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Through turbulent skies: how fluid dynamics experts are uncovering the secrets of bird flight

For human-built aircraft, turbulence is an old and knotty problem. One of the first recorded human flight attempts, by an 11th-century monk called Eilmer, ended when his birdlike wood-and-leather wings couldn’t handle what the chronicler calls “the violence of the wind and the swirling of air”. A thousand years later, the same phenomenon continues to bedevil the aerospace industry, racking up costs in lost fuel, lost lunches, lost missions and even lost lives.

Curiously, though, the birds that inspired Eilmer seem to cope with turbulence just fine. Indeed, some birds actually exploit it, using the energy in unstable air currents to keep themselves aloft.

In a series of talks at last month’s annual meeting of the American Physical Society’s Division of Fluid Dynamics, an international lineup of speakers offered clues to how birds handle flying conditions that challenge modern aircraft – never mind intrepid medieval monks. Among the speakers was Cyprien de Sepibus, a PhD student at the EPFL in Switzerland who is studying pelican flight. Pelicans are often seen gliding just above the surface of water, and researchers have long assumed they must be taking advantage of a well-known phenomenon called ground effect to reduce the energy they need to stay aloft.

The problem with this assumption, de Sepibus explained, is that when pelicans approach the water, they turn their wingtips down (see photo above). This change forces the wing into a pronounced arch, leaving most of it too far away for ground effect to kick in. But if pelicans aren’t exploiting ground effect, why do they bother repositioning their wingtips? “It must be for a reason,” de Sepibus said.

To find out what that reason is, de Sepibus and colleagues turned to a tried-and-tested tool of fluid dynamics research: a wind tunnel. After testing several wing shapes in the tunnel, they found that a dipped (anhedral) shape provides the most lift when mounted on a ground-simulating fixed plate. This result is suggestive, de Sepibus said, but also limited because the set-up does not capture all the possible interactions between the wing and the water surface. He and his supervisor Flavio Noca are therefore performing follow-up experiments that involve towing model wings over the surface of a long, narrow tank of water. Their preliminary observations indicate that different wing types deform the water’s surface in different ways, suggesting that pelicans may be exploiting more complicated effects.

Red-tailed hawks handle turbulence with ease…

Photo of Petey, a red-tailed hawk, flying against a background of trees — Intelligent flyer: As a human-imprinted bird, Petey the red-tailed hawk cannot be released into the wild, so the Auburn University Raptor Center keeps him for educational purposes – and the occasional fluid dynamics experiment. (Courtesy: Auburn University Raptor Center)

de Sepibus’ towing tank was not the only inventive experimental technique on show in the session. To study how pigeons change the pitch of their tails when they land, Ariane Gayout and her colleagues at the University of Groningen, Netherlands, built a “biohybrid” tail out of real pigeon feathers and stuck it in a wind tunnel. To study how air flows around bat wings in flight, Chintan Panigrahi and colleagues at Johns Hopkins University, US, employed a similar technique with a real, dissected bat wing (from a bat that died of natural causes, he hastened to note).

The top prize for experimental realism, though, went to researchers who study raptors. Rather than focusing on model birds or pieces of real ones, Vrishank Raghav of Auburn University persuaded an actual red-tailed hawk called Petey to fly over a bank of upward-facing fans. This scenario is important because flapping-wing drones deal with this type of turbulence very badly; in his talk, Raghav showed a video of one crashing pathetically after just a few seconds. Petey, though, handled the sudden updraft with aplomb. “The bird flies through it like nothing happened,” Raghav explained.

Based on data from four high-speed cameras that tracked 10 points on Petey throughout each test flight, Raghav and colleagues think the bird’s primary way of mitigating gusts is wing pitch. However, their flight dynamics model still can’t predict Petey’s flight path at high “gust ratios” (that is, when the wind speed is much higher than the bird’s flying speed)

Working with a real live animal also brings challenges as well as advantages. “There’s a lot of entropy in these experiments,” Raghav told Physics World. Because Petey would only fly if offered food, the researchers could only do six test flights per day. On some days they would get everything set up and calibrated only for Petey to decide he wasn’t interested. Worse, Petey developed a disconcerting ability to predict when he was about to face a high gust ratio, despite the team’s best efforts at randomizing the fan speeds. “We believe the bird has learned,” Raghav said ruefully.

…and golden eagles exploit it

Photo of a golden eagle in flight against a blurry backdrop of mountains — Where eagles soar: Golden eagles exploit the energy in air turbulence to help them stay aloft. (Courtesy: iStock/Daniel Jara)

A final talk in the series ventured still further into real-world bird flight. To understand how birds handle turbulence in the wild, Greg Bewley and colleagues at Cornell University, US attached GPS-enabled accelerometers to the backs of six golden eagles and collected data on their natural flight.

Based on the transmitted accelerometer data, Bewley and his team created a probability distribution of the differences in the eagles’ vertical accelerations. When they matched this data with the birds’ GPS-determined locations and weather records, they found long “tails” in the probability distribution consistent with the eagles amplifying, rather than suppressing, strong intermittent upward gusts. Though Bewley claimed that theirs is the first evidence of birds taking advantage of turbulence, he suggested it wasn’t entirely a surprise. “This [turbulence] is something these animals have evolved to move in,” he told the audience.

