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Liquid nitrogen cleans lunar dust, new source of helium may be lurking underground

The Moon is a dusty place, and the fine, sharp particles can cause lots of problems if they get into the wrong areas. This is an important consideration for people who are developing equipment and spacesuits for future missions to the Moon. The dust could also cause lung disease in astronauts if it is inhaled.

During the Apollo missions of the 1960s and 1970s, astronomers used brushes to deal with moondust, but it didn’t work very well. Indeed, the fact that the dust is electrostatically charged means that it tends to stick to surfaces.

Now, researchers at Washington State University have developed a new way to remove moondust that involves the Leidenfrost effect. This occurs when drops of liquid are placed on a hot surface, creating a layer of vapour that levitates the drops. When very cold liquid nitrogen is sprayed on a dust-covered surface, the nitrogen vapour that is formed lifts the dust particles and carries them away.

The team tested their dusting technique at atmospheric pressure and in a vacuum chamber to mimic conditions on the Moon. They found that the technique worked even better in vacuum.

The research is described in Acta Astronautica.

Bubbling up

Helium is a finite resource on Earth and there is currently a shortage of the gas. It is created by radioactive decay deep underground. The gas then rises up through rock and gets trapped in some geological structures. Today, almost all helium being used is a by-product of the extraction of oil and gas – and as we reduce our consumption of fossil fuels, this source will diminish. And to make matters worse, Russia is a large producer of helium, and this source is not available to many users.

As well as floating party balloons, liquid plays a crucial role in cooling the superconducting magnets in medical MRI scanners. So, running low on the gaseous element is not a good thing.

Now, a team lead by researchers at the University of Oxford have taken an important step forward in understanding how helium can sometimes get trapped at very high concentrations in underground structures that don’t contain natural gas or the greenhouse-gas carbon dioxide.

Instead, these helium reserves are associated with nitrogen, which is an environmentally benign gas. The team believes that nitrogen bubbles can form in water deep underground. Helium can then get trapped in these bubbles, which rise until they hit impervious rock, trapping the nitrogen and helium. The team also believe that hydrogen could be trapped in the same way. So, such geological structures could also hold reserves of hydrogen – which could be used as a carbon-free source of energy.

The team reports its findings in Nature.

Innovation in diamond applications from Element Six

ElementSix
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      Element Six is a company that takes a totally customer-centric approach to R&D and focuses on communication to create solutions for its customers. So says Michael Pearson, head of CVD applications and commercial development at the business, in this short video filmed at Photonics West 2023, which was held in San Francisco, California, in January.

      Diamond has many different uses in industry. As Pearson and his colleague Teodoro Graziosi, senior research scientist, explain, the material’s high thermal conductivity makes it great at dissipating heat, while its nitrogen-vacancy centres allow it to be used for quantum applications. It also has a very low optical absorption, making it useful in a wide range of laser and optical applications.

       

       

       

      Female academics migrate shorter distances and to fewer countries than men, finds study

      Female researchers who migrate for work tend to pick nearby destinations and go to fewer countries than their male counterparts. That is according to a new analysis of worldwide migration patterns, carried out by demographers in Germany and the UK. The study finds, however, that the gender gap of internationally mobile academics is closing faster than the general gender gap in science.

      Academics have a long tradition of moving abroad to set up new collaborations, raise their profile and boost their careers. The new study – led by Xinyi Zhao from the Max Planck Institute for Demographic Research in Rostock and the Leverhulme Centre for Demographic Science at the University of Oxford in the UK – set out to understand how migration patterns differ by gender. They also wanted to see if it this leads to any inequalities.

      The study involved analysing more than 33 million research papers published between 1998 and 2017 using data from the Scopus academic database. By extracting data on institutional affiliations, the team identified “mobile” scholars as anyone whose country of affiliation changed between papers.

      Over the two decades studied, the authors found that both the number of “origin” countries (where the moving researcher came from) and “destination” nations (where the researcher ended up) increased for both male and female academics. However, the range of origin and destination countries for women remained smaller than it was for men.

      The study also found that the gender gap is narrowing faster among mobile scholars across all disciplines compared to the general gender gap in science. The researchers found that between 1998 and 2017, the proportion of women in research grew from around 32% to 36%. The proportion of women among mobile academics rose more sharply, jumping from 24% to 32%.

      The paper speculates that the increase in mobile female scientists could be due to women increasingly migrating independently of families. The authors also point out that many initiatives now exist to promote women and gender parity in academia, and that these programmes are also focused on drawing on overseas talent.

      Geographic inequality

      The analysis also found geographic disparities. Despite increasing globalization, the pool of destination countries remained smaller than the pool of origin countries. This indicates that researchers tend to concentrate in a smaller range of nations – particularly those in the “global north” – leading to a brain drain elsewhere.

      Furthermore, the data showed larger gender gaps in lower-income countries, for both mobile scholars and researchers in total.

      “We hope more attention can be given to female researchers from countries in the Global South to help them engage in international migration and global brain circulation,” Zhao told Physics World. “Funding agencies and support schemes could also help countries that have been mainly sending researchers overseas to attract talented people to return and develop the local science system.”

      Are you an early-career quantum scientist? Here’s your chance of recognition

      Nominations are now open for two awards in quantum technologies for early-career researchers. The two prizes from IOP Publishing, which publishes Physics World, are designed to recognise scientific excellence and to help support the development of scientists at the start of their careers.

      The International Quantum Technology Early Career Scientist Award is open to scientists who have completed their PhD no more than eight years ago. The winner will recieve £2000 plus a certificate.

      The International Quantum Technology Emerging Researcher Award, meanwhile, is aimed at scientists who completed their PhD no more than three years ago. They will receive £1000 and a certificate.

      Both winners will be invited to give a lecture at World Quantum Day, which is being held on 14 April. They will also be invited to submit a perspective article based on their research to the IOP Publishing journal Quantum Science and Technology.  

      The deadline for nominations is 15 March 2023, with applications being reviewed by an eight-strong committee chaired by Chaoyang Lu, a quantum physicist from the University of Science and Technology China (USTC), who is on the board of Quantum Science and Technology.

      The two award winners will be announced on 14 April on World Quantum Day. 

      See here for more information about the awards. 

      Knowledge sharing about the commissioning of the MRIdian and the optimization of the film quality assurance with online solution

      Want to learn more on this subject?

      From Laura Bassi to Marie Curie, for centuries, women have been making important contributions to the world of physics. Now with ViewRay’s MRIdian system, women are leading the charge in bringing the latest advancement of MRI-guided radiation therapy to the forefront of radiation oncology and expanding the medical physics landscape.

      Three months were dedicated to commissioning MRIdian through an extensive quality-assurance protocol.

      In this webinar, we will first focus on the Beam Model validation and the evaluation of multiple detectors behaviours under a 0.35T magnetic field for both absolute and relative dosimetry.

      We will then focus on the quality-assurance workflow and its optimization with the presentation of our online solution for film analysis. Indeed, film dosimetry is an extremely labour-intensive and operator-dependent process. As there were no dedicated commercially available tools to benefit from a standardized, robust and automated way of working with film, we built our own online platform to analyse the results.

      This series of five webinars will specifically highlight women physicists across the globe that are using MRIdian to transform cancer care as we know it. Cathérine Jenny and Mathilde Croise will present this webinar.

      This presentation is the fourth in a series of Women in Medical Physics, supported by ViewRay.

      Want to learn more on this subject?

      Mathilde Croisé is a medical physicist at La Pitié Salpêtrière Hospital (Paris, France) since 2017. After getting a combined honours degree with an engineer diploma and a MSc in images and robotics, she pursued studies with a second MSc in medical physics and then entered the French School (INSTN, Paris, France) to become a medical physicist. Her internships were at McGill University Health Center (Montreal, Canada), in UZB (Brussel, Belgium), and in the Institut Curie (Paris, France). Today, she is fully involved in the clinical activities of the radiotherapy department with multiple TPS dosimetries and quality assurance of the machines (Clinac, Truebeam, GammaKnife, MRIdian, Tomotherapy, brachytherapy). In 2021, Mathilde became responsible for the commissioning of the MRIdian (ViewRay) and manages the quality-assurance workflow of the machine and its optimization.

