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Home » Page 174

Speed of sound in quark–gluon plasma is measured at CERN

The speed of sound in a quark–gluon plasma has been measured by observing high-energy collisions between lead nuclei at CERN’s Large Hadron Collider. The work, by the CMS Collaboration, provides a highly precise test of lattice quantum chromodynamics (QCD), and could potentially inform neutron star physics.

The strong interaction – which binds quarks together inside hadrons – is the strongest force in the universe. Unlike the other forces, which become weaker as particles become further apart, its strength grows with increasing separation. What is more, when quarks gain enough energy to move apart, the space between them is filled with quark–antiquark pairs, making the physics ever-more complex as energies rise.

In the interior of a proton or neutron, the quarks and gluons (the particles that mediate the strong interaction) are very close together and effectively neutralize one another’s colour charge, leaving just a small perturbation that accounts for the residual strong interaction between protons and neutrons.  At very high energies, however, the particles become deconfined, forming a hot, dense and yet almost viscosity-free fluid of quarks and gluons, all strongly interacting with one another. Calculations of this quark gluon plasma are non-perturbative, and other techniques are needed. The standard approach is lattice QCD.

Speed of sound is key

To check whether the predictions of lattice QCD are correct, the speed of sound is key. “The specific properties of quark–gluon plasma correspond to a specific value of how fast sound will propagate,” says CMS member Wei Li of Rice University in Texas. He says indirect measurements have provided constraints in the past, but the value has never been measured directly.

In the new work, the CMS researchers collided heavy ions of lead instead of protons because – like cannonballs compared with bullets – these are easier to accelerate to high energies and momenta. The CMS detector monitored the particles emitted in the collisions, using a two-stage detection system to determine what type of collisions had occurred and what particles had been produced in the collisions.

“We pick the collisions that were almost exactly head-on,” explains Li, “Those types of collisions are rare.” The energy is deposited into the plasma, heating it and leading to the creation of particles. The researchers monitored the energies and momenta of the particles emitted from different collisions to reconstruct the energy density of the plasma immediately after each collision. “We look at the variations between the different groups of events,” he explains. “The temperature of the plasma is tracked based on the energies of the particles that are coming out, because it’s a thermal source that emits particles.”

In this way, the researchers were able to measure the speed at which heat – and therefore energy density – flowed through the plasma. Under these extreme conditions, this is identical to the speed of sound i.e. the rate at which pressure travels. “In relativity, particle number is not conserved,” says Li; “You can turn particles into energy and energy into particles. But energy is conserved, so we always talk about total energy density.”

Even more stringent tests

The team’s findings matched the predictions of lattice QCD and the researchers would now like to conduct even more stringent tests. “We have extracted the speed of sound at one specific temperature,” says Li. “Whereas lattice QCD has predicted how the speed of sound goes with temperature as a continuous function. In principle, a more convincing case would be to measure at multiple temperatures and have them come out all agreeing with the lattice QCD prediction.” One remarkable prediction of lattice QCD is that, as the temperature of the quark–gluon plasma drops to its lowest possible temperature, the sound speed reaches a minimum before then increasing as the temperature drops further and the quarks become bound into hadrons. “It would be remarkable if we could observe that,” he says.

The research is described in a paper in Reports on Progress in Physics.

“I think it’s a good paper,” says nuclear theorist Larry McLerran of the University of Washington in Seattle – who is not a CMS member. He believes its most interesting aspect, however, is not what it shows about the theory being tested but what it demonstrates about the techniques used to test it. “The issue of sound velocity is interesting,” he says. “They have a way of calculating it – actually two ways of calculating it, one of which is kind of hand waving, but then it’s backed up with detailed simulation – and it agrees with lattice gauge theory calculations.”

McLerran is also interested in the potential to study heavy-ion collisions at low energies, and hopes these might give clues about the cold, dense matter in neutron stars. “In heavy ion collisions, you can calculate the sound velocity squared as a function of density using numerical methods, whereas these numerical methods don’t work at high density and low temperature, which is the limiting case for neutron stars. So being able to measure a simple bulk property of the matter and do it well is important.”

Scientists uncover hidden properties of rare-earth element promethium

For the first time, researchers have experimentally examined the chemistry of the lanthanide element promethium. The investigation was carried out by Alex Ivanov and colleagues at Oak Ridge National Laboratory in the US – the same facility at which the element was first discovered almost 80 years ago.

Found on the sixth row of the periodic table, the lanthanide rare-earth metals possess an unusually diverse range of magnetic, optical and electrical properties, which are now exploited in many modern technologies. Yet despite their widespread use, researchers still know very little about the chemistry of promethium, a lanthanide with an atomic number of 61, which was first identified in 1945 by researchers on the Manhattan project.

“As the world slowly recovered from a devastating war, a group of national laboratory scientists from the closed town of Oak Ridge, Tennessee, isolated an unknown radioactive element,” Ivanov describes. “This last rare-earth lanthanide was subsequently named promethium, derived from the Greek mythology hero Prometheus, who stole fire from heaven for the use of mankind.”

Despite its relatively low atomic number compared with the other lanthanides, promethium’s chemical properties have remained elusive in the decades following its discovery. Part of the reason for this is that promethium is the only lanthanide with no stable isotopes. Only small quantities of synthetic promethium (mostly promethium-147 with a half-life of 2.62 years) are available, extracted from nuclear reactors, through tedious and energy-intensive purification processes.

