Category: Physics

by Osaka Metropolitan University

Electrons spin even without an electric charge and this motion in condensed matter constitutes spin current, which is attracting a great deal of attention for next-generation technology such as memory devices. An Osaka Metropolitan University-led research group has been able to gain further insight into this important topic in the field of spintronics.

To investigate the characteristics of spin currents, OMU Graduate School of Science Professor Katsuichi Kanemoto’s group designed a multilayer device consisting of a ferromagnetic layer and an organic semiconductor material.

The findings were published in Advanced Electronic Materials.

By adopting a doped conducting polymer with a long spin relaxation time, the team succeeded in observing the effects of spin transport and spin current generation from the non-magnetic, organic semiconductor side.

The long spin relaxation times not only make for more efficiency in spintronics, but also enable direct observation of phenomena due to spin current generation in the organic layer side. Moreover, the researchers were able to find that, contrary to a theory that has been generally accepted, the width of the ferromagnetic resonance measurements for the layer of the spin current supplier slightly narrowed in the device system using the organic semiconductor with a long spin relaxation time.

“The use of the organic semiconductor makes it possible to pursue physical properties from the non-magnetic layer side, for which there was no information until now,” explained Professor Kanemoto. “Our work can be expected to contribute to a deeper understanding of the properties of spin currents.”

More information: Kohei Takaishi et al, Spin Current Generation at the Hybrid Ferromagnetic Metal/Organic Semiconductor Interface as Revealed by Multiple Magnetic Resonance Techniques, Advanced Electronic Materials (2024). DOI: 10.1002/aelm.202400322

by Tejasri Gururaj , Phys.org

In a new study, scientists have investigated the newly discovered class of altermagnetic materials for their thermal properties, offering insights into the distinctive nature of altermagnets for spin-caloritronic applications.

Magnetism is an old and well-researched topic, lending itself to many applications, like motors and transformers. However, new magnetic materials and phenomena are being studied and discovered, one of which is altermagnets.

Altermagnets exhibit a unique blend of magnetic characteristics, setting them apart from conventional magnetic materials like ferromagnets and antiferromagnets. These materials exhibit properties observed in both ferromagnets and antiferromagnets, making their study enticing.

The current research, published in Physical Review Letters, explores the thermal properties of altermagnets and was led by Prof. Wanxiang Feng and Prof. Yugui Yao from the Beijing Institute of Technology.

Speaking of their motivation behind exploring altermagnets, Prof. Feng told Phys.org, “Magnetism is an ancient and fascinating topic in solid-state physics. While exploring non-collinear magnets over the past decades, we encountered a new type of collinear magnet, the altermagnet.”

Prof. Yao added, “With a dual nature resembling both ferromagnets and antiferromagnets, altermagnets intrigued us with the potential for novel physical effects. Our motivation stemmed from the desire to understand and unlock the unique properties of these magnetic materials.”

The emergence of magnetism

Magnetic properties emerge from the behavior of atoms, particularly the arrangement and movement of electrons within a material.

“In magnetic materials, due to the exchange interaction between atoms, the spin magnetic moments arrange parallel or antiparallel, forming the most common ferromagnets and antiferromagnets, respectively, which have been studied for over a century,” explained Prof. Feng.

Altermagnets defy conventional norms by embodying a dual nature—resembling antiferromagnets with zero net magnetization and ferromagnets with non-relativistic spin splitting.

In altermagnets, collinear antiparallel magnetic order combines with non-relativistic spin splitting, resulting in zero net magnetization akin to antiferromagnets and ferromagnetic spin dynamics simultaneously.

This unique behavior emerges from the intricate interplay of atoms within the crystal structure. For instance, ruthenium dioxide, the subject of this research, showcases spin degeneracy induced by nonmagnetic oxygen atoms, breaking spatial and time symmetries. This leads to the unique magnetic properties of the material.

Additionally, altermagnets exhibit a unique spin polarization. The term “spin polarization” means that a preponderance of electron spins tends to align in a particular direction.

The spin polarization is noteworthy in altermagnets because it occurs in the physical arrangement of atoms (real space) and in the momentum space, where the distribution of electron spins in the material is considered.