      Catherine Jenny, PhD, is the chief of the medical physics department of Sorbonne University Hospital group in Paris, France, since the department was created in 2020. Prior to that she was the chief of the medical physicists at La Pitié Salpêtrière Hospital, since 2012. She manages a team of 30 staff involved in radiation therapy, nuclear medicine and imaging, and tends to create a link as often as possible between the different specialties. She participates in high-decision meetings within the direction board and coordinates work groups for the hospital project. Catherine is regularly called upon to carry out reasearch projects inside the departement or even in collaboration with other french research institute. The implementation of the MRIdian in 2021 was a great project for her team as much as for the imaging physicist (with the MRI quality assurance) and the radiotherapy physicist (with the Linac under a magnetic field challenge). She takes great pleasure in supervizing her team and to defend the values of the public-hospital service.

      Vibration isolation products from Minus K Technology

      Minus K Technology
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          Minus K Technology, celebrating 30 years in the market, presents its vibration isolation products in this short video filmed at Photonics West 2023. As Erik Runge, the company’s vice president of engineering explains, the firm’s isolators operate at 0.5 Hz and are totally passive. They use no air or electricity, are easy to set up and are particularly good for low-frequency building vibrations – easily out-performing air and active isolators.

          Runge introduces Minus K Technology’s range of isolation products, which, he says, can all be made vacuum compatible. These isolators are used in a wide range of settings: for atomic-force microscopes, interferometers, micro-hardness testers and electron microscopes. Runge goes on to say that Minus K Technology even did the test isolation for the James Webb Space Telescope – a huge structure weighing almost 30,000 kg.

           

          If we live in a multiverse, where does Wally exist?

          Several years ago, I went to an astronomy conference in London where Brian Cox was the main speaker. In his talk, Cox touched on the notion of the “multiverse”, reasoning that there may be an infinite number of other universes out there. What’s more, he said, if something has a non-zero probability of occurring, then it must take place somewhere in one of those universes. Everything that could possibly happen, will actually happen.

          If Cox is right, it means that somewhere out there is a real universe – very similar to ours – where I was too late for his lecture and never actually got to experience it. It’s an intriguing notion that immediately got me thinking about Where’s Wally? – the children’s picture puzzle books where readers have to pinpoint Wally (known as Waldo in North America) in a crowd of similar-looking people.

          It’s fun trying to track down Wally, who is unique in that he is the only person in the book wearing a red-and-white striped jumper, bobble hat and glasses. But if Cox is right, Wally doesn’t just exist; somewhere out there is an entire universe made completely of Wallys. However, the idea that there might be thousands of Wallys perturbed me, as to my mind it did not accord with common sense.

          The idea that there might be thousands of Wallys perturbed me, as to my mind it did not accord with common sense

          I soon forgot about my Wally worries, but they all came back to me recently when I read an article (I can’t remember by whom) that argued that if there were a finite number of particles in a particular universe, there would be only a finite number of ways to arrange them. In other words, every possible combination of particles must exist in an infinite number of universes.

          I saw Wally appearing over the horizon again and this time I wasn’t going to let him lie. Casting my mind back to my university days, I remembered being told that infinity comes in two distinct types. It can be countable (i.e. discrete) where individual elements can be mapped on a one-to-one basis to the sequence of integers. Or infinity can be uncountable (i.e. continuous) where those elements cannot be mapped to integers.

          One mathematical problem that was posed early on during my undergraduate degree was to prove that no matter how small a section of real numbers is taken, it is impossible to map it to the integer set. Simply put, there are far too many real numbers. Countable infinities are big, but uncountable infinities are infinitely big, which led to the inescapable conclusion that “countable” divided by “uncountable” (if we ever get round to defining it) could only ever tend to zero.

