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MRI shows potential for verification of proton beam range

Proton beam visualization using MRI — **Seeing the proton beam** Top row: relative dose distribution in a water phantom for 200, 207 and 215 MeV proton beams at 32 nA, as measured by radiochromic film. Middle row: MR images showing the residual beam range as a function of beam energy at 32 nA. Bottom row: MRIs showing the beam signal intensity as a function of beam current at 207 MeV. (Courtesy: S Gantz *et al* PNAS 10.1073/pnas.2301160120)

Proton therapy is an advanced cancer treatment technique that offers a significant advantage over conventional photon-based radiotherapy: protons have a finite range at which they deposit the majority of their dose, thus sparing healthy tissues located near the tumour. Accurate targeting, however, is essential to fully exploit the dose conformality of proton beams. And currently, there’s no imaging technique available that can provide real-time beam range monitoring for routine clinical use during proton therapy.

As a result, proton treatments employ safety margins around the tumour to account for uncertainties caused by morphological changes along the beam path and to ensure adequate target coverage. Unfortunately, such margins (commonly 2.5–3.5% of the nominal range plus 1–3 mm) compromise the potentially high dose conformality.

One approach proposed to address this dilemma and improve targeting accuracy in treatments of moving tumours is the use of MRI guidance – as implemented for photons with hybrid MR-linac technology. With this aim, a research team at OncoRay and HZDR has successfully integrated a low-field open MR scanner into a proton research beam line.

Aswin Hoffmann and his team have now used this research system to demonstrate that online MRI can visualize the proton beam and reveal its range during irradiation of liquid-filled phantoms. They report their findings in Proceedings of the National Academy of Sciences.

Seeing the beam

The set-up at OncoRay comprises an open 0.22 T MR scanner, radio-frequency-shielded by a Faraday cage and installed in the path of a horizontal proton research beam line. For this latest study, the researchers placed a 10 × 10 × 6.5 cm polyethylene box filled with tap water centrally in the MRI receiver coil. They then irradiated the phantom using proton beam energies of 200, 207 and 215 MeV (at a beam current of 32 nA) and currents of 8, 16, 32 and 64 nA (at 207 MeV).

During each irradiation, the researchers performed time-of-flight angiography MRI, acquiring images for 5 s, starting 15 s after the start of irradiation. They observed energy- and current-dependent proton beam signatures that resembled the shape of the dose distribution measured using radiochromic film.

With increasing beam energy, the range (seen as a hypointense signal on the MR image) was increasingly displaced along the beam direction. The measured range shifts relative to the 200 MeV beam – 1.6 and 3.4 cm, for 207 and 215 MeV beam energies, respectively – agreed with calculated range values to within 2 mm. The intensity of the signature decreased with decreasing beam current and faded out below 8 nA.

The researchers note that the MRI contrast mechanism underlying these observations is not yet fully understood. However, they suggest that as similar signatures are found in other liquids, but not in flow-restricted water phantoms or gels, the effect may be due to convection arising from radiation-induced local heating and thermal expansion of the water.

QA and beyond

The imaging technique could find immediate application for geometric quality assurance in MR-integrated proton therapy systems currently under development. Further ahead, it may be possible to use MRI to provide real-time feedback on the beam range and energy deposition during proton therapy, although the method has so far only proven feasible in liquids and is likely not transferable to patients in its current form.

One step closer to real-time MR imaging in proton therapy

“Therefore, our research group is continuing to unravel the underlying MRI contrast mechanisms behind these observations, in order to ideally design a novel MRI sequence that would allow MRI-based in vivo proton range verification,” explains first author Sebastian Gantz. Such a scheme could provide an alternative to proton range monitoring approaches based on ionoacoustics or detection of secondary radiation.

“While both ionoacoustics and prompt gamma detection are indirect methods capable of detecting the proton beam end-of-range, the appeal of the MRI-based method is that we are able to visualize the proton beam in 2D,” Gantz tells Physics World. “Potentially, in the future, we can use one imaging modality, in-beam MRI, to concurrently visualize both the beam and the patient anatomy.”