Nernst and Hall effects

The researchers focused on studying the emergence of crystal Nernst and crystal thermal Hall effects in rubidium dioxide (RuO₂), chosen as a showcase representative of altermagnetism.

The crystal Nernst effect (CNE) observed in altermagnets is a result of their distinctive magnetic nature. In simple terms, as the material experiences a temperature difference across its dimensions, it leads to the emergence of a voltage perpendicular to both the temperature gradient and the magnetic field. This phenomenon reveals that the material’s magnetic properties influence its response to temperature changes, providing insights into the intricate connection between thermal and magnetic behaviors in altermagnets.

In altermagnets, this effect is significantly influenced by the direction of the Néel vector, which represents the direction in which neighboring magnetic moments align. This adds an extra layer of complexity to the thermal response.

Similarly, the crystal thermal Hall effect (CTHE) sheds light on how heat moves in altermagnets. Like the traditional thermal Hall effect, it occurs perpendicular to the temperature gradient and magnetic field. In altermagnets, the CTHE shows significant variation depending on the Néel vector direction. This anisotropy is a central factor in understanding the thermal transport behavior unique to altermagnetic materials.

Thermal properties of RuO₂

The research methodology employed a dual strategy, combining symmetry analysis and cutting-edge first-principles calculations, to unravel the thermal transport properties of RuO₂. Symmetry analysis played a crucial role in unraveling the fundamental reasons behind the emergence of altermagnetism.

Through two symmetry operations involving spatial inversion, time reversal, and lattice translation, the study showcased the intricate interplay of atoms within the crystal structure, demonstrating how nonmagnetic oxygen atoms induced non-relativistic spin splitting in energy bands.

This process resulted in the breaking of crystalline time-reversal symmetry, giving rise to distinct crystal thermal transport properties.

“Through detailed analysis, we identified three physical mechanisms contributing to crystal thermal transport: Weyl pseudo-nodal lines, altermagnetic pseudo-nodal planes, and altermagnetic ladder transitions,” said Prof. Yao.

In simple terms, the Weyl pseudo-nodal lines are pathways that guide heat within the material, altermagnetic pseudo-nodal planes can be pictures as designated zones influencing heat flow, and altermagnetic ladder transitions can be thought of as the material’s way of climbing a heat ladder.

These findings are exciting as they play a significant role in how heat travels within altermagnets.

The researchers discovered an extended Wiedemann-Franz law in RuO₂, linking the material’s unusual thermal and electrical transport characteristics. Contrary to conventional expectations, this extended law operates over a broader temperature range, extending beyond 150 Kelvin.

Spin caloritronics

The researchers believe that altermagnets could have a pivotal role in spin caloritronics, a field of research that explores the interplay between spin and heat flow, which are not achievable with ferromagnets or antiferromagnets. This field has potential applications in developing new technologies for information processing and storage.

“Altermagnetic materials with collinear antiparallel magnetic order exhibit faster spin dynamics and lower sensitivity to stray magnetic fields compared to ferromagnetic materials. This makes them promising for achieving higher storage density and faster spin caloritronic devices,” explained Prof. Feng.

The researchers also intend to investigate higher-order crystal thermal transport and magneto-optical effects in the future.

Speaking of this, Prof. Yao said, “We are curious about the differences in higher-order crystal thermal transport and high-order magneto-optical effects in altermagnets compared to antiferromagnets or ferromagnets. We are in the early stages of this technology, and there’s a long journey ahead before it becomes practically achievable.”

by Chinese Academy of Sciences

Introducing light conversion materials into silicon-based photovoltaic devices is an effective way to improve their photoelectric conversion efficiency. Light conversion materials include quantum cutting materials and upconversion materials.

The purpose of introducing quantum cutting materials is to divide a short-wavelength photon into two or more photons that can join the photoelectric conversion in silicon-based photovoltaic devices. Introducing upconversion materials is done to combine two or more infrared photons into one photon that can also be used for photoelectric conversion in silicon-based photovoltaic devices.

