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The museum exhibit that you inspired

Robert P Crease at the Mind Museum in Manilla, the Philippines — Inspired thinking – Robert P Crease in front of an exhibit at Manila’s Mind Museum that was inspired by *Physics World* readers.

By Robert P Crease in Singapore

It’s not often that you come across a museum exhibit based on a Physics World article. But I did on Saturday at the Mind Museum – an extraordinarily beautiful and original science museum in Taguig, on the outskirts of Manila in the Philippines.

Not only that, the exhibit is right at the entrance. You may recall that I once asked Physics World readers for their thoughts on the 10 most beautiful experiments and wrote up the results in an article in September 2002. The project turned into a book, The Prism and the Pendulum: The Ten Most Beautiful Experiments in Science, which came out the following year and which Physics World reviewed.

Maria Isabel Garcia, who was planning exhibits for the then-future Mind Museum, saw the article and book, and created an exhibit based on it, consisting of videos and explanations of each of the 10 experiments, along with a sculpture designed by the Philippine artist Daniel de la Cruz.

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New maze-like beamsplitter is world’s smallest

An ultracompact beamsplitter – the smallest one in the world – has been designed and fabricated by researchers in the US. Using a newly developed algorithm, the team built the smallest integrated polarization beamsplitter to date, which could allow computers and mobile devices of the future to function millions of times faster than current machines.

Beamsplitters divide light waves into two separate channels of information, and will be crucial for the development of so-called silicon photonic chips that compute and shuttle data using light instead of electrons. “Light is the fastest thing you can use to transmit information,” says Rajesh Menon, an electrical and computer engineer at the University of Utah. “But that information has to be converted to electrons when it comes into your laptop. In that conversion, you’re slowing things down. The vision is to do everything in light.”

Light maze

Silicon photonics could significantly increase the power and speed of machines such as supercomputers and data-centre servers. In theory, devices employing such chips should not only be faster, but also consume far less power as well. Measuring only 2.4 × 2.4 μm², the new beamsplitter is nearly 50 times smaller than any beamsplitter created to date. It also has an unorthodox maze-like shape. “Most polarizing beamsplitters do not look like this today,” says Menon. “We wanted our device to be as easy as possible to fabricate using existing techniques, and to be as efficient as possible.”

To do this, Menon and his team created an algorithm that tried various geometries, until it found the smallest and most efficient design. Menon described this process as a “smart” search, explaining that “the ‘smartness’ is important because there are too many possibilities to try and the alternatives would take a very long time.” As the design takes existing manufacturing techniques into account, the team says its beamsplitter could be produced on an industrial scale almost as inexpensively as electronic transistors are today.

Tech library

Menon noted, however, that many other technological advances will be needed before a fully photonic computer is possible. “For our device to be utilized fully, we need a whole library of other complementary devices, all of which are highly miniaturized and efficient. These devices will enable different functions such as bending the light, splitting the light, transporting light, modulating the light, and so on,” Menon says. “Once such a library is available to designers, one can expect them to put such devices together into functional circuits. That’s when the most fun and unexpected results will come.”

Andrea Alù, a researcher at the University of Texas, Austin, who did not participate in the research, thinks the team’s algorithm could have other uses as well. Last year, Alù and his collaborators proposed the idea of designing artificial materials that can perform mathematical operations as light propagates through them. “I believe the concept pushed forward by Menon and his colleagues is not limited to polarization control,” says Alù. He told physicsworld.com that it may also be “a viable platform to imprint mathematical operations of choice on a CMOS compatible chip” – a widely used type of semiconductor.

Zongfu Yu, an electrical and computer engineer at the University of Wisconsin-Madison who was also not involved in the study, called the new beamsplitter design a significant advance in silicon photonics. He adds that the work shows, for the first time, that “computational optimization can be used to achieve ultra-compact devices that are absolutely beyond the intuition of even the most experienced device designer”.

The research is published in Nature Photonics.

On top of the volcano – part two

By Matin Durrani at Sierra Negra, Mexico

Just as my Physics World colleague James Dacey mentioned earlier, neither of us felt super-wonderful yesterday visiting the Large Millimeter Telescope (LMT), which sits at a height of 4600 metres above sea level. Spectacular though the facility is, the air pressure is roughly 60% of that at sea level and there is so little oxygen that even walking up a flight of stairs made me feeling pretty light-headed.

So, James and I were both quite glad to descend with LMT director David H Hughes to a height of 4100 metres, where it was time to visit another leading Mexican astronomy facility – the High-Altitude Water Cherenkov (HAWC) gamma-ray observatory.