Tiny levitating spheres could join the hunt for dark matter

Physicists in China want to widen the search for dark matter using a minuscule levitating oscillator. By tuning the resonant frequency of their sensor across three orders of magnitude, they say they should be able to place new lower limits on the interaction strength of putative low-mass dark matter with an equally large range of masses. However, they have still to show that they can screen out all possible sources of noise.

Scientists inferred the presence of dark matter in the universe decades ago, having observed that stars far from the centre of galaxies rotate more quickly than expected. Despite much effort in the meantime, however, researchers have still to detect any dark matter directly. The leading candidate for many years has been weakly interacting massive particles (WIMPs), which weigh 10¹⁰–10¹²eV/c² and tie in with supersymmetry theory. But multiple searches at the Large Hadron Collider at CERN and at dedicated underground facilities have so far drawn a blank.

At the same time, researchers have stepped up the hunt for much lighter particles. Most prominent among these is the axion, a spin-0 boson with a mass somewhere between 10^-6and 10^-3eV/c² that was originally proposed to resolve a quandary with the strong nuclear force. But beyond this lies a zoo of hypothetical “axion-like particles” (ALPs), which, unlike axions themselves, can in principle take on any of a vast range of masses and interaction strengths.

Coherent waves

Searching for these particles using mechanical oscillators relies on the fact that such low-mass and therefore abundant entities would behave as coherent waves. As the Earth passes through the cloud of dark matter thought to envelop the Milky Way, the wavelike nature of ALPs would lead to a periodic variation in the motion of a suitably sensitive oscillator. The size of the effect would be proportional to the number of neutrons in the detector and a specific but unknown coupling strength, while the oscillation frequency would be proportional to the ALP mass. Any variation at some specific frequency that couldn’t be explained by more humdrum noise sources might therefore indicate the presence of dark matter.

Researchers have looked for such modulations using France’s MICROSCOPE space mission and experiments on the ground. In one ground-based experiment, Eric Adelberger and colleagues at the University of Washington in the US monitored the movement of a rotating torsion balance. Obtaining a null result after analysing nearly seven years of data, in 2019 they were able to impose strict new limits on interaction strengths of about 10^-9–10^-4Hz. This corresponds to particle masses of 10^-23–10^-18eV/c².

In the latest work, Jiangfeng Du at the University of Science and Technology of China in Hefei and colleagues in Hefei and Nanjing instead turn their attention to a magnetically levitated oscillator. A discovery in this case would come in the form of an enhanced vertical oscillation at some particular frequency beyond that expected from straightforward thermal vibrations.

Two tiny spheres

The oscillator – which has yet to be built – would consist of two tiny levitating spheres joined by a thin vertical glass rod. The uppermost sphere, a diamagnet measuring 1 mm across, would be held inside a ring of magnets. The lower one, a paramagnet with a radius of only 11 μm, would be suspended just above a smaller set of magnets (see figure). As the connected spheres move up and down their motion would be monitored by measuring the scattering of a laser beam from the upper sphere.

Du and colleagues say that the sensitivity of the oscillator could be enhanced by varying its resonant frequency. The idea is to move the lower magnet up and down, so varying the distance between it and the lower sphere. Smaller distances would mean higher magnetic gradients, which in turn would yield lower resonant frequencies. In this way they could probe frequencies of 0.1–100 Hz.

The researchers explain that experiments would involve monitoring the oscillator’s motion continuously for just over a day at a time, scanning its resonant frequency across the range as they do so. By repeating this process about 100 times, they calculate that they should be able to push down the upper limit on ALP coupling strength for masses of 10^-16–10^-13eV/c² by at least an order of magnitude compared to previous results.