The introduction of light conversion materials can improve photoelectric conversion efficiency without changing the performance of silicon-based solar cells themselves. This method can greatly reduce the technical difficulty of improving the efficiency of silicon-based photovoltaic systems. In addition, silicon-based photovoltaic devices are exposed to sunlight, so their temperature must be managed. Managing this temperature necessitates measuring it in advance.

However, it is possible that if three materials that can individually achieve quantum cutting, upconversion, and temperature sensing are simultaneously introduced into silicon-based solar cells, it will lead to difficulties in solar cell structure design and unnecessary increase in the product costs. Therefore, finding and developing high-performance materials that combine the above three functions is a challenge.

In a new paper published in Light: Science & Applications, researchers from the School of Science, Dalian Maritime University reports that they have achieved highly efficient photo split, nearly pure infrared upconversion emission, and suitable temperature sensing for thermal management in silicon-based solar cells by adjusting the doping concentrations of Er³⁺ and Yb³⁺ in NaY(WO₄)₂ phosphor.

The work reveals that this all-in-one material is an excellent candidate for application in silicon-based solar cells for improving their photoelectric conversion efficiency and enhancing their heat management.

An in-depth understanding of the quantum cutting mechanism is significant for designing and assessing the quantum cutting materials. However, in many cases, quantum cutting processes are complicated. In this work, the authors carefully decrypted the photo-splitting steps in Er³⁺/Yb³⁺ co-doped NaY(WO₄)₂ to assist the doping-concentration-dependent spectroscopy and fluorescence dynamics.

The team states, “Based on the optical spectroscopic analyses, the quantum cutting mechanism was discovered, and the photon splitting process includes two-step energy transfer processes, namely, ⁴S_3/2+²F_7/2 ⁴I_11/2 +²F_5/2 and ⁴I_11/2 + ²F_7/2 ⁴I_15/2 + ²F_5/2.”

The quantum cutting efficiency can be confirmed experimentally and theoretically. In the ideal case, the measured quantum cutting efficiency is also defined as the internal quantum efficiency, but it is different from the traditional definition of internal quantum efficiency. The measuring technique for the quantum efficiencies is still not satisfactory since the measuring results are complicated by too many uncontrollable factors.

Therefore, the theoretical internal quantum cutting efficiency becomes significant. The authors claim, “The quantum cutting mechanism was discovered by the optical spectroscopic analyses, and the quantum cutting efficiencies were calculated in assistance of Judd-Ofelt theory, Föster-Dexter theory, energy gap law.” The authors estimated the internal quantum cutting efficiencies for NaY(WO₄)₂: Er³⁺/Yb³⁺ by taking radiative transitions, non-radiative transitions, and energy transfers into account, and achieved an efficiency as high as 173%.

Another important point of this work is that the researchers achieved nearly pure near-infrared emission of Yb³⁺.

The team observes, “These upconversion mechanisms tell us that both Er³⁺ and Er³⁺/Yb³⁺ doped NaY(WO₄)₂ phosphors exhibit strong near-infrared emissions from ⁴I_11/2⁴I_15/2 of Er³⁺ and ²F_5/2²F_7/2 of Yb³⁺ that indicates the studied phosphors are good light conversion candidate[s] for silicon-based solar cell applications.”

More information: Duan Gao et al, Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO4)2:Er3+/Yb3+ with thermal management capability for silicon-based solar cells, Light: Science & Applications (2024). DOI: 10.1038/s41377-023-01365-2

Provided by Chinese Academy of Sciences 

by Brookhaven National Laboratory

Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and DOE’s Pacific Northwest National Laboratory (PNNL) have used a combination of scanning transmission electron microscopy (STEM) and computational modeling to get a closer look and deeper understanding of tantalum oxide. When this amorphous oxide layer forms on the surface of tantalum—a superconductor that shows great promise for making the “qubit” building blocks of a quantum computer—it can impede the material’s ability to retain quantum information.

Learning how the oxide forms may offer clues as to why this happens—and potentially point to ways to prevent quantum coherence loss. The research was recently published in the journal ACS Nano.