Ultimately, this limited availability means that researchers are still in the dark about even the most basic aspects of promethium’s chemistry: including the distance between its atoms when bonded together, and the number of atoms a central promethium atom will bond to when forming a molecule or crystal lattice.

Ivanov’s team revisited this problem in their study, taking advantage of the latest advances in isotope separation technology. In a careful, multi-step process, they harvested atoms of promethium-147 from an aqueous solution of plutonium waste, and bonded them to a group of specially selected organic molecules. “By doing this, we could study how promethium interacts with other atoms in a solution environment, providing insights that were previously unknown,” Ivanov explains

Using synchrotron X-ray absorption spectroscopy to study these interactions, the researchers observed the very first appearance of a promethium-based chemical complex: a molecular structure whose central promethium atom is bonded to several neighbouring organic molecules.

Altogether, they observed nine promethium-binding oxygen atoms in the complex, which allowed them to probe several of the metal’s fundamental chemical properties for the first time. “We discovered how promethium bonds with oxygen atoms, measured the lengths of these bonds, and compared them to other lanthanides,” Ivanov describes.

Based on these results, the researchers then studied a complete set of comparable chemical complexes spanning all lanthanide elements. This enabled them to experimentally observe the phenomenon of “lanthanide contraction” across the whole lanthanide series for the first time.

Lanthanide contraction describes the decrease in the atomic radii of lanthanide elements as their atomic number increases, due to increasingly poor shielding from nuclear charge by inner-shell electrons. The effect causes the lanthanide–oxygen bond length to shrink. Ivanov’s team observed that this shortening accelerated early in the lanthanide series, before slowing down as the atomic number increased.

The team’s discoveries have filled a glaring gap in our understanding of promethium’s chemistry. By building on their results, the researchers hope that future studies could pave the way for a wide range of important applications for the element.

“This new knowledge could improve the methods used to separate promethium and other lanthanides from one another, which is crucial for advancing sustainable energy systems,” Ivanov describes. “By understanding how promethium bonds in a solution, we can better explore its potential use in advanced technologies like pacemakers, spacecraft power sources and radiopharmaceuticals.”

The researchers report their findings in Nature.

Physics and sport: flying balls, perfecting technique, and wellbeing in academia

For sports fans, the next few weeks will bring excitement and drama. The Euro 2024 football (soccer) tournament is under way in Germany and the Copa América is about to kick off in the US. Then at the end of July, the Olympics starts in Paris as athletes from across the world compete to run, jump, sail, cycle and dance themselves into the history books. In this episode of Physics World Stories, you will hear from two US physicists with a profound connection with sport.

The first guest is John Eric Goff of the University of Lynchburg, author of Gold Medal Physics: the Science of Sports. After training as a condensed-matter theorist, Goff has focused his research career the physics of sport. In a wide-ranging conversation with podcast host Andrew Glester, Goff discusses everything from the flight of balls to the biodynamics of martial arts. He also considers how data and AI in sport are changing the practice and the spectacle of sport.

Our second guest is Harvard University’s Jenny Hoffman, who recently set the record for the fastest woman to run across the US. In November 2023 Hoffman completed the 3000 mile (5000 km) journey in just 47 days, 12 hours and 35 minutes, running from San Francisco to New York City. Hoffman, who studies the electronic properties of exotic materials, speaks about the benefits of having hobbies and passions outside of work. For her, running plays an essential role in wellbeing during her successful career in academia.

SNMMI ‘Image of the Year’ visualizes the brain as never before

SNMMI Image of the Year
Ultrahigh-resolution images A series of PET images recorded by the NeuroEXPLORER brain PET scanner was chosen by the Society of Nuclear Medicine and Molecular Imaging as its Image of the Year. (Courtesy: Richard E Carson et al. Yale University, New Haven, CT).

A series of ultrahigh-resolution brain PET images has been selected as the SNMMI Image of the Year. At each of its annual meetings, the Society of Nuclear Medicine and Molecular Imaging chooses an image that represents the most promising advances in the field, with this year’s winner picked from more than 1500 submitted abstracts.

The winning images, recorded by the ultrahigh-performance NeuroEXPLORER human brain PET scanner, highlight targeted tracer uptake in specific brain nuclei (clusters of neurons), providing detailed information on neuronal and functional activity. The technology could dramatically expand the scope of brain PET studies, with potential to advance the treatment of brain diseases.

NeuroEXPLORER was built by a collaboration of researchers from Yale University, the University of California, Davis and United Imaging Healthcare. They designed the scanner to provide ultrahigh sensitivity and ultrahigh spatial resolution, as well as to perform continuous correction for head motion.

“If we are going to get high resolution, we have to deal with patient motion,” Richard Carson from Yale University explained at the recent SNMMI Annual Meeting in Toronto. “But the challenge has always been sensitivity, even with a high-resolution system. In a late frame for a carbon-11 study, you’re really scanning on fumes, it’s hard to generate the quality of images you’d like to really use the resolution that’s possible.”

To achieve the highest possible resolution, ideally better than 2 mm, the team designed a detector micro-block comprising a 4 x 2 array of 1.56 x 3.07 x 20 mm LYSO crystals, read out by four silicon photomultipliers. The 1.5 mm transaxial pitch provides extremely high resolution, while the larger axial pitch is used to read out depth-of-interaction (DOI) data.