Minimizing noise

This would involve cutting out various noise sources. It would limit unwanted vibrations through a multi-stage suspension system and minimize thermal noise by operating at just 30 mK. It would also reduce measurement noise in the form of detector imperfections and laser pressure fluctuations. The researchers acknowledge that the suspension system cannot filter out seismic waves, tidal forces and other low-frequency interference, but they are looking to deal with this by making better use of active vibrations to cancel out noise.

What is more, they say it should be possible to extend the search for ALPs by employing a sensor array – enhancing the sensitivity by at least the square root of the number of detectors.

David Moore of Yale University in the US is enthusiastic about the new research, describing it as “a nice proposal” for using mechanical sensors to hunt for dark matter. But he emphasizes just how hard it can be to eliminate noise, having himself had to battle with the tiniest of vibrations when searching for dark matter using a minuscule mass levitated optically. “Some of the background events arose from just having people in the room talking,” he recalls.

The research is described in Chinese Physics Letters.

Wireless ultrasound monitor is ready for a workout

Researchers in the US have designed an ultrasound transducer that transmits information wirelessly and can be worn comfortably on the skin, overcoming two major shortcomings of previous devices. Developed by Muyang Lin, Sheng Xu and colleagues at the University of California San Diego (UCSD), the new transducer could be used to monitor patients with serious cardiovascular conditions, as well as to help athletes keep track of their training.

Ultrasound transducers work by transmitting high-frequency sound waves into the body, then detecting the waves reflected from tissues that have different densities and acoustic properties. Over the past several decades, improvements to probe and circuit designs, combined with better algorithms for processing ultrasound signals, have produced transducers that can conform to the folds of a person’s skin. This has allowed the devices to measure ultrasound signals continuously, which is especially useful for monitoring the pulsing of veins and arteries.

Researchers in Xu’s lab had previously developed wearable ultrasound probes that could monitor several physiological parameters of deep tissues, including blood pressure, blood flow and even cardiac imaging. Even so, the technology had some shortcomings. “These wearable probes are all wired to a bulky machine for power and data collection, and will shift in relative position during human motion, making them lose track of targets,” explains Lin, a PhD student in nanoengineering at UCSD and lead author of a paper in Nature Biotechnology on the device.

Because of these flaws, previous continuous ultrasound sensors could seriously inhibit a wearer’s mobility. They also required frequent readjustments as wearers moved around.

Ultrasound untethered

To address these problems, the UCSD team developed a new device based on a miniaturized, flexible control circuit that interfaces with an array of transducers. This device collects the ultrasound signals but does not process them directly. Instead, it relays them wirelessly to a computer or smartphone, which processes them using machine learning.

“We developed an algorithm to automatically analyse the signal and select the channel that has the best signal on moving target tissue,” Lin explains. “Therefore, the signals from the target tissue are continuous, even during human motion.”

The researchers tested this capability by using the device to track the position of a human subject’s carotid artery while monitoring the pulsation of blood within. This artery supplies blood to the head and neck, so they trained the algorithm to recognize displacements caused by different motions of the subject’s head.

Although the team only trained the algorithm on a single subject, a further advanced adaptation algorithm allowed new wearers to use the sensor with minimal retraining. Once trained, the device could detect ultrasound signals of the carotid artery’s pulsation as deep as 164 mm beneath the skin, even when the wearer was exercising.

Multi-use monitor

Xu and colleagues originally intended to test the sensor’s capabilities as a blood pressure monitor. Through their experiments, however, they discovered it could also monitor other important parameters, including arterial stiffness, the volume of blood pumped out by the heart and the amount of air exhaled by the wearer.

Ultimately, the researchers predict their design could open up a wide range of possibilities for continuous ultrasound monitoring. “By using wearable ultrasound technology, we can untether the patient from bulky machines and automate the ultrasonic examinations,” Lin says. “Deep tissue physiology can be monitored in motion, which provides unprecedented opportunities for medical ultrasonography and exercise physiology.”

