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A broad systematic review has revealed that quantum computing applications in health care remain more theoretical than practical, despite growing excitement in the field.

The comprehensive study published in npj Digital Medicine, which analyzed 4,915 research papers published between 2015 and 2024, found little evidence that quantum machine learning (QML) algorithms currently offer any meaningful advantage over classical computing methods for health care applications.

“Despite exponential growth in research claiming quantum benefits for health care, our analysis shows no consistent evidence that quantum algorithms outperform classical methods for clinical decision-making or health service delivery,” said Dr. Riddhi Gupta from the School of Mathematics and Physics and the Queensland Digital Health Center (QDHeC) at the University of Queensland.

The review identified several critical gaps in current research approaches:

• Only 16 of 169 eligible studies actually tested their algorithms under realistic quantum hardware conditions, with most relying solely on idealized simulations
• Most research failed to address critical factors like noise characterization, error mitigation, or performance scaling as problem size increases
• Applications were narrowly focused on clinical diagnosis and prediction, with minimal exploration of health service delivery or public health applications
• Data encoding scalability remains problematic, often requiring hardware assumptions that don’t exist in current quantum systems

Dr. Gupta said that while quantum computing holds tremendous theoretical promise for health care, this review provides an important reality check on the current state of the technology.

“The field needs to address these methodological challenges before quantum methods can deliver meaningful advantages in health data processing,” she said.

The researchers propose new standards for evaluating quantum computing applications in health care, including minimum requirements for demonstrating scalability and performance under realistic conditions.

QDHeC’s Deputy Director, Professor Jason Pole, said that this study confirms that while quantum technology is promising, it is not going to change health care next week.

“Decision makers get understandably excited when we talk about the possibilities of quantum computing in health care, but Dr. Gupta’s study affirms that we still have a lot of work to do before we can apply this technology in a useful and strategic way.”

Senior author of the study, Associate Professor Sally Shrapnel who leads the QDHeC Quantum Program and is Deputy Director of the Australian Research Council’s Center of Excellence for Engineered Quantum Systems (EQUS) says that despite these challenges, researchers are optimistic about the future of quantum computing in health care.

“This review captures the current state of play, but the field is advancing rapidly with impressive progress from both universities and companies,” she said.

“I have no doubt we will see exciting quantum applications in digital health care in the future.”

In recent years, many physicists and material scientists have been studying superconductors, materials that can conduct direct current electricity without energy loss when cooled under a particular temperature. These materials could have numerous valuable applications, for instance generating energy for imaging machines (e.g., MRI scanners), trains, and other technological systems.

Researchers at Fudan University, Shanghai Qi Zhi Institute, Hong Kong University of Science and Technology, and other institutes in China have recently uncovered a new mechanism to generate anisotropically-enhanced in-plane upper critical field in atomically thin centrosymmetric superconductors with topological band inversions. Their paper, published in Nature Physics, specifically demonstrated this mechanism on a thin layer of 2M-WS₂, a material that has recently attracted much research attention.

“In 2020, a paper by our theoretical collaborator Prof. K.T. Law proposed that 2D centrosymmetric superconductors with a topological band inversion, such as 1T′-WTe₂ exhibit a distinct type of superconductivity, called spin-orbit-parity coupled (SOPC) superconductivity,” Enze Zhang, one of the researchers who carried out the study, told Phys.org.

“SOPC is predicted to produce novel superconductivity near the topological band crossing with both largely enhanced and anisotropic spin susceptibility with respect to in-plane magnetic field directions. At that time, we were conducting research on the superconducting properties of atomically thin 2M-WS₂, so after talking with Prof. K.T. Law, we felt that the emergent van der Waals superconductor 2M-WS₂ would most likely be a promising candidate for spin-orbit-parity coupled superconductivity.”

The structure of monolayer 2M-WS₂ is identical to that of 1T′-WTe₂, the material previously investigated by Prof. Law and his team. 2M-WS₂, however, has a unique stacking mode, which distinguishes it from other transition metal dichalcogenides.

The researchers previously found that in its bulk form, this material exhibit a high superconducting transition temperature T_C of 8.8 K. In addition, theoretical calculations suggested that atomically thin layers of 2M-WS₂ hold topological edge states with band inversion.

In their experiments, Zhang and his colleagues measured the in-plane upper critical field at a high magnetic field and confirmed the violation of the Pauli limit law. They also observed a strongly anisotropic two-fold symmetry in the material, in response to the in-plane magnetic field direction.

