As editor of Physics World, which is published by the Institute of Physics (IOP), I’ll be joined by representatives from other physical societies around the world.
Terahertz generators: Gianqian Liao (left) and Yutong Li.
By Hamish Johnston in Beijing
Today was the last day of the Fall Meeting of the Chinese Physical Society here in Beijing and this morning I grabbed a coffee with Yutong Li and Giuqian Liao. I was hoping to learn more about their work that we covered in May in “Coherent terahertz radiation created in laser plasmas“.
Their technique involves firing a powerful laser pulse at a thin metal foil. This creates a plasma in which electrons are accelerated to high energies before bursting out of the foil. When they emerge, coherent terahertz radiation is given off.
Weyl theorists: Zhong Fang (left) and Hongming Weng.
By Hamish Johnston in Beijing
This morning I had a wonderful visit to see some condensed-matter physicists at the Institute of Physics of the Chinese Academy of Sciences (IOP CAS). First I met with theorists Zhong Fang and Hongming Weng and if you know your equations you can see from the above photo that they work on Weyl semi-metals. Fang is deputy director of the institute and is head of a theoretical physics group that includes six faculty members and about 20 postgraduate students. Avid readers might recall that Fang and Weng were named in the Physics World Top 10 Breakthroughs of 2015 for their work on Weyl fermions.
Physicists and artists have long been intrigued and drawn in by the various mysteries that light and its many colours offer. In the latest installation to be unveiled at the Natural History Museum in London, artist Liz West has unveiled her stunning new work dubbed Our Spectral Vision. The exhibit aims to delve into the long and complex history of the development of colour and vision “through the eyes of nature”. Our regular readers will recall the many physics papers that look into the same, from the structural colour of butterflies to the nanostructures in avian eggshells to the mantis shrimp’s visual superpowers. West’s exhibit deals with many of these topics and more including some fantastic “350 rarely seen specimens, from beautiful birds to fossils of the first organisms with eyes”. If you are based in the UK, do visit the exhibit and otherwise, take a look at the video above to see through West’s eyes.
Scientists have long believed that diffraction limits the minimum distance that can be measured between two adjacent sources of light: if the distance is too short, then the sources appear as one. Now, however, engineers in Singapore have used quantum mechanics to show this not to be the case. The researchers say that new optical techniques based on their discovery might increase the resolving power of microscopes and telescopes by several orders of magnitude.
The resolution of any imaging device is limited by the wave nature of light. That is because light striking a device’s aperture – a lens or mirror, say – are diffracted. These waves arrive at different points on the aperture interfere to produce a diffraction pattern around each point in the image. If the diffraction maximum of one point lies within its neighbour’s minimum, then those two points appear to be merged and are said to be unresolved – a criterion laid down by Lord Rayleigh in the 19th century.
Cursed criterion
In the latest work, Mankei Tsang and colleagues at the National University of Singapore looked at how to measure the distance between two adjacent light sources that are so close that they violate Rayleigh’s criterion. At that point, noise caused by light’s quantum nature – where an image is built up from discrete photons arriving randomly – means the measurement becomes far more difficult with every tiny decrease in separation. The Singapore group has dubbed this problem “Rayleigh’s curse”.
To date, scientists have devised many clever techniques to essentially sidestep this problem. In microscopy, for example, the distance between fluorescent particles is kept to a manageable minimum by ensuring that only a small subset of particles emits at any one time. Astronomers, meanwhile, can sometimes use signal processing to resolve objects that are slightly closer than the Rayleigh criterion allows.
Tsang and co-workers instead used a theory known as “quantum metrology” to work out which physical measurements would yield the most information when carried out on light. In this way, they found it is possible to measure the distance between two light sources with an accuracy that doesn’t depend on how close the sources are to one another. Even when violating Rayleigh’s criterion, they discovered that the error on their measurements remains roughly constant as they reduce the distance, rather than skyrocketing as it does with existing techniques. “Our study shows that Rayleigh’s curse is not a fundamental limit,” says Tsang.
Various schemes
In addition to this result, the researchers also put forward schemes to implement their approach in practice. The key here was to find ways of separating the “useful parts” of the light from the “noisy parts”. In their current paper, published this week in Physical Review X (originally on the arXiv server last November), the group proposes carrying out this sifting using waveguides with spatially varying refractive indices. In a follow-up paper uploaded to the arXiv in December, and published in Optics Express two months later, they proposed a second scheme where incoming light interferes with its spatially inverted counterpart.