The paper builds on earlier research by a team at Brookhaven’s Center for Functional Nanomaterials (CFN), Brookhaven’s National Synchrotron Light Source II (NSLS-II), and Princeton University that was conducted as part of the Co-design Center for Quantum Advantage (C²QA), a Brookhaven-led national quantum information science research center in which Princeton is a key partner.

“In that work, we used X-ray photoemission spectroscopy at NSLS-II to infer details about the type of oxide that forms on the surface of tantalum when it is exposed to oxygen in the air,” said Mingzhao Liu, a CFN scientist and one of the lead authors on the study. “But we wanted to understand more about the chemistry of this very thin layer of oxide by making direct measurements,” he explained.

So, in the new study, the team partnered with scientists in Brookhaven’s Condensed Matter Physics & Materials Science (CMPMS) Department to use advanced STEM techniques that enabled them to study the ultrathin oxide layer directly. They also worked with theorists at PNNL who performed computational modeling that revealed the most likely arrangements and interactions of atoms in the material as they underwent oxidation.

Together, these methods helped the team build an atomic-level understanding of the ordered crystalline lattice of tantalum metal, the amorphous oxide that forms on its surface, and intriguing new details about the interface between these layers.

“The key is to understand the interface between the surface oxide layer and the tantalum film because this interface can profoundly impact qubit performance,” said study co-author Yimei Zhu, a physicist from CMPMS, echoing the wisdom of Nobel laureate Herbert Kroemer, who famously asserted, “The interface is the device.”

Emphasizing that “quantitatively probing a mere one-to-two-atomic-layer-thick interface poses a formidable challenge,” Zhu noted, “we were able to directly measure the atomic structures and bonding states of the oxide layer and tantalum film as well as identify those of the interface using the advanced electron microscopy techniques developed at Brookhaven.”

“The measurements reveal that the interface consists of a ‘suboxide’ layer nestled between the periodically ordered tantalum atoms and the fully disordered amorphous tantalum oxide. Within this suboxide layer, only a few oxygen atoms are integrated into the tantalum crystal lattice,” Zhu said.

The combined structural and chemical measurements offer a crucially detailed perspective on the material. Density functional theory calculations then helped the scientists validate and gain deeper insight into these observations.

“We simulated the effect of gradual surface oxidation by gradually increasing the number of oxygen species at the surface and in the subsurface region,” said Peter Sushko, one of the PNNL theorists.

By assessing the thermodynamic stability, structure, and electronic property changes of the tantalum films during oxidation, the scientists concluded that while the fully oxidized amorphous layer acts as an insulator, the suboxide layer retains features of a metal.

“We always thought if the tantalum is oxidized, it becomes completely amorphous, with no crystalline order at all,” said Liu. “But in the suboxide layer, the tantalum sites are still quite ordered.”

With the presence of both fully oxidized tantalum and a suboxide layer, the scientists wanted to understand which part is most responsible the loss of coherence in qubits made of this superconducting material.

“It’s likely the oxide has multiple roles,” Liu said.

First, he noted, the fully oxidized amorphous layer contains many lattice defects. That is, the locations of the atoms are not well defined. Some atoms can shift around to different configurations, each with a different energy level. Though these shifts are small, each one consumes a tiny bit of electrical energy, which contributes to loss of energy from the qubit.

“This so-called two-level system loss in an amorphous material brings parasitic and irreversible loss to the quantum coherence—the ability of the material to hold onto quantum information,” Liu said.

But because the suboxide layer is still crystalline, “it may not be as bad as people were thinking,” Liu said. Maybe the more fixed atomic arrangements in this layer will minimize two-level system loss.

Then again, he noted, because the suboxide layer has some metallic characteristics, it could cause other problems.

“When you put a normal metal next to a superconductor, that could contribute to breaking up the pairs of electrons that move through the material with no resistance,” he noted. “If the pair breaks into two electrons again, then you will have loss of superconductivity and coherence. And that is not what you want.”

Future studies may reveal more details and strategies for preventing loss of superconductivity and quantum coherence in tantalum.