These capabilities could be life-changing for patients living with cardiovascular conditions, Lin says. “For at-risk populations, abnormal values of blood pressure and cardiac output at rest or during exercise are hallmarks of heart failure,” he explains. But the applications don’t end there. “For a healthy population, our device can measure cardiovascular responses to exercise in real-time. Thus, it can provide insights into the actual workout intensity exerted by each person, which can guide the formulation of personalized training plans.”

Thrown away: what is the real impact of our waste?

Up to 7% of the world’s gold reserves may currently be contained in old electronic devices left in cupboards “just in case” those gadgets may one day be needed again.

And it’s not just gold stowed away. One tonne of electronic waste can contain 50 times more copper than a tonne of copper ore. There’s also iron, aluminium and several rare earth elements in those devices too. Yet only 17.4% of electronic waste is being recycled – and nobody seems to know what’s happened to the rest.

I learnt these facts in Wasteland: the Dirty Truth About What We Throw Away, Where It Goes, and Why It Matters by journalist Oliver Franklin-Wallis, an engrossing book that educates the reader on what actually happens to the things we throw away.

And why does that un-recycled electronic waste in our cupboards matter?

Wealthy countries have largely outsourced their waste problems to the global south

If metals are not recycled, then more will be dug up by the mining industry, which produces a staggering 100 billion tonnes of waste a year. Franklin-Wallis follows the story to Brumadinho in Brazil where, on 25 January 2019 a dam containing waste from an iron ore mine broke, releasing nearly twelve million cubic metres of toxic slurry and killing 272 people. In Wasteland, this disaster is presented to us in the context of a world where wealthy countries have largely outsourced their waste problems to the global south, and rarely confront the complexity of dealing with it all.

Franklin-Wallis highlights that our relationship with waste was reshaped by the emergence of plastic, meaning that now one third of what we throw away is less than a year old. The concept of the disposable society has also spread to the clothing-industry. He describes, for example, how a power station in Stockholm has switched from burning coal to burning clothing. The author also mentions the textile industry of Ghana, which has collapsed due to the enormous quantities of discarded clothes shipped there from Europe and America.

Wasteland does not hide from the difficulty of finding solutions to any of the problems discussed. But it does not offer an entirely negative message either. Despite many failures and the pernicious effects of greenwashing, we learn that recycling can work: 80% of the copper ever mined, for example, is still in circulation. However, Franklin-Wallis argues that the solution to our waste problem is, ultimately, simple: we should just buy less stuff!

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Graphene’s ‘cousin’ makes a switchable topological insulator

Germanene – a two-dimensional, graphene-like form of the element germanium – can carry electricity along its edges with no resistance. This unusual behaviour is characteristic of materials known as topological insulators, and the researchers who observed it say the phenomenon could be used to make faster and more energy-efficient electronic devices.

Like graphene, germanene is an atomically thin material with a honeycomb structure. Like graphene, germanene’s electronic band structure contains a point at which the valence and conduction bands meet. At this meeting point, spin-orbit coupling creates a narrow gap between the bands within the material’s bulk, causing it to act as an insulator. Along the material’s edges, however, special topological states arise that bridge this gap and allow electrons to flow unhindered.

Materials with this property – conducting electricity along their edges, while acting as insulators in their bulk – are called topological insulators. Since the edge-state electric current induces a transverse spin current, they are also known as quantum spin Hall systems by analogy with the better-known quantum Hall effect, in which strong magnetic fields induce electric current to flow along the edge of a semiconductor.

A new topological insulator emerges

In graphene, the quantum spin Hall effect is too weak to observe, but researchers led by Pantelis Bampoulis of the University of Twente in the Netherlands have now spotted it in germanene. To do this, they employed a variety of experimental and theoretical techniques, including low-temperature scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) as well as density functional theory and tight-binding calculations.

“With STM and STS, we could directly measure the electronic band structure of germanene and showed that it has a band gap in its interior and conductive states at its edges,” Bampoulis explains. “This means that it doesn’t conduct electricity in the middle, but does along its edges.”