Why peregrine falcons wear eyeliner, golden eagles could accelerate using turbulence

Unfortunately, the nature of the study didn’t allow Bewley and colleagues to explore how the eagles are doing this. (“We have no way of discriminating between different kinds of behaviour the bird is exhibiting,” he noted.) That said, they think the eagles might be pushing down on updrafts and venting the downdrafts through their feathers – a dynamic and asymmetric response that human-built aircraft cannot yet mimic. Maybe Eilmer the monk didn’t do so badly after all.

How networking can bolster diversity in physics

Whether it’s providing clean water around the world or designing space craft to monitor the impact of climate change, today’s young people are keen to find solutions to the many challenges society is facing. That effort needs many different approaches, but studying physics undoubtedly increases the arsenal of tools a young person can use towards these aims.

However, what is often not taught in the physics classroom is that soft skills – such as networking and communicating your work – can be just as important for your career as getting your head around nuclear fusion or quantum mechanics. Not only that, but practising these skills is helpful for giving young people confidence in all areas of life – and in turn, promotes diversity in physics.

Battling biases

Unfortunately some people’s confidence in their scientific ability is diminished by the conscious and unconscious biases they constantly have to negotiate. Some are put off by misconceived ideas they are told about physics – such as it being a solitary field for anti-social “nerds”. Others are denied the opportunity to study physics due to the prejudice and stereotypes that they experience because of who they are. Girls, for example, are often presented with the myth that physics is more suited to boys, while many young people are told that physics is not for the likes of them based on their ethnicity, sexual orientation, disability or social background.

The harmful and upsetting message that physics is not for women was reinforced very publicly in 2019 in a talk by Alessandro Strumia at CERN’s first workshop on High Energy and Gender. He wrongfully argued that women are inherently less capable of physics research than men and that this supposed discrepancy is the main reason for the disparity between the genders in theoretical physics. If that wasn’t enough, Strumia also claimed that the biases women face in physics actually work in their favour.

In reality, there is plenty of evidence to the contrary (PNAS 109 16474; Nature Chem. 14 1203; PNAS 111 4403). For example, women in science, technology, engineering and mathematics (STEM) subjects are more likely to have their e-mails ignored when enquiring about potential PhD positions; are less likely to be awarded funding and grants; and need to have, on average, published three times more papers in top-tier journals than their male colleagues to secure the same job in academia. In addition, there is frequent harassment and bullying that forces some to leave science altogether.

The end result is that too many young people, especially young women, are made to feel that they can’t do physics or that they don’t fit in, and so they don’t pursue their physics education.

It’s a problem exacerbated by the lack of visible role models in physics that under-represented groups can identify with. As a report jointly published by the Institute of Physics (IOP), the Royal Astronomical Society and the Royal Society of Chemistry showed, young people are much more likely to study a STEM subject or pursue a STEM career if they can see someone they identify with, who has gone there first and who inspires them. However, finding such role models is often hard unless you are pointed in the right direction.

Networking for change

Among those trying to address the root causes of gender bias that permeate much of physics is the IOP, which realizes that a key strategy to remedy this bias is to promote a diverse range of role models to inspire school students. In fact, this was the motivation behind the event Networking with Leading Influencers in the Physics Community, held at Royal Holloway University of London, UK, in May 2023. It brought together school students, undergraduates and postgraduates with an all-women panel of physicists at different points in their careers and in different industries. I took part in this panel, in which we demonstrated that an interest in physical sciences opens doors to a career not only in academia but also a huge variety of other options. Journalism, patent law and mechanical engineering were represented on the panel too.

Events such as this don’t just show the wide variety of career pathways you can go into with a physics degree. They also give students, in a supportive and informal setting, the chance to develop their networking skills, which are extremely useful but can only be learned by experience and yet are often overlooked during the early stages of higher education. Networking helps promote collaborations, build confidence in talking about your work, and exposes you to what else is happening in the field.

In addition, networking events like the one in May are invaluable for improving diversity in STEM. They give young people the chance to find role models who could have a positive influence on their entire careers. And by letting students see people with whom they identify working as successful physicists, such events combat stereotypes and show that people from a wide range of backgrounds can be scientists.

By listening to the career stories of physicists at these events, students also can see that science is not the solitary activity it’s often portrayed as being. As the speakers made clear, pursuing a scientific career does not imply that you will focus solely on your chosen area of expertise to the exclusion of other disciplines. For example, experiments in my own field of particle physics involve many thousands of scientists and engineers from different disciplines working together on a daily basis. These lessons are often missed from the pages of physics textbooks.

Despite the obvious advantages of networking, it can feel scary or even in some way devious – almost a dark art

Despite the obvious advantages of networking, it can feel scary or even in some way devious – almost a dark art. This an unhelpful and incorrect misconception that could hold some young people back in their careers. Sure, networking requires a certain level of confidence and practice, as with any skill. But by introducing students to networking situations early in their careers, we can show that it is just another skill that you can get good at if you practise hard enough.

The lesson that your career can helped by chance conversations at conferences is much easier to impart through real-life stories than through, say, pamphlets from the careers office. We need to teach future physicists that if you want to solve humanity’s greatest problems, then teamwork and reaching out to people from different backgrounds are as important as being able to model water supplies, launch rockets and do the all the technical stuff we traditionally think physics is all about.