More information: Junsik Mun et al, Probing Oxidation-Driven Amorphized Surfaces in a Ta(110) Film for Superconducting Qubit, ACS Nano (2023). DOI: 10.1021/acsnano.3c10740

Journal information: ACS Nano 

Provided by Brookhaven National Laboratory 

by Luke Auburn, University of Rochester

Scientists from the University of Rochester’s Laboratory for Laser Energetics (LLE) led experiments to demonstrate an effective “spark plug” for direct-drive methods of inertial confinement fusion (ICF). In two studies published in Nature Physics, the authors discuss their results and outline how they can be applied at bigger scales with the hopes of eventually producing fusion at a future facility.

LLE is the largest university-based U.S. Department of Energy program and hosts the OMEGA laser system, which is largest academic laser in the world but still almost one hundredth the energy of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California.

With OMEGA, Rochester scientists completed several successful attempts to fire 28 kilojoules of laser energy at small capsules filled with deuterium and tritium fuel, causing the capsules to implode and produce a plasma hot enough to initiate fusion reactions between the fuel nuclei. The experiments caused fusion reactions that produced more energy than the amount of energy in the central hot plasma.

The OMEGA experiments use direct laser illumination of the capsule and differ from the indirect drive approach used on the NIF. When using the indirect drive approach, the laser light is converted into X-rays that in turn drive the capsule implosion. The NIF used indirect drive to irradiate a capsule with X-rays using about 2,000 kilojoules of laser energy. This led to a 2022 breakthrough at NIF in achieving fusion ignition—a fusion reaction that creates a net gain of energy from the target.

“Generating more fusion energy than the internal energy content of where the fusion takes place is an important threshold,” says lead author of the first paper Connor Williams ’23 Ph.D. (physics and astronomy), now a staff scientist at Sandia National Labs in radiation and ICF target design. “That’s a necessary requirement for anything you want to accomplish later on, such as burning plasmas or achieving ignition.”

By showing they can achieve this level of implosion performance with just 28 kilojoules of laser energy, the Rochester team is excited by the prospect of applying direct-drive methods to lasers with more energy. Demonstrating a spark plug is an important step, however, OMEGA is too small to compress enough fuel to get to ignition.

“If you can eventually create the spark plug and compress fuel, direct drive has a lot of characteristics that are favorable for fusion energy compared to indirect drive,” says Varchas Gopalaswamy ’21 Ph.D. (mechanical engineering), the LLE scientist who led the second study that explores the implications of using the direct-drive approach on megajoule-class lasers, similar to the size of the NIF. “After scaling the OMEGA results to a few megajoules of laser energies, the fusion reactions are predicted to become self-sustaining, a condition called ‘burning plasmas.'”

Gopalaswamy says that direct-drive ICF is a promising approach for achieving thermonuclear ignition and net energy in laser fusion.

“A major factor contributing to the success of these recent experiments is the development of a novel implosion design method based on statistical predictions and validated by machine learning algorithms,” says Riccardo Betti, LLE’s chief scientist and the Robert L. McCrory Professor in the Department of Mechanical Engineering and in the Department of Physics and Astronomy. “These predictive models allow us to narrow the pool of promising candidate designs before carrying out valuable experiments.”

The Rochester experiments required a highly coordinated effort between large number of scientists, engineers, and technical staff to operate the complex laser facility. They collaborated with researchers from the MIT Plasma Science and Fusion Center and General Atomics to conduct the experiments.

More information: C. A. Williams et al, Demonstration of hot-spot fuel gain exceeding unity in direct-drive inertial confinement fusion implosions, Nature Physics (2024). DOI: 10.1038/s41567-023-02363-2

V. Gopalaswamy et al, Demonstration of a hydrodynamically equivalent burning plasma in direct-drive inertial confinement fusion, Nature Physics (2024). DOI: 10.1038/s41567-023-02361-4

Provided by University of Rochester 

by John Toon, Georgia Institute of Technology

A new cooling technique that utilizes a single species of trapped ion for both computing and cooling could simplify the use of quantum charge-coupled devices (QCCDs), potentially moving quantum computing closer to practical applications.