“Tunneling experiments conducted under high in-plane magnetic fields also showed that the superconducting gap in atomically thin 2M-WS₂ possesses an anisotropic magnetic response along different in-plane magnetic field directions, and it persists much above the Pauli limit,” Zhang explained. “Using self-consistent mean-field calculations, our theoretical collaborators conclude that these unusual behaviors originate from the strong spin-orbit-parity coupling arising from the topological band inversion in 2M-WS₂.”

The researchers’ experiments spanned across several steps. Firstly, the team performed magneto-transport measurements on atomically thin 2M-WS₂ and found that its in-plane upper critical field is not only far beyond the Pauli paramagnetic limit, but also exhibits a strongly anisotropic two-fold symmetry in response to the in-plane magnetic field direction.

Subsequently, they used tunneling spectroscopy to collect measurements under high in-plane magnetic fields. These measurements revealed that the superconducting gap in atomically thin 2M-WS₂ possesses an anisotropic magnetic response along different in-plane magnetic field directions, which persists much above the Pauli limit.

Finally, the researchers performed a series of self-consistent mean-field calculations to better understand the origin of the unusual behaviors they observed in their sample. Based on their results, they concluded that these behaviors originate from the strong spin-orbit-parity coupling arising from the topological band inversion in 2M-WS₂, which effectively pins the spin of states near the topological band crossing and renormalizes the effect of external Zeeman fields anisotropically.

“We uncovered a new mechanism for generating an anisotropically-enhanced in-plane upper critical field in atomically thin centrosymmetric superconductors with topological band inversions, highlighting 2D 2M-WS₂ as a wonderful platform for the study of exotic superconducting phenomena such as higher-order topological superconductivity and further device applications,” Zhang said.

“The novel properties found here are highly nontrivial as they directly reflect a strong SOPC inheriting from the topological band inversion in the normal state of 2M-WS₂, which had been ignored for many years in previous studies of centrosymmetric superconductors.”

In recent years, more research teams worldwide have been exploring the properties and mechanisms of centrosymmetric superconducting transition metal dichalcogenides (TMDs), such as monolayer superconducting 1T′-MoS₂, and 1T′-WTe₂, due to the characteristic co-existence of topological band structure and superconductivity within them.

The recent paper by Zhang and his colleagues could pave the way towards the exploration of large enhanced and strongly anisotropic in-plane upper critical fields, which could further improve the current understanding of these materials’ exotic physics.

“We now plan to explore the usual superconducting properties (such as the in-plane upper critical field and tunneling spectroscopy behavior at high magnetic field) of more atomically thin centrosymmetric superconductors with topological band inversions,” Zhang added.

More information: Enze Zhang et al, Spin–orbit–parity coupled superconductivity in atomically thin 2M-WS2, Nature Physics (2022). DOI: 10.1038/s41567-022-01812-8

Ying-Ming Xie et al, Spin-Orbit-Parity-Coupled Superconductivity in Topological Monolayer WTe2, Physical Review Letters (2020). DOI: 10.1103/PhysRevLett.125.107001

Journal information: Physical Review Letters  , Nature Physics 

© 2022 Science X Network

In the current issue of Nature Photonics, Prof. Dr. Oliver G. Schmidt, Dr. Libo Ma and partners present a strategy for observing and manipulating the optical Berry phase in Möbius ring microcavities. In their research paper, they discuss how an optical Berry phase can be generated and measured in dielectric Möbius rings. Furthermore, they present the first experimental proof of the existence of a variable Berry phase for linearly or elliptically polarized resonant light.

A Möbius strip is a fascinating object. You can easily create a Möbius strip when twisting the two ends of a strip of paper by 180 degrees and connecting them together. Upon closer inspection, you realize that this ribbon has only one surface that cannot be distinguished between inside and outside or below and above. Because of this special topological property, the Möbius strip has become an object of countless mathematical discourses, artistic representations and practical applications, for example, in paintings by M.C. Escher, as a wedding ring, or as a drive belt to wear both sides of the belt equally.

Optical ring resonators

Closed bands or rings also play an important role in optics and optoelectronics. Until now, however, they have not consisted of Möbius strips and they are not made of paper, but are made of optical materials, for example, silicon and silicon dioxide or polymers. These “normal” rings are also not centimeters in size, but micrometers. If light with a certain wavelength propagates in a micro ring, constructive interference causes optical resonances to occurs. This principle can be exemplified by a guitar string, which produces different tones at different lengths—the shorter the string, the shorter the wavelength, and the higher the tone.