Switching between states

The fact that germanene is slightly buckled, rather than completely flat like graphene, introduces a potentially useful property, Bampoulis adds. “In our study, we were also able to apply an electric field to our sample using the STM to change the topological state of germanene,” he tells Physics World. “When a critical field is reached, the topological band gap closes and the material becomes a topological semimetal. Beyond this field, a conventional band gap opens up and the topological edge states disappear – in other words, the germanene becomes a normal insulator.”

Because germanene transitions so readily between a perfect conductor and an insulator, the researchers say it could be used to make a novel type of field-effect transistor. In the “on” state of such a device, current would flow without energy loss along the topological edge states. The team also suggests that such edge states could be useful in quantum computing, where their robustness could make quantum devices more stable and resistant to errors.

The University of Twente researchers say they are now busy trying to increase the number of conductive channels and further tune the quantum state of germanene. “These efforts will involve fabricating germanene nanoribbons (thin, elongated strips) and implementing a twist in stacks of two germanene layers,” Bampoulis reveals.

The present work is detailed in Physical Review Letters.

Novel breathalyser rapidly tests for COVID-19

A new medical diagnostic tool based on the use of optical frequency comb technology can rapidly test for COVID-19 in exhaled breath. The technique, developed by researchers at JILA, the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, could also be used to diagnose other conditions or diseases, particularly those of respiratory, gastrointestinal or metabolic origin.

Being able to rapidly test for infection by viruses like SARS-CoV-2, the virus responsible for COVID-19, is crucial for fighting future pandemics. Testing exhaled human breath could come into its own here since each breath contains more than 1000 distinct molecules, some of which can indicate underlying medical conditions or infections. These molecules can be detected and identified by measuring their selective absorption of laser light at different optical frequencies.

In 2008 researchers led by Jun Ye of JILA demonstrated that frequency comb spectroscopy – a technique originally developed for optical atomic clocks and precision metrology – could potentially identify disease biomarkers in exhaled human breath. The technique, which essentially uses laser light to distinguish between different molecules, lacked sensitivity, however, and could not link specific molecules to disease states. They did not, therefore, test it to diagnose illnesses.

Parts-per-trillion level sensitivity

In 2021 Ye and colleagues improved the sensitivity of their technique by 1000 times, meaning that it could now detect certain biomolecules at the parts-per-trillion level. In their new study, detailed in the Journal of Breath Research, they applied supervised machine learning to process the light absorption patterns and make a direct connection to potential disease states without going through the intermediate step of identifying molecules first.

To test their method, the researchers collected breath samples from 170 individuals, half of whom had SARS-CoV-2 when tested using conventional PCR (polymerase chain reaction). They then piped the samples through a tube into their new breathalyser, which consists of optical frequency combs that generate mid-infrared laser light at tens of thousands and sometimes hundreds of thousands distinct optical frequencies. Using a pair of high-reflectivity mirrors, the frequency comb light multi-passes the breath gas samples around 4000 times so that the molecular absorption strengths are significantly enhanced.

The team then used machine learning algorithms to analyse the ultrasensitive absorption signals measured at around 15,000 frequencies to detect whether the subjects were infected or not. The study was verified by asking the machine to predict the COVID status of each individual and then comparing this to the results from their PCR test.

An alternative to PCR tests

The results from the new laser spectroscopy technique matched 85% of those from PCR, which is “excellent” according to medical diagnostic standards.

“The technique could be an alternative to PCR tests for COVID-19,” says study lead author Qizhong Liang. “The laser-based breath test is much faster at obtaining the result and in future systems we are implementing a real-time detection capability by asking people to breathe directly into our apparatus.”

The detection is also, of course, non-invasive – in contrast to the nasal swabs that we all have bad memories of from the pandemic. “It might thus encourage more people to get tested,” he says. “Another interesting note is that the breath sample remains intact after the test, allowing time-dependent studies on these samples if there is future interest.”

The JILA researchers will now be looking into the applicability of the technique to diagnose other conditions or diseases, particularly those of respiratory, gastrointestinal or metabolic origin. Indeed, they are setting up a collaboration with paediatricians to analyse the breath of asthmatic children. They also plan to reduce the dimensions of the instrument, which is currently metres in size.