Both papers have already led four other groups – another at the National University of Singapore, two in Canada and one largely from the Czech Republic – to carry out experiments on similar schemes. All of the groups were able to overcome the Rayleigh limit, while two of them got to within a factor of two of the fundamental quantum limit identified by Tsang and colleagues. “Our schemes can easily be built using today’s technology, they just require low-loss dielectric optical components,” says Tsang. “People could have done this 20 years ago, if only they knew.”
Seth Lloyd of the Massachusetts Institute of Technology in the US is impressed. “This is awesome work and I am amazed that it hasn’t been done before,” he says. “Perhaps everyone thought it was too good to be true.”
Pushing limits
Currently, the team is concentrating on applying their work to fluorescence microscopy, which, says Tsang, is “the lowest hanging fruit”. However, the results may also have applications in astronomy, the most obvious of which would be astrometry – the meticulous measurement of stars’ positions and movements. The team is also in the process of generalising its theory to widen its application. By using the distance measurements to establish whether bright sources actually conceal multiple objects, he says, the work might become useful in detecting binary stars or hunting for exoplanets.
Tsang also points out that their findings could only be used to improve the performance of telescopes whose resolution is already at the point where it is limited by diffraction and quantum noise. This, he explains, will generally be true of space-based observatories, but on Earth will depend on a telescope’s precise specifications. “If a telescope’s adaptive optics is good enough to minimize the effect of turbulence, then there’s no question that our techniques can help,” says Tsang.
“90% of new products are targeted at the richest 10% of the world’s population” – that’s my take-home message from a fascinating presentation by Surya Raghu at the Fall Meeting of the Chinese Physical Society here in Beijing. An engineer by training, Raghu founded US-based Advanced Fluidics in 2001 after a career in academia.
Raghu was speaking to a group of Chinese students about how to embark on a career as an entrepreneur. Student-age is the best time to acquire the mindset of an entrepreneur, says Raghu and he emphasized the concept of “inclusive knowledge transfer”. This a way of ensuring that products developed at universities benefit even the most disadvantaged in the world.
Thanks to in situ measurements from the Micro-Imaging Dust Analysis System (MIDAS) on board the Rosetta spacecraft, researchers have now found out more about the structure of the dust particles on comet 67P/Churyumov–Gerasimenko. Their findings show that the particles are made up of aggregates and cover a range of sizes – from tens of microns to a few hundred nanometres. They also appear to have formed from the hierarchical assembly of smaller constituents and come in a range of shapes, from single grains to larger, porous aggregated particles with some dust grains being elongated. The study could shed more light on the processes that occurred when our solar system formed nearly five billion years ago.
Planetary systems like our own solar system started out as dust particles in protoplanetary nebulae – clouds of gas and dust that gave rise to stars and planets. The particles collided and agglomerated to form planetesimals – the building blocks of planets. Comets are leftover planetesimals and are made of ice and dust particles. They range in size from a few hundreds of metres to ten of kilometres and are mainly found on the outskirts of the solar systems, far from damaging radiation, high temperatures and collisions with other objects.
Pristine particles?
“They are a kind of cold storage,” says team-leader Mark Bentley of the Space Research Institute (IWF) in Graz, Austria, “and so the dust particles they contain should be almost pristine. We hope that these particles can teach us something about the processes of dust agglomeration that took place 4.6 billion years ago.”
“Until now, we have had a hard time trying to understand the very early phases of planet formation,” he adds. “In our solar system, this occurred so long ago, and in other star systems we can only measure the average properties by looking at the way light interacts with dust particles, not study them individually.”
Previous studies to analyse cometary dust include that from the Stardust spacecraft that collected dust particles during its flyby of comet Wild 2. However, the particles here were not pristine as they were collected as far away as hundreds or even thousands of kilometres from the comet’s surface. They would also have fragmented upon their journey and since they were also travelling at more than 6 km/s relative to the spacecraft, they were irrevocably damaged when they collided with Stardust’s sample collector.