The NeuroEXPLORER assembles 20 detector modules, each containing five or six detector blocks (12 × 12 microblocks), in a cylindrical ring with a diameter of 52.4 cm. The scanner’s high sensitivity is enabled by having a long (49.5 cm) axial field-of-view, building on pioneering work from UC Davis on the EXPLORER system. Motion correction is performed using a Vicra tracking system with a built-in camera that collects data from the face for markerless motion tracking.

In performance tests, the NeuroEXPLORER demonstrated a sensitivity of 46 kcps/MBq at the centre, a transverse spatial resolution of less than 1.4 mm with OSEM (ordered-subset expectation-maximization) reconstruction, and a DOI resolution of less than 4 mm. The scanner also performs time-of-flight measurements with an average resolution of 236 ps. The team provide detailed system characteristics in the Journal of Nuclear Medicine.

Exceptional images

In their latest study, presented by Carson at the SNMMI Annual Meeting, the researchers compared human brain images from the NeuroEXPLORER with images from the current state-of-the-art scanner, the High Resolution Research Tomograph (HRRT).

The team scanned healthy volunteers, using both PET systems on different days, after administration of five different radiotracers. The tracers target various features in the brain, including synaptic density (imaged with 18F-SynVesT-1), dopamine receptors (11C-PHNO) and transporters (18F-FE-PE2I), and glucose metabolism (18F-FDG). Carson also shared some late-breaking data using the tracer 18F-Flutabine.

Overall, the team observed a dramatic improvement in the resolution and quality of NeuroEXPLORER images compared with those recorded by the HRRT. Carson presented a series of examples to the SNMMI audience.

NeuroEXPLORER images using 18F FDG, for instance, visualized extremely small substructures with much higher contrast than corresponding HRRT scans. Time activity curves in the caudate and thalamus quantified that NeuroEXPLORER showed higher standard uptake values (SUV) than HRRT. Likewise, late images of synaptic density, recorded 60–90 min postinjection, showed higher contrast and greater SUV with the NeuroEXPLORER than the HRRT scanner.

Carson also presented binding potential images using the dopamine receptor tracer 11C-PHNO. While noise is higher with a 11C-based tracer, NeuroEXPLORER scans showed higher values than the HRRT images. “This was one of the really good days,” he said. “We saw two hotspots in the anterior thalamus, we’re not sure exactly which subnucleus within there, but we’re seeing beautiful hotspots consistent with high dopaminergic intervention in those regions. If you look at the HRRT images, it’s there, but not something you could commit to.”

Carson noted that the NeuroEXPLORER’s long axial field-of-view enables the scanner to also image the carotid arteries in the neck. In addition, the team is using 18F-FDG to image head-and-neck tumours, for example to visualize lymph nodes in the neck. “This is an exciting opportunity in terms of being able to see much smaller tumours,” he said.

The team’s ongoing projects include optimization of the reconstruction parameters, further improving the camera for motion correction, and fully characterizing the resolution of the PET images using brain phantoms with variable contrast.

As well as imaging of small brain structures with targeted pharmaceuticals, future studies will also include more imaging in the spinal cord, and looking at the dynamics of neurotransmitter release. “One exciting part to think about doing is, because of the sensitivity, we can drop the radiation dose and begin to scan adolescents, for example with autism or schizophrenia,” said Carson.

“The dramatic improvement in resolution and overall quality of the NeuroEXPLORER images compared to the HRRT images is clear,” says Heather Jacene, chair of SNMMI’s Scientific Program Committee, in a press statement. “The NeuroEXPLORER has the potential to be a gamechanger in research for conditions such as Alzheimer’s disease, Parkinson’s disease, epilepsy and mental illnesses.”

Birds save up to 25% of their energy when they follow a leader

A painstaking study of sensor-laden European starlings has confirmed what scientists have long suspected: birds use significantly less energy when they fly behind a leader. The study, which was carried out by an interdisciplinary team of researchers in the US, is the first to measure birds’ in-flight energy expenditure directly, and team co-leader Ty Hedrick thinks the findings could have implications for other bird species, too.

“There’s nothing particularly ‘special’ about a trio or pair of starlings that would lead us to believe that we’d find the effect in them but not in (for example) small shorebirds,” says Hedrick, a biologist at the University of North Carolina, Chapel Hill who conducted the work alongside postdoctoral researcher Sonja Friman and colleagues in physics and engineering departments at the University of Massachusetts Amherst, Brown University, Howard University, the Rochester Institute of Technology and the University of Southern California, Los Angeles. According to Hedrick, the energy savings he and his colleagues identified may even apply to birds that fly in dynamic flocks, not just those that adopt the familiar, fixed V-formation used by geese and other large migratory species.

First, catch some starlings

To measure how a starling’s position in a flock affects its energy use, Hedrick, Friman and colleagues needed three things. The first was a controlled flying environment big enough to accommodate up to three starlings without compromising their safety or impeding their natural flight. The team found this at Brown, which operates a purpose-built, mesh-enclosed animal flight wind tunnel with an active volume 1.2 m wide, 1.2 m tall and 2.8 m long.

The second thing the researchers needed was a way to monitor the starlings’ movements in flight. They achieved this by fitting the birds with miniature backpacks containing inertial measurement units (IMUs) and different-coloured LEDs. The IMUs recorded three-dimensional data on the birds’ linear accelerations and angular velocities, while the LEDs helped the team distinguish the positions of individual birds on video recordings of test flights.