“We have extended the spectral coverage of the method to allow for the detection of many more molecules,” Ye tells Physics World. “In this way, we can detect even more chemical information from breath and further improve diagnostic accuracy.”

‘More than Moore’ webinar explores the future of neuromorphic and quantum computing

Left to right: Steve Furber, Chaoran Huang, Bhavin Shastri, Renbao Liu

Last week I had the pleasure of moderating a webinar panel session that looked at the future of computer technology beyond the current era of ever shrinking silicon transistors as defined by Moore’s law.

Called “More than Moore”, the webinar featured three panellists working in neuromorphic computing, a field that seeks to create information processing systems that mimic the human brain. We were also joined by a physicist who believes that quantum computing will play a role in the information processing of the future.

The panellists were Steve Furber of the UK’s University of Manchester, who does research on neural systems engineering; Chaoran Huang of the The Chinese University of Hong Kong, who works on silicon photonics, photonic integrated circuits, and nonlinear optics; Bhavin Shastri at Canada’s Queen’s University, who designs and builds programmable nanophotonic processors; and Renbao Liu of the The Chinese University of Hong Kong, who works on quantum nonlinear spectroscopy.

Lively and fascinating

It was a lively and fascinating discussion and I learned a lot about both neuromorphic and quantum computing. You can watch the webinar free of charge, and I hope that you enjoy it as much as I did.

The podcast is sponsored by IOP Publishing, which also brings you Physics World.

Symmetry breaking in ‘galactic tetrahedrons’ linked to parity violation

Astronomers in the US have discovered an unexpected asymmetry in the relative positions of galaxies that are hundreds of millions of light-years apart. The phenomenon could be explained by a breaking of the symmetry of the laws of nature that is believed to have occurred shortly after the Big Bang. As a result, the observation could help explain why there appears to be much more matter than antimatter in the observable universe.

The discovery was made by analysing a database of over one million galaxies observed by the Baryon Oscillation Spectroscopic Survey (BOSS). The research was done by Jiamin Hou and Zachary Slepian at the University of Florida, and Robert Cahn at the Lawrence Berkeley National Laboratory in California, who found the unexpected pattern.

The observation is related to parity symmetry, which applies to the long-range electromagnetic and gravitational interactions in the Standard Model of particle physics. Parity requires that a physical system will behave the same way as its mirror image. Human hands, for example, are mirror images of each other but the laws of physics apply equally to right and left hands.

Parity violation

In the microscopic world, however, parity symmetry can be violated by the weak interaction and possibly by the strong interaction – which both act at very short distances.

The trio explored parity symmetry on a very large scale by drawing lines between quadruplets of galaxies that are separated by distances between 65 million and 500 million light-years. As they showed in a recent paper in Physical Review Letters, the tetrahedrons created by this exercise could then be analysed for evidence of parity violation.

Now, they report the result of such a study, which Slepian describes as a “huge surprise”.

The researchers defined right and left-handed galactic tetrahedrons based on how galaxies were connected to their closest and farthest partners. They found that there were significantly more galaxies with one type of handedness than the other.

Galactic tetrahedrons

“For any given galaxy distribution we assume that the clustering is invariant under rotation about any galaxy,” explains Slepian. “So, if I’m sitting in one galaxy, I should see that the pattern of clustering is on average the same wherever I rotate my head and look. Yet instead we see an excess of tetrahedra over their mirror images.”

Despite strength of the effect, the reason for this handedness remains a mystery. Gravity is the only known force that can act over the huge distances separating the galaxies, and it should not violate parity. Instead, Slepian says that the asymmetry, “must have been imprinted even earlier in the universe’s history when other forces were at play”.