An optical resonance or constructive interference occurs exactly when the circumference of the ring is a multiple of the wavelength of the light. In these cases the light resonates in the ring and the ring is called an optical ring resonator. In contrast, the light is strongly attenuated and destructive interference occurs when the circumference of the ring is an odd multiple of half the wavelength of the light. Thus, an optical ring resonator enhances light of certain wavelengths and strongly attenuates light of other wavelengths that do not “fit” in the ring. In technological terms, the ring resonator acts as an optical filter that, integrated on a photonic chip, can selectively “sort” and process light. Optical ring resonators are central elements of optical signal processing in today’s data communication networks.

How polarized light circulates in the Möbius strip

Besides the wavelength, polarization is an essential property of light. Light can be polarized in various ways, for example linearly or circularly. If light propagates in an optical ring resonator, the polarization of the light does not change and remains the same at every point in the ring.

The situation changes fundamentally if the optical ring resonator is replaced by a Möbius strip or better, a Möbius ring. To better understand this case, it helps to consider the detail of the geometry of the Möbius ring. The cross-section of a Möbius ring is typically a slender rectangle in which two edges are much longer than their two adjacent edges, such as in a thin strip of paper.

Let us now assume that linearly polarized light circulates in the Möbius ring. Because the polarization prefers to align itself in the direction of the long cross-sectional side of the Möbius ring, the polarization continuously rotates up to 180 degrees while passing completely around the Möbius ring. This is a huge difference to a “normal” ring resonator, in which the polarization of the light is always maintained.

And that’s not all. The twisting of the polarization causes a change in the phase of the light wave, so that the optical resonances no longer occur at full wavelength multiples that fit into the ring, but at odd multiples of half the wavelength. Part of the research group had already predicted this effect theoretically in 2013. This prediction, in turn, is based on work by physicist Michael Berry, who introduced the eponymous “Berry phase” in 1983, describing the change in the phase of light whose polarization changes as it propagates.

First experimental evidence

In the current article published in the journal Nature Photonics, the Berry phase of light circulating in a Möbius ring is experimentally revealed for the first time. For this purpose, two rings with the same diameter were made. The first is a “normal” ring and the second is a Möbius ring. And as predicted, the optical resonances in the Möbius ring appear at different wavelengths compared to the “normal” ring.

The experimental results, however, go much beyond previous predictions. For example, the linear polarization not only rotates, but also becomes increasingly elliptical. The resonances do not occur exactly at odd multiples of half the wavelength, but quite generally at non-integer multiples. To find out the reason for this deviation, Möbius rings with decreasing strip width were made. This study revealed that the degree of ellipticity in the polarization and the deviation of the resonance wavelength compared to the “normal” ring became progressively weaker as the Möbius strip became narrower and narrower.

This can be easily understood because the special topological properties of the Möbius ring merge into the properties of a “normal” ring when the width of the band decreases to that of its thickness. However, this also means that the Berry phase in Möbius rings can be easily controlled by simply changing the design of the band.

In addition to the fascinating new fundamental properties of optical Möbius rings, new technological applications are also opening up. The tunable optical Berry phase in Möbius rings could serve for all-optical data processing of classical bits as well as qubits and support quantum logic gates in quantum computation and simulation.

More information: Jiawei Wang et al, Experimental observation of Berry phases in optical Möbius-strip microcavities, Nature Photonics (2022). DOI: 10.1038/s41566-022-01107-7

Journal information: Nature Photonics 

Provided by Chemnitz University of Technology

A team of physicists, biologists and engineers at Cornell University, in the U.S., has discovered some of the factors that lead to more or less spray when cutting onions and found a couple of ways to reduce the amount of eye irritation. The group has published a paper describing their study on the arXiv preprint server.

Prior research has shown that eye irritation when cutting onions is caused by the release of syn-propanethial-S-oxide into the air along with other juices in the onion. For this new study, the team in New York wanted to know what factors led to more or less of the juices being spewed into the air during slicing.

To find out, the research team outfitted a special guillotine that could be fitted with different types of blades. They also coated onion chunks with paint to allow for better viewing of the cutting process. They used the guillotine to cut samples, each of which was recorded. Trials varied knife size, sharpness and cutting speed. They even used an electron microscope to accurately measure the knives before use.

The videos revealed that the differences in the amount of spray released, and thus the amount of eye irritation, were due to the sharpness of the knife and the speed at which it cut the onion. The sharper the knife, and slower the cut, the less spray. This was because duller knives tended to push down on the onion, forcing its layers to bend inward—as the cut ensued, the layers sprang back, forcing juice out into the air.

They also noted that as the juice droplets were flung into the air, they tended to fragment into smaller drops, which allowed them to persist longer. Faster cutting also resulted in more juice generation, and thus more mist to irritate the eyes.

They conclude that onion cutters use the sharpest knife they can find and cut their onions slowly.

The ZEUS laser facility at the University of Michigan has roughly doubled the peak power of any other laser in the U.S. with its first official experiment at 2 petawatts (2 quadrillion watts).

At more than 100 times the global electricity power output, this huge power lasts only for the brief duration of its laser pulse—just 25 quintillionths of a second long.

“This milestone marks the beginning of experiments that move into unexplored territory for American high field science,” said Karl Krushelnick, director of the Gérard Mourou Center for Ultrafast Optical Science, which houses ZEUS.

Research at ZEUS will have applications in medicine, national security, materials science and astrophysics, in addition to plasma science and quantum physics. ZEUS is a user facility—meaning that research teams from all over the country and internationally can submit experiment proposals that go through an independent selection process.

“One of the great things about ZEUS is it’s not just one big laser hammer, but you can split the light into multiple beams,” said Franklin Dollar, professor of physics and astronomy at the University of California, Irvine, whose team is running the first user experiment at 2 petawatts.

“Having a national resource like this, which awards time to users whose experimental concepts are most promising for advancing scientific priorities, is really bringing high-intensity laser science back to the U.S.”

Dollar’s team and the ZEUS team aim to produce electron beams with energies equivalent to those made in particle accelerators that are hundreds of meters in length. This would be 5–10 times higher energy than any electron beams previously produced at the ZEUS facility.

“We aim to reach higher electron energies using two separate laser beams—one to form a guiding channel and the other to accelerate electrons through it,” said Anatoly Maksimchuk, U-M research scientist in electrical and computer engineering, who leads the development of the experimental areas.

They hope to do this in part with a redesigned target. They lengthened the cell that holds the gas that the laser pulse rams into, helium in this experiment. This interaction produces plasma, ripping electrons off the atoms so that the gas becomes a soup of free electrons and positively charged ions. Those electrons get accelerated behind the laser pulse-like wakesurfers close behind a speedboat—a phenomenon called wakefield acceleration.

Light moves slower through plasma, enabling the electrons to catch up to it. In a less dense, longer target, the electrons spend more time accelerating before they catch up to the laser pulse, enabling them to hit higher top speeds.

This demonstration of ZEUS’s power paves the way for the signature experiment, expected later this year, when the accelerated electrons will collide with laser pulses coming the opposite way. In the moving frame of the electrons, the 3-petawatt laser pulse will seem to be a million times more powerful—a zettawatt-scale pulse. This gives ZEUS its full name of “Zettawatt Equivalent Ultrashort laser pulse System.”

“The fundamental research done at the NSF ZEUS facility has many possible applications, including better imaging methods for soft tissues and advancing the technology used to treat cancer and other diseases,” said Vyacheslav Lukin, program director in the NSF Division of Physics, which oversees the ZEUS project.

“Scientists using the unique capabilities of ZEUS will expand the frontiers of human knowledge in new ways and provide new opportunities for American innovation and economic growth.”

The ZEUS facility fits in a space similar in size to a school gymnasium. At one corner of the room, a laser produces the initial infrared pulse. Optical devices called diffraction gratings stretch it out in time so that when the pump lasers dump power into the pulse, it doesn’t get so intense that it starts tearing the air apart. At its biggest, the pulse is 12 inches across and a few feet long.

After four rounds of pump lasers adding energy, the pulse enters the vacuum chambers. Another set of gratings flattens it to a 12-inch disk that is just 8 microns thick—about 10 times thinner than a piece of printer paper. Even at 12 inches across, its intensity could turn the air into plasma, but then it is focused down to 0.8 microns wide to deliver maximum intensity to the experiments.

“As a midscale-sized facility, we can operate more nimbly than large-scale facilities like particle accelerators or the National Ignition Facility,” said John Nees, U-M research scientist in electrical and computer engineering, who leads the ZEUS laser construction. “This openness attracts new ideas from a broader community of scientists.”

The road to 2 petawatts has been slow and careful. Just getting the pieces they need to assemble the system has been harder than expected. The biggest challenge is a sapphire crystal, infused with titanium atoms. Almost 7 inches in diameter, it is the critical component of the final amplifier of the system, which brings the laser pulse to full power.

“The crystal that we’re going to get in the summer will get us to 3 petawatts, and it took four and a half years to manufacture,” said Franko Bayer, project manager for ZEUS. “The size of the titanium sapphire crystal we have, there are only a few in the world.”