Five top tips for networking

Networking is often perceived as a scary dark art that only the most confident people can excel at. This is not true – it’s just a matter of practice. Here are five tips to help you get the most out of networking.

1 You can’t network if you’re not there

It sounds simple, but the first thing is to show up. Departments, universities and organizations such as the Institute of Physics (IOP) put on many events where the opportunity to network arises. These can be department lectures, lunchtime talks, day conferences, careers events and more. Try to take up as many opportunities as possible to talk to people. Even if the occasion is not relevant to your interests, it can be good practice in networking. It’s important to have the confidence that people will want to talk to you. Everyone there has the same goal of meeting new people. Be one of those people they meet.

2 “Who are you?” and “what do you do?”

An easy thing to practise before any networking opportunity is how you would describe yourself and your interests. Often the first questions people will ask are “who are you?” and “what do you do?”, and answers to these can be easily prepared in advance. It’s a good idea to have a roughly 30-second “pitch” describing yourself and your research and/or career interests. However, be aware that the people you speak to will have different backgrounds and you may need to tailor your pitch. For example, when I talk to particle physicists, I describe my PhD research in terms of quarks and supersymmetry, whereas when I am talking to scientists in other fields, I describe my research in terms of the question of the missing matter of the universe.

3 The give and take of a conversation

Remember that a conversation is a two-way process and take an active role in steering its flow so that it doesn’t focus only on one person. Showing an interest in the people you are talking to and responding positively to them will help make a good impression and a connection.

4 Stay connected

To make sure your hard work doesn’t go to waste, you will need a way to stay in touch with the people you meet. This can be on LinkedIn, via e-mail or through a professional social media account. You may also need a way to note down contact details as well as give your own – business cards can be very useful for this. Afterwards, make contact soon after the event to maintain that connection you have created. This doesn’t have to be prolonged – it can just be saying how nice it was to meet somebody at the event and that you hope to talk again sometime soon.

5 Be aware of your online presence

Last, with the predominance of social media, it’s important to be aware of your online footprint. Social media is a wonderful way to stay connected, but it also serves as a record attached to your name. Permanently removing information can be difficult so it’s worth knowing what is publicly accessible and how easy it is for people to find when they look you up.

Bacteria-resistant alloy improves infection control in implant surgeries

Orthopaedic implant surgeries, such as hip and knee replacements, are common procedures performed daily around the world. Bacterial colonization of the implants, however, can lead to complications, implant failure and, in about 7% of cases, necessitate revision surgery. Current infection control methods rely on antibiotics, but are far from optimal. So a team at Washington State University has developed a novel titanium (Ti) alloy to create load-bearing implants with an inherent antibacterial response.

“Infection is a problem for which we do not have a solution,” explains corresponding author Amit Bandyopadhyay in a press statement. “In most cases, the implant has no defensive power from the infection. We need to find something where the device material itself offers some inherent resistance – more than just providing drug-based infection control.”

Orthopaedic implants are typically made from the Ti alloy Ti6Al4V (containing 6% aluminium and 4% vanadium), which offers excellent mechanical performance and corrosion resistance, but is less biocompatible than commercially pure Ti (CpTi). In this latest work, Bandyopadhyay and colleagues aimed to design an alloy that combines the biocompatibility of CpTi with the mechanical strength of Ti6Al4V.

The researchers used 3D printing techniques to create Ti3Al2V, an alloy with 3% Al and 2% V. They found that minimizing the Al and V components did not compromise the material’s mechanical properties. In terms of strength and modulus of elasticity, Ti3Al2V performed significantly better than CpTi, without considerable degradation in strength from that of Ti6Al4V.

The team notes that the modulus of elasticity observed for porous Ti3Al2V was closer to that of natural bone than commercially used alloys. This is important as this is the strongest determining factor for long-term fixation and healing of a surgical implant. Both Ti6Al4V and Ti3Al2V samples exhibited high fatigue resistance, surviving 10 million cycles at 21% of their respective compressive yield strength without failure.

Antibacterial action

For fast healing and successful long-term integration of a metallic implant, it’s vital that bone tissue covers its surface faster than any contaminating bacteria. To protect the implant against bacterial infection, the researchers added 3 wt.% copper (Cu) to the new alloy. Copper is known to exhibit antibacterial activity, likely due to contact killing, in which bacteria coming into close contact with Cu surfaces are rapidly eliminated via cell wall rupture and disruption of the cell membrane.

To assess the bacterial inhibition afforded by adding Cu, the researchers tested the various materials against two bacteria that commonly infect implants: S. aureus and P. aeruginosa. The Ti3Al2V–3Cu alloy exhibited roughly 80% higher antibacterial efficacy than CpTi and Ti6Al4V against these two high-risk bacterial strains. For S. aureus, which is responsible for around two-thirds of implant infections, Ti3Al2V–3Cu killed 87% of the bacteria after 24 hr.

While Cu imparts microbial resistance to Ti3Al2V alloys, it could also alter bone response when implanted in vivo. To compensate for any potentially compromised biocompatibility and enhance healthy growth of surrounding bone tissue into the implant, the team added 10 wt.% tantalum (Ta) to create the alloy Ti3Al2V–10Ta–3Cu.