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On top of the volcano – part one

By James Dacey at Sierra Negra, Mexico

Friday was the final full day of the Physics World Mexican adventure and we ended with a breathtaking experience, quite literally.

Matin and I rose early in Puebla to travel over a hundred kilometres east to the ominously named Sierra Negra volcano. This extinct beast is home to two of Mexico’s finest astrophysics facilities.

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The Dark Matter Garden, gravitational atoms, boys and girls with toys, and more

Gravitational gardening: the Dark Matter Garden at Chelsea — Gravitational gardening: the Dark Matter Garden at this year’s RHS Chelsea Flower Show. (Courtesy: National Schools’ Observatory)

By Hamish Johnston

Gardening is something that the British take very seriously and this week’s RHS Chelsea Flower Show is the pinnacle of that obsession. Indeed, it is so popular that it is covered live on television by the BBC. One highlight of the show is the garden competition, in which designers transform an empty plot into a dazzling garden in just 10 days. This year’s entries include the Dark Matter Garden, which “brings the mysteries of the universe to Chelsea”. That’s the claim of the designers of the garden (including several astronomers), who built it for the UK’s National Schools’ Observatory. The team says that its gold-medal-winning design includes “innovative structures and planting, and represents the effect of dark matter on light”.

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Nanomachine pumps molecules ‘uphill’

A new molecular pump capable of pumping other small molecules up an energy gradient has been developed by researchers at Northwestern University in the US. The new pump is very much like the protein pumps in living cells, and might be used to design artificial molecular machines similar to those found in nature. Such machines could be important for a range of applications, including synthetic muscles, tiny robots and advanced mechanical motors.

Molecular machines are ubiquitous in nature and have evolved over billions of years to exploit energy from sunlight or complex chemical reactions in the body. They are made up of complicated assemblies of proteins that are responsible for a host of processes in living organisms, such as ion transport, ATP synthesis and cell division. In fact, our muscles are controlled by the co-ordinated movement of thousands of these machines.

“Our new molecular pump is, in a sense, reminiscent of the pump proteins in our cells, which are vital components of life involved in transferring energy from food to a form that is compatible with our cells,” explains Paul McGonigal, who is part of Fraser Stoddart’s team at Northwestern. “We have designed a relatively simple small molecule that can also drive a system away from equilibrium with chemical energy from redox (oxidation-reduction) reactions.”

One-way valves and rings

The new pump is based on a molecule called a rotaxane, which has already been used to create other molecular machines. The molecule contains a linear axle capable of restricting the motion of a ring-shaped component threaded onto it. The chemical structure of the axle is such that the rings can move in one direction via a complex mechanism that involves two one-way valves (see figure above).

The machine contains several components. The first is a positively charged pyridinium unit (red) that acts as the first one-way valve. The second is a viologen unit (orange) that acts as the pump. The third is a bulky isopropylphenyl chemical group that acts as the second one-way valve (purple). Finally, the fourth component is an alkyl chain (green) that acts as the collection unit. This chain contains a chemical group at its end that is big enough to stop the rings from de-threading.

Pumping process transfers and stores energy

“The machine works thanks to reduction-oxidation cycles and precisely organized non-covalent bonding interactions,” explains team member Chuyang Cheng. “It pumps positively charged rings from solution and ensnares them around an oligomethylene chain. The redox-active viologen unit at the heart of this dumb-bell-shaped molecular pump plays a dual role in first of all attracting and then secondly repelling the rings during redox cycling,” he says.

“The pumping process is actually a way of transferring and storing energy at the molecular level,” he continues. “Part of the energy released during a reaction is siphoned off and stored in the high-energy molecules produced. In the long term, we could imagine that the energy stored by such an artificial molecular pump might be used to power another molecular machine – perhaps one that is part of an artificial muscle, for example.”

The team, reporting its work in Nature Nanotechnology, says that it would now like to be able to anchor its molecular pump in a membrane so that it pumps molecules from one side to another during operation. “Such a pump would be directly inspired by nature’s molecular machines, and especially carrier proteins,” adds McGonigal.

This article first appeared on nanotechweb.org

Creating craters, Mexican style

By Matin Durrani in Puebla, Mexico

So it’s day five of the Physics World Mexican adventure and today we’ve been to the Benemérita Universidad Autónoma de Puebla (BUAP), which is one of the oldest universities in the country. After taking a peek at a new facility containing one of the most advanced supercomputers in Latin America, we headed over to the Institute of Physics, where we bumped into Felipe Pachecho Vázquez.