A photo of two starlings in flight in a wind tunnel, one wearing a bluish light and the other a yellow one
Two’s company: A view from below of two European starlings flying together in a wind tunnel while wearing inertial measurement units with a coloured LED marker to help researchers distinguish them in video footage. (Courtesy: Siyang Hao)

The final ingredient was a means of measuring the starlings’ energy use. For this, the researchers injected the birds with a dose of sodium bicarbonate that contained carbon-13. This non-radioactive isotope of carbon is often used as a label in metabolic testing because biological processes preferentially take up carbon-12 atoms, which are lighter. By placing the starlings in a metabolic chamber and using a spectrometer to monitor the 13C/12C ratio in their exhaled breath before and after flights, the team could therefore calculate how much energy the birds used.

Together, these three elements enabled the team to go beyond previous bird-flight studies that measured biomechanical and physiological correlates of energy use, but not energy itself, Hedrick says. “The effect of formation flight on flight costs has been investigated for so long and in so many ways, but we realized that the existence of a large animal flight wind tunnel and the new ‘turn-key’ equipment for doing the metabolic measurements would let us go after the question experimentally in a way that had not been done before,” he tells Physics World.

“A lot of effort”

Even with the latest equipment, things did not always go to plan. “The most challenging part was getting everything to work together at once,” Hedrick says. “We needed two (or three) birds to fly well in the wind tunnel, all of the inertial measurement unit backpacks to function at least well enough to provide the bird ID light colours, and the 13C sodium bicarbonate metabolic measurement to work as well.”

As for what happened when things went wrong, the materials and methods section of the team’s paper makes illuminating reading. Data from several test flights had to be discarded after birds “repeatedly veered toward the floor, attempted to land on the floor or cameras, or clung to the front or rear mesh” of the wind tunnel. Noise from whirring feathers masked the indicator tones meant to help synchronize IMU data with video images. And of course, the researchers needed to catch the birds cleanly and transfer them to the metabolic chamber quickly to avoid messing up the post-flight 13C/12C readings. “All of these things are pretty likely to [work] on their own, but getting them to all work at once took a lot of effort from a skilled and dedicated research team,” Hedrick says.

The reward for this effort was twofold. First, the researchers found that when a starling spent most of a test flight in a “follower” position, it expended up to 25% less energy than it did when flying solo. Second, they noticed that the most energy-efficient solo flyers were far more likely to adopt the “leader” role when flying with other birds. The researchers say that this difference is likely related to the birds’ wing-flapping frequency, which was generally lower for “leader” birds. A more complete explanation, however, will require additional experiments.

“The next thing we’d really like to do is directly visualize the wake interaction between a lead bird and a follower using digital particle image velocimetry to get a better understanding of the fluid dynamic mechanism that produces the energy savings,” Hedrick says.

The research is published in PNAS.

‘I was always interested in the structure of things’: particle physicist Çiğdem İşsever on the importance of thinking about physics early

Çiğdem İşsever
Çiğdem İşsever “My main focus is to shed light, experimentally, on the so-called Higgs mechanism.” (Credit: DESY Courtesy of Cigdem Issever)

The 2012 discovery of the Higgs boson at CERN’s Large Hadron Collider (LHC) was a momentous achievement. Despite completing the so-called Standard Model of particle physics, the discovery of this particle opened up the search for physics beyond the Standard Model and the elements of nature that assist the Higgs boson in granting all other matter particles their mass. One researcher who is taking a deeper look at the Higgs boson is the experimental particle physicist Çiğdem İşsever – lead scientist in the particle physics group at Deutsches Elektronen-Synchrotron (DESY) in Hamburg, and the experimental high-energy physics group at Humboldt University of Berlin.

After obtaining her degree in physics and completing a PhD in natural sciences at the University of Dortmund in Germany by 2001, İşsever was a postdoc at DESY and at the University of California, Santa Barbara in the US. From 2004 to 2019, she was based at the University of Oxford, where from 2014 she held a professorship in elementary particle physics. From 2015 onwards she also was a Fellow at Lincoln College in Oxford. She was appointed in 2019 a professor at Humboldt-University of Berlin and a leading scientist at DESY.

As a member of the ATLAS collaboration at CERN since 2004, İşsever’s research has focused on how the Higgs boson defines our reality. “My main focus is to shed light, experimentally, on the so-called Higgs mechanism, which explains how elementary particles and gauge bosons acquire mass in nature,” explains İşsever.

The Higgs mechanism is a key parameter of the Higgs boson, which particle physicists are trying to experimentally constrain, to gain important insight about the shape of the so-called Higgs potential. Determining if the Higgs potential is exactly as predicted by our theories or “if nature has chosen a different shape for it influences the very physics that determines the shape of our universe and even its eventual fate,” she explains.

What lies within

İşsever was fascinated by the inner workings of nature from a very young age. “I was always interested in how things are made, or why something is the way it is,” she says. “My father is not a physicist, but when I was in the first or second year of primary school, we would talk like adults about physics. He would discuss with me how nuclear reactors split the atom and if it was possible to bring it back together.”

As a child of six or seven, İşsever recalls industriously dissecting the vegetables on her plate, to reveal their inner structure. “This might sound really weird, but I wouldn’t just eat vegetables and fruit… I would really carefully cut them open. Look where the seeds are, see how many chambers a tomato has.”

