– Einstein condensate experiment – lasers and all – has been dropped repeatedly from a height of 146 m. Designed by an international team of physicists, the experiment has shown that delicate multiparticle quantum systems can be created and analysed in microgravity environments created during freefall. The result also suggests that it is possible to launch similar experiments into space, where they could test predictions of Einstein’s general theory of relativity.

Bose–Einstein condensates (BECs) are formed when identical atoms with integer spin are cooled until all the atoms are in the same quantum state. This means that a BEC comprising tens of thousands of atoms behaves as a single quantum particle. BECs can be used in matter interferometers, in which a quantum particle is “split” and sent along two different paths before being recombined at a detector – just like a pulse of light in an optical interferometer. Although such experiments have been done with single atoms, their precision is boosted significantly when a BEC is used.

Because BECs are massive objects they are particularly suited to interferometry experiments that measure tiny differences in gravity between two paths. Placing BEC interferometers in microgravity environments such as drop towers or parabolic flights, would allow physicists to test aspects of general relativity to much higher precision than is possible today. These include the geodetic effect and the Lense–Thirring effect, which describe the space-distorting effects of the Earth’s mass and rotation respectively.

Huge technical challenges

However, launching a BEC into space – or even dropping it a few hundred metres – involves huge technical challenges because the BEC must be prepared and maintained in ultrahigh vacuum at ultracold temperatures in a process involving the precise application of magnetic fields and laser light.

Now, Ernst Rasel and colleagues at Leibniz University in Hanover, Germany have built an entire BEC experiment that can be dropped repeatedly from a height of 146 m. The team, which also includes researchers from other universities in Germany, the UK and France, begins with collection of about 10 million cold rubidium-87 atoms. These are loaded into a magneto-optical trap within the drop capsule – a 215cm-long cylinder with a 60 cm radius. The capsule is positioned at the top of the ZARM drop tower in Bremen. When in freefall, gravity inside the capsule can be as little as 10^–5 of terrestrial gravity.

The capsule is released and the team allow it to drop for 1 s to allow for the initial vibrations of the capsule to dampen out. The freefall continues as the atoms are further cooled by a laser technique called “optical molasses”, followed by evaporative cooling to create a BEC of about 10,000 atoms at a temperature of about 10 nK.

Expanding BEC

Next, the BEC is released very gently from the magnetic trapping potential, putting it in a state of very slow expansion. This is necessary for long observation times since faster expansion would quickly make the condensate too dilute for imaging – which is done by shining a laser on the BEC and looking at the shadow it casts on a CCD camera.

The team were able to track the motion of the BEC relative to the capsule as the freefall continued for another 1 s. They found that the centre of mass of the BEC moved about 3 mm relative to the capsule over this time. This motion is not of gravitational origin. Instead, the team has shown that most of this effect is caused by tiny residual magnetic fields inside the experiment.

Analysis of the expansion of the BEC also revealed the presence of residual fields, which stretched the BEC along the vertical direction and squeezed it horizontally.

Rasel told physicsworld.com that the team will soon repeat their measurements using a BEC made from atoms in a slightly different quantum state. These are not affected by stray magnetic fields and will therefore lead to a better tool for making gravitational measurements.

Atom interferometer planned

Looking further into the future, the team also plans to build a microgravity atom interferometer in which the atoms are split into two states and then recombined by the absorption and emission of photons. They also plan to create BECs containing two types of atom to see if both behave in the same way.

The research is partially funded by the German Space Agency, and Rasel hopes that it could lead to BECs being studied in space. Such experiments could be used to detect gravitational waves and the comparison of experiments in space and Earth could provide very precise tests of the equivalence principle of general relatively.

Holger Mueller of the University of Calfornia, Berkeley, said that the experiment “represents a very important milestone” in the development of atom interferometers that can be deployed in space. “Space operation requires new technology that is very, very challenging to develop”, he added.

The work is described in Science.

Brazil and Spain top the table

Ibero-America Courtesy: Wikimedia Commons

By James Dacey

Academic institutions in Spain and Brazil account for nearly 70% of all scientific papers from Ibero-America published during the period 2003–2008. This political region incorporates Spain, Portugal and countries in the Americas that are former colonies of these two European nations.

The study, carried out by the SCImago Research group, found that Spain and Brazil each produced around 200,000 papers during this period, while Portugal was lagging in third place with just 50,000.

There are nearly 670 higher-education institutions within Ibero-America, with nearly 50% of these in Brazil, Colombia and Spain. Colombia’s relatively modest scientific output – just 9792 papers – is attributed to the country’s high number of small academic institutions.

The study also ranked the nations on other factors, including quality of publications (based on citations) and extent of international collaboration.

The full report (in Spanish) is available here.

Browse articles by content type

Nanotubes boost battery performance

A simple swap

Bridging the technology

Exoplanet mass calculated directly

Doppler shift

A raging storm

Quantum states controlled in silicon

Superposition of states

Slipping out of phase

Optical control

Speedy star points to more massive Milky Way

Racing towards us

Distance a difficulty

‘Interesting and important’

Glimpsing the birth of a distant star

Neutrino plot gets thicker

Topological quintet bags Europhysics prize

Topological framework

Since extended to 3D

Particle and anti-particle

Neutrino surprise emerges from MINOS

Dips and troughs

Out of the blue

Condensate created in freefall

Huge technical challenges

Expanding BEC

Atom interferometer planned

Brazil and Spain top the table

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A simple swap

Bridging the technology

Doppler shift

A raging storm

Superposition of states

Slipping out of phase

Optical control

Racing towards us

Distance a difficulty

‘Interesting and important’

Topological framework

Since extended to 3D

Particle and anti-particle

Dips and troughs

Out of the blue

Huge technical challenges

Expanding BEC

Atom interferometer planned