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Catching and Guiding an Elastic Rainbow

Two experiments demonstrate a promising platform for trapping, sorting, and directing vibrational energy.

In a rainbow, sunlight separates into colors because each wavelength of light follows a different path. This familiar image has inspired an analogous idea in wave physics: A designed material can slow down different frequency components of a broadband signal at different positions, thereby sorting the signal in space. This concept, known as rainbow trapping, was introduced as a route to storing light in metamaterials [1] and has since motivated efforts to control sound, vibration, and other classical waves. But rainbow trapping has been difficult to realize for elastic waves—vibrations that temporarily deform a material as they move through it. Many rainbow designs have relied on vibrational modes confined to a sample’s edges or interfaces, limiting the available trapping area, or have lacked a way to access and route energy once it has been localized.

Now two teams have taken complementary steps toward overcoming these limitations. Yafeng Chen at Tongji University in China and colleagues have created and directly visualized an elastic rainbow in which different megahertz-frequency vibrations stop at different positions [2]. Meanwhile, Riyi Zheng at the South China University of Technology and colleagues have shown that a similar rainbow can be captured and redirected using topological edge states [3]. Together, these two studies transform elastic rainbow trapping into a platform for sorting, confining, and guiding vibrational energy.

Electron cooling tames highly charged ions in Penning trap for first time

Researchers at Technical University of Darmstadt and the GSI Helmholtz Center for Heavy Ion Research have succeeded for the first time in decelerating highly charged ions from the GSI accelerator to low energies and subsequently storing them in a Penning trap. They were also successful in performing the first electron cooling of highly charged ions in such a trap. The results have been published in Physical Review X (PRX).

Highly charged ions are typically produced at high energies and travel at high velocities. However, many experiments in atomic, nuclear and fundamental physics require these ions to be strongly decelerated, captured and cooled. The HITRAP facility at GSI was specifically developed for this purpose and will provide unique opportunities for experiments with slow highly charged ions.

In the work now published, carried out in close collaboration with GSI’s Decelerator Division, researchers succeeded for the first time in decelerating and trapping fully ionized argon ions from the accelerator system through several stages.

Noninvasive AI-based system translates brain signals into written text

Some physical injuries and neurological conditions can temporarily or permanently impair movement, leaving some people unable to speak, type on keyboards or use electronic devices. Brain-computer interfaces (BCIs), systems that can decode brain activity patterns and convert them into computer commands or written text, could be of great value for paralyzed patients.

Despite their potential, most of the best-performing BCIs developed to date require patients to undergo invasive surgical procedures. These systems typically rely on small sensors that need to be implanted on or within the brain and can detect electrical signals associated with neural activity.

Researchers at Meta artificial intelligence (AI), Université PSL and Hospital Foundation Adolphe de Rothschild recently introduced a noninvasive brain activity-to-text approach that does not require surgical procedures. Their proposed approach, presented in Nature Neuroscience, combines a new deep learning algorithm with electroencephalography (EEG) or magnetoencephalography (MEG) recordings.

New models shed light on how an exotic phase of hydrogen in Earth’s core may behave

While Earth’s core consists mostly of iron, its density implies that lighter elements are also mixed in. Because hydrogen is abundant in the universe and can mix with iron under certain conditions, scientists suspect it makes up part of the lighter-element composition. Data from earthquakes suggest the inner part of the core also changes with depth, but scientists aren’t sure exactly how this occurs. Now, a new study published in the Proceedings of the National Academy of Sciences indicates that hydrogen likely exists in a gradient within the inner and outer core that arises from thermodynamic equilibrium.

Hydrogen can dissolve into iron under extreme conditions, like the high-temperature, high-pressure conditions in Earth’s core. In the inner core, hydrogen may become superionic, allowing it to move through a solid iron crystal structure almost like a liquid. This superionic state does not behave like a conventional solid and can affect the thermodynamic properties of different phases. It’s thought that the inner core has a hexagonal close-packed (hcp) crystal structure, but other elements can take on a body-centered cubic (bcc) phase under similar conditions.