This early fascination with the natural world on small scales deeply influenced İşsever and led to her interest in science communication. Keen to inspire young minds, and help children engage with science from a early age, the ATLAScraft project was developed by İşsever together with her husband and fellow DESY physicist Steven Worm, and physicist Becky Parker, from Queen Mary University, London. The project was a collaboration between the University of Birmingham, University of Oxford, the Institute for Research in Schools and the Abingdon Science Partnership, with technical expertise from CERN.

ATLAScraft provides users a map of CERN, the ATLAS detector and the LHC; all which have been created in the hugely popular computer game Minecraft. The idea behind the project was to bring the LHC and its scientific endeavours to a whole new generation, but it was also about breaking cultural stereotypes, especially getting more women in physics.

“Children decide quite early in their life, as early as primary school, if science is for them or not,” İşsever explains. They decided to visit pupils between five and 11, and “talk to them before they buy into science-related stereotypes of the male scientist and his female assistant,” says İşsever, adding that “When we went to schools in the UK to talk about our physics, I would be the main presenter of the physics concept, and Steve would be my sidekick. This was something we did deliberately to challenge these stereotypes.” Thanks to ATLAScraft, you can now take a virtual tour of ATLAS, via a 3D interactive map complete with the buildings, beamline tunnels and the actual ATLAS detector, all within Minecraft.

Pairing up

This year İşsever will also be involved in CERN’s 70th anniversary celebrations. She sees these as further opportunities to communicate CERN’s discoveries to a wider audience. However, İşsever’s research is still her prevailing passion. She is currently excited about her work to discover Higgs “pair production” at the LHC. Experimentally detecting these pairs of Higgs bosons is a crucial step in understanding how the Higgs boson may interact with itself, as this will determine the shape of the potential of the Higgs field.

“This hasn’t yet happened. When it does, if we collect enough data, we should be able to constrain the Higgs coupling as a parameter,” says İşsever. She adds that this search could also lead to the discovery of physics beyond the Standard Model. “To me, this represents the true thrill of discovering something new, which would be amazing.”

When it comes to the future of CERN and particle physics in general, the proposed successor to the LHC – the Future Circular Collider (FCC) – is an interesting prospect. More than 90 km in diameter – three times that of the LHC – the FCC would allow for a significant upgrade in collision energies.

One of the LHCf detectors
One of the Large Hadron Collider forward (LHCf) detectors. (Courtesy: CERN)

While she acknowledges how useful the FCC would be, İşsever believes that a less energetic electron–positron collider, could be vital as a next step. Such an instrument could lead to a deeper understanding of the Higgs boson and its associated phenomena, as well as allowing particle physicists to “infer the energy scale we should investigate with future machines,” she adds.

Looking ahead

Beyond the Higgs boson, İşsever is also involved with the Large Hadron Collider forward (LHCf) experiment, that captures and measures forward-travelling particles that escape “standard” detectors like ATLAS. LHCf could help build a better understanding of the cosmic rays that bombard the atmosphere of Earth from space.

İşsever also acknowledges the importance of non-collider experiments, even though they are unlikely to end the collider-dominated era of particle physics. “Collider experiments are much more general-purpose experiments. If you think of, for example, the ATLAS experiment, it’s not just one experiment. At any time, there are something like 200 or more analyses going on in parallel. You can think of each of them as an individual experiment. So, it is a very efficient way to perform experimental physics.”

Researchers build 0.05 T MRI scanner that produces diagnostic quality images

Magnetic resonance imaging (MRI) is an essential tool used by radiologists to visualize tissues and diagnose disease, particularly for brain, cardiac, cancer and orthopaedic conditions. However, the high cost of an MRI scanner and dedicated MR imaging suite, combined with the scanner’s operational complexity, has severely limited its use in low- and middle-income countries, as well as in rural healthcare facilities.

Among member countries of the Organization for Economic Co-operation and Development (OCED), the number of MRI scanners (in 2021) ranged from just 0.24 per million people in Columbia to 55 per million in Japan. This significant disparity negatively impacts the quality of healthcare for the global population.

Aiming to close this gap in MRI availability, researchers at the University of Hong Kong’s Laboratory of Biomedical Imaging and Signal Processing are developing a whole-body, ultralow-field 0.05 T MR scanner that operates from a standard wall power outlet and does not require radiofrequency (RF) or magnetic shielding cages.

Targeted as both an alternative and a supplement to conventional 1.5 T and 3 T MRI systems, the novel scanner incorporates a compact permanent magnet and employs data-driven deep learning for image formation. This simplified design not only makes the MRI scanner easier to operate, but should significantly lower its acquisition and maintenance costs compared with current clinical MRI systems.

Writing in Science, principal investigator Ed X Wu and colleagues describe how they used the 0.05 T scanner, along with deep-learning reconstruction methods developed by the team, to obtain anatomical images of the brain, spine, abdomen and knee with comparable image quality to that of a 3T system. In one example, they acquired spine MRI scans showing details of intervertebral disks, the spinal cord and cerebrospinal fluid, in 8 min or less.

Whole-body scanner design

Central to the scanner’s hardware design is a permanent neodymium ferrite boron (NdFeB) magnet with a double-plate structure. Permanent magnets are safer to operate than superconductive magnets as they generate less heat and acoustic noise during imaging. Ultralow-field MRI also benefits from low sensitivity to metallic implants, fewer image susceptibility artefacts at air–tissue interfaces and an extremely low RF specific absorption rate.

The magnet features two NdFeB plates connected by four vertical pillars, chosen to optimize openness and patient comfort. Its key components – including yokes, magnet plates, pole pieces, anti-eddy current plates and shimming rings – were designed to create a uniform field suitable for whole-body imaging while maintaining shoulder and chest accessibility. The final magnetic field was 0.048 T at room temperature (corresponding to a 2.045 MHz proton resonance frequency).

Prototype ultralow-field MRI scanner
Low-cost, low-power, shielding-free The prototype MRI scanner has a compact footprint of roughly 1.3 m2 and requires neither magnetic nor RF shielding cages. (Courtesy: Ed X Wu)

The magnet assembly has exterior dimensions of 114.0 x 102.6 x 69.9 cm, with a 40 x 92 cm gap for patient entry, and weighs approximately 1300 kg, making it potentially portable for point-of-care imaging.

In the absence of RF shielding, the researchers used deep learning to eliminate electromagnetic interference (EMI). Specifically, they positioned 10 small EMI sensing coils around the scanner and inside the electronics cabinet to acquire EMI signals. During scanning, the EMI sensing coils and the MRI receive coil simultaneously sample data within two windows: one for MR signal acquisition, the other for EMI signal characterization. The team then used a deep-learning direct signal prediction (Deep-DSP) model to predict EMI-free MR signals from the acquired data.

For the study, 30 healthy volunteers were scanned with the 0.05 T system, using standard protocols and optimized contrasts for the various anatomical structures. To overcome the weak MR signal at 0.05 T, the team also designed a data-driven deep-learning image formation method – the partial Fourier super-resolution (PF-SR) model – that integrates image reconstruction and 3D multiscale super-resolution, validating the model by comparing 0.055 T brain scans with 3 T images from the same subjects (as described in Science Advances). This PF-SR reconstruction improved the 0.05 T image quality by suppressing artefacts and noise and increasing spatial resolution.

The researchers are currently optimizing the scanner design and algorithms. They plan to perform experimental assessment and optimization of ultralow-field data acquisition and deep-learning image reconstruction, to yield the optimal trade-offs between image fidelity, resolution, contrast, scan time and cost for each specific application. They are also evaluating clinical applications of the 0.05 T scanner in depth.

“We shall continue to refine our data-driven approaches in order to minimize the hardware requirements while advancing imaging quality and speed,” Wu tells Physics World. “We are starting to plan our research of the PF-SR in detecting various pathologies, and are currently training the PF-SR models with datasets from both normal and abnormal subjects.”

Huge fault-tolerant quantum computers on the agenda at Commercialising Quantum 2024 conference

On 5–6 June I was in the City of London for Economist Impact’s Commercialising Quantum 2024 conference. Held in a shiny new skyscraper in Bishopsgate, the technology being discussed felt as new and exciting as the venue itself. As someone who was taught quantum mechanics well before the second quantum revolution, I felt more akin to the ancient churches that I walked past to get there – a vestige of a different era.

I was at the conference last year, so I was keen to see how the commercialization of quantum was proceeding. Was it rapidly rising to the heavens like a modern skyscraper, or was construction proceeding at a more leisurely pace like a medieval cathedral?

One company that has taken great strides since June 2023 is US-based PsiQuantum, which earlier this year received a staggering A$940m ($620m) from Australian federal and state governments to build “the world’s first utility-scale quantum computer” in Brisbane.

The company’s founder and CEO Jeremy O’Brien spoke at the event and I was very keen to find out how the company was scaling-up the production and integration of its photonic quantum chips. The Brisbane facility will need about one million physical qubits so that quantum error correction can be used to create the thousand or so logical qubits required to create a fault-tolerant computer. The ultimate goal being to use this system to do certain calculations that are beyond the means of even the most powerful supercomputers.

Mass production

O’Brien, who is Australian, said that PsiQuantum is using technology first developed by the semiconductor industry to mass produce their chips right now. He said that integration will be key to the company’s success and using photonics to connect qubits using light is the way forward. He described the system as a hybrid of photonic and electrical components and said that it will have to be cooled to cryogenic temperatures because of its superconducting photon detectors.

He suggested that the system will be up and running in a little over three years – which seems very soon to me! Incidentally, it took about three years to build the skyscraper (22 Bishopsgate) in which O’Brien spoke.

Echoing O’Brien’s assertion that millions of physical qubits are needed to create the 1000s of qubits required to do useful calculations was Oded Melamed, who is CEO of Quantum Source. The Israel-based company is designing a quantum computing system that integrates atomic qubits – which Melamed said are entangled easily – with photonic qubits, which are much more easy to connect up. The atomic qubits comprise rubidium atoms, which are stored in small vacuum cells and coaxed out individually to interact with photons in optical resonators.

Quantum Source is a much newer company than PsiQuantum, which was founded in 2015. The Israeli company came into being in 2021 with $27 million in seed funding.

Quantum factories

Melamed referred to large, integrated implementations of millions of qubits as “quantum factories”. They would be huge – possibly the size of a football pitch. When you connect millions of logical elements – quantum or otherwise – together, it will be possible to do calculations. However, a debate I can see looming on the horizon is whether calculations done at such facilities are actually quantum rather than classical.

