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Closing the skills gap

There are several big challenges in physics where we are constantly told to “mind the gap”. There’s the gender pay and promotions gap. There’s the student attainment gap. And then there’s the graduate skills gap, which refers to the difference between the skills commonly exhibited by physics graduates and the skills employers commonly report as being required. All three gaps can be confusing and frustrating for students, academics, industry and government, but progress in the skills gap is fortunately being achieved.

In 2019 we, the South-East Physics Network (SEPnet), were challenged by a group of university leaders to characterize this physics skills gap: what skills were missing, why and which actions were proving effective in addressing it. We took initial lessons from the Higher Education Academy, UK Physical Sciences Centre’s extensive 2010 study Skills Required by New Physics Graduates and their Development in Degree Programmes by Steve Hanson and Tina Overton. We also considered many industry, university and political voices that have shaped the issue subsequently, not least the 2016 Wakeham Review of STEM Degree Provision and Graduate Employability.

A joint problem

Crucially, we acquired insights from hundreds of physics students and employers who have taken part in the SEPnet Employer Engagement programme. Consistently, one activity stood out as particularly beneficial: short, structured, paid summer work placements. Moreover, such placements can benefit employers in all regions of the country – not just in the capital – as well as small and medium-sized enterprises (SMEs) in a range of different sectors. This key finding and others are outlined in our recent report The Physics Graduate ‘Skills Gap’ – What it is and How to Address it.

Universities and businesses need to work together, in effective and meaningful ways, to reduce the impact of the skills gap on physicists’ futures and on industry

The report found that universities and businesses need to work together, in effective and meaningful ways, to reduce the impact of the skills gap on physicists’ futures and on industry. There is also an onus on academia to make sure that physics departments are providing the specialist and transferable skills that graduates need and employers seek. Employers of physics graduates continue to cite the importance of both technical and transferable skills – they do not want to see the core physics content diminished or degraded. Nevertheless, employers frequently report that physicists’ transferable skills (often described as soft skills) tend to be poorly developed – students, for example, often lack commercial understanding. Such messages can put students and academics on the defensive, so it is important not to view the debate as a blame game.

Indeed, the skills gap may equally be considered an expectations gap on the part of employers, reflecting the mismatch between what individual employers expect from graduates, and the experience students can reasonably develop over three or four years in a non-commercial university environment. Closing the skills gaps requires co-operation, not antagonism, between students, universities and employers.

Short, structured, paid

The potential to address the skills gap by placing students in physics-related work mid-way through their degrees is not rocket science. However, the historical sandwich-degree model, which involves a full-year placement during a degree, has rarely achieved a high uptake. SEPnet students pointed out some of the core failings of that model – a year added to their degree, the opportunity cost of delayed graduate employment, and the dephasing of their study paths from that of their peers (with knock-on effects for social support and accommodation). In contrast, the SEPnet eight-week summer placement scheme provides enough time for students to develop some commercial awareness, and to understand how their knowledge and skills relate to industry needs, but is not so long as to disrupt their degree-completion timescale, earnings trajectory or peer networks.

For employers, such an eight-week placement scheme represents a much lower financial and human-resource risk than a traditional placement scheme. It has also proven to be well within reach of many SMEs, for which a full-year placement may be beyond consideration. Feedback from both students and employers alike is positive, despite the placement only being two months long. Moreover, SEPnet’s short placement scheme is also open to PhD students during or at the end of their thesis, providing them with equivalent opportunities to develop industry-relevant skills, while also enabling employers to explore higher-skilled graduates.

These summer placements are not just short, they are also structured and paid. The existence of a structured scheme ensures that the diverse pool of undergraduates from across the nine SEPnet member universities can participate, crucially including students who do not already have social connections in physics-related industry. While an employer’s efforts to find a work placement for the child of an employee might engender staff goodwill, it can also perpetuate gender and racial stereotypes seen in physics-based industry.

In contrast, in the summer 2020 cohort of SEPnet placement students, 32% were women and 24% were from BAME backgrounds. Paying the placement students, even at the modest level of the SEPnet scheme, is similarly important. By doing so, both employers and students can attach monetary value to the scheme in addition to its non-monetized benefits, and avoid excluding students who are not able to sustain a summer of unpaid work.

The principal limitation on the SEPnet scheme is the number of employers offering placements – typically 75 students undertake placements each year, but four times that number submit full applications. If graduates are not exhibiting the full range of industry-relevant skills that employers desire, it is clearly not because of any unwillingness from students to develop those skills.

