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Quantum computers turn mechanical

Ultra-fast computers of the future might consist of tiny pieces of superconducting material linked electrically to equally small mechanical resonators, the former providing the processing power and the latter the memory. That is the prospect raised by new work carried out by an international group of physicists, showing that quantum information can be passed between the two kinds of component in such a way that this delicate information might be protected from environmental interference.

Quantum computers exploit the counterintuitive idea that tiny objects can exist in more than one state at the same time. Rather than processing bits – which are either 0 or 1 – such devices instead manipulate qubits – which can be 0 and 1 simultaneously – potentially allowing vast numbers of operations to be carried out in parallel and rendering these devices far quicker than classical computers.

Physicists are working on a number of different kinds of quantum computer but all have their downsides. Some exploit the spin of individual particles, such as atoms, molecules or photons. The quantum states in these devices can be made quite robust against interference from outside – one of the biggest challenges in building a workable quantum computer – but they require bulky apparatus that is not well suited to building computers with large numbers of qubits. Suitable scaling up should not be a problem for solid-state designs, however, such as devices that exploit the quantum-mechanical properties of superconductors. But these devices are extremely susceptible to electromagnetic interference.

Hybridization

“Hybrid quantum systems” attempt to overcome these problems by combining the best aspects of different approaches. In the latest research, Mika Sillanpää and colleagues at Aalto University in Finland have combined a superconducting qubit with two kinds of resonators – one mechanical and the other electrical. They have shown that vibrational quanta – known as phonons – from the mechanical resonator can be sent to and from the superconducting qubit, which acts like an artificial atom, and then be detected in the form of electromagnetic quanta (photons) using the electrical resonator.

All three components are made from aluminium laid down onto a single sapphire substrate measuring a little over 1 mm2. The moving part of the mechanical resonator consists of a flat piece of aluminium measuring 5 μm by 4 μm suspended some 50 nm above one end of the superconducting circuit, while its main components are two Josephson junctions – pairs of superconductors separated by a thin insulator. This circuit, in turn, is connected to one end of the electrical resonator – a waveguide into which microwaves are fed.

The researchers’ first step in testing their device was to expose the superconducting circuit to a magnetic field so as to set up two “charge states” within the circuit as if they had created an atom with two energy levels. They then fed an alternating current into the circuit with a frequency equal to the energy-level difference of the created atom. This stimulated the atom to “Rabi oscillate” between these two states. Having determined that the qubit worked as planned, the researchers then coupled the qubit to the mechanical resonator. This was done by reducing the frequency of the alternating current feeding the qubit, to the point where the resulting shortfall in the energy quantum required for Rabi oscillations was exactly equal to the energy quantum of the vibrating arm.

Coupling

To prove that they really had coupled the qubit to the resonator, the researchers monitored the phase of the microwaves in the waveguide. As predicted, they found that they got almost exactly the same phase change as they did when applying all the energy directly to the qubit. Put another way, the phonons had combined with the states of the artificial atom, and these combined states modulated the photons in the waveguide just as the qubit alone had done.

Collaboration member Pertti Hakonen says that the result opens up interesting possibilities for exploring various non-classical states, such as those with a well-defined quantum number of phonons. This is particularly the case, he adds, if the amount by which a single phonon changes the energy spacing in the qubit can be made large as compared with the decay rates of mechanical or electrical oscillations.

Down memory lane

According to Hakonen, the latest research might also form the basis for a quantum memory analogous to the read-only memory of conventional computers in which quantum information is stored as superpositions of different vibrational amplitudes. Many hurdles would need to be overcome to realize this kind of memory, he cautions, such as increasing the frequency of the mechanical resonators in order to raise their energy spacings above the level of thermal noise. This would require making the resonators shorter, which would reduce their coupling with the qubit, thereby making the experiment even harder to perform.

Andrew Briggs of Oxford University in the UK believes that the latest work is an “important step” on the road to long-lived quantum memory. “This shows that an adequate strength of coupling can be achieved to move into the quantum regime,” he says. “It also constitutes progress towards demonstrating quantum phenomena in increasingly macroscopic structures.” He adds that it will be important to extend this research to demonstrate mechanical resonators in the ground state. The lowest state of the Finnish device, which was operated at a temperature of about 25 millikelvin, corresponded to an energy of about 20 quanta.

The research is published in Nature.