Using a technique called rapid ion exchange cooling, scientists at the Georgia Tech Research Institute (GTRI) have shown that they could cool a calcium ion—which gains vibrational energy while doing quantum computations—by moving a cold ion of the same species into close proximity. After transferring energy from the hot ion to the cold one, the refrigerant ion is returned to a nearby reservoir to be cooled for further use.

The research is reported in the journal Nature Communications.

Conventional ion cooling for QCCDs involves the use of two different ion species, with cooling ions coupled to lasers of a different wavelength that do not affect the ions used for quantum computing. Beyond the lasers needed to control the quantum computing operations, this sympathetic cooling technique requires additional lasers to trap and control the refrigerant ions, and that both increases complexity and slows quantum computing operations.

“We have shown a new method for cooling ions faster and more simply in this promising QCCD architecture,” said Spencer Fallek, a GTRI research scientist. “Rapid exchange cooling can be faster because transporting the cooling ions requires less time than laser cooling two different species. And it’s simpler because using two different species requires operating and controlling more lasers.”

https://www.youtube.com/embed/Uj9ITEhh3Pc?color=whiteVideo shows how a computational ion can be cooled by bringing it near a refrigerant ion of the same atomic species. Credit: Georgia Tech Research Institute

The ion movement takes place in a trap maintained by precisely controlling voltages that create an electrical potential between gold contacts. But moving a cold atom from one part of the trap is a bit like moving a bowl with a marble sitting in the bottom.

When the bowl stops moving, the marble must become stationary—not rolling around in the bowl, explained Kenton Brown, a GTRI principal research scientist who has worked on quantum computing issues for more than 15 years.

“That’s basically what we’re always trying to do with these ions when we’re moving the confining potential, which is like the bowl, from one place to another in the trap,” he said. “When we’re done moving the confining potential to the final location in the trap, we don’t want the ion moving around inside the potential.”

Once the hot ion and cold ion are close to each other, a simple energy swap takes place and the original cold ion—heated now by its interaction with a computing ion—can be split off and returned to a nearby reservoir of cooled ions.

The GTRI researchers have so far demonstrated a two-ion proof-of-concept system, but say their technique is applicable to the use of multiple computing and cooling ions, and other ion species.

A single energy exchange removed more than 96% of the heat—measured as 102(5) quanta—from the computing ion, which came as a pleasant surprise to Brown, who had expected multiple interactions might be necessary. The researchers tested the energy exchange by varying the starting temperature of the computational ions and found that the technique is effective regardless of the initial temperature. They have also demonstrated that the energy exchange operation can be done multiple times.

Heat—essentially vibrational energy—seeps into the trapped ion system through both computational activity and from anomalous heating, such as unavoidable radio-frequency noise in the ion trap itself. Because the computing ion is absorbing heat from these sources even as it is being cooled, removing more than 96% of the energy will require more improvements, Brown said.

The researchers envision that in an operating system, cooled atoms would be available in a reservoir off to the side of the QCCD operations and maintained at a steady temperature. The computing ions cannot be directly laser-cooled because doing so would erase the quantum data they hold.

Excessive heat in a QCCD system adversely affects the fidelity of the quantum gates, introducing errors in the system. The GTRI researchers have not yet built a QCCD that uses their cooling technique, though that is a future step in the research. Other work ahead includes accelerating the cooling process and studying its effectiveness at cooling motion along other spatial directions.

The experimental component of the rapid exchange cooling experiment was guided by simulations done to predict, among other factors, the pathways that the ions would take in their journey within the ion trap. “We definitely understood what we were looking for and how we should go about achieving it based on the theory and simulations we had,” Brown said.

The unique ion trap was fabricated by collaborators at Sandia National Laboratories. The GTRI researchers used computer-controlled voltage generation cards able to produce specific waveforms in the trap, which has a total of 154 electrodes, of which the experiment used 48. The experiments took place in a cryostat maintained at about 4 degrees Kelvin.

GTRI’s Quantum Systems Division (QSD) investigates quantum computing systems based on individual trapped atomic ions and novel quantum sensor devices based on atomic systems. