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Zoom video call is powered by Google’s quantum computer

An international team of researchers has used Google’s Sycamore quantum computer to power an online Zoom meeting for the first time. The US tech giant’s device, which consists of 53 programmable superconducting quantum bits, has already been shown to outperform classical computers at certain tasks. The new discovery could allow meeting participants to appear in more than one break-out room at the same time – a phenomenon that the team has dubbed “quantum Zoom advantage”.

Conventional, classical computers store and process information as bits that can have one of two states – “0” or “1”. But quantum computers like Sycamore exploit the ability of quantum particles to be in “superposition” of two or more states at the same time. N such qubits can therefore be combined or “entangled” to represent 2N values at once, allowing quantum devices to process information in parallel on a massive scale.

This unprecedented power has now been exploited for the first time in a video call when Benedetta Brassard – a quantum physicist at the the University of Waterloo in Canada – accidentally installed Zoom on Sycamore during an online meeting. Brassard is part of the International Fault Tolerant Benchmarking Team (FiT/BiT), which she set up to diversify participation in measuring the performance of quantum computers.

Distracting meme

“I was in a FiT/BiT board meeting and just thought I would have a quick check of the Sycamore dashboard to see how my quantum calculation was going,” Brassard told Physics World. But after being distracted by an amusing Shor’s algorithm meme, she somehow ported the Zoom meeting to Google’s quantum processor.

The 11 participants became encoded in Sycamore’s 53 superconducting qubits and found themselves in confusing quantum superpositions of Zoom settings. “Some colleagues were telling me that I was on mute, while others could hear me,” recalls Brassard.

“I knew something was really wrong when multiple versions of the meeting kept popping up on my screen”. Brassard now believes that Sycamore was using the “many worlds” interpretation of quantum mechanics while running Zoom. “The only way to steer it back to the classical world was to keep making measurements – which meant that I actually had to pay attention to what other people were saying”.

Fortunately for her fellow FiT/BiT members, Brassard had supervised a PhD student on the implementation of Instagram on D-Wave’s 2000Q quantum annealer. “The problem was to work out the optimum time of the day for influencers to post pet-related images – which we discovered is an NP hard problem,” she explained.  As a result, Brassard already knew how to transform an app from a quantum to a classical state.

Brassard and colleagues have published a paper describing the Zoom incident in the journal Quantum Advances in Computing and Correlation (QUACC). They now hope to develop a quantum formalism to allow meeting participants to exist in multiple break-out rooms at once. “This could lead to the real quantum advantage of making online meetings shorter and more bearable,” she said.

Non-destructive detection could speed up cold-atom quantum sensors

Quantum sensors based on cold-atom interferometry are among the most accurate instruments in fundamental physics, with predicted applications that include mapping underground structures and creating more precise navigational systems. Their speed, however, is limited by the fact that the measurement process typically destroys the carefully prepared atomic sample, meaning that a new sample must be created for each measurement. This takes a few hundred milliseconds for even the fastest sensors.

Researchers at SYRTE in France’s Observatoire de Paris have developed a new non-destructive method that uses microwaves to measure the number, or population, of atoms in specific quantum states. The new method enables experimenters to perform quantum sensing measurements nearly 30 000 times a second – a rate that could make it possible to complete large surveys on a timescale competitive with current commercial devices.

The principle of microwave detection

Non-destructive measurements of cold atoms can be performed using existing methods. However, the complex optical systems often required make it difficult to create compact, practical sensors. The SYRTE team of William Dubosclard, Seungjin Kim, and Carlos L Garrido Alzar solved this problem by developing a system based on microwaves instead. Their solution uses the fact that microwave power radiated by an antenna into a medium depends on the radiation resistance of that medium.

Diagram showing the atomic reflection coefficient as a function of frequency. The value of the coefficient dips markedly at the atomic resonant frequency
Detection boost: A diagram illustrating the spectral sensitivity of reflected microwaves due to the presence of an atomic resonant transition. This is the working principle of the non-destructive detection. (Courtesy: C L Garrido Alzar)

In the SYRTE experiment, the medium is a sample of 10 000 rubidium atoms prepared at temperatures of around 3 µK. By using an antenna to direct a beam of microwaves onto the atoms, and then observing the microwave signal the atoms reflect, the experimenters could detect the atoms’ quantum state. Although the microwave reflections are weak, the researchers saw clear variations in them when they scanned the microwave frequency across a resonant atomic transition.

Proving it works: detecting cold atoms

The team proved the non-destructive nature of their detection method by measuring coherent quantum effects known as Rabi oscillations. These sinusoidal patterns appear as populations of atoms oscillate between two atomic energy states when near-resonant light is applied, and they form the basis of cold-atom interferometry. In a typical experiment, these patterns are observed by creating multiple atom samples and taking one data point per sample. In this case, however, the researchers managed to observe Rabi oscillations with a single sample – by using one microwave antenna to drive the oscillations and another to perform repeated detection.

They observed no difference between the amplitude of the oscillations obtained with their method compared with the multiple sample method. This validates that their technique did not cause any additional atom and decoherence losses even as it increased the detection bandwidth to 30 kHz.

Garrido Alzar tells Physics World that they now plan to characterize the noise level of their novel detection method and investigate how it would affect the performance of quantum inertial sensors.

The research is reported in Communications Physics.

Sub-diffraction imaging of the human eye visualizes photoreceptors with unprecedented detail

Researchers in the US have improved the resolution for imaging the human eye by a third. This has enabled them to visualize the mosaic of rod and cone photoreceptors at the back of the eye in greater detail than ever before and allows the assessment of individual photoreceptors. The new imaging technique could facilitate earlier detection of diseases such as age-related macular degeneration and enhance the monitoring of treatments for eye diseases, the team claims.

Age-related macular degeneration is a progressive eye disease and a leading cause of sight loss. People with age-related macular degeneration lose the ability to see fine detail in their central vision, as the cells at the centre of their retina become damaged. Early diagnosis and treatment are crucial to preserve sight, in macular degeneration and other eye diseases.

“The goal of our research is to discern disease-related changes at the cellular level over time, possibly enabling much earlier detection of disease,” says Johnny Tam, at the National Eye Institute in Maryland. As well as improving the monitoring of degenerative changes in retinal tissue, enhanced image resolution could also help doctors see whether treatments for eye diseases are working and assist with the development and assessment of new therapies.

Imaging the eye is challenging. The light-distorting properties of parts of the eye like the lens and cornea reduce image resolution. Then there’s the diffraction limit of light to consider, with most conventional techniques for imaging beyond the diffraction limit using too much light to be safe for the eyes. Current retinal imaging techniques that use near-infrared light have a resolution of around 2−3 µm, while the smallest rod and cone photoreceptors range from 1–3 µm in diameter.

To improve resolution beyond the diffraction limit, and allow these individual cells to be distinguished, Tam and colleagues combined two imaging techniques: annular pupil illumination and sub-Airy disk confocal detection. By combining these two approaches, the researchers improved upon a conventional retinal imaging technique known as adaptive optics scanning light ophthalmoscopy, which uses deformable mirrors and computational methods to correct for optical imperfections of the eye in real time.

Annular pupil illumination generates a hollow beam of light. This improves the transverse resolution across the mosaic of photoreceptors, but reduces depth resolution. However, the researchers then used a very small pinhole – known as a sub-Airy disk – to block the light coming back from the eye, which allowed them to regain the depth resolution.

“One might think that more light is needed to get a better image, but we demonstrate that we can improve resolution by strategically blocking light in various locations within our instrument,” explains Tam. “This approach reduces the overall power of light delivered to the eye, making it ideal for live imaging applications.”

The researchers tested their technique on five adults with no sign of eye disease. Describing their research in Optica, they claim that this approach improved resolution across the photoreceptor mosaic by 33% and depth resolution by 13%, compared with conventional adaptive optics scanning light ophthalmoscopy. This allowed them to reveal subcellular features of photoreceptors that were not clearly visible with previous techniques.

Imaging photoreceptors
The new imaging technique can acquire images of the smallest cone photoreceptors in the living human eye (left). The team also combined this approach with non-confocal split detection (right) to better see the inner segments of the same photoreceptors. (Courtesy: Johnny Tam, National Eye Institute)

“The ability to noninvasively image photoreceptors with subcellular resolution can be used to track how individual cells change over time,” says Tam. “For example, watching a cell begin to degenerate, and then possibly recover, will be an important advance for testing new treatments to prevent blindness.”