Billy Bragg knows nothing

By Matin Durrani

When I was a PhD student at Cambridge in the early 1990s, I remember going to a concert by singer-songwriter Billy Bragg at the Cambridge Corn Exchange. Riding high at the time on a string of classic songs such as “She’s Got a New Spell”, “Shirley” and “Great Leap Forward”, Bragg had an ear for a great tune and was a great lyricist to boot – who can forget the classic line “How can you lie there and think of England if you don’t even know who’s in the team?”.

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Physicists discover key to ultra-stable bearings

Networks of rotating bearings can better recover from perturbations to their harmonious motion if the masses of the individual discs are proportional to their radii – this is the finding of a team of physicists based in Switzerland and Brazil. Although surprising, the result hints at how to construct more robust mechanical bearings, as well as offering fresh insight into the synchronization of complex oscillating systems such as electrical networks and the Internet.

Bearings are the small workhorses at the heart of many mechanical devices used today. The secret to their success is that they reduce the friction between two surfaces that need to slide past one another by offering them a chance to roll. Think of the Ancient Egyptians transporting gigantic slabs of rock on beds of rolling logs – would the pyramids ever have been realized if the rocks had been shunted along the ground unaided? A more sophisticated example is the wheel on a rollerblade. Its internal casing houses a ring of tiny ball-bearings that allows the outer part to spin smoothly against the inner part, affording the wearer speed for very little effort.

Scale-free synchronization

Hans Herrmann, of the Swiss Federal Institute of Technology (ETH) and colleagues investigated a particular type of bearing known as a 2D space-filling bearing. This component consists of a hierarchical distribution of successively smaller rotating 2D discs nestled into the spaces between larger ones, also known as a “scale-free distribution”.

Each disc turns in the opposite way to any other disc that it is in contact with, and the tangential velocity – the distance traced by a point on the edge of a disc in a given time – is equal for all the discs, regardless of their size. This means that at each contact point the discs roll together without slipping and the whole system is in a stable, synchronized state.

“The synchronization of a regular grid of oscillators is an old problem that has been solved, but rather new is synchronizing oscillators that are connected in a very complex network like ours,” explains Herrmann. A number of recent papers deal with the theoretical conditions necessary for such grand-scale oscillators to synchronize but, says Herrmann, “What we did was to create, for the first time, a physical example that you could realize mechanically.”

Mechanical realization

Herrmann’s colleagues used a mathematical model of the space-filling bearing to explore the forces on the discs, toying with each disc’s inertia by placing holes of different sizes at their centres to hollow them out and rob them of mass. A disc’s mass is normally proportional to the square of its radius, but the researchers found that they could markedly enhance the synchronizability of the whole system by making the holes large enough that the discs’ masses were always simply proportional to their radii. A system with higher synchronizability will, if perturbed, return more quickly to a balanced, no-slip rotating state.

By obeying the one-to-one relation, their system showed it could quickly overcome perturbations and absorb changes. “This is a non-trivial issue that is surprising about the whole work,” says Herrmann, “particularly because the effect is so strong; if you change the relation even slightly, the signal is very strongly diminished.”

In addition, explains co-author Nuno Araújo, also of ETH, the team managed to confirm a key theoretical prediction about scale-free networks – that the most stable synchronization states occur when the interaction strength is inversely proportional to the number of interacting partners of an individual oscillator. “In such networks, synchronizability is improved when there is a coupling strength that is related to the number of contacts. In our network, the large discs obviously have more contacts, but they also have more inertia and this [tempers] the strength of the interaction between the discs,” says Araújo.

“Synchronization in real networks is a timely line of research,” says Adilson Motter, a physicist at Northwestern University who was not involved with the study. “Previous network-synchronization studies have focused mostly on random networks…the specific optimization results [in this study] are also interesting, as they deviate significantly from the results my collaborators and I have previously established for random networks.”

Applications and analogies

“Any mechanical bearing [with spheres/wheels of different sizes] could benefit from this result in principle,” explains Herrmann. Since greater synchronizability would render a bearing both more resistant to failure from perturbation and more durable (reduced time out-of-sync means reduced wearing of parts), finessing the famously accurate and reliable mechanical Swiss watch would be one possible option.

For the more philosophically inclined, by showing that bearings are physical realizations of complex networks of oscillators, the team has constructed something akin to a metaphor for the Internet. “Only in our case it is rolling. The Internet is not rolling anywhere,” says Herrmann. “So I would say that our results have analogies in the world of the Internet.”