Crucial experience

Physics students across the UK – not just those we meet through SEPnet – need more businesses ton provide short, structured, paid summer placements that will let them develop industry-relevant skills in employment. Universities, for their part, need to ensure that students focus on the applicability and transferability of their knowledge and skills, and that they are materially supported in gaining crucial experience that the university alone cannot provide.

CityU physics: where regional connections underpin global research ambitions

Ambition, agility, connection, diversity: it’s uncanny how often these themes are echoed and amplified in conversations with faculty in the City University of Hong Kong’s Department of Physics. As such, the sense of shared and collective endeavour is hard to miss among senior CityU physics scholars and early-career scientists, all seemingly pulling in the same direction. Their goal is certainly ambitious – to create one of the leading centres of excellence for physics research and education in the Asia-Pacific region – and doubly so for a department that only came into being in July 2017 after CityU chose to create distinct disciplinary specialisms from the former combined physics and materials science programme.

Fast forward to the turbulent here and now – navigating the perfect storm of the coronavirus pandemic against a backdrop of ongoing political tension in Hong Kong – and it’s clear that ambition alone will not suffice if CityU’s Department of Physics is to sustain its fast-track growth trajectory. The development roadmap is certainly non-trivial, with a target of around 30 physics faculty members on board by 2027 (versus a current staff cohort of 21). It’s also the intention that postgraduate numbers, currently at 79, will scale significantly over the same timeframe to around 150 PhD students, while the number of postdoctoral researchers and research assistants, currently 30, is forecast to triple by 2027.

Think fast, move faster

With the world in flux, agile thinking and adaptive execution look like the “new normal” for organizations big and small, whether academic, governmental or corporate. Just as well that those attributes are reflected in the start-up mindset at CityU Department of Physics – manifest in an ability to pivot at pace unlike some of the bigger, more established physics programmes in Asia and further afield.

A case in point is CityU’s Science Summer Camp. This high-profile event, which was held back in July, seeks to woo outstanding prospective PhD candidates as they embark on their postgraduate studies within physics and other core research disciplines. In normal times, the Summer Camp would see international students attend a five-day programme of seminars, meetings and laboratory visits across the CityU campus. These are not normal times, however, and faced with ongoing Covid travel restrictions, CityU management successfully transformed the 2020 event into a two-day online meeting that engaged a diverse cohort of 40 students, all of them able to join safely from their homes in mainland China, Australia, Bangladesh, India, Vietnam, the US and Hong Kong.

Photo of Sunny Wang from CityU Hong Kong
Sunny Wang: “Hong Kong connects east and west at scale.” (Courtesy: CityU Hong Kong)

Beyond that, CityU Department of Physics appears open to further experimentation, flexing and aligning its approach to postgraduate recruitment to address the unprecedented uncertainty facing research students globally. Witness CityU’s fast-track consideration of prospective physics PhD candidates starting their research studies this autumn, opportunistically targeting graduates from Hong Kong and mainland China who are no longer able (or willing) to study in Europe or North America owing to the pandemic restrictions. It helps, of course, that CityU was ranked number one in terms of “International Outlook” in the Times Higher Education World University Rankings for 2020.

“Nobody knows what the future holds just now, but one thing is certain: Hong Kong will remain a special city with a special role at the nexus between east and west,” explains Xin (Sunny) Wang, a CityU theoretical physicist who specializes in fundamental studies of quantum systems and quantum computation. “My group and the wider CityU physics programme are at the start of a journey,” he adds. “There are all sorts of exciting research opportunities here – as well as generous funding – for talented physics graduates who can help us to grow our visibility, recognition and impact.”

Sunny Wang exemplifies the relative youth of CityU’s physics faculty – around a third of the academic staff are under 40. After graduating from Peking University in 2005, he spent the next decade working in the US – a PhD at Columbia University in the City of New York followed by postdoctoral studies at the University of Maryland – before returning to CityU as an assistant professor in 2015 (he was promoted to associate professor earlier this year). “There’s real unity, energy and a spirit of togetherness across the physics faculty,” he notes. “Ultimately that means students benefit from a staff team that’s approachable, accessible and here to help.”

Currently, Sunny Wang supervises a team of six PhD students, four of them drawn from universities in mainland China, one from Malaysia, and the other a local Hong Kong graduate. In the medium term, though, he hopes to diversify that talent pool, adding one to two graduate students a year, ideally from the near abroad in Asia and perhaps further afield. “International collaboration is the engine-room of our future research success,” he explains. “It’s a virtuous circle. We need talented international students coming here to establish their research careers, subsequently reinforcing CityU’s reputation with their friends and colleagues as they progress and move on elsewhere.”