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Spin currents endure at room temperature in germanium

Currents of electron spin can travel more than half a micron through germanium at room temperature, according to researchers in Japan and the UK. While physicists already know that germanium is a good conductor of spins at very low temperatures, this is the best measurement yet of its ability to transport spin at room temperature. The results suggest that the semiconductor could be used to create spintronic devices, which make use of the spin magnetic moment of the electron to store and process information.

The idea of spintronics has been around for several decades, and the nascent technology promises to deliver devices that are smaller and more energy efficient than conventional electronics. Another potential application of spintronics is to use individual electron spins – which can point up or down – to store and transfer information in quantum computers.

However, practical spintronic devices have proven to be very difficult to build, because electron spin does not travel very far in most materials and therefore the information is quickly lost. The main challenge is overcoming a well-known effect in physics called the “spin–orbit interaction”. As the electron travels through a material, the relative motions of the positively charged atoms create magnetic fields that tend to rotate the electron’s spin. In most materials, this results in the rapid destruction of a spin current across very short distances. Fortunately, some semiconductors already used in electronics – including silicon and germanium – have very weak spin–orbit interactions, and so a lot of effort has been put into studying the spin-transport properties of these materials.

Electrical injection

Before you can measure how far a spin current will travel, you have to inject it into a semiconductor, which is not easy to do. One technique involves shining circularly polarized light onto the semiconductor, which tends to spin-polarize the conduction electrons. However, this requires a light source, and is therefore not very practical for miniaturization and mass production of spintronic components. Another option is to place a ferromagnetic material next to the semiconductor so that a spin current can be driven out of the magnet and into the semiconductor. While this “electrical injection” sounds like a great idea, in practice, spin–orbit and other interactions at the interface between the two materials tend to scramble most of the spins before they make it into the semiconductor.

Several studies have suggested that electrical injection should be possible for germanium at room temperature. However, these measurements have not been conclusive because of experimental difficulties. Now, Sergei Dushenko of Osaka University, Masashi Shiraishi of Kyoto University and colleagues have used a microwave “spin-pumping” technique to inject a spin current into germanium.

Their experiment comprises a flat piece of n-doped germanium with a piece of ferromagnetic iron/nickel alloy at one end and a piece of the non-magnetic metal at the other end. An external magnetic field aligns the spins in the alloy along a specific direction. Microwave radiation is then shone onto the alloy, which causes the spins to rotate about the direction of the applied field. This causes a current of spins to be “pumped” into the germanium and flow a short distance to the metal. When the spin current enters the metal, it encounters a strong spin–orbit interaction that creates a voltage across the metal – a phenomenon called the “inverse spin Hall effect”. This voltage is then detected and related to the size of the spin current.

Theory backed up

From these measurements, the team was able to show that the spin current travels about 660 nm before it begins to suffer significant degradation. This applies at room temperature (about 290 K), and when the germanium was cooled down to 130 K, the spin current could travel about twice as far. This backs up a new theory of spin transport that was proposed last year by Yang Song, Oleg Chalaev and Hanan Dery of the University of Rochester in the US.

While 660 nm may not seem like very far, it is much larger than the size of a feature in a modern integrated circuit. In principle, this means that spins could move from one tiny spintronic device to the next without suffering degradation. Furthermore, this distance is on a par with other candidate materials for spin circuits, giving scientists another building block to create spintronic devices.

The research is described in Physical Review Letters.

Examining precious artefacts without breaking them

By James Dacey in Mexico

From pre-Hispanic archaeological treasures to the Modernist paintings of Frida Kahlo and Diego Rivera, Mexico is brimming with cultural artefacts. Yesterday I visited a centre at the National Autonomous University of Mexico (UNAM) that has developed techniques for investigating precious objects without damaging them.

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An interstellar culture clash

Ever since we first dreamed of life on other planets, science-fiction writers have explored the potential consequences of an interstellar culture clash. Typically, they depict alien species as either hostile and seeking to conquer Earth – as in H G Wells’ War of the Worlds – or friendly and misunderstood, as in the blockbuster film E.T. It is the former scenario that drives the fictional events of Cixin Liu’s The Three-Body Problem.