“A multifunctional device providing both infection control and good bone tissue integration can provide a paradigm-shifting tool to orthopaedic and dental clinicians,” co-author Susmita Bose tells Physics World. “Because infection is such a big issue in today’s surgical world, if any implant enhances biocompatibility with good bone quality and does infection control, there’s nothing like it.”

In vivo implants

Next, the researchers assessed the in vivo performance of the various Ti-based materials, implanting samples of six different materials (CpTi, Ti6Al4V, Ti3Al2V, Ti3Al2V–3Cu, Ti3Al2V–10Ta and Ti3Al2V–10Ta–3Cu) in the leg bones of rats. After six weeks, they euthanized the rats and examined the implant–bone sections. Histological analysis revealed no sign of inflammatory response or infection for any of the implant materials, suggesting non-toxicity. The team also saw evidence of tissue ingrowth into the implant and new bone formation for all compositions except Ti6Al4V.

Examining the host tissue response to the alloys revealed that adding Cu to Ti3Al2V delayed the onset of osseointegration compared with Ti3Al2V alone. However, the researchers note that adding Ta to Ti3Al2V–3Cu “reverses the delayed onset of osseointegration and shows the overall best performance among all six compositions”.

“Our best-performing Ti3Al2V–10Ta–3Cu alloys offer microbial resistance, enhanced biomechanical performance and enhanced biocompatibility compared to CpTi, Ti6Al4V, Ti3Al2V–3Cu alloys alone,” the team concludes. “Thousands of patients have reported implant failures due to external causes such as microbial infection, which a Ti6Al4V implant is not tailored to overcome. We feel a material like Ti3Al2V–10Ta–3Cu could only improve patients’ postoperative quality of life and reduce revisional surgeries that arise from multiple scenarios, including bacterial infection.”

The study is reported in the International Journal of Extreme Manufacturing.

Get offline and meet in person to make breakthroughs, claims study

The online world makes it easier for researchers to collaborate – but does not result in more groundbreaking work. That is according to a new study, which finds that teams of scientists working remotely are less likely to make big research breakthroughs. The discovery could help to explain a recently observed slowdown in the rate of innovation in science and technology (Nature 623 987).

Carried out by a team led by Carl Frey, an economist at the University of Oxford in the UK, the study looked at over 20 million papers published between 1960 and 2020 across the sciences, arts and humanities. The team also analysed four million patent applications filed between 1976 and 2020.

Using information on researchers’ affiliations, the authors first worked out how far apart collaborators are, finding a steep rise in all fields. For science and engineering, the average distance between workers increased from around 110 km to 920 km during the period studied. For physics patents, the collaboration distance grew from 280 km to 840 km.

The authors then assigned papers and patents a “disruptiveness” score by looking at citation records. If a paper is deemed highly disruptive, then subsequent articles that cite it will be less likely to also cite earlier work on the topic. This is because the paper has broken with previous ideas and established a new paradigm.

When the researchers plotted the average disruptiveness of papers against collaboration distance, they found the disruptiveness falls with increasing distance. This effect was seen across all fields and for both papers and patents. For a distance of 600 km or more, physics papers were about 37% less likely to be disruptive than papers whose authors were all in the same city. The drop was about 13% for physics patents.

To explain their findings, the authors distinguish between two types of task: conceptual work that involves developing new ideas and theories, and practical tasks like experimentation and data analysis. They speculate that the former type of work may be more likely to produce breakthroughs, but also requires intensive communication and opportunities for informal conversations.

To test this hypothesis, the authors analysed data on over 89,000 researchers’ roles in papers. They found that the same individuals were more likely to be involved in conceptual work when collaborating on-site, and more often conducted practical tasks remotely.

The next generation

While the study could have different implications for theoretical and experimental work, the authors caution that a lot of research involves both. “Even in projects with a strong experimental focus, the early stages – centred around theoretical work like designing the experiments – are still critical,” co-author Yiling Lin from the University of Pittsburgh told Physics World. “This underscores the need for supporting projects with appropriate funding for frequent in-person meetings.”

As well as encouraging policymakers to invest in physical infrastructure, the authors recommend that principal investigators engage junior colleagues in conceptual tasks, rather than just assigning them technical work. “This approach brings the team a wealth of cognitive power and helps train the next generation of scientists,” adds Lin.

The authors now plan to delve further into the mechanisms behind the creative fusion of different ideas. “Merely assembling experts from varied fields does not automatically lead to successful knowledge integration,” explains Lin. “We want to understand the nature of knowledge integration – whether having more knowledge available makes it easier or harder to integrate this knowledge for innovation.”

Simultaneous production of a top quark and a photon observed for the first time

For the first time, particle physicists have observed the simultaneous production of a photon and a top quark. The milestone was achieved by the ATLAS collaboration, which operates a giant detector at CERN’s Large Hadron Collider (LHC). The discovery could lead to a deeper understanding of the electroweak interaction, and its enigmatic relationship with the Higgs field.

According to the Standard Model of particle physics, the Higgs field provides mass to some fundamental particles via electroweak symmetry breaking (a process called the Higgs mechanism). This idea was first proposed in 1964 and confirmed in 2012, when physicists working on ATLAS and CMS (also at the LHC) made the first observation of the Higgs boson – which is the particle manifestation of the Higgs field.