For Sunny Wang, those international connections, and the ideas flowing from them, are the lifeblood of his work as a theoretician – and indeed Hong Kong’s great strength as a regional research hub. “Hong Kong connects east and west at scale,” he explains. “Leading physicists and early-career researchers come and go through the Territory, sharing their work and their insights – like bees cross-pollinating a field of wild-flowers.”

Wanted: rising stars

Connection and diversity are themes endorsed enthusiastically by Shubo Wang who, as head of graduate admissions for CityU Department of Physics, is responsible for building the pipeline of prospective PhD students into the physics programme. Another faculty member on the right side of 40, Shubo Wang heads up a team of five PhD students and two research assistants working on theoretical aspects of photonics, including metamaterials, photonic crystals and optomechanical systems.

“The priority is clear,” he explains. “We want to increase the cultural diversity of our PhD students by recruiting graduates with high potential from all over the world, bringing in their unique research experiences, ideas and perspectives.”

Shubo Wang: “We want to recruit physics graduates with high potential from all over the world.” (Courtesy: CityU Hong Kong)

Shubo Wang, for his part, reckons the pedigree of CityU’s physics faculty, and the staff’s extensive international connections, are among the big selling points for would-be PhD students. Four of the senior team are Fellows of the American Physical Society, while many younger faculty members have already established top-tier reputations in disciplines as diverse as topological materials, quantum computing, low-dimensional systems and laser spectroscopy.

The generous funding environment also helps, geared towards attracting the best overseas graduate talent to Hong Kong (see “CityU physics: PhD applications in brief”, below). The Hong Kong PhD Fellowship Scheme is a case in point. This selective programme (there are around 300 recipients each year) provides postgraduates with an annual salary of around US$40,000. That salary is topped up with US$1700 a year for work-related travel, with supplements from CityU. 

Ultimately, claims Shubo Wang, the strong financial support plus high-class research facilities make Hong Kong a great place for a young physicist to establish their career and forge lasting connections in Asia. “Our job at CityU is to help rising stars to shine brighter,” he concludes.

CityU physics: PhD applications in brief

Planet-forming disc is torn apart in triple star system

The young triple star system GW Orionis appears to be surrounded by a ring of gas and dust that has torn away and become misaligned with the rest of the system’s circumstellar disc. That is the conclusion of an international team of astronomers led by Stefan Kraus at the University of Exeter – who combined observations with numerical simulations to identify disc structures that have been confined to theory until now.

Astronomers believe that most stars are born with one or more companions, which interact in complex ways with the disc of planet-forming gas and dust surrounding the stellar system. If this disc is misaligned with the orbital planes of the host stars, previous simulations have predicted that it will warp and tear under their gravitational torque, forming distinct rings in separate planes from the rest of the disc. So far, however, astronomers have yet to identify this tearing in their observations of misaligned discs.

In their study, Kraus’ team aimed to verify this tearing process by making detailed observations of the triple star system, GW Orionis. At just around 1 million years old, the system’s circumstellar disc has yet to collapse to form planets; while at its centre, the orbital planes of its three stars are highly misaligned with each other. Over 11 years beginning in 2008, the researchers used the Very Large Telescope (VLT) and Atacama Large Millimeter Array (ALMA) telescopes in Chile to measure thermal emissions and scattered visible light originating from the system. This allowed them to map the distribution of material in the disc.

Casting a shadow

The team identified three distinct rings from these measurements; the outer two of which are closely aligned with each other, but not with the innermost. Containing roughly 30 Earth masses of material, this innermost ring is highly misaligned both with the circumstellar disc, and the orbital planes of its three host stars. This means that the ring casts a shadow on the rest of the disc, allowing the astronomers to define its 3D shape and orientation.

The team followed up these observations with advanced numerical simulations of GW Orionis. As they hoped, the innermost part the virtual disc warped and tore off into a separate, misaligned ring, with the same shape as they had observed. By tearing material out of the main disc in this way, such a ring could potentially form planets with exotic tilted orbits and long orbital periods; and which may even travel in the opposite directions to the rotations of their host stars.

These ideas will be explored in more detail through further observations with both the VLT and ALMA, potentially leading to discoveries of newly formed planets within the GW Orionis system. In turn, theories about such formation mechanisms could uncover an as-yet unknown population of exoplanets in binary and tertiary systems.

The research is described in Science.