The research is published in Physical Review Letters.

Supernova origin of galactic cosmic rays confirmed

The first direct evidence that galactic cosmic rays are accelerated within supernova remnants has been provided by observations by the Fermi Large Area Telescope collaboration. The results make use of four years of data collected by the telescope observing two supernova remnants – IC 443 and W44 – within our galaxy. The observations fit very neatly with predictions of neutral pion decay.

Galactic cosmic rays – the hypothesis

Cosmic rays are highly energetic particles, mainly protons, whizzing through space, most of which have their origins outside the solar system. A popular explanation of the origins of galactic cosmic rays – those produced within the Milky Way – is that they come from supernova remnants (SNRs), but until now there has been no unambiguous observational evidence linking the two.

When a star goes supernova, its remnants – including strong magnetic fields – can linger for thousands of years. According to the SNR cosmic-ray hypothesis, protons are accelerated by the shock front created in a supernova and then further accelerated by the magnetic fields until they gain enough energy to escape this process and become a newly formed cosmic ray. These energetic protons, the hypothesis claims, sometimes collide with other protons – in interstellar clouds, for example – to produce a neutral pion, which decays almost instantly into two gamma-ray photons.

Observing gamma rays

The 4303 kg Fermi Gamma-ray Space Telescope was launched in June 2008 on a five-year-minimum mission. The Fermi Large Area Telescope (Fermi LAT) is an instrument on board this observatory that uses sophisticated particle detectors to measure the trajectories and energies of incoming photons. Between 4 August 2008 and 16 July 2012, the Fermi LAT collaboration studied the SNRs IC 443 and W44 – which are about 5000 and 10,000 light-years from us, respectively – paying particular attention to gamma rays with sub-GeV (a billion electronvolts) energies. Although gamma rays can have significantly larger energies in some objects, the Fermi LAT focused on a range that would provide data crucial to distinguishing between gamma rays emerging from pion decays and those produced by other means, such as accelerated electrons.

Protons can only be accelerated to a certain level by the SNRs before they are ejected. This places an upper bound on the energies of these protons, which also places limits on the energy of the intermediate pions and subsequent gamma rays. More importantly, though, because the neutral pion is a heavy particle with a mass of 135 MeV (more than 260 times heavier than the electron), the gamma rays into which the pions decay are expected to have a minimum energy – that is, below a certain energy, one expects no gamma rays if they are indeed produced from protons accelerated in SNRs. “That is the smoking-gun signature for gamma-ray emission from the decay of pions, which can only be created by accelerated protons,” says Stefan Funk, a physicist at Stanford University and SLAC National Accelerator Center, and a member of the Fermi LAT collaboration.

Finding the smoking gun

Given the abundance of cosmic rays and the many models that could explain them, Funk and colleagues had to take into account the various backgrounds affecting their data before confirming the source of the observed gamma rays. And they believe they have finally observed the smoking gun.

Referring to the SNR spectra (click on the image above), Funk tells physicsworld.com that “if you look at the data points, you will see that they show the two cut-offs: the high-energy one, which corresponds to the maximum energy to which protons can be accelerated within the SNRs in question, and the low-energy one, which corresponds to the pion-decay cut-off, the minimum energy that the gamma rays receive in the pion decay”. Of course, there are several models that could explain the data, including the possibility that the gamma rays are produced by the acceleration of electrons, but the team was unable to match its data to any of them. “The curve labelled ‘pion-decay’, on the other hand, shows what you expect for gamma rays from protons that decay via the pion, which is very consistent with our data,” explains Funk. The significances of these observations are 19σ and 21σ for IC 443 and W44, respectively.

“This paper offers very important information that can shed light on the characteristics of supernova remnants from the point of view of cosmic-ray production,” says Jozef Masarik, of Comenius University in Bratislava, who was not involved in the research. “Understanding of the origin of cosmic rays can even contribute to the verification or dismissal of some beyond-the-Standard-Model theories.”

Cosmic rays were first observed by Victor Hess in the early 20th century. A century later, this result from Fermi LAT is the first to confirm the supernova origin of galactic cosmic rays. What the researchers cannot yet say is whether supernova remnants are the only source of these mysterious particles.

The research is published in Science.

What's the most important feature of a successful science blog?

The good ol’ blog, a stalwart of Web 2.0. (iStockphoto/malerapaso)

 By James Dacey

The dramatic rise in traffic on social-networking sites such as Facebook and Twitter in recent years could have left the good “old-fashioned” blog looking a bit like a frumpy relic of the noughties. But I’m convinced that this is not yet the case.