Error correction is required because the quantum nature of most types of qubit is very quickly degraded and destroyed in a process called decoherence. A big problem with current error-correction schemes is that they use a very large number of physical (real) qubits to create one logical (virtual and useful) qubit. Today, that ratio is greater than 1000 to one. When you consider that useful quantum calculations (those that far outperform conventional computers) will require thousands of logical qubits, a quantum computer that uses error correction would need millions of physical qubits – as O’Brien and Melamed pointed out.

But what if the number of physical qubits could be reduced significantly? That was at hinted by the physicist Peter Knight, who advises the UK government on all matters quantum. He told the conference that great strides have been taken in the development of error correction schemes that are less demanding in terms of physical qubits. However, he also pointed out that it is possible that the effects of some types of noise – the absorption of cosmic rays, for example – may always plague quantum computers. This is one reason why the UK government is looking at expanding the Boulby Underground Laboratory – to provide low cosmic-ray background facility for developing quantum devices. And, maybe even running a quantum computer more than 1 km under the North Sea.

Keeping an eye on quantum

Many of the delegates that I spoke to at the conference did not work for quantum-technology companies – but rather work for large companies such as Nestlé and Johnson & Johnson. These people are charged with understanding what quantum computers could do for their companies in the future.

Indeed, many of these companies have gone beyond the observing phase and are actively engaging with quantum technologies. I attended a fascinating talk by the physicist Lene Oddershede of Denmark’s Novo Nordisk Foundation – which (amongst other things) is the majority voting shareholder in the pharmaceutical giant Novo Nordisk. She said that the foundation is three years into its “quantum mission” to support the development of quantum simulations of natural systems and quantum sensors for biomedical applications. To this end, the for-profit foundation has created a company called Quantum Foundry Copenhagen with the sole function of protecting the intellectual property developed during the quantum mission. She said that because of Danish law, universities would not be able to protect this IP.

What bad actors could do with quantum technologies is a concern of Matija Matokovic, who is deputy head of innovation at NATO. He described quantum technologies as disruptive and emerging technologies with the potential to change the nature of security. He also pointed out the strategic importance for countries to develop and nurture quantum technology companies that are developing strategically important technologies.

Few physicists

Oddershede, Knight and O’Brien are all physicists – and that put them a distinct minority at the conference. I spent some time at the Institute of Physics’ exhibition stand chatting with delegates (the IOP publishes Physics World). The first question I normally asked was “are you a physicist?” and the answer was almost always “no”. That came as no surprise because the focus of the conference was commercialization.

Many of the talks that I attended were not given by physicists (or other technical experts), but rather by start-up CEOs, who are often serial tech entrepreneurs. While I cannot claim to be an expert in quantum computing, I did find it much easier to follow talks at the conference that were given by technical experts. And, the presentations that I struggled with the most tended to be discussions about the future benefits of quantum computing.

One puzzling example – and I will give a general description because I don’t want to cast aspersions on the speakers, whom I believe were sincere – was a fireside chat between the representative of quantum computing company and one of its customers. The customer was talking about the success that they had in showing that a quantum algorithm could be used to solve a business-related problem. But, it wasn’t clear whether this quantum algorithm was run on a quantum processor or on a conventional computer that was simulating a quantum computer. To me, this is an important distinction that may have been lost on non-technical audience members.

While most of the focus of the conference was on quantum computing, there was much said about quantum sensors – which are often much more mature technologies than quantum processors. I watched a fascinating presentation by Margot Taylor, who is director of functional neuroimaging at Toronto’s Hospital for Sick Children and David Woolger, who is CEO of UK-based Cerca Magnetics. Cerca makes a brain scanner that uses quantum sensors and Taylor described how she is using it to study cognitive development in children.

Avoiding hype

While the science, engineering and business strategies of the future discussed at the conference were fascinating, it was easy to get swept away by the hype – something that speakers including Peter Knight warned against.

However, there were also some real success stories. My favourite comes from Cerca’s David Woolger, who pointed out that his company was formed in 2020, and has been in profit ever since.

Could the answer to the Antikythera astronomical device emerge from a Manhattan basement?

“You can’t understand it unless you build it yourself,” says Michael Dubno, a scientist, inventor and explorer. He’s talking to me in the richly equipped basement workshop of his Manhattan townhouse, standing in front of a long table, crammed with partly built mechanical devices to replicate the relative positions of astronomical objects.

By “it”, Dubno is referring to the Antikythera, an ancient device whose fragments were found by sponge divers in 1901 in a sunken ship near the Greek island of that name. Over the next few decades, archaeologists figured out that the object was a sophisticated ancient Greek instrument to predict the movement of astronomical bodies – and that it dates from around the 2nd or 3rd century BCE.

The device radically changes what historians thought of the astronomical, mathematical and engineering capabilities of ancient Greece

Historians of technology are still shocked by the Antikythera. Though encrusted, degraded and with only 30 of its supposed 60 gears discovered, nothing remotely as complicated has ever been found dating from anywhere near that time. The device radically changes what historians thought of the astronomical, mathematical and engineering capabilities of ancient Greece.

Other mysteries include how the Antikythera works. Its gears evidently drove a pointer around a moveable calendar ring, allowing ancient Greeks four millennia ago to predict the motions of the Sun, Moon and five planets. But it’s unclear what the remaining gears were or how they worked.