This takes us all the way back to the period of cosmic inflation, which occurred about 10⁻³³s after the Big Bang. At this point the universe experienced a brief period of extremely rapid expansion. Physicists believe that quantum fluctuations during inflation have since expanded to become the large-scale structure of the universe. Therefore, any parity violation present during inflation could become imprinted in how galaxies are distributed in the universe 13.7 billion years later.

The origin of this parity violation remains unknown. “It could have been a new force, or a new particle, acting on a quantum scale at that time,” says Slepian.

Missing antimatter

This potential observation of parity violation in how galaxies are distributed is exciting news. As well as suggesting the existence of physics beyond the Standard Model, could also help solve another of physics’ deepest mysteries: why is there much more matter than antimatter in the universe.

The Standard Model predicts that equal amounts of matter and antimatter should have been formed in the Big Bang. Had that happened, matter and antimatter would have annihilated each other, leaving the universe with neither. Luckily for us there seems to have been an excess of matter left over – a phenomenon called baryogenesis.

It is possible that the mechanism that caused parity violation that led to this latest astronomical observation could also related to baryogenesis.

“There’s a range of mechanisms that can cause parity violation, all pretty speculative,” says Slepian. He cites hypothetical particles called axions, or one of the fundamental forces behaving differently in the high energies of the Big Bang. “While it’s not guaranteed that whatever mechanism is producing this parity violation in the galaxies could also explain baryogenesis, I think there certainly could be a relationship.”

While the existence of this galactic asymmetry has not been established beyond any doubt, the findings provide strong evidence for inflation and physics beyond the Standard Model. However, a systematic error in the data could be responsible for the observation. “I’ll feel a lot better once the same signal is seen in a different dataset taken by a different instrument with different software and different people,” says Slepian.

Slepian, Hou and Cahn are all members of the science team of the Dark Energy Spectroscopic Instrument (DESI) at Kitt Peak National Observatory. It will observe over 35 million galaxies, and the trio intend to use DESI to make further observations to confirm their findings.

The results are described in Monthly Notices of the Royal Astronomical Society.

Defect engineering for quantum memory chips

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Atomic-scale defects in crystals can make excellent quantum memories that can be written and read out using lasers, and could form the basis of future quantum communications and computing systems. Creating these defects “on demand” and engineering memory chips with arrays of defects is very challenging.

In this webinar, Jason Smith will talk about the methods used, the current state of the art, and what we are learning along the way.

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Jason Smith is professor of photonic materials and devices at the University of Oxford, and founding editor-in-chief of the new IOP Publishing journal Materials for Quantum Technology. His research focuses on engineering materials and devices in which photons and electrons communicate in controlled ways, as a means to develop new technologies in sensing, communications and computing.

Boron arsenide single crystals with ultrahigh thermal conductivity and carrier mobility

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Semiconductors are the most important part of modern electronics. A good semiconductor should have the right band gap, high carrier mobility in both electrons and holes, and high thermal conductivity, but the semiconductors currently available do not meet the requirements. Boron arsenide (BAs) seems to be the ideal semiconductor. It has a bandgap of ~2.1 eV, carrier mobility above 1400 cm² s^-1 V^-1for both the electrons and holes, isotropic thermal conductivity higher than 1300 W m^-1 K^-1 at room temperature.

In this webinar, the speaker, Zhifeng Ren, will present on what has been done and what is expected for this special material.

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Zhifeng Ren is a M D Anderson Chair Professor in the Department of Physics at the University of Houston, and director of the Texas Center for Superconductivity at the University of Houston (TcSUH). He obtained his PhD from the Institute of Physics of the Chinese Academy of Sciences in China in 1990. He was a postdoctoral fellow and research faculty member at SUNY Buffalo (1990–1999) before joining Boston College as an associate professor in 1999. He specializes in fields such as nanostructured thermoelectric materials, non-noble-metal catalysts for water electrolysis, novel semiconductor boron arsenide single crystals with ultrahigh thermal conductivity and carrier mobility, sodium nanofluid for enhanced oil recovery and cleaning, superconductor levitated super system for energy transport and storage and people/goods transport.

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