While it’s believed that hydrogen exists in a superionic state in an hcp lattice, it’s not clear whether hydrogen can also exist as a superionic species in a bcc lattice. The study authors say it’s also unclear how hydrogen might influence the competition between hcp and bcc phases in the inner core. It’s also not clear how or whether hydrogen abundance changes between the liquid outer core and the solid inner core. Previous modeling attempts have yielded conflicting results.

Prototype glasses can turn infrared into color vision

The human eye, as good as it is, misses out on so much of the world because it is limited in what it can perceive. It can’t see X-rays, ultraviolet rays or infrared light. While X-ray goggles are still the stuff of science fiction, we may be moving closer to wearable glasses that make infrared light look almost like everyday vision. Scientists at the Beijing Institute of Technology have developed a device that transforms infrared light into a full-color visible image.

Human eyes cannot see infrared because infrared photons don’t have enough energy to trigger our retinas. Night-vision goggles and thermal cameras help, but they tend to show the world in one color, usually grainy green or black-and-white.

What this team has done is develop a technology that converts invisible infrared into multiple colors based on its wavelength and intensity. And because the eye is good at telling colors apart, the new technology allows people to distinguish subtle differences in infrared light much more easily than with traditional night-vision goggles. The researchers describe their work in a paper published in Science Advances.

Turning molecules into reliable electronic devices with a new fabrication platform

Molecules are among the smallest building blocks available for making next-generation devices. Their unique, customizable properties enable promising applications in emerging computing, sensing, optical and quantum technologies.

But integrating molecules into functional devices at scale remains a challenge. Traditional semiconductor manufacturing processes can damage small, fragile molecular materials. Now, MIT researchers have developed a scalable fabrication technique that incorporates delicate molecular materials into electronic devices on a chip without causing damage.

Their method extends the capabilities of standard semiconductor manufacturing processes to accommodate molecules. The researchers first prefabricate the device components using traditional processes. Then, they introduce the molecules and harness nanoscale surface forces to mechanically transform the fabricated device, which self-assembles without damaging the molecules.

Simulations hint at a hidden population of companionless black holes

So far, almost all stellar-mass black holes detected by astronomers have been found in binary systems. However, astronomers have long suspected that these binary black holes are the exception and that, within the Milky Way, most exist on their own.

Through new simulations, researchers led by Wagg at the Flatiron Institute in New York have calculated that more than 90% of stellar-mass black holes in our galaxy could be isolated in this way, hinting at the possibility of a vast reservoir of as-yet unobserved bodies. Their results have been published on the arXiv preprint server.

Pixel patterns harness diffraction for faster, more accurate nanoscale 3D printing

Researchers at the George W. Woodruff School of Mechanical Engineering have developed a new approach to nanoscale 3D printing that improves both speed and fidelity, overcoming a challenge that has limited the technology’s broader use in manufacturing.

Their work, led by Sourabh Saha, associate professor and Woodruff Faculty Fellow, and Harnjoo Kim, who conducted the research during his doctoral studies and later as a postdoctoral fellow in Saha’s lab, was recently published in the journal Nature Communications.

Nanoscale 3D printing allows researchers to create structures thousands of times smaller than the width of a human hair. These structures have potential applications in fields ranging from advanced computing and optics to biomedical devices and clean energy technologies. However, increasing printing speed often comes at the expense of quality.

Light controls nanoscale ‘bubble’ domains in a ferroelectric crystal

Researchers at Flinders University have discovered an unexpected way light can control tiny electronic structures inside advanced materials, a development that could help pave the way for more energy-efficient memory devices, sensors and future computing technologies.

The new study, involving experts from around the world, explores electronic properties and optical science to uncover new energy and material capabilities.

“We discovered that light can control nanoscale ‘bubble’ domains (about the size of just a few billionths of a meter across) inside a special ferroelectric crystal,” says Dr. Pankaj Sharma, senior lecturer in experimental condensed matter physics at Flinders University.

New quantum encryption method prevents ciphertext from being cloned

Digital security currently relies on difficult equations to protect data. For example, when you use a credit card online, the information is locked inside a math problem that would take a modern computer thousands of years to solve. However, if someone builds a powerful enough computer, that security breaks.

To make systems safer, there is a major shift toward quantum security. This is where the unbreakable laws of quantum physics can be used to protect data instead.

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