While it is true that we science writers are becoming Face-Twits in our droves, it seems that many of us still see the blogosphere as an important forum for discussion and debate. I view it as a place where you can express yourself candidly in a more freeform style, and do so without stripping away all the complexities of an issue to nothing more than a witty 140-character soundbite #BitterJournoTakesSwipe@Twitter.

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Boston bound

(CC BY-SA 3.0 Riptor 3000)

By Michael Banks

I have just arrived in Boston for the 2013 American Association for the Advancement of Science (AAAS) meeting, which began in earnest today.

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Visible improvements

We are living in a golden age for scientific communication, a time of increasing appreciation for all things quantitative, when particle colliders find themselves at the heart of novels and scientists and statisticians can write bestsellers. In this golden age, the likes of Nate Silver, political statistician for the New York Times, and Hans Rosling, a medical doctor, public health statistician and frequent TED speaker, have attained near rock-star status thanks to their heady combination of stunning results and ability to bring mathematics to the public sphere with seemingly effortless grace.

The growing popularity of science, however, has made the effective communication of complex scientific results more important than ever: with a bigger audience comes a bigger responsibility to get things right. The popularity of Silver, Rosling and their intellectual kin has also highlighted the gap between researchers who communicate well, and those who struggle to present their results even to specialist audiences. Visual Strategies is a book that should appeal to people in both categories. Billed as a “practical guide for scientists and engineers”, it lies somewhere between a coffee-table conversation piece and a reference manual for wizened data masters, and its goal is to educate researchers about the foundations of good design, in the hopes of improving the way they communicate about science.

The thing that struck me immediately when I picked up Visual Strategies was that it is unlike any other textbook or reference manual on my shelf. The book’s jacket is covered with a colourful pattern of arrows, and it employs a technique called lenticular printing to make the arrows change from warm red to yellow depending on which way you look at them. The effect is instantly engaging, compelling you to pick up the book and flip through the richly coloured pages.

The authors, Felice Frankel and Angela DePace, have chosen a tabbed layout for the book, reminiscent of a cookbook or children’s story, which not-so-subtly indicates that Visual Strategies is not meant to be read front to back. Instead, its structure encourages nonlinear browsing, and each subsection is colour-coded for quick reference. This is very unusual for a publication aimed at scientists and engineers, since most journals or textbooks are simply black on white, with sparing colour and apparently little thought given to the design of the physical article itself. One of the book’s best features is the “visual index” at the end, which contains small thumbnail versions of the major graphics featured within each section. This is an absolute treat, and in my view it ought to become a standard feature for all textbooks and scientific journals.

Readers who do start from the front of the book will find that it begins with a conversation between the authors (who are both research scientists) and the book’s graphic designer about choices made in construction and layout. This conversation sets the tone for the entire book, which is ultimately about the decisions and changes that go into making scientific figures better and more easily understood by colleagues or members of the public. This same decision-making process carried through to the choices the authors made in creating the book itself. The interior of Visual Strategies is filled with graphs, photos and figures (both hand drawn and computer generated) from a dozen different scientific disciplines, creating an anthology of visual communication. The graphics chosen for Visual Strategies also include many hand-drawn sketches and early rough drafts, which highlight the way some figures were developed and conceptualized. Being able to see these early versions, and the changes made to them, gives readers much to consider in their own visualizations.

The effective communication of complex scientific results is more important than ever now

The book’s visual strategies are presented in two ways: as the authors’ own suggestions for improving various published graphics, or as case studies on the evolution of graphics written by a handful of expert contributors. Differences between the “before” and “after” images are sometimes subtle, and a few may even seem arbitrary. Other changes, however, are dramatic and once shown they seem obvious and almost inevitable. These can sometimes be as simple as adding a bit of colour, or removing labels and lines to declutter the image. The authors note early on that, while you may not agree with a particular change in font or colour, the mere process of considering these factors will improve and enrich your own visualizations, as well as your ability to convey their underlying scientific meaning.