COVID Research and Resources Group brings physicists together

Physics has an important role to play in tackling the COVID-19 pandemic. Many physicists are already contributing to COVID-related research, in areas including computational modelling, medical imaging and development of protective and therapeutic equipment. Many such physicists are working in isolation, however, and only interacting on a local level. The newly formed COVID Research and Resources Group (CRRG) aims to bring these physicists and related researchers together, allowing them to benefit from a more coordinated approach.

Robert Jeraj
Robert Jeraj.

Leading the initiative is Robert Jeraj, professor of medical physics at the University of Wisconsin–Madison. He tells Physics World how the CRRG originated: “The American Physical Society [APS] has a Topical Group on Medical Physics, GMED, and we had a discussion about how we can help to bring together physicists that are interested in COVID-related research, those already doing research and those who want to contribute and share resources. Partnering with many other APS units, this turned into the COVID Research and Resources Group.”

The CRRG aspires to be a global initiative, connecting physicists, engineers, and other medical and biological experts from groups and societies worldwide. To achieve this, it created an online community on the APS Engage platform where members can share ideas and conduct discussions. Jeraj notes that this group, which now has 100 members, is not limited to physicists or APS members but is open to anyone to join.

Established back in the summer, the first job for the CRRG organizing committee was to understand the needs of the community and set up resources and initiatives to meet these needs. The first idea to emerge from their brainstorming was a series of APS COVID webinars, which will launch later this week, on 23 September.

The webinars are aimed at a broad audience, from college students upwards, and will be presented by experts, at a level that’s understandable to non-experts. The first speaker will be epidemiologist Marc Lipsitch, director of the Center for Communicable Disease Dynamics at Harvard University. Lipsitch will describe key features of the epidemiology of the COVID-19 pandemic, focusing on the complexity of the data-generating mechanisms.

“For the first talk, we wanted to have somebody to set the stage, to present the problem in a form that physicists can respond to,” explains Jeraj.  “We’ve seen a lot of physicists wanting to help, but either not having access to the data or not understanding the challenges of the publicly available dataset. Marc Lipsitch has had a career in modelling data, he understands the heterogeneity of data, the difficulties of obtaining data and the impact of data imperfections on the model outcome. He can explain the current challenges; physics can then bring the solutions.”

The APS COVID webinars will continue on a fortnightly basis, with the next three speakers already lined up (see box below). Members are encouraged to use the CRRG community website to suggest questions ahead of time and then discuss the webinar coverage afterwards. In addition, some of the presenters will also create webinars aimed at high-school students and provide resources for physics teachers. The CRRG also plans to conduct a survey to determine future topics and gather suggestions for additional speakers.

Another project involves a “post-review” of recently published COVID-19 literature to highlight high-impact papers. In partnership with Johns Hopkins University, the CRRG aims to create a library of the most important research.

“COVID-19 research is an area where I think medical physics needs to be heavily engaged,” says Jeraj. “I feel responsibility to dedicate my time to this.”

The APS COVID webinars

Epidemiology of COVID-19: Implications for control

Marc Lipsitch, professor of epidemiology and director of the Center for Communicable Disease Dynamics at Harvard University. 23 September, 12.00 ET

What we know and don’t know about SARS-CoV-2: physics of viruses

Raul Rabadan, director of the Program for Mathematical Genomics and director of the Center for Topology of Cancer Evolution and Heterogeneity at Columbia University. 7 October, 12.00 ET

What we know and don’t know about the role of droplets and aerosol transmission of SARS-CoV-2

Adriaan Bax, section chief of the Biophysical NMR Spectroscopy Section at the National Institutes of Health. 21 October, 12.00 ET

Immune interactions and SARS-CoV-2 evolution

Benjamin Greenbaum, associate attending in the Computational Oncology Service at Memorial Sloan Kettering Cancer Center. 4 November, 12.00 ET

Details of forthcoming webinars can be found on the APS COVID Webinar Series web page, which also provides instructions for joining the CRRG community on the APS Engage platform.

Thermal diodes bridge the gap

Electronic devices are hard to keep cool. Mechanical fans suck up energy. Heat sinks add unwanted bulk and mass. And thermal diodes – devices that allow heat to flow more easily in one direction than the other – are fragile, inefficient and require gravity to operate. Now, however, a new type of thermal diode looks set to overcome some of these drawbacks, with developers at Virginia Tech in the US suggesting that a future commercialized version could help manage heat in computer chips and aircraft components.