Gathering dust
The Rosetta mission, on the other hand, is different in that it provided researchers with the first chance to collect cometary dust “at a ‘walking pace’ rather than a fast fly-by, and the chance to get within a few kilometres of comet 67P/Churyumov-Gerasimenko,” says Bentley. “We obtained our data from the MIDAS instrument on board, which is the first ever atomic force microscope (AFM) to have been launched into space.”
Particle pictures: Three representations of the same scan of a calcite particle on the MIDAS Flight Spare instrument. (Courtesy: Rosetta mission/MIDAS)
MIDAS collects dust in the vicinity of the comet on small (1.4 × 2.4 mm) targets and then scans them with the AFM to reveal their size, shape and texture in 3D, he explains. The device scans the collected dust particles using a sharp, needle-like tip and produces a 3D image of the particle with a maximum resolution of 4 nm. Unlike a standard AFM, it does not scan its tip continuously over the surface of a sample but carefully approaches the target at each point in the image.
The images show that the dust particles are built from smaller sub-micron grains, themselves apparently aggregates. Such hierarchical structures have only been hypothesised in theory until now and never observed directly.
“Our results also confirm that the grains forming the particles are elongated, which is similar to the shape of interstellar particles measured in remote observations,” says Bentley. “One question is how much of the material that went into building asteroids, planets and comets was reprocessed (melted and reformed for example) as opposed to that which remained as original ‘stardust’, and our results hint that at least some is original material.”
New models
Ludmilla Kolokolova of the University of Maryland in the US, who was not involved in this work, says that the Bentley and colleagues’ new work “enhances our fundamental understanding of cometary dust, and the processes that ultimately gave rise to planetary systems such as the solar system. Their discovery of a hierarchical structure in cometary-dust particles and their description of the basic building blocks of such particles might lead physicists to reconsider the interpretation of data obtained from ground-based observations of comets and re-evaluate the processes in protoplanetary nebulae – and will probably give rise to new models of how planets were formed,” she writes in a related Nature News & Views article.
“The particles described in this study were collected early on in Rosetta’s mission – before the dust density forced the spacecraft to fly farther from the comet (and reduce our chances of collecting more dust),” explains Bentley. “Fortunately, in February this year, we collected a large sample of dust. With only a few weeks left before the orbiter lands on comet 67P, so ending the mission, we are scanning as much of this target as possible to continue the story!”
Quantum star: Jian-Wei Pan before his television appearance.
By Hamish Johnston in Beijing
A few weeks ago China launched the world’s first “quantum satellite” from the Jiuquan Satellite Launch Center, which about 1600 km from Beijing. This morning I met the lead scientist on the mission, Jian-Wei Pan of the University of Science and Technology of China, who is visiting Beijing on his way home to Hefei from Jiuquan.
I asked Pan how the mission (called QUESS) was going, and in particular if his team has managed to get the satellite to send entangled pairs of photons back to Earth. He said we would have to wait for the team to write a paper about the satellite’s initial performance – so let’s just say he was in a very good mood! Stay tuned for more information about this pioneering mission that could lead to quantum communications in space.
Florence Bascom had to take classes for her geology PhD behind a screen so that she wouldn’t “distract” her male classmates. Maria Goeppert-Mayer didn’t have a full-time paid job as an academic physicist until 1960 – three years before she won the Nobel prize. And when Patricia Bath became the first female faculty member in the ophthalmology school at the University of California, Los Angeles, her peers tried to assign her an office next to where the lab animals were kept (she refused it, moved to Europe and later invented a device that removes cataracts). Their stories – and those of 47 other notable women – are told in Rachel Ignotofsky’s richly illustrated book Women in Science: 50 Fearless Pioneers Who Changed the World.
Ignotofsky’s choice of women to profile is admirably diverse, with a significant number of African-American women in the list and famous names such as Ada Lovelace and (of course) Marie Curie sharing space with less well-known figures. Each profile is dotted with anecdotes and quotations, including this gem from engineer and suffragette Hertha Ayrton: “An error that ascribes to a man what was actually the work of a woman has more lives than a cat.” The truth of Ayrton’s words is frequently apparent in other profiles. Rosalind Franklin is perhaps the most famous example of a woman whose scientific contributions were downplayed in her lifetime, but she was certainly not alone. Other once-overlooked figures include the geneticist Nettie Stevens, who identified the XY chromosome as male; the chemist Alice Ball, who developed an early treatment for leprosy; and the microbiologist Esther Lederberg, whose husband and lab partner failed to thank her in his Nobel prize speech even though they had done the prize-winning work together. (They soon divorced.)