          As physicists, we are still unclear if space–time is continuous or discrete, but no such problem exists in mathematics. For example, the continuous group of co-ordinates that contains our universe (three of space and one of time; other dimensions are available) will by definition have an uncountable number of continuous possible positions within it. If we think about a dartboard, there are an uncountable number of possible locations where the dart could land. And yet the dart will definitely land on one of them, which to me suggests that something with zero probability can happen.

          Of course, the converse is also true. Imagine, for example, our dartboard divided into the complete set of points represented by co-ordinates made wholly of rational numbers (countable) and also into other points represented by irrational numbers, or a mix of the two (uncountable). All points can be hit by a dart, but the mixed positions overwhelmingly dominate and must have a probability of being hit of 1.

          To return to our original question: how many combinations of a finite number of particles are possible in a universe? To answer that, consider just one of them. A single particle can sit in uncountably many places along a non-zero line of finite length, which means that the arrangement of a finite number of particles in an open space must also be uncountably infinite.

          Wally is very unlikely to exist in this or any other universe, even if he could in principle

          So there we have it: the number of infinite universes is countable, while the number of particle combinations within them is uncountable. Wally, in other words, is very unlikely to exist in this or any other universe, even if he could in principle. Whoever originally dreamed up the phrase “Everything that can possibly happen, will actually happen”, was probably a right wally.

          Finally, for all the fans of Oscar contender Everything Everywhere All at Once, it is not strictly necessary for everything to exist everywhere all at once. But then again, it might. And who knows, we may even be living in a universe where Wally turns up to collect an Oscar.

          Scanning probe with a twist observes electron’s wavelike behaviour

          When the scanning tunnelling microscope made its debut in the 1980s, the result was an explosion in nanotechnology and quantum-device research. Since then, other types of scanning probe microscopes have been developed and together they have helped researchers flesh out theories of electron transport. But these techniques probe electrons at a single point, thereby observing them as particles and only seeing their wave nature indirectly. Now, researchers at the Weizmann Institute of Science in Israel have built a new scanning probe – the quantum twisting microscope – that detects the quantum wave characteristics of electrons directly.

          “It’s effectively a scanning probe tip with an interferometer at its apex,” says Shahal Ilani, the team leader. The researchers overlay a scanning probe tip with ultrathin graphite, hexagonal boron nitride and a van der Waals crystal such as graphene, which conveniently flop over the tip like a tent with a flat top about 200 nm across. The flat end is key to the device’s interferometer function.  Instead of an electron tunnelling between one point in the sample and the tip, the electron wave function can tunnel across at multiple points simultaneously.

          “Quite surprisingly we found that the flat end naturally pivots so that it is always parallel with the sample,” says John Birkbeck, the corresponding author of a paper describing this work. This is fortunate because any tilt would alter the tunnelling distance and hence strength from one side of the plateau to the other. “It is the interference of these tunnelling paths, as identified in the measured current, that gives the device its unique quantum-wave probing function,” says Birkbeck.

          Double-slit experiment

          This interference is analogous to the effects of firing electrons at a screen with two slits in it, like the famous Young’s double-slit experiment, as Erez Berg explains. Berg, together with Ady Stern, Binghai Yan and Yuval Oreg led the theoretical understanding of the new instrument.

          If you measure which slit the particle passes through – like what happens with the measurements of other scanning probe techniques – the wave behaviour is lost and all you see is the particle. However, if you leave the particle to pass with its crossing position undetected, the two available paths produce a pattern of constructive and destructive interference like the waves that ripple out from two pebbles dropped in a pond side by side.

          “Since the electron can only tunnel where its momentum matches between the probe and sample, the device directly measures this parameter, which is key for theories explaining collective electron behaviour,” says Berg.