The directional thermal effect was first observed in the 1930s, when physicist Chauncey Starr of the Rensselaer Polytechnic Institute in New York developed a thermal diode based on a copper-cuprous oxide interface. The new device, dubbed a “bridging-droplet” diode, consists of two opposing copper plates separated by an insulating micron-thick gasket.

The surface of the first plate has a wick-like structure consisting of micropillars that hold and conduct water. The second plate, meanwhile, is coated with a water-repelling layer. In the diode’s forward operation mode, water on the wicking plate absorbs heat from its surroundings and evaporates into steam. The steam propagates across the narrow gap between the plate and condenses into dew-like droplets on the hydrophobic plate. When the droplets grow large enough to bridge the gap, they get sucked back into the wick structure, starting the process anew.

A “diodicity” as high as 85

During the device’s reverse mode of operation, the situation is different. In this case, the heat source is now on the hydrophobic plate, but no steam can be produced because the water remains in the wicking structure on the other plate. This transfer of water, explains team leader Jonathan Boreyko, is what allows the device to conduct heat unidirectionally. The new device can also be used upright, sideways or even upside-down and would thus work just as well in space.

The researchers measured the ratio of heat transferred from the wick side to the hydrophobic side – a quantity known as “diodicity” – to be as high as 85. While assymmetric heat pipes offer an even larger diodicity of around 100, their 1D heat transfer is ineffective for large 3D systems, Boreyko says. Placing an array of directional heat pipes into a wall panel solves this problem, but this is both complex and decreases the effective diodicity by more than a factor of 10, he explains.

Boreyko notes that the water-repellent coating he and his colleagues used to create their test device (a mixture of 1-hexadecanethiol in ethanol) is not suitable for practical applications. However, he says this coating could be replaced with more durable alternatives such as graphene or grafted polymers. This gives the Virginia Tech device a potential advantage over a conceptually similar device known as a “jumping-droplet” thermal diode, which requires a fragile superhydrophobic nanostructure to operate.

Members of the team, who report their work in Advanced Functional Materials, have filed a provisional patent for their diode and are now looking to collaborate with industry partners to continue the research. One of the items on their to-do list is to boost the diodicity of their device to 100. This could be achieved, for example, by decreasing the height of the micropillars so that smaller droplets could bridge the insulating gap between the two copper plates. The researchers would also like to test more durable hydrophobic coatings.

CERN’s emissions equal to a large cruise liner, says report

Greenhouse-gas emissions emitted by the CERN particle-physics lab near Geneva in 2018 were 223 800 tonnes of carbon-dioxide equivalent – similar to the emissions from a large cruise liner. That is according to the lab’s first public Environment Report that details the status of CERN’s environmental footprint and outlines some objectives to reduce it in the coming years. The report finds that three quarters of these emissions came from the fluorinated gases used for particle detection and cooling of the particle detectors.

Covering the years 2017 and 2018, the report underlines the scale of the challenge that CERN faces to reduce its emissions. “It has provoked debate and increased the environmental awareness of all the people who work here as well as our user community, and made us think hard about what we do now and how we design the next generation of accelerators,” says Frédérick Bordry, CERN director for accelerators and technology.

It’s really positive that CERN staff are being transparent about their impacts and that they have set themselves an absolute reduction in emissions target, as opposed to a greenwash-style intensity metric

John Barrett

The report covers everything from noise and biodiversity to water use and radiation. Comparing all these aspects, reducing the use of fluorinated gases will have the greatest positive impact and the report sets out a path to do this such as repairing gas leaks in the LHC, optimizing gas re-circulation systems. The ultimate goal is to replace fluorinated gases in the detector cooling systems with carbon dioxide, whose global warming potential is a few thousand times lower. “When we built the Large Hadron Collider we didn’t appreciate the global-warming potential of these gases; our main concern was the ozone hole,” says Bordry. The facility has set itself an objective of reducing its direct greenhouse gas emissions by 28% by the end of 2024.

The report also sets out plans for tackling CERN’s indirect greenhouse emissions – those due to its small-city-sized appetite for electricity. “We are implementing energy-recovery systems at the LHC, and pioneering the use of superconductivity on a large scale, which could improve the efficiency of electricity distribution networks,” says Bordry. But until the LHC’s successor arrives – maybe in the 2040s or 2050s – there is a limit to how much CERN can reduce its environmental footprint and some will question whether probing the mysteries of the universe can justify such significant greenhouse emissions.