Such mysteries have enveloped the Antikythera with mystique. In fact, it appears as the McGuffin – the central but meaningless plot device – of the 2023 adventure film Indiana Jones and the Dial of Destiny. The movie’s villains are looking for the Antikythera because its supposed time-travelling properties would give them unlimited powers.

The movie’s hero is an archaeologist (played by Harrison Ford) who, reluctantly, joins a team of people seeking to keep the Antikythera from the villains. He’s initially dismissive, calling it “an ancient hunk of gears”. But he recovers the missing parts of the device, is kidnapped and taken through a time fissure back to Archimedes’ time, defeats the villains, and, reluctantly, returns.

Hunk of gears

That hunk of gears attracted Dubno.

A Brooklyn-born New Yorker, he attended the Bronx High School of Science, which is famous for producing seven Nobel-prize winners. Dubno entered Rensselaer Polytechnic Institute but dropped out to start a software company. He then built a robot, advanced for the time, that navigated around with GPS-like and sonar sensors.

Michael Dubno in his workshop.
Trial and error Michael Dubno is learning more about the Antikythera by trying to reproduce it in his workshop. (Courtesy: Robert P Crease)

Dubno also pioneered risk programming and financial analysis for the investment banking company Goldman Sachs, becoming its chief technology officer, and later worked for Bank of America. After quitting the finance world, Dubno led scientific expeditions to the North Pole, into the Mariana Trench and inside the Masaya Volcano.

But on my visit, he mainly wants to talk about the Antikythera, and the orreries that he is working on based on its gearing. Dubno is not alone in his fascination with this strange object, which numerous scientists and hobbyists have studied for over a century, developing theories and collecting data about its operation.

Dubno, however, came at it indirectly. About 15 years ago he bought a laser cutter/etcher and wondered what novel things he could do with it. “For the first time I was able to make gears quickly”, he says. “And I thought, ‘How hard could it be to make a model of the Antikythera?’”

He joined some like-minded people: Chris Budiselic, a machinist from Australia, Andrew Thoeni a professor of business and marketing at the University of North Florida, and Andrew Ramsey, an X-ray imaging scientist from Michigan. They soon ran into unexpected difficulties with their model.

One had to do with drag on the mechanism due to galling. “The Antikythera mechanism with the 30 known gears”, Dubno says, “already has enough drag in it that by the time you start adding the other gears to drive the planets there’s a good chance you can barely squeak out the performance.”

Oil doesn’t help; it increases surface tension. Jewelled bearings might do, but the Greeks almost certainly didn’t have them. Graphite seems to work, but it is unclear what the Greeks used. “You might have a theory of how it works, but it probably won’t work the way you think – you must build it.”

Another problem had to do with the Antikythera’s gears. They used triangular teeth, but such teeth quickly wear into a different shape, and Dubno had to figure how to cut those gears to replicate it.

Still another issue concerned the Antikythera’s moveable calendar ring, which used marks for days and a series of holes for adjustment. Researchers had assumed the lines and holes laid out an Egyptian solar calendar of 365 days. But after extensive calculations, Dubno and his team determined that the calendar ring was most likely based on 354 days, representing 12 lunar cycles.

They presented their findings in a research paper in the Horological Journal (2020) that has recently been confirmed using different mathematical techniques (arxiv.org:2403.00040v1). This discovery suggests the need for historians to revise their understanding of calendars in ancient Egypt.

Dubno is still shocked by the confidence of the Antikythera’s makers. “We don’t see any corrections”, he confides. “That means whoever built it knew what they wanted to do and didn’t see the need to change it when finished. That means there must have been previous prototypes. Where are they?”

The critical point

Historians can make surprising discoveries by doing things the way the ancients say they did. An example concerns Galileo’s observation that, when two bodies of different masses are dropped, the light one first moves ahead before the heavy one catches up. Some historians therefore concluded that Galileo was a poor observer, because “everyone knows” that all bodies fall at the same rate.

But in the 1980s the late science historian Thomas Settle repeated Galileo’s experiments exactly as he had written – and was startled to observe exactly what Galileo said. Further investigation found that the hand holding the heavy object becomes slightly fatigued, making the release slightly slower, though the heavy body soon catches up due to air resistance.

The finding about the Antikythera’s calendar would not have come to light without rebuilding the device. As Dubno point outs in his team’s paper about their work, doing so demonstrates the value of rebuilding other ancient mechanisms and instruments with the original skills. This would not only help reveal true and false interpretations, but also “assist in properly illuminating the reality embodied in an ancient device”.

As for the full purpose of the Antikythera and its makers, the mystery continues.

The Kavli Prize in Astrophysics: meet the 2024 laureates David Charbonneau and Sara Seager

This episode features a wide-ranging interview with Sara Seager and David Charbonneau, who share the 2024 Kavli Prize in Astrophysics. Charbonneau is at Harvard University and Seager is at the Massachusetts Institute of Technology, and they won the prize for their discoveries of exoplanets and the characterization of their atmospheres.

Exoplanets are planets that orbit stars other than the Sun. Astronomers have confirmed the existence of more than 5000 exoplanets, and that number keeps increasing.

In this podcast, the two laureates talk about the astonishing range of exoplanets that have been observed and explain how astronomers study the atmospheres of these faint and distant objects. Seager and Charbonneau also talk about the search for biosignatures of life on distant exoplanets and look to the future of exoplanet astronomy.

This podcast is sponsored by The Kavli Prize.

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