However, more than decade after that famous discovery, the inner workings of this symmetry-breaking mechanism have remained a stubborn mystery. And much effort is being made at the LHC to solve this mystery.

In this latest study, ATLAS researchers delved deeper into electroweak symmetry-breaking by examining detections of the top quark in data gathered by the experiment during the collisions of high-energy protons. The top quark is especially well-suited to the task as it interacts with the Higgs field more strongly than any other fundamental particle, making it the heaviest particle in the Standard Model.

Easier said than done

Ideally, this study would involve studying the decay products of individual top quarks – looking for deviations from predictions of the Standard Model that could shed light on electroweak symmetry-breaking. But this is easier said than done, according to John Alison at Carnegie Mellon University in the US – who belongs to the CMS collaboration and is a former member of ATLAS.

“Single top quark production is hard to see, as it is produced by the weak interaction. This makes it far smaller than top-quark pair production, which is controlled by the strong interaction.”

However, these quark–antiquark pairs are far less sensitive to the electroweak interaction and do not tell us about origins of symmetry breaking nearly as effectively as single top quarks.

To work around this issue, the team searched for evidence of an alternative pair of particles in ATLAS’ data. “This analysis takes single quark observations one step further,” Alison explains. “The ATLAS team tried to observe a single-top with an extra photon interacting with the top quark, whose charge is directly related to the size of the signal.”

Plethora of pairs

These single top quarks exist within a plethora of quark–antiquark pairs, and to find them the researchers looked for simultaneous detections of the top quark’s specific set of decay products.

Following its production, a top quark quickly decays into a bottom quark and a W boson, which itself decays either into either an electron or muon, and a neutrino. Simultaneously, the bottom quark combines with other quarks to form new hadrons. These particles then decay into a collimated spray of particles called a “b jet”.

Detecting these specific products presented a further challenge. Looking for a top quark–photon pair is hard enough, but the ATLAS team went beyond, using machine-learning techniques to directly probe the top–photon coupling,” Alison explains.

Trained using simulations of top quark–photon events, the team’s machine-learning algorithm could specifically pick out simultaneous detections of the gamma-ray photon, b jet, electron or muon, and some missing energy associated with the neutrino – which passes invisibly through ATLAS’ detectors.

High degree of confidence

Their results were incredibly promising. “The process was observed with a high degree of confidence, far beyond the 5σ confidence level that is the benchmark in the field,” Alison says. Altogether, the top quark–photon observations identified by the algorithm had a statistical significance of 9.8σ. This means it is extremely improbable that the events could have emerged randomly.

What’s more, “The number of signal events observed roughly agrees with that predicted by our theory,” Alison continues. This detection rate was some 30–40% higher than that predicted by the Standard Model.

The ATLAS team now hopes to probe the properties of top quark–photon events in more detail in future studies – with the aim of uncovering new clues about the inner workings of electroweak symmetry breaking. If achieved, this could be a key step towards understanding the mass-giving nature of the Higgs boson.

“The result could be used to constrain hypothetical theories that are deeper than the Standard Model,” Alison adds. “Observing this process also offers a new way to test the predictions of the Standard Model, and demonstrates how we can tease out a small, complex signal from much larger backgrounds.”

The research is described in Physical Review Letters.

Charge qubits get a thousand-fold boost

Researchers in the US have improved the coherence time of charge quantum bits (qubits) by a factor of 1000 thanks to advances in the materials used to construct them. Led by Dafei Jin of the Argonne Center for Nanoscale Materials and David Schuster of Stanford University and the University of Chicago, the multi-institutional team also showed it was possible to read out the state of these qubits with a fidelity of 98.1% – a value Jin says will increase further with the aid of more sophisticated readout technologies.

Coherence time is vitally important within quantum computing, as it denotes how long a qubit can remain in a superposition of multiple states before environmental noise causes it to decohere, or lose its quantum nature. During this period, a quantum computer can perform complex computations that classical computers cannot.

Many quantum systems can act as qubits. Spin qubits, for example, encode quantum information in the spin of an electron or nucleus, which can be up, down or a superposition of the two. Charge qubits, for their part, represent quantum information through the presence or absence of excess charge on an electron contained within the qubit system. They are relatively new – members of the team created the first in 2022 – and Jin says they have several advantages over spin qubits.

“Charge qubits typically permit much faster operation speed because charges couple strongly with electric fields,” he explains. “This is advantageous over spin qubits because spins couple weakly with magnetic fields. Charge qubit devices are generally much easier to fabricate and operate, because most existing fabrication and operation infrastructures are based on charges and electric fields, rather than spins and magnetic fields. They can often be made more compact.”

Ultraclean is ultraquiet

Jin explains that the researchers created their charge qubits by trapping an electron within a quantum dot, which is a nanoscale collection of atoms that behaves like a single quantum particle. The quantum dot rests on a surface made from solid neon and is placed in a vacuum.

According to Jin, this ultraclean environment is key to the experiment’s success. Neon, as a noble gas, will not form chemical bonds with other elements. In fact, as the team point out in a Nature Physics paper on the research, neon in a low-temperature and near-vacuum environment will condense into an ultrapure semi-quantum solid devoid of anything that could introduce noise into the qubit. This lack of noise enabled the team to boost the coherence time of the charge qubit from the 100 nanoseconds typical of previous efforts to 100 microseconds.