          In fact the idea of measuring the momentum of an electron using the interference of its available tunnelling routes dates back to the work of Jim Eisenstein at Caltech in the 1990s. However, the Weizmann researchers move things up several gears with some key innovations thanks to two explosive developments since. These are the the isolation of graphene prompting research into similar atomically thin van der Waals crystals; and the subsequent experimentally observed effects of a twist in the orientation of layered van der Waals materials.

          When layered with a twist, materials like graphene form a moiré lattice, so named after textiles where the mesh of the fabric is slightly out of register and has funny effects on your eyes. The electrons in these moiré 2D materials are subjected to the potential of this additional artificial moiré lattice, which has a period determined by the twist angle. Hence twisting through the relative angles between two layers of van der Waals crystal using a piezoelectric rotator on the quantum twisting microscope, makes it possible to measure a much wider range in momentum than was possible with the magnetic fields used previously, as well as exploring many other electronic phenomena too. The natty device also makes it easy to study a range of different van der Waals crystals and other quantum materials.

          From problem to solution

          Following the discovery of twist effects, people were keen to experiment with materials at different twist angles. However they had to go through the painstaking process of producing each device afresh for each twist angle. Although it had been possible to twist through angles is a single device, the twist tends to get locked at certain angles where, it’s basically game over for the experiment. In the quantum twisting microscope the atomically thin material on the tip has strong adhesion along the tip sides as well as the end, so that the net forces easily outweigh the attraction between the two van der Waal crystal layers of probe and sample, even for these most attractive twist angles. It was fabrication challenges like these that the Weizmann researchers had originally set out to tackle.

          Twisted graphene pioneer Cory Dean, who was not involved with this research, describes how some of the most detailed understanding of twisted layer systems is coming from scanning probes over them. This way each region with its unique albeit uncontrolled twist can be identified and treated as its own device. “In the Weizmann approach, they have taken this step to a really creative new direction where the twist angle control and spectroscopic analysis are integrated into the same platform,” says Dean, who is at Columbia University. “This idea, that the device is also the instrument, is a rare and exciting combination in condensed matter systems.” He also highlights that the device is not limited to twisted layer systems.

          Ilani says of his team’s invention, “To be honest every week we discover a new type of measurement that you can do with the quantum twisting microscope – it’s a very versatile tool”. For example,  the researchers can also press the tip down to explore the effects of pressure, which decreases the distance between van der Waals layers. “There are experiments on 2D materials done with pressure, also in the context of magic angle graphene,” says Birkbeck, as he refers to experiments with pistons in oil chambers plunged to low temperatures that need to be reset from scratch for each pressure value. “We’ve reached comparable pressures with the quantum twisting microscope but now with the ability to quickly and continuously tune it in situ.”

          The results are reported in Nature.

          Machine learning joins the search for extraterrestrial intelligence

          In this episode of the Physics World Weekly podcast we meet three scientists who are trying to answer a question that humanity has long pondered: does intelligent life exist elsewhere in the universe?

          Peter Ma and Leandro Rizk of the University of Toronto and Cherry Ng of the French National Centre for Scientific Research in Orleans are part of a team that has used machine learning to identify eight potential “technosignatures” in data from the Robert C Byrd Green Bank Telescope. The trio explain how they look for signs of intelligent life in radio-telescope data and how machine learning gives a helping hand.

          Ng also talks about her research on how signals from pulsars could be used to detect gravitational waves.

          Black holes destroy nearby quantum superpositions, thought experiment reveals

          A new thought experiment suggests that the mere presence of a black hole can destroy a nearby quantum spatial superposition. Developed by physicists in the US, the experiment implies that the long-range gravitational field of the particle in the superposition will interact with the black hole’s event horizon, causing cause the quantum superposition to decohere within finite time.

          Coherence is a concept in quantum mechanics that allows a system to exist in a superposition of several different quantum states at the same time. Decoherence is the process of destroying a superposition by making a measurement that puts the system into a specific state. Measurement in this case is a general term and refers to an interaction between a quantum system and its surroundings. A measurement could, for example, be a stray magnetic field or a fluctuation in temperature as well as a lab-based determination of a property of the system (such as the polarization of a photon).