“It’s really positive that CERN staff are being transparent about their impacts and that they have set themselves an absolute reduction in emissions target, as opposed to a greenwash-style intensity metric,” says John Barrett, from the Sustainability Research Institute at the University of Leeds. “The advancement of scientific understanding is clearly important and you don’t get much bigger than CERN. Personally, I would prefer to spend our carbon budget on CERN than short high-impact flights for a drunken weekend in Prague.”

Curved toes point to sore feet, the chaos of the knuckleball

Most conventional running shoes have a “toe spring” – a gentle upward curve of the sole towards the tip of the shoe. While this makes stepping more comfortable and easier, Harvard University’s Daniel Lieberman, Oliver Hansen,  Freddy Sichting and Nicholas Holowka have found that a toe spring can weaken the foot’s ability to push off the ground. This, they say, could be associated with a range of foot problems including plantar fasciitis – a painful condition affecting the tissue that connects the heel to the toes.

“We think that what happens is that people are relying on their plantar fascia to do what muscles normally do,” explains Lieberman. “When you get weak muscles and the plantar fascia has to do more work, it’s not really evolved for that, and so it gets inflamed.”

In their experiment, 13 participants walked barefoot and in four pairs of custom-made sandals on a treadmill equipped with force plates and an infrared camera system. You can read more about the team’s research in “Your shoes were made for walking. And that may be the problem”.

Enigmatic pitch

“The knuckleball is perhaps the most enigmatic pitch in baseball,” is the opening line of the abstract of a paper by Nicholas Nelson and Eric Strauss at California State University in Chico. The knuckleball pitch involves the slow rotation of the ball as it speeds towards the batter. Because a baseball has prominent seams that disrupt airflow around the ball, the aerodynamics of the ball changes as it rotates, which causes its trajectory to change repeatedly during flight. This makes it very difficult for the batter to anticipate the motion of the ball and hit it effectively. Conversely, it is also a very difficult pitch to throw because tiny changes in technique can have huge effects on outcome. Indeed, some pitchers say that identically thrown knuckleballs can take very different trajectories.

In their paper, Nelson and Strauss develop a model of the knuckleball and show the motion of the ball is chaotic. The duo’s model predicts that the position of the ball when it reaches the batter can vary by as much as 1.2 m for typical initial conditions used by knuckleball pitchers. This variation can take the ball well outside the strike zone (where the pitch must be), which illustrates why the knuckleball can be a dangerous choice for a pitcher.

You can read more in their paper “Dynamical chaos in a simple model of a knuckleball”.

 

Astronomers plan huge neutrino observatory in the Pacific Ocean

Astrophysicists in Germany and North America have published plans to build the world’s larg­est neutrino telescope on the sea floor off the coast of Canada. The Pacific Ocean Neutrino Experiment (P-ONE) is designed to snare very-high-energy neutrinos generated by extreme events from beyond our galaxy.

Neutrino telescopes observe the Cerenkov radiation that is emitted when neutrinos passing through the Earth interact very occasionally with atomic nuclei resulting in the production of fast-moving secondary particles. Being uncharged and exceptionally inert, neutrinos can penetrate gas and dust as they travel through the universe, allowing astronomers in principle to identify the exceptionally energetic phenomena that generate them. Photons from such events, in contrast, are absorbed on their journey.

We are now on the verge of opening up neutrino astronomy

Elisa Resconi

The world’s largest neutrino tele­scope, known as IceCube, consists of dozens of strings of photomultiplier tubes suspended in holes drilled deep into the ice at the South Pole. Covering a volume of 1 km3, Ice­Cube made history in 2013 when it reported intercepting the first extra­galactic neutrinos. Four years later it then recorded an event that could be tied to a very distant, bright galactic nucleus known as a blazar, thanks to concurrent gamma-ray observations.

According to P-ONE head, Elisa Resconi at the University of Munich, IceCube’s 2017 result strictly speak­ing only constitutes “evidence” for the blazar source. To really claim a discovery and pinpoint the origin of other cosmic neutrinos, she argues, requires the construction of addi­tional neutrino observatories as well as the extension of IceCube. “We are now on the verge of opening up neutrino astronomy,” she says, “but if we base this process on just one telescope it could take a really long time, perhaps decades.”

Heading underwater

P-ONE will consist of seven groups of 10 detector strings creat­ing an instrument volume of about 3 km3. Being larger than IceCube, it will detect rarer, higher-energy neutrinos, and will be most sensi­tive at a few tens rather than a hand­ful of teraelectronvolts. It will also observe a different part of the sky, mainly capturing neutrinos from the southern hemisphere rather than the north. But there will be some over­lap between the two, says Resconi, potentially allowing independent observations of the same event.