In the meantime, jumping from the 300 terawatt power of the previous HERCULES laser to just 1 petawatt on ZEUS resulted in worrying darkening of the gratings. First, they had to determine the cause: Were they permanently damaged or just darkened by carbon deposits from the powerful beam tearing up molecules floating in the imperfect vacuum chamber?

When it turned out to be carbon deposits, Nees and the laser team had to figure out how many laser shots could run safely between cleanings. If the gratings became too dark, they could distort the laser pulses in a way that damages optics further along the path.

Finally, the ZEUS team has already spent a total of 15 months running user experiments since the grand opening in October 2023 because there is still plenty of science that could be done with a 1 petawatt laser.

So far, it has welcomed 11 separate experiments with a total of 58 experimenters from 22 institutions, including international researchers. Over the next year—between user experiments—the ZEUS team will continue upgrading the system toward its full power.

My telescope, set up for astrophotography in my light-polluted San Diego backyard, was pointed at a galaxy unfathomably far from Earth. My wife, Cristina, walked up just as the first space photo streamed to my tablet. It sparkled on the screen in front of us.

“That’s the Pinwheel galaxy,” I said. The name is derived from its shape—albeit this pinwheel contains about a trillion stars.

The light from the Pinwheel traveled for 25 million years across the universe—about 150 quintillion miles—to get to my telescope.

My wife wondered: “Doesn’t light get tired during such a long journey?”

Her curiosity triggered a thought-provoking conversation about light. Ultimately, why doesn’t light wear out and lose energy over time?

Let’s talk about light

I am an astrophysicist, and one of the first things I learned in my studies is how light often behaves in ways that defy our intuitions.

Light is electromagnetic radiation: basically, an electric wave and a magnetic wave coupled together and traveling through space-time. It has no mass. That point is critical because the mass of an object, whether a speck of dust or a spaceship, limits the top speed it can travel through space.

But because light is massless, it’s able to reach the maximum speed limit in a vacuum—about 186,000 miles (300,000 kilometers) per second, or almost 6 trillion miles per year (9.6 trillion kilometers). Nothing traveling through space is faster. To put that into perspective: In the time it takes you to blink your eyes, a particle of light travels around the circumference of Earth more than twice.

As incredibly fast as that is, space is incredibly spread out. Light from the sun, which is 93 million miles (about 150 million kilometers) from Earth, takes just over eight minutes to reach us. In other words, the sunlight you see is eight minutes old.

Alpha Centauri, the nearest star to us after the sun, is 26 trillion miles away (about 41 trillion kilometers). So by the time you see it in the night sky, its light is just over four years old. Or, as astronomers say, it’s four light years away.

With those enormous distances in mind, consider Cristina’s question: How can light travel across the universe and not slowly lose energy?

Actually, some light does lose energy. This happens when it bounces off something, such as interstellar dust, and is scattered about.

But most light just goes and goes, without colliding with anything. This is almost always the case because space is mostly empty—nothingness. So there’s nothing in the way.

When light travels unimpeded, it loses no energy. It can maintain that 186,000-mile-per-second speed forever.

It’s about time
Here’s another concept: Picture yourself as an astronaut on board the International Space Station. You’re orbiting at 17,000 miles (about 27,000 kilometers) per hour. Compared with someone on Earth, your wristwatch will tick 0.01 seconds slower over one year.

That’s an example of time dilation—time moving at different speeds under different conditions. If you’re moving really fast, or close to a large gravitational field, your clock will tick more slowly than someone moving slower than you, or who is farther from a large gravitational field. To say it succinctly, time is relative.

Now consider that light is inextricably connected to time. Picture sitting on a photon, a fundamental particle of light; here, you’d experience maximum time dilation. Everyone on Earth would clock you at the speed of light, but from your reference frame, time would completely stop.

That’s because the “clocks” measuring time are in two different places going vastly different speeds: the photon moving at the speed of light, and the comparatively slowpoke speed of Earth going around the sun.

What’s more, when you’re traveling at or close to the speed of light, the distance between where you are and where you’re going gets shorter. That is, space itself becomes more compact in the direction of motion—so the faster you can go, the shorter your journey has to be. In other words, for the photon, space gets squished.

Which brings us back to my picture of the Pinwheel galaxy. From the photon’s perspective, a star within the galaxy emitted it, and then a single pixel in my backyard camera absorbed it, at exactly the same time. Because space is squished, to the photon the journey was infinitely fast and infinitely short, a tiny fraction of a second.

But from our perspective on Earth, the photon left the galaxy 25 million years ago and traveled 25 million light years across space until it landed on my tablet in my backyard.

And there, on a cool spring night, its stunning image inspired a delightful conversation between a nerdy scientist and his curious wife.