The biochemist Gerty Cori was more fortunate: she and her husband Carl shared the 1947 Nobel Prize in Medicine after a career in which he refused to work at institutions that wouldn’t allow her to join him. After illness sapped her strength, he carried her around their laboratory so they could continue working together (how romantic!). But while supportive mentors, parents and spouses get their due, the real glory in Ignotofsky’s book belongs to the female scientists who, as she puts it “in the face of ‘No’ said ‘Try and stop me’ ”
What are the main aims of the National Natural Science Foundation of China (NSFC)?
The NSFC was set up 30 years ago in 1986 after being proposed by a group of scientists led by the Nobel-prize-winning physicist Tsung-dao Lee. They told the then Chinese leader Deng Xiaoping that the US has its own National Science Foundation and China should have something similar. He agreed.
How big is your budget?
It’s increased 300-fold since the NSFC was founded. Back then it was about ¥80m ($12m) annually. Now it’s about ¥24.8bn per year.
What areas does the NSFC fund?
We support all the main branches of natural science including mathematics, physics, chemistry, biosciences, earth science, engineering and materials, IT and medicine. We also support some data-driven social and management science too.
How much money does physics get?
We have two main budget lines. Physics I is mainly condensed-matter physics, while Physics II is particle physics, theoretical physics and astronomy. Altogether, they get more than ¥1bn a year.
How many researchers does the NSFC support?
We hand out about 40,000 new research grants each year, which together support about 150,000 people when you take into account students, postdocs and research assistants too. The success rate for those applying for funding is about 22–25%, which is okay. I think a quarter is the golden ratio – neither too high nor too low.
You were appointed president of the NSFC in 2013 – what have been your main achievements during that time?
I have secured a total budget increase of 50% during my three-year tenure. And as well as paying for researchers’ “direct” costs, the NSFC now also funds their “indirect” costs, such as the money for lab space, infrastructure and so on to the hosting institutions. Previously that money went to institutions as a lump sum and they’d charge scientists a certain percentage as a management fee. I’ve also changed the regulations so that someone applying for a grant can support however many graduate students, postdocs and so on that an individual researcher needs. There’s no upper limit on how many they can request.
What are your main challenges as NSFC boss?
I’ve just written an article in Nature saying the importance of raising the quality, integrity and applicability of Chinese science (534 467). In the article, I describe how the NSFC’s mission is to be a “FRIEND” of scientists: fair in reviews; rewarding in fostering research; international in global participation; efficient in management; numerous in grants; and diversified in disciplinary coverage. I also want to get more “monumental” contributions to different branches of science, not researchers just doing more of the same.
How do you evaluate whether grant money has been well spent?
Every year we have an external evaluation where independent experts check a certain percentage of grants in our eight main areas. We don’t monitor every single grant though. We also don’t evaluate the performance of individual researchers funded by the NSFC as we feel that would make them conservative and suppress their creativity.
So how do you measure success?
Publication records are one factor, of course, though we think quality is more important than the sheer number of papers produced. We also survey researchers to find out if they were satisfied with the performance of the NSFC – and that includes asking scientists who failed to receive grants. What’s interesting is that 20 years ago, when you look at the top 0.1% most cited papers, Chinese researchers accounted for less than 0.5% of those publications. Now they contribute a fifth of those articles.
What about tackling fraud and misconduct?
That’s important, yes. I want to reduce cases of misconduct, which have gone up a bit recently, and raise the overall reputation of Chinese research work.
What’s your view on open access?
Chinese researchers can publish in any journals – they don’t have to be open-access journals. However, the official policy of the NSFC is to support green open access, which means that scientists have to place a copy of their final paper in our own NSFC electronic repository 12 months after it’s been published in a peer-reviewed scientific journal. Having said that, China published 45,000 papers in open-access journals last year, which is 21% of the world’s total and exceeds the amount from the US.
Do you follow developments in physics?
It’s been very exciting to see the Laser Interferometer Gravitational-Wave Observatory detect gravitational waves and we are planning several initiatives of our own in China in this area. We’re also building the China Jingping Underground Laboratory in south-western China and we’ve got our satellite programme to search for dark matter and carry out space-to-Earth quantum communication.