The new facility will be located at a depth of about 2.6 km in the Cas­cadia Basin, some 200 km from the coast of British Columbia. As such, it will take advantage of pre-existing infrastructure – an 800 km-long loop of fibre-optic cable operated by the University of Victoria’s Ocean Net­works Canada that supplies power and ferries data to and from existing sea-floor instruments.

Having already confirmed that this site has the necessary optical prop­erties by sending down two initial strings of light emitters and sensors in 2018, the P-ONE collaboration are now planning to deploy a steel cable with addi­tional detectors to investigate the site – including spectrometers, lidars and a muon detector. The plan then, says Resconi, is to install the first part of the observatory – a ring containing seven 1 km-long strings – around the end of 2023. And if that succeeds, the researchers will then apply for the bulk of the $50–100m needed to complete the project, with personnel costs adding roughly $100m more.

Resconi hopes that the full obser­vatory will be installed and taking data by the end of the decade. But she describes this timeline as “very ambitious”. In addition to delays caused by the ongoing COVID- 19 pandemic, she says it will be a challenge to ensure that the detec­tors work as planned – given the huge pressures and the presence of salt and sea creatures, which together make the seabed such a harsh environment.

Indeed, scientists had already planned on operating a cubic-kilome­tre scale neutrino telescope known as KM3NeT on the floor of the Mediter­ranean Sea back in 2014, which was delayed to 2020. According to col­laboration member Feifei Huang, just two of the 230 strings due to be installed off the coast of southern Italy are so far in place, while another site in French waters currently has six out of a planned 115 strings running – with completion not foreseen until 2026 and 2024 respectively.

Resconi says that part of the problem with that project is a lack of specialist personnel, with the physicists essentially doing everything themselves – for example, their self-built junction boxes, which connect cables on the sea floor, having failed. She hopes that the experience acquired by Ocean Networks Canada will mean a similar fate can be avoided for P-ONE. With 30 or 40 people dedicated to laying cables in the ocean, she says that her team “can focus on the physics”.

Floating oil droplet contains hundreds of degenerate optical modes

Microscopic oil droplets held aloft with optical tweezers can contain more than 200 resonant optical modes of similar energies, creating “hyperdegeneracy” for the first time. That is the claim of researchers in Israel, Spain and the US, who say that their breakthrough could ultimately find application in high-speed optical communications, sensing, quantum data processing and even the creation of dynamic optical circuits.

When optical materials with a high refractive index are formed into certain symmetrical shapes — such as rings, cylinders or spheres —light can be repeatedly reflected around the inside of the material, much in the same way that sound waves pass around the inside edge of St Paul’s Cathedral’s famous “whispering gallery”. The circulating light undergoes constructive interference, forming discrete resonant modes – or so-called degenerate states – with similar energies.

The number of modes is dependent on the ratio between the light’s wavelength and the circumference of the resonator — meaning that, in theory, a spherical object with a circumference tens of microns in size could support hundreds of modes of either visible or near-infrared light. In practice, however, achieving such hyperdegeneracy has proven impossible with conventional fabrication techniques. This is because even a single stem supporting the sphere will reduce the object’s symmetry and thereby reduce the extent of the potential degeneracy.

Clean and unscratched

In a new study, however, mechanical engineer Tal Carmon of the Technion-Israel Institute of Technology and his colleagues have circumvented this issue by supporting a 10 micron spherical droplet of silicone oil within an optical tweezer, thereby removing the need for a disruptive structural support. In fact, the radiation pressure from the laser-based tweezers acts to almost completely preserve the spherical symmetry of the oil droplet – along with the potential for hyperdegeneracy. In addition, the researchers explain, the levitation keeps the surface of the microresonator clean and unscratched.

Writing in the journal Physical Review X ,they say “unlike solids, the liquid droplet does not contain any dislocation, inclinations, and thermally induced stresses, which are typical for solid resonators and reduce their quality”.

To reveal the modes, the team placed a tapered fibre close to the surface of the oil microsphere and passed near-infrared laser light into and out of the droplet by means of an evanescent coupling. In the resulting transmission spectrum, the team observed signals of more than 200 modes – the largest-recorded set of degenerate states to ever be measured. The modes did exhibit slight differences in energy; this was a product of the droplet not being perfectly spherical, but distorted slightly as a result of the pressure from the optical tweezers, the presence of the coupled fibre, and the effect of gravity.