What is more, the researchers read out the state of these qubits with 98.1% fidelity without using a quantum-limited amplifier, which Jin describes as “a special device placed at very low temperature (in our case 10 millikelvin) that can amplify weak electromagnetic signals but bring in nearly zero thermal noise”. Because such devices enhance readout ability, obtaining 98.1% fidelity without them is, Jin says, especially impressive. “In our future experiments, once we use them, our readout fidelity can only go much higher,” he adds.

The next milestone

While a thousand-fold increase in coherence time is already a major improvement over previous charge qubit systems, the researchers expect even more in the future. According to Jin, the team’s theoretical calculations suggests that the charge qubit system could reach a coherence time of 1–10 milliseconds, representing another factor of 10–100 improvement over current values. To realize this, though, scientists will need to gain better control over every aspect of the experiment, from device design and fabrication to qubit control.

Beyond that, Jin and colleagues continue to look for ways to improve the system even further.

“The biggest milestone next is to show two charge qubits can be entangled together,” Jin says. “We have been working on that and have had a lot of progress. Once we accomplish that, our qubit platform is then ready for universal quantum computing, even though some detailed performance can keep being improved.”

Sustainable success demands joined-up thinking

The ongoing drive towards more sustainable development, defined by the United Nations as meeting “the needs of the present without compromising the ability of the future to meet its needs”, manifests itself in many different ways. For scientists and engineers, it is most commonly translated into the pursuit of innovative technologies that aim to safeguard the future of our planet, such as cleaner sources of energy, manufacturing processes that minimize the use of toxic substances, or recycling and recovery schemes that make more efficient use of limited natural resources.

However, such a tight focus on the technology can ignore other factors that determine whether a novel solution is sustainable, which might include the cost of production and operation, the long-term availability of materials, and the social impact of introducing a new product or process. “Green technologies that are designed primarily to protect the environment are not always sustainable,” says Jonas Baltrusaitis, associate professor of chemical engineering at Lehigh University in Bethlehem, US, and the editor-in-chief of a new open-access journal, Sustainability Science and Technology, that has just been launched by IOP Publishing. “Sustainability demands a more comprehensive perspective that balances environmental, social and economic considerations, with the aim of creating enduring systems and practices that benefit both current and future generations.”

By way of example, Baltrusaitis explains how the distinction applies to building design. “A green building might incorporate energy-saving technologies, use recycled materials, and implement efficient water management systems,” he says. “Such measures are undoubtedly positive steps toward environmental conservation, but they might not be sustainable if they do not consider the long-term social and economic impacts of the building’s construction and operation.”

Baltrusaitis argues that most scientific discourse, as represented in the growing number of journals within the field of sustainability, tends to overlook the complex factors that determine whether a novel technology will deliver an effective and workable solution that will have a positive impact both now and in the future. “Existing journals focus all their attention on the technology, since pretty much any scientific or engineering discipline can demonstrate some level of progress towards sustainability,” he says. “With this new journal we want to consider the development of innovative technologies within a broader social and economic context, rather than just glorifying the technology itself.”

Indeed, various scientific approaches have been developed to determine whether or not a new product, process or technology can drive sustainable change. Perhaps best known is life-cycle assessment, which evaluates the environmental impacts of a product or process throughout its lifetime, from the initial extraction of raw materials through to routine operation and its eventual disposal. Other methodologies have been developed to provide quantifiable measures of a technology’s ecological footprint, socio-economic impact, and use of energy and resources, while decision-making analysis offers a way to combine multiple criteria for an objective comparison of alternative solutions.

Jonas Baltrusaitis, the editor-in-chief of *Sustainable Science and Technology*, hopes that the journal can inspire and inform readers about effective strategies for driving sustainable change in a rapidly changing world. (Courtesy: J Baltrusaitis)

“We want to encourage submissions that might, for example, analyse the long-term value of the products, technologies or processes being created, or assess their benefit or detriment to people and local communities,” says Baltrusaitis. “Our aim for the journal is to offer equitable publishing that represents all three pillars of sustainability – social, environmental and economic – as they relate to the development of novel technologies and processes.”

Taking such a holistic approach to the intricate and interconnected challenges of sustainability will require engagement between different disciplines and stakeholder communities. “We want to provide a platform for scholars, researchers, and experts from diverse fields to collaborate and share their findings,” continues Baltrusaitis. “The development of sustainable solutions across various areas of science and technology offers a rich opportunity for interdisciplinary learning, allowing different communities to benefit from innovative approaches and methodologies developed in other fields.”

As an example, says Baltrusaitis, sustainable energy solutions developed in the engineering sector can inspire new ideas in agriculture or urban planning. “This exchange of knowledge helps to avoid redundant efforts and accelerate progress toward a more sustainable future,” he says. “Bringing together diverse ideas can also spark creativity, leading to the development of cross-disciplinary solutions that address complex sustainability challenges.”

Such collaborative efforts will need to combine the scientific expertise of the research community with the real-world experience offered by policymakers, industry leaders and local organizations. That interplay between sustainable technology development and public policy can clearly be seen, for instance, in the adoption rates of electric vehicles around the world. While technology improvements have helped to expand the global fleet of electric vehicles to 14% of all new cars sold in 2022, concerted government action in Norway – which includes financial incentives for motorists, co-ordinated investment in charging infrastructure, and a long-standing commitment to ban sales of new fossil-fuel cars by 2025 – has boosted that figure to almost 80%.

“Collaborations between the scientific community and other key stakeholders are pivotal in driving sustainable change,” says Baltrusaitis. “Partnering with policymakers can help scientists to understand real-world pressures that can guide research toward practical solutions, while innovative collaborations between scientists and business can facilitate the development of sustainable technologies and practices. We want the journal to showcase successful partnerships, share best practice, and inspire and inform readers about effective development strategies.”

Establishing this type of cross-disciplinary forum will require an innovative publishing approach. While the journal will be centred around traditional scientific articles that present significant technical advances, the aim is to offer different publishing options that reflect the wider ethos of sustainability, such as proof-of-concept demonstrations, life-cycle assessments, and roadmaps that assess economic and social factors alongside the development of novel technologies. “As the journal evolves we will find better ways to include these important contributions,” comments Baltrusaitis.

One common aspect across all the studies published in the journal will be a strong connection to one or more of the UN’s 17 sustainable development goals (SDGs). These interlinked objectives are designed to provide a “shared blueprint for peace and prosperity for people and the planet, now and into the future”, and many have a clear technological component – such as clean water and sanitation, climate action, affordable and clean energy, and responsible consumption and production. Reflecting the broad themes of the SDGs, the subject scope for the journal spans everything from carbon capture and storage through to sustainable chemistry, waste reduction and recycling, and water management.

Within these wide-ranging areas it will be particularly important for the journal to reflect global sustainability initiatives, since the priorities for research and action are likely to depend on regional needs and concerns. Indeed, a UN-supported study published in 2022 showed that some 64% of research publications from low-income countries are aligned with the SDGs, compared to just 34% in high-income nations that are likely to have the largest budgets for academic research. “We want to represent all geographic locations and all disciplines through the editorial board and through the work that we showcase in the journal,” says Baltrusaitis. “Collaborative efforts within the global scientific community will be essential to identify and prioritize initiatives that will have the most positive impact on the future of the planet.”

Sustainability Science and Technology is a new open-access journal from IOP Publishing, which also publishes Physics World. The journal opens for submissions in January 2024, with all publication charges waived until the end of 2026.

Slippery surface could improve your toilet experience, why ice can be sticky or slippery

Going into a public toilet is sometimes not for the faint hearted. Not only could there be visible evidence of previous use, but also the unseeable germs that may lurk on surfaces.

Now researchers in Germany and Turkey have come up with a new transparent coating that makes porcelain more water-repellent and toilets cleaner. They used an oil containing the silicone polymer polydimethylsiloxane, or PDMS, and milled the solution for an hour with small tungsten carbide balls. This process breaks apart some of the polymer’s chemical bonds so it forms a durable, oily layer.

After applying the milled oil to one side of a sterilized toilet bowl, with the other half left untreated, they then poured human urine combined with E.coli and Staphylococcus aureus into the toilet. When swabbing what was left behind on both halves of the bowl, they found that the PDMS-treated area stopped 99.99% of the bacterial growth that was seen in the other half. The work could finally put an end to making a visit to the toilet such a shock to the cistern.

The research is described in ACS Applied Material Interfaces.

Sticky ice

While slippery toilet bowls seem like a great idea, slippery ice can be a bad thing – unless you like ice skating or operate a ship in the Arctic. Like many properties of water, exactly why some ice is more slippery that others is a bit of a mystery. Now, researchers at the University of Illinois Chicago have studied the stickiness of ice that contains common substances including salt, soap and alcohol.

“Be it dirty sidewalks or the hull of Arctic-going ships, there’s always impurities [in ice],” explains team leader Sushant Anand. “So, the natural question that comes to mind is: What is the influence of these compounds on how strongly ice sticks to surfaces?”

The experiments revealed that pure ice is much stickier than ice containing impurities, under certain circumstances. The stickiness, or slipperiness, of ice depends on a quasi-liquid layer that occurs on the surface of the solid material – and this layer is notoriously difficult to study. The team did molecular dynamics simulations that suggest that when water freezes, impurities are pushed towards the surface, where they enhance the quasi-liquid layer.

Arctic mystery

However, this discovery led to a another question – if a small amount of salt makes ice less sticky, then why does frozen seawater stick to the hulls of ships? The answer, according to the team, is that ice freezes on hulls slowly. This affects how impurities are distributed within the ice, reducing the concentration on the surface – making the ice more sticky.

“Our study represents just the tip of the iceberg, opening new lines of investigation of how impure ice adheres with widespread implications across multiple disciplines,” Anand says.

The team reports its results in Materials Horizons.

Six planet system is perfectly tuned

A rare system of six exoplanets, all smaller than Neptune but larger than Earth, has been found with orbits that are all resonant with each other. The system was discovered by astronomers led by Rafael Luque of the University of Chicago, who suggest that the planets have remained undisturbed in this configuration since their formation a billion years ago.

The planetary treasure trove also provides one of the best opportunities for characterizing “mini-Neptunes”, which are a mysterious class of planet that are absent from the Solar System.

The planets orbit an orange star called HD 110067, which lies about 100 light–years away. The innermost two planets, dubbed b and c, were discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission. Luque and colleagues then noticed that the orbits of planets b and c were in resonance. This is because their orbital periods of 9.114 days and 13.673 days have a ratio of 2:3. There was also something else in the data – rogue transits that could not be attributed to planet b or c.

Given the resonant orbits of b and c, it stood to reason that if there were other transiting planets in the HD 110067 system, then they might share orbital resonances. Using the rogue transit events as starting points, and guessing that any third planet called d might also have a 2:3 orbital ratio with planet c, allowed the team to predict when planet d might transit next. They followed this up with the European Space Agency’s CHEOPS telescope and discovered the planet as predicted.

From the orbital period of planet d, which is 20.519 days, Luque’s team were then able to predict a fourth planet called e, with a 30.793-day orbit that is in 2:3 resonance with planet d, and which matched one of the unassigned transits seen by TESS.

Laplace angles

There were still several unexplained transits in the TESS data. To figure out what planets these transits belonged to, Luque’s team took advantage of the complex rules of resonant orbits as laid down by the eighteenth century mathematician Pierre-Simon Laplace, who studied the resonant orbits of some of Jupiter’s moons.

Like Jupiter’s moons, HD 110067’s planets “always have to be within certain angles of each other in order that any perturbations they exert on each other can’t grow,” says team member Andrew Collier Cameron of the University of St Andrews, who focused on measuring the masses of the planets with the radial-velocity technique.

The angles that Cameron alludes to are referred to as Laplace angles, and they provide stable configurations of orbits. Any deviations from them would result in the gravitational perturbations growing over time. The result would be the planets being thrown out of resonance and quite possibly sent into orbits that cross each other, where they might collide.

By estimating what the Laplace angles should be, Luque’s team were able to predict that planets f and g would have orbital periods of 41.0575 and 54.7433 days respectively. These matched the two remaining unexplained transits in the Kepler data. The pairs of planets e and f, and f and g, each have a 3:4 orbital resonance.

There is the possibility that there are even more planets orbiting HD 110067 on wider orbits within the star’s habitable zone. However, if there are more planets, neither TESS nor CHEOPS has recorded a transit. This means that an attempt to find a seventh or eighth planet would be a “blind search”, says Luque. “But if we did get lucky and found an extra planet, then certainly it would be very interesting due to its potential prospects for habitability.”

However, there is no prospect of searching for more planets any time soon. If there was a planet on a 75-day orbit, for example, CHEOPS would have to observe HD 110067 for at least that time to observe one transit. However, observing time is very precious, as Luque explains; “We prefer to invest observing resources in refining the parameters of the known planets in the system”.

Characterizing the planets

Further work on the system will instead involve refining the parameters of the known planets – which is dependent upon measuring their masses. The radius of each planet is determined from how much starlight they block when they transit in front of the star – they range in size from 1.9 to 2.85 Earth radii. Masses are determined by radial velocity measurements, which look at how the planets cause the star to wobble. Once both their radius and mass are known, the densities of the planets can be calculated. Whether the planets have thick atmospheres could be determined by the James Webb Space Telescope.

So far, masses have only been obtained for three of the planets, specifically planets b (5.69 Earth masses), d (8.52 Earth masses) and f (5.04 Earth masses). This was done using the HARPS-North instrument on the Galileo National Telescope in the Canary Islands and the CARMENES spectrograph on the 3.5-metre Calar Alto Observatory in Spain.

“The remaining three planets are still flying slightly under our detection capabilities,” says Cameron. In particular, stellar activity can mask the radial velocity signals of the planets. “So the next thing to do is to push deeper with the radial velocities so that we can determine the masses of the planets.”

Transit-timing measurements provide another way of measuring the planetary masses. As the planets orbit their star, their gravity can pull each other back, or speed each other up, resulting in slight discrepancies in when the planets are seen to transit. The size of the discrepancy is determined by the gravitational pull, and hence their mass.

Regardless of what these planets are like, their existence in resonant orbits alone is notable. Theory suggests that the planets formed in these resonances. Ordinarily these resonances are then destroyed by gravitational perturbations from passing stars or marauding giant planets, but around HD 110067 this doesn’t seem to have happened.

“Given a dynamically stable environment this idealistic kind of planetary system could form and even more remarkably it can actually survive for a very long time,” says Cameron.

As such, HD 110067 may provide a window through time, retaining the configuration that the planets had immediately after their formation.

The findings are described in Nature.

Why Alice & Bob are making cat qubits, IOP calls for action on net-zero target

This episode of the Physics World Weekly podcast looks at two very different and very difficult challenges — how to build a quantum computer that can overcome the debilitating noise that plagues current processors; and how to ensure that the UK meets its target for net-zero greenhouse gas emissions by 2050.

Our first guest is the nuclear physicist and sustainable energy expert, Martin Freer, who coordinated the writing of a report from the Institute of Physics (IOP) called Physics Powering the Green Economy. Freer, who is at the University of Birmingham, explains why more investment and support will be needed to ensure that the UK meets its target to achieve net-zero greenhouse gas emission by 2050.

Meanwhile in Paris, the quantum-computer maker Alice & Bob is developing “cat qubits” that promise to reduce the amount of hardware required to do quantum error correction. The company’s co-founder and CEO Théau Peronnin explains how the technology works and how it could be used to build quantum computers that could solve practical problems. He also explains why the company chose its quirky name.

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