This book – the first in a trilogy that is already a bestseller in Liu’s native China, and has now been translated into English by Ken Liu – offers a refreshing take on the well-worn “hostile aliens” trope, creating an intricate, suspenseful and multi-layered novel peppered with memorable characters marked by tragedy. Among these characters is an astrophysicist called Ye Wenjie who, as a young woman during China’s violent Cultural Revolution, witnesses the brutal murder of her physics professor father at the hands of his former students during a public rally, or “struggle session”. His crime: refusing to denounce modern physics theories deemed ideologically incompatible with the Communist regime.

Ye Wenjie is more fortunate than her father. She survives the purge, and as part of her cultural redemption, she is recruited to work on a secret military project to transmit radio signals into space in search of intelligent life – the Chinese equivalent of SETI. Those signals eventually reach an alien race on the brink of extinction, who set forth to conquer Earth.

Fast forward 40 years. New and wildly inconsistent results from particle accelerators are baffling physicists, including many members of the Frontiers of Science, an elite cadre of influential scholars. Several members have begun committing suicide, purportedly devastated by the possibility that invariance might not hold across the universe. “All the evidence points to a single conclusion: physics has never existed and never will exist,” one despairing string theorist writes in her suicide note.

Meanwhile, a nanomaterials researcher named Wang Miao is recruited by the military and asked to infiltrate the Frontiers of Science as part of a top-secret programme to prepare the planet for interstellar warfare. In the course of his investigations, Wang soon finds himself enthralled by a strange online immersive video game called Three-Body.

The name of the game alludes to a problem outlined in Isaac Newton’s Principia in 1687: predict the movement of three moving objects, taking into account the effects of their mutual gravitational attraction. It is a relatively simple matter to calculate the movement of two objects, such as the Earth and the Sun, but adding a third body, like the Moon, makes for a much more difficult calculation.

Three-Body players attempt to solve the three-body problem in order to predict the strange weather patterns on a virtual world with three suns. This world vacillates between chaotic and stable eras, and civilization can thrive only during stable eras. Players propose solutions and then see how their hypothesis plays out in the ensuing simulation – how long can their virtual civilization survive?

It is not a frivolous exercise. The game turns out to be part of an elaborate campaign by the same aliens who received those radio signals 40 years ago – inhabitants of an actual planet with three suns – to recruit possible allies from the disillusioned ranks of mankind. Those who think humanity is beyond redemption square off against those seeking to defend our planet from the coming invasion, and the fate of two different species lies in the balance.

Liu infuses his world with impressively accurate scientific detail, deftly straddling the boundary between real-world research and imaginative speculation. While Wang’s ultrathin, high-strength nanomaterial – code-named “Flying Blade” because a mere hair’s breadth filament could slice a car in half – is fictional, the molecular self-assembly technique he is trying to develop to scale up production of Flying Blade will be recognizable to any materials researcher. The discussions of invariance and descriptions of modern astronomical instruments and accelerator technology are spot on. Even the Three-Body gaming platform, with its panoramic viewing helmet and haptic feedback V-suit, is firmly rooted in today’s cutting-edge gaming technology.

Unfortunately, after taking so much care to set his plot in motion, in the end, Liu brings his various narrative threads together in uncharacteristically clumsy and ham-fisted fashion. The final pages seem rushed, with long stretches of dry exposition, some of which doesn’t make much sense. Also, the notion that theoretical physicists would be killing themselves in despair over discovering that invariance does not hold across space and time strains credibility. In reality, theorists are made of sterner stuff, like the more pragmatically minded Wang. Most would be thrilled at the prospect of exciting new physics, particularly since whoever solved the conundrum would be a lock for a Nobel prize.

Liu shines most in his gut-wrenchingly evocative depiction of the Cultural Revolution, particularly its bewildering hostility to science. It may strike modern readers as strange that relativity was once considered hopelessly bourgeois, part of a “reactionary academic authority” – especially since Albert Einstein visited Shanghai in 1922. This was an era when teaching general relativity, the Big Bang or the Copenhagen interpretation of quantum mechanics would lead to arrest and torture – and in the case of Ye Wenjie’s father, death. As one of his former students observes when explaining his decision to focus on applied physics, “It’s easy to make ideological mistakes in theory.”

Blind ideology has no place in science. Granted, physicists continue to debate the viability of the Copenhagen interpretation of quantum mechanics, although they need not risk their lives to do so. Yet while the specific points of controversy might be different, a similar strain of denialism still runs through our society. The Three-Body Problem is set in China, but its central theme about the danger of valuing politics and personal belief over objective science transcends time, culture and geography. It’s a warning we should all heed. We may need that science one day to fight off invading alien hordes.

2014 Tor Books £17.99/$25.99hb 336pp

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The museum exhibit that you inspired