Simulating atomic optics

The technology could have several practical applications, write Peking University physicists Qi-Tao Cao and Yun-Feng Xiao in a commentary on the Physical Review X paper. “As a mesoscopic analogue to a single atom, levitated microresonators could serve as well-controlled platforms for simulating atomic optics,” they explain. Other potential applications could lie in using single-photon versions of the resonators as qubits for quantum processing, the creation of malleable circuits using multiple droplets, and high-capacity optical communications through the use of different modes to form densely packed information channels.

Cao and Xiao also point out that the microspheres could be used in existing sensing applications. “The frequency of hyperdegenerate modes is extremely sensitive to external perturbation, and even a tiny [such disturbance] – such as a biomolecule near the resonator surface — could lead to measurable modulation [of the light modes]”.

Dmitry Skryabin at the University of Bath adds, “The extremely high degeneracy and ability to manipulate it for fundamental studies of many coupled oscillators in linear, nonlinear and quantum regimes links these results to many cross-area ideas”. “Ultra-high finesses and near degeneracies in resonators also link to the cross-disciplinary concept of Arnold tongues and oscillator synchronization in the context of frequency comb research.”

Microswimmers benefit from thermoelectric guidance

Microscopic devices made from so-called Janus particles can be made to “swim” through liquid with the help of light-induced thermoelectric fields. The devices, which can travel 100μm along a straight course in 39 seconds, might find applications in biomedical sensing and the targeted, non-invasive delivery of drugs, according to developers at the University of Texas at Austin, US.

Janus particles – named for the famously two-faced Roman god of beginnings and transitions – are tiny spheres coated with different materials on each side. With the right choice of coatings, such particles will act as “microswimmers”, travelling in a specific direction when placed in a chemical solution and driven by light, magnetic, electric or ultrasonic fields.

Light-driven microswimmers are particularly promising for applications inside the body, as they can be controlled remotely with high spatial and temporal resolution. Their chief drawback is that their direction of travel becomes increasingly erratic over time thanks to rotational Brownian motion – the random motion of particles suspended in a medium.

Asymmetric photothermal response

In designing their microswimmers, Yuebing Zheng and colleagues found a way of overcoming this problem. The researchers made the microswimmers by covering a glass substrate with a single layer of pristine polystyrene beads using a technique called spin coating. They then used physical vapour deposition to cover one side of the beads with a gold film. The resulting Janus particles were freely dispersed in an aqueous solution containing a cation surfactant called CTAC. This surfactant makes the beads positively charged, while also introducing spherical fatty molecules, or micelles, of CTAC into the solution along with Cl– ions.

While the gold sides of the Janus particles heat up when illuminated with laser light, the uncoated sides do not. The temperature gradient thus produced redistributes the CTAC micelles and Cl– ions, causing an electric field to build up around the charged particles. According to Zhihan Chen, the study’s co-first author, this opto-thermoelectric force plays a key role in determining the particle’s behaviour.

Comparison with swimming microorganisms

When the researchers illuminated the particles with de-focused laser light, the particles swam in the direction of the optothermally-generated light fields. When they switched to a focused laser beam, however, the particles rotated in-plane. The combination of linear travel and rotations is similar to the “run-and-tumble” motion of swimming microorganisms such as E. Coli bacteria, and it can be maintained thanks to the balance between the opto-thermoelectric, optical and Stokes drag forces.

To keep their Janus particles moving in the right direction, Zheng and colleagues developed a feedback control algorithm to switch between the particles’ swimming and rotating states. By carefully observing the particles in real time, the researchers were able to adjust their control algorithm to make it automatically set the particles rotating whenever they deviate from the desired path. Once the particles realign, the algorithm re-activates their swimming state. Through repeated switching between states, the researchers showed that they could make the Janus particles travel in a straight line – behaviour that could be exploited for non-invasive drug delivery in the body, Chen says.

Improving navigation efficiency

The researchers, who report their work in Light: Science & Applications, now plan to improve the navigation efficiency of their microbots. “In our present study, we showed that 5-μm microswimmers can directionally transport over 110 μm in 39 seconds, but we would like to double this figure and deliver the particles over the same distance in just 18 seconds,” Chen says. “We could achieve this by further improving the response time of our imaging camera and laser shutters.”

The team also plan to further develop their control algorithm so it can steer multiple particles at the same time, while also adding non-collision and path optimization functions.

The half-gold, half-uncoated Janus particles studied in this work are a common type, but in the future, Zheng and colleagues hope to functionalize their polystyrene beads by loading macromolecules onto their uncoated surfaces. “This strategy would enable efficient and targeted cargo delivery totally driven by light,” Chen tells Physics World.

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