The researchers say that this clear improvement in the ability to obtain higher resolution images of the retina could help answer fundamental questions about photoreceptor health. They add that their technique provides a straightforward method of achieving sub-diffraction limited resolution in point-scanning-based microscopy and imaging approaches. This could enable routine sub-diffraction imaging of cells in the human body, they state, and be useful in other applications where it is important to image with low levels of light.

Physics in the pandemic: making particles from space tangible for schoolkids

Photo of Andrew Ferguson with a muon detector
(Courtesy: A Ferguson)

Primary-school children, and the rest of us too, are continuously being showered by unseen muons, a heavier relative of the more familiar electron. These muons are created when energetic cosmic rays, including protons and alpha particles, hit our atmosphere and produce a shower of particles as they slow down. At sea level, muons arrive at a rate of about one per square centi-metre per minute.

Muons remain unnoticed unless you have the right equipment to look for them. Several years ago I was therefore excited to read about a successful US-based outreach project called Cosmic Watch. Started by particle physicists, it allows members of the public to make muon detectors for less than $100 and observe these tiny particles for themselves. At the heart of the detector is a silicon photomultiplier chip, which measures the few blue photons emitted by a plastic scintillator whenever a muon passes through.

Inspired, I started to build muon detectors based on the Cosmic Watch design. But when I had got one working, I needed something to do with it. A work trip to Belgium on the Eurostar train presented one such opportunity. I took the detector with me (curiously, no questions were asked at security) and, sure enough, as we travelled through the Channel Tunnel between Britain and France, it recorded a lower rate of muons than at sea level. The sea and seabed were shielding the detector.

Muon counter graph in channel tunnel
The rate of muon detections dropped as the detector went through the Channel Tunnel.

As fun as that was, muonic measurements are better shared. So, along with another physicist parent, Lisa Ibberson, I got in touch with Kate Cooke, who teaches science at Coton Church of England Primary School in Cambridgeshire, where my son attends. Together, the three of us applied for money from the Institute of Physics School Grants Scheme. Our idea was to work with pupils to teach them about muons, get them to design a muon detector and finally install it in the school.

In July 2019 we were delighted to hear that our grant was successful and the real work began. We held an initial assembly at school that October using a water pistol and a few slides to introduce ourselves and muons. With the pupils in years 3 and 4 (ages 7–9), we drew pictures of the cascading particles resulting from a cosmic-ray air shower. Meanwhile, the children in years 4 and 5 (ages 8–10) were in charge of how the detector looked.

Together we decided that it should have a muon counter and a display that flashed different colours, depending on the muon’s energy. We jointly defined various parameters of the display, including its size, the colours of the flashes and the number of digits on the counter. Finally, we talked with year-6 pupils about the data the detector would produce, with the help of some edible Smartie bar graphs of course. And behind the scenes we were busy ordering printed circuit boards, soldering components and programming microcontrollers.

In January 2020 we returned to the year 4/5 class with a red flashing prototype encased in a shoe box. We got some great feedback. The colour red was no good – it was too much like a warning light and too bright. We therefore dimmed the display and democratically chose blue, green and amber for the colours. The pupils also told us we needed a switch to turn off the display when the flashing got too distracting. Finally, we decided to have eight digits in the detector so it could count to 99,999,999 muons – over roughly the time pupils spend in school (at a count every two seconds we were expecting about 15 million counts per year).

Muon detector for primary school outreach project
The pupils designed the muon detector with 8 digits, so it could count up to 99,999,999 muons.

Unfortunately, when the pandemic struck we couldn’t continue to work directly with the children. Instead, over the summer I worked at home, quietly improving the detector’s electronics. In fact, on walks through the village where I live, people would often ask me what had happened to the muon project. I’d tell them we’d get back to it when we can and fortunately, by September 2020, schools re-opened and we started to think about the final switch-on.

Originally we envisaged a school assembly with a rowdy group countdown to the detector being turned on. We couldn’t do that with social-distancing measures in place, so instead planned a virtual switch-on for December 2020 with pupils from years 4 to 6 in their classrooms, Cooke at school, and me and Ibberson joining from our homes. And so, after revving the pupils up with a quiz to remind them about muons, we turned the device on.

It worked, phew! We then spent a few minutes watching the detector count up to 60, before opening the floor to questions. And, wow, what great questions they asked. How can a muon travel through 10 metres of concrete? Why do they decay into electrons? If the detector had a bigger area, would it count more muons? Has a detector like this ever been made before? Where do the cosmic rays that generate the muons come from?

Overall, the project was a great success. We had wonderful engagement from the pupils, who had contributed to the design of a fun scientific instrument. In fact, the switch-on of the detector, though virtual, was every bit as exciting as if it had happened in school. Looking to the future, we hope that this strange machine from a strange year counts up to 99,999,999 many times over its lifetime – and that it continues to provoke curiosity from primary-school pupils in Coton for years to come.

Flexible detector takes high-resolution X-ray images in 3D

While X-ray imaging is routinely employed in medical diagnosis and in industry for inspecting materials like semiconductors for defects, existing X-ray machines cannot image curved three-dimensional objects with high resolution. A team led by researchers at the National University of Singapore (NUS) and Fuzhou University in China has now developed a new flexible X-ray sensor that can do just this. The device, which relies on a series of nanoparticles that emit light for a long time after being excited with X-rays – a phenomenon known as persistent radioluminescence – might find use in healthcare applications such as portable X-ray detectors for mammography and imaging-guided therapeutics.

The X-ray detectors in today’s X-ray machines are usually flat panels in which each pixel has its own integrated circuit. This set-up makes the pixels bulky and limits the resolution of the detector, explains team member Xiaogang Liu at the NUS’ Department of Chemistry. The panels’ flatness also means the detectors struggle to capture images of curved objects.

Wrap-around device

In their work, Liu and colleagues focused on lanthanide-doped nanomaterials, which have unique luminescent properties that are already widely exploited in X-ray scintillation, optical imaging, biosensing and optoelectronics. They began by doping sodium lutetium fluoride (NaLuF4) nanocrystals with ions of the rare-earth element terbium (Tb3+). They then embedded the doped nanocrystals (which are denoted as NaLuF4:Tb@NaYF4) into silicone rubber to make a highly flexible X-ray detector that can be wrapped around 3D objects.

The next step was to excite the NaLuF4:Tb@NaYF4 with X-rays at an energy of 50 kV. When they did this, the team observed that the material emitted intense light long after the source of X-rays had been removed. The light persisted for more than 30 days, which means it can be used to image objects throughout this time.

Slow “hopping” charge carriers

Liu and colleagues explain that the light is emitted as the lutetium ions in the NaLuF4:Tb@NaYF4 lattice absorb the energy of the X-rays, generating many energetic electrons in the process. When X-ray photons collide with small fluoride ions in the material, flaws known as anion Frenkel defects form in the nanocrystal and trap the energetic charge carriers (electrons and holes) created. The prolonged radioluminescence in the material comes from these electrons slowly “hopping” through the crystal scaffold towards the Tb3+ ions and radiatively recombining with hole-Tb3+ centres, they say.

Liu acknowledges that other persistently luminescent materials already exist. Phosphors are one prominent example, and in 2011 a team at the University of Georgia, US, reported that ZnGa2O4:Cr3+ phosphors have an afterglow lifetime of approximately 15 days. However, Liu notes that these other materials are either not very sensitive to X-rays or are difficult to manufacture at the nanoscale, which makes them unsuitable for making flexible detectors.

Sub 25-micron image resolution

The NUS team’s imaging technique, which they call X-ray luminescence extension imaging (Xr-LEI), can be used to produce images with a resolution of less than 25 micrometres, the researchers say. “Many research groups, including ours, have been taking on challenges in X-ray imaging over the past few years,” Liu notes. “The technology we report on may provide a much-needed solution for imaging highly-curved 3D objects. It could be particularly suitable for applications like point-of-care X-ray radiography and screening mammography without having to compress the breast, which is uncomfortable for the patient.”

As well as healthcare applications, the technique might also be used to detect defects in electronic materials like semiconductors, authenticate works of art and to examine archaeological objects at the micron scale, he adds.

The researchers, who report their work in Nature, say they now plan to optimize the performance of their persistent luminescent nanomaterials to further reduce X-ray dosage and exposure time. “We will also be pursuing the development of dynamic X-ray imaging techniques that would benefit real-time monitoring of biological processes of living organisms,” Liu tells Physics World.

LATTICE radiotherapy plus immunotherapy shows promise for treating advanced bulky tumours

The combination of LATTICE radiation therapy (LRT), a spatially fractionated radiotherapy technique, and immunotherapy dramatically shrank a large metastatic lung cancer mass in one month and resulted in a complete local response within five months, according to a case report in Frontiers in Oncology. The patient, a woman with advanced non-small cell lung cancer and multiple metastases, did not experience any side effects from the high radiation dose she received. The dramatic effectiveness of this combined treatment is spearheading the development of future clinical studies.

Bulky tumours are challenging to treat using radiotherapy due to large tumour sizes and limitations of normal tissue toxicity. Spatially fractionated techniques such as high-dose 2D grid radiotherapy and LRT – a 3D lattice-like reconfiguration of grid therapy – have been employed to safely treat bulky tumours. LRT uses multiple high-dose regions (vertices), distributed within the tumour volume according to its size and shape and the proximity of critical structures, with valleys of much lower dose in between.

The technique’s principal developer, Xiaodong Wu from Executive Medical Physics Associates in Miami, FL, explains that when 3D LRT is delivered using intensity-modulated radiation therapy, volumetric modulated arc therapy or ion beams, highly customized peak-to-valley dose distributions can be generated within the tumour volume, while sparing skin and normal tissue.

Xiaodong Wu and Benhua Xu
Researchers Xiaodong Wu (left) and Benhua Xu.

LRT is currently used for palliative tumour debulking or boost treatments and to safely deliver high radiation doses to partial volumes of large tumours. It can be administered alone or in combination with conventionally fractionated radiotherapy.

Led by Benhua Xu, chief of the Department of Radiation Oncology at Fujian Medical University Union Hospital in China, this case study represents the first use of LRT in conjunction with immune checkpoint blockade – a treatment that help the body’s immune system recognize and attack cancerous cells.

The 33-year old patient was diagnosed with advanced invasive adenocarcinoma in the lower lobe of her right lung. Within months following surgery and chemotherapy, she had developed multiple metastases in both lungs, the thyroid, the spine and on the posterior chest wall. While the patient was receiving checkpoint inhibitor therapy, the metastatic mass in the posterior chest wall grew from 2.0 to 63.2 cm3, with maximum dimensions of 5.0 x 5.4 x 5.3 cm.

The team administered a single fraction of LRT (20 Gy prescribed to six high-dose vertices) to this fast-growing mass. The patient continued checkpoint inhibitor therapy, receiving six cycles over the next six months. She also underwent stereotactic body radiotherapy to treat multiple metastases and received drug therapies.

Although all of the patient’s metastatic lesions responded to the various palliative treatments, only the posterior chest wall tumour that received high-dose LRT achieved a complete response. While this tumour had not responded to the initial immune checkpoint blockade (anti-PD1), after high-dose LRT, it shrank by 77.84% within a month and continued to regress until achieving complete local response five months later. There were no toxic side effects in the area of the treatment, and the site remained disease free until the patient died several months later.

The researchers note that with only 6.5% of the large tumour’s volume receiving a dose of 20 Gy and higher, the effective uniform dose was calculated as 1.2 Gy. “Based on the traditionally understood mechanism of radiobiology, the probability of achieving complete local control with such a dose for a tumour of 63 cc would be nearly zero,” they write. “The synergetic effect combining high-dose LRT with anti-PD1 becomes a plausible speculation.”

They further hypothesize: “In high-dose LRT, the dose in the vertices are sufficiently high to induce neo-antigen release and initiate the cascade of antigen presenting cell (APC)-based T-cell priming. The dose in between the vertices is low enough to preserve internal tumour circulation/perfusion to potentially facilitate the infiltration of APCs and the primed cytotoxic T-cells. The highly heterogeneous dose configuration could reprogram the immunosuppressive tumour microenvironment to become more immunogenic, and when synergistically treated by checkpoint inhibitors, the primed T cells could attack tumour cells without being exhausted.”

Wu tells Physics World that the researchers are currently preparing systemic clinical studies using this combined treatment for patients with lung cancer, liver cancer, breast cancer and melanoma. He notes that interest in and use of LRT, and spatially fractionated radiotherapy in general, are increasing. Following the early clinical experiences primary made by Innovative Cancer Institute in Miami and Fujian Union Hospital, more institutions, including the Mayo Clinic in Rochester, have begun to offer LRT to their patients.

Strolling in the deep

At the bottom of the North Central Pacific Ocean, some 5000 m beneath the waves, lies a small, fist-sized black rock, with a knobbly surface texture, like a head of broccoli. It holds a secret at its heart – a single tooth, long ago shed by a shark swimming in the waters above. In the manner of a pearl forming around a piece of grit in an oyster, the tooth has become encapsulated by layers of waterborne minerals that settled out of the water around it. It took millions of years to reach its current size – but it shall grow no bigger.

A vast unmanned, electric submersible ploughs across the seabed like a bulldozer, heaving up our rock (among others) with its teeth, before sucking it up a hose to a ship waiting on the surface. These nodules are rich in metals like nickel, copper and cobalt – and industry has come to mine them. But the abyss is not empty, making this activity not without its victims. Our rock and its peers supported an abundance of life, from worms and starfish to crustaceans and ghost-like octopuses. As the mining machine lurches onwards, it leaves a trail of devastation in its wake – not to mention kicking up a lingering muddy cloud that chokes and smothers those survivors such as corals and sponges that are unable to flee and escape it.

Raising the alarm about this ecological vandalism against a realm about which we know precious little is the raison d’être of marine biologist Helen Scales’ beguiling new book The Brilliant Abyss: True Tales of Exploring the Deep Sea, Discovering Hidden Life and Selling the Seabed. With her light and engaging prose, Scales takes the reader on an introductory dive into the mysterious depths to reveal the myriad of life hidden within, from red and green bone-devouring worms that flourish whenever whales fall down to the abyss, to the world’s fishiest-smelling fish. There’s even a hunt for yetis – not of the elusive kind, but tiny, blind, pale crabs that survive living around deep-sea hydrothermal vents and cold seeps by farming bacteria to feast on. Like their abominable namesakes, however, they are very hairy.

As The Brilliant Abyss’ subtitle suggests, the work periodically segues into arresting tales from Scales’ career, from recovering experiments to determine what species of clams, worms and sea cucumbers colonize logs swept out to sea by floods and hurricanes, to weathering out high winds that suspended scientific activity during a research expedition in the Gulf of Mexico.

Fascinating titbits abound in Scales’ writing – including the revelation (to me, at least) that diving mammals such as whales and dolphins have evolved a special, “non-stick” form of the oxygen-carrying, haemoglobin-related protein myoglobin in their muscles. These each have a slightly negative electric charge that repels other myoglobin molecules, allowing the mammals to carry 10 times the protein that we do without the molecules clumping together and causing their bodies to go completely stiff.

Scales’ book also explores such fascinating cases as whether coronal mass ejections from the Sun could have contributed towards stranding numerous young male sperm whales in the North Sea in 2015; as well as explaining why some fish have scales that are blacker than the darkest material man has ever engineered – the multiwalled carbon nanotube, Vantablack, which is up to 99.965% absorbent. One thing that struck me while reading The Brilliant Abyss is that despite being an erstwhile student of geology and having learnt the names given to Earth’s past supercontinents, I don’t recall ever having given thought to the corresponding “superoceans” that surrounded them, such as Mirovia and Panthalassa. A shift of perspective is always fascinating.

It is perhaps in the final third of the book that Scales’ argument for the preservation of the deep from exploitation becomes most clear. She explores the medical potential of deep-sea organisms – such as sponges that harbour anti-cancer compounds – and weighs up the benefits and risks of farming the deep for food and mining it for its mineral resources, before calling for the reader to join her in campaigning for humanity to leave the deep free from excessive interference. It’s a compelling argument – although one that might perhaps have been more strongly seeded in the opening chapters of the work.

One mild disappointment of the book for me is that there are not more illustrations or pictures of the weird and wonderful creatures introduced in the text (at least in my preview copy). Scales’ descriptions may be beautifully written and highly evocative, yet a picture is, as the cliché goes, worth a thousand words. The exception is the gorgeous cover art of various deep-sea species by the artist Aaron Gregory, in a style that seems to evoke the illustrations of the German zoologist and artist Ernst Haeckel, whose work is discussed in the book.

This quibble aside, The Brilliant Abyss is a wonderfully written read that I would highly recommend – it’s the ideal plunge into the depths of Earth’s last great wilderness. 

  • 2021 Bloomsbury Sigma 352pp £16.99hb

Super Earth is astronomer’s dream for atmospheric studies

A newly discovered exoplanet called Gliese 486b could offer the best opportunity yet for studying the atmosphere of a terrestrial planet beyond the solar system. An international team, made up of astronomers at the CARMENES project and NASA’s TESS mission, showed that several aspects of Gliese 486b make it ideal for atmospheric spectroscopy. Indeed, team member Ben Montet of the University of New South Wales says, “This is the kind of planet we’ve been dreaming about for decades”. The discovery could improve our prospects for finding extrasolar atmospheres capable of supporting life.

Exoplanets orbit stars other than the Sun and in the three decades since the first one was found, the discovery of more than 4000 exoplanets have been confirmed by astronomers. Super Earths are among the most sought-after targets of all exoplanet searches. Slightly larger than Earth, these planets have stable, rocky surfaces and could have substantial atmospheres – which astronomers hope could support life in some cases.

Studying atmospheres typically involves observing how light from the exoplanet’s star is affected as it passes through the atmosphere when the exoplanet transits across the star when viewed from Earth – something that Gliese 486b does.

As this light shines through the atmosphere, certain wavelengths are absorbed by its component gases. Astronomers can use these characteristic absorption lines to determine the composition and temperature of the atmosphere. Alternatively, they can study light emitted or reflected by the planet, just before it passes behind the star.

Nearby red dwarf stars

CARMENES and TESS use complementary techniques to discover super Earths and determine whether they are suitable for further analysis. In their study, the researchers searched for exoplanets orbiting nearby red dwarf stars – which are far more likely to host rocky planets than Sun-like stars. Through their search, they detected a particularly interesting super Earth orbiting the star Gliese 486, just 26 light-years away.

The exoplanet Gliese 486b is three times the mass of Earth and 1.3 times the radius, yet it has an orbital period of just 36 hours – placing it extremely close to its star. The astronomers also predict that Gliese 486b has a surface temperature of around 430 °C – making it slightly cooler than Venus.

While these conditions may sound extreme, they are not harsh enough to strip away the exoplanet’s atmosphere. This could mean that Gliese 486b has retained some atmospheric hydrogen and helium from its initial formation. Moreover, the planet’s temperature is sufficiently high to puff out its atmosphere, without any gas escaping, making it ideal for spectroscopic studies. Indeed, the astronomers report that Gliese 486b is the best rocky planet ever discovered for studying with emission spectroscopy; and the second best for transmission spectroscopy.

Although red dwarfs are seen as strong candidates for hosting habitable exoplanets, their high levels of stellar activity also threaten to destroy their exoplanets’ atmospheres. Through further studies of Gliese 486b’s atmosphere, astronomers will be able to better assess whether the search for extrasolar life should be focused on red dwarfs.

The research is described in Science.

The development of new ionic electrolytes for energy storage devices

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Electrolyte development is a critical component in the quest for higher-performing energy storage devices. Ionic electrolytes such as ionic liquids, plastic crystals and their polymer composites can offer important safety and performance advantages over traditional molecular-solvent based systems, particularly for devices utilizing reactive metals such as lithium or sodium.

An important approach to developing ionic electrolytes that can meet the complex challenges of next-generation electrochemical devices is increasing the range of known and well-characterized electrolyte materials. Understanding how different ion structures affect the physical, thermal, electrochemical properties, and the phase behaviour when combined with Li salts, is vital to optimizing device performance.

This webinar, hosted by Jenny Pringle, will overview our recent work on the design and use of new ionic materials and their application as liquid, quasi-solid state, composite or very high Li salt content electrolytes.

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Prof. Jenny Pringle works at the Institute for Frontier Materials at Deakin University, Australia. She is a chief investigator in the ARC Centre of Excellence for Electromaterials Science (ACES) and the ARC Industrial Transformation Training Centre “StorEnergy”. She received her degree and PhD at The University of Edinburgh in Scotland, UK, before moving to Monash University, Australia, in 2002. From 2008–2012 she held an ARC QEII Fellowship, investigating the use of ionic electrolytes for dye-sensitized solar cells. Pringle moved to Deakin University in 2013. There she leads research into the development of new ionic liquids and organic ionic plastic crystals for applications including thermal energy harvesting, gas separation membranes, and lithium and sodium batteries.

Nanoparticle sensors detect arsenic in drinking water

“About 785 million people are living without access to safe and clean drinking water; 140 million people in more than 50 countries have been exposed to arsenic-contaminated water.” These were the stark opening statements from Muhammad Abbas, speaking at the recent APS March meeting.

Arsenic poisoning is one of the most significant public health concerns worldwide. Arsenic is used in semiconductors, pharmaceuticals, wood preservatives, insecticides and chicken feed, and it leaches into the groundwater. Long-term exposure can lead to cancers of the kidney, liver, lungs and skin, as well as causing skin diseases and other health issues such as hypertensive heart disease. As such, the World Health Organization and Environmental Protection Agency recommend a maximum limit of 10 µg/l arsenic in drinking water.

Despite these serious health concerns, testing for arsenic in water currently requires expensive laboratory instruments that cannot be used for on-site detection and are unsuitable for developing nations. Abbas and colleagues at LUMS in Pakistan hope to address this shortfall by designing a low-cost sensor that can detect arsenic in drinking water. “We aim to develop a sensor that’s sensitive and selective, robust and reliable, affordable, portable and easy to use for local technicians,” he said.

The sensor will be based on gold nanoparticles (AuNPs), which are excellent candidates for sensing applications as they absorb in the visible spectrum and change colour according to their size, shape and surface chemistry. To create their sensor, Abbas and colleagues coated AuNPs with dihydrolipoic acid. This coating stabilizes the nanoparticles, which form in a dispersed state in water and are wine-red in colour. Adding an electrolyte such as salt does not affect the AuNPs, which remain dispersed and stay red.

If the water contains arsenic, however, the arsenic will bind to the dihydrolipoic acid, making it unavailable to protect the AuNPs surfaces. In this scenario, adding salt causes the AuNPs to aggregate and change colour. “This aggregation is directly proportional to the amount of arsenic present, which decides the strength in the colour change,” explained Abbas, now a PhD student at the University of Texas at Dallas.

Colour change
Gold nanoparticle solutions change colour when exposed to arsenic. (Courtesy: Muhammad Abbas)

To test this approach, the team performed UV-visible spectroscopy on AuNP solutions containing different concentrations of arsenic. “We could see a visual colour change with increased amounts of arsenic, with the nanoparticles changing from red towards blue,” said Abbas. Scanning electron microscopy images of the AuNPs before and after addition of arsenic confirmed the clumping mechanism that caused the colour change.

The sensor’s detection limit was 50 µg/l (50 parts per billion) of arsenic when viewed with the naked eye, or 3 µg/l using UV-visible spectroscopy. This sensitivity is lower than that offered by existing high-tech methods, such as atomic fluorescence spectroscopy, atomic absorption spectroscopy or mass spectrometry, which can detect up to parts per trillion of arsenic. But Abbas emphasizes that these systems are costly, not portable and need trained personnel to operate them.

“The colourimetric method is affordable and portable. The limit of detection is lower right now, but it can be improved,” he said.

The team also investigated potential interference from a range of other metal contaminants and found that, with the exception of mercury, none of the metals interfered strongly, and even mercury only impacted the absorption spectrum slightly.

“This suggests that the sensor would be selective and not disturbed by other elements present in the drinking water,” Abbas explained. “In future, this method may lead to the design of a microfluidic device for detection of arsenic.”

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