          Superposition and other aspects of quantum mechanics do a fantastic job of describing the behaviour of microscopic systems. However, physicists have not been able to incorporate gravity into quantum theory’s description of nature. Today, gravity is best described by Albert Einstein’s general theory of relativity and unifying the two theories in a theory of quantum gravity is an important aim of modern physics. However, this has proven very difficult because the effects of quantum gravity are only expected to be relevant at very short length scales corresponding to extremely high energies – which are well beyond the capabilities of current and future particle accelerators.

          Quantum thinking

          Because real experiments cannot be done, physicists use thought experiments to try to develop a consistent theory of quantum gravity. These seek to understand the behaviour of quantum systems under extreme gravitational conditions such as those that exist at the event horizon of a black hole. This is a boundary surrounding a black hole, beyond which nothing – not even light – can escape the black hole’s immense gravitational field. This implies that information can enter a black hole, but it cannot leave.

          This latest thought experiment has been devised by physicists at the University of Chicago and Princeton University and is described in a preprint on the arXiv server. Co-author Daine Danielson says that the experiment considers a hidden observer behind a black hole’s event horizon.

          The thought experiment involves a massive particle, such as an electron, that is fired at barrier that contains two slits. According to quantum mechanics, the electron will behave as a wave that diffracts through both slits simultaneously. In other words, the electron is in a coherent spatial superposition of two states, each travelling through its own slit. If the electrons strike a screen behind the slits, the two states are recombined and create an interference pattern.

          Alice and Bob

          The new thought experiment describes a double-slit experiment that is conducted near to a black hole by a physicist called Alice. There is also an observer called Bob who is inside the black hole.

          As Alice conducts her double slit experiment, a quantum theory of gravity requires that the massive particle interacts with the black hole via “soft gravitons”. Gravitons are hypothetical carriers of the gravitational field and are analogous to photons – which are carriers of the electromagnetic field.

          These soft gravitons can be absorbed by the black hole, where they can be measured by Bob – at least in principle. By making multiple measurements of soft gravitons over time, Bob should be able to deduce the state of the quantum superposition in Alice’s experiment. In other words, Bob is making a measurement on Alice’s experiment from beyond the black hole’s event horizon, from where he is causing the spatial superposition to decohere.

          Causal paradox

          Therein lies the paradox. How can Bob decohere Alice’s experiment if information cannot travel out of the event horizon? Indeed, doing so violates causality. Danielson and colleagues argue that this paradox can only be resolved if the black hole itself decoheres Alice’s experiment before Bob can.

          In other words, they say, the black hole affects the quantum superposition in the same way as a classical observer. “Here, we have a precise situation where the geometry of the universe itself is giving a ‘definiteness’ to a quantum superposition,” Danielson says.

          In their paper, the researchers argue that their analysis also applies to other types of horizons, such as the cosmological horizon – which defines the size of the observable universe.  Such thought experiments are useful for probing the fundamental rules that a consistent theory of quantum gravity may one day have, the researchers say. “Any theory of quantum gravity, for example, must have the fundamental feature that black holes which act as quantum systems act as observers,” says co-author Gautam Satishchandran.

          Vlatko Vedral, a quantum physicist at the University of Oxford, says that he has reservations about some of the treatments in the paper. He says that the superposition is treated quantum mechanically, but the authors treat the background gravitational field – such as the black hole itself – classically. “It’s not clear that an approximation like this is valid in the context they consider,” he says. However, if the conclusions are correct, Vedral considers them to be profound. The thought experiment suggests that black holes can serve as a source of irreversibility – the destruction of a quantum state that can never be fully recovered. Since gravitation is infinitely long-range, it does not matter how far an experiment is from a black hole, he says, the decoherence effect that the authors calculate would be non-zero. Therefore, the creation and recombination of quantum spatial superpositions can never be fully efficient because “part of [the system] is always irreversibly lost to beyond the horizon,” he says.

          Copyright © 2025 by IOP Publishing Ltd and individual contributors