For all the innovation and charming creativity of Visual Strategies, however, its lack of broad structure may limit its utility. The use of coloured tabs, chapter headings and a very dynamic layout is confusing at times, and it lacks a treatment of more traditional graphs, such as scatter plots, bar charts and the growing varieties of density maps. Error bars, plotting symbols and dotted versus dashed lines in plain figures are not always the most thrilling things to discuss, and perhaps they are better left to works such as Edward Tufte’s classic The Visual Display of Quantitative Information (Graphics Press, 1983). Still, because they are the most common forms of data visualization for many researchers, their absence is felt. Along with the many decisions about detail and design that went in to creating the book, the authors also made a conscious choice to aim it at more experienced scientists and researchers. It would be difficult for novices or young students to gain a foundation in data visualization using this text alone.

The book’s supplemental website (http://visual-strategies.org) is full of good-quality content and links, and may yet provide an interesting forum for data-visualization discussions and resources. Anyone interested in visualization should spend at least a little time browsing through it. It is fitting, too, that the book discusses interactive graphics, since researchers can now convey complicated structures or hierarchies within data to anyone with a web browser – making interactivity a hallmark of this new era in science communication.

The tips and discussions throughout this book give scientists a foundation for making their visualizations more honest and more obvious. It lacks the structure needed to be a teaching tool for novices, and is not quite encyclopedic enough to truly be a reference guide for professionals. But Visual Strategies is effective and entertaining at sparking discussion and thought, particularly for those in the trenches of discovery.

  • 2012 Yale University Press £25.00/$35.00pb 160pp

Teaching an old blog new tricks

By Hamish Johnston

(iStockphoto/webphotographeer)

When the Physics World editorial team started blogging in earnest early in 2008, it was our first chance to interact much more directly and informally with the physics community – prior to that we had been mainly restricted to conventional news stories and features. Since then, of course, the social-media world has grown out of all recognition and Physics World is now on Twitter, Facebook, Flickr, Google+ and YouTube, with these sites giving us new ways of communicating with you (and vice versa).

But we think the Physics World blog still has a big role to play in what we do and today marks a major upgrade to it. While most of the improvements are behind the scenes, I thought I’d mention a few new features we hope you’ll enjoy.

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The quantum coin toss

All unpredictability in the world around us, be it the outcome of a coin flip or the weather conditions a month from now, is a fundamentally quantum rather than classical phenomenon. This is the conclusion of two physicists in the US, who have worked out that molecular interactions in gases and liquids can amplify tiny quantum fluctuations, to the point where the fluctuations are large enough to account for the uncertainties we experience at the macroscopic scale. This insight, they argue, could prove important in cosmology, as it might rule out some theories of the multiverse that rely on classical as opposed to quantum probabilities.

Classical to quantum predictions

In classical theories of probability the chances we attribute to a flipped coin landing either heads-up or tails-up simply reflect how much or how little we know about the coin flipping. To say that there is a 50:50 chance means we have no idea how the coin will land. In principle, however, if we understood exactly which physical processes determine the outcome of the flip and also know with enough precision all of the relevant parameters – such as the force imparted to the coin, the height at which it lands and the air resistance – we could predict the outcome with certainty.

According to the latest research, this view is not correct. Andreas Albrecht and Daniel Phillips of the University of California at Davis argue that the probabilities we use in our everyday lives and in science do not “quantify our ignorance” but instead reflect the inherently random nature of the physical world as described by quantum mechanics. They maintain that quantum fluctuations can be amplified sufficiently by known physical processes to the point where they can entirely account for the outcome of these everyday macroscopic events. In fact, they claim that all practically useful probabilities can be accounted for in this way. In other words, all classical probabilities can be reduced to quantum ones.

To back up their case Albrecht and Phillips consider an idealized fluid of billiard-ball-like molecules that continually collide with one another. The Heisenberg uncertainty principle dictates that the trajectory of a billiard ball will have an inherent uncertainty, resulting from the uncertainties in its position and momentum. The researchers worked out – by inputting suitable values of radius, mean free path, average speed and mass of the billiard balls into a couple of simple equations – how much this uncertainty grows with each collision between the balls. They show that in water and air (nitrogen) the uncertainty becomes so large in the space of one collision that every single fluctuation in the properties of these fluids has a fully quantum-mechanical origin.

Quantum outcomes

The researchers then show that the quantum fluctuations manifest in the water can wholly determine the outcome of a coin flip. They calculate that a typical flipped coin can spin through half a revolution in about 1 ms. This is also the temporal uncertainty in the neuronal process governing the coin flipping, a process that a group of neuroscientists in 2008 argued is caused by fluctuations in the number of open neuron ion channels. Since these fluctuations are, in turn, caused by the Brownian motion of molecules called polypeptides in a fluid that is largely water, quantum uncertainty (which drives the Brownian motion) can completely randomize the coin flipping.

Cat’s tail

As such, the researchers say that anyone tossing a coin is, in fact, performing a Schrödinger’s cat style experiment. But rather than a cat that is both alive and dead, the quantum object in this case is a coin, the final state of which is simultaneously heads and tails. The outcome of the flip therefore remains genuinely open until the upwards face of the coin is looked at, at which point the system takes on a definite value of either heads or tails.

The researchers admit that their example is very simplified and that they would have a hard job tracing the amplification of quantum uncertainties in all familiar contexts, be it rolling dice or picking out a card at random. They also point out that it would only take one counterexample to falsify their idea – a use of classical probabilities that is clearly isolated from the physical, quantum world.

David Papineau, a philosopher at King’s College London, believes that Albrecht and Phillips are likely to be correct but he doesn’t think their conclusion is terribly surprising. “It is very likely that all serious probabilities, be it a coin landing heads-up or a child being female, are manifestations of quantum chanciness,” he says. “Indeed we have devices, such as Geiger counters, that show how big results are often caused by chancy micro-events.”

Albrecht replies that he and Phillips are perhaps the first physicists to have tackled the relationship of quantum and classical probabilities head-on, and he argues that the latest research might also rule out some theories in which physical processes (such as “eternal inflation”) produce multiple copies of pocket universes like the one we observe around us. Such theories of the “multiverse”, he says, need to import purely classical probabilities because a quantum wave function on its own cannot determine in which universe a particular measurement would be made. But Albrecht points out that such a move would not be possible if classical probabilities are, at root, quantum.

A preprint of the research is available on arXiv.

Tungstenite triangles emit light

Researchers in the US have succeeded in growing single atomic layers of the naturally occurring mineral tungstenite for the first time. The sheets appear to have unusual photoluminescence properties that might be exploited in optics devices like lasers and light-emitting diodes.

2D materials have dramatically different electronic and mechanical properties from their 3D counterparts and so may find use in a host of novel device applications. Until now, however, most research in this field has focused on the most famous of 2D materials, graphene, but the fact that this material lacks a direct electronic band gap means that scientists are now starting to look at other 2D candidates too.

A team led by Mauricio Terrones and Vincent Crespi of Penn State university in the US grew monolayers of tungstenite (WS2) by depositing tiny crystals of tungsten oxide less than a nanometre tall and then passing these crystals though sulphur vapour at high temperatures of 850 °C. The result – monolayers of tungsten disulphide arranged in a honeycombed pattern of triangles comprising tungsten atoms bonded to sulphur atoms.

“We were astonished that we could grow such perfect, atomically thick triangle shapes using a chemical vapour deposition method,” Terrones told physicsworld.com. “Moreover, and again to our surprise, we observed that these triangles glow quite strongly at their edges rather than at their centres – a peripheral photoluminescence effect that we never expected and which has not been reported on before.”

Photoluminescence occurs when charge carriers (electrons and holes) recombine in a structure to emit light of a different wavelength from that used to initially excite the material. Normally, light emission is a delicate thing, explained Crespi, and structural defects – like edges – prevent light emission as they tend to give excited electrons and holes ways of recombining without emitting light. “We saw just the opposite effect,” he said, “in that the structural defects created close to the edges of a triangle seem to be the favoured place for emitting light.”

Direct band gap

2D systems are intrinsically different from their bulk 3D counterparts, and WS2 is no exception. While the bulk material is an indirect band gap semiconductor, the single-layer material boasts a direct band gap. Direct band gaps are important in semiconductors because they allow devices made from these materials to emit light efficiently – as in this case.

According to the Penn State team, the WS2 triangles might find applications in optoelectronics. “They might even come in handy as biomarkers or in drug delivery, but much more research still needs to be carried out before we can say this with any certainty,” added Terrones. “They could also be useful in a new generation of planar, 2D optoelectronic devices, such as light-emitting diodes – where we control the propagation of light in thin film layers of material – and even in laser technology.”

The researchers now plan to grow other 2D materials that have different optical and electronic properties. Some examples in the pipeline include MoSe2, NbS2 and WSe2, revealed Crespi. “We would also like to better understand and control the light emission from 2D materials in general, and try our hand at sculpting the triangles into multicomponent devices.”

The work is detailed in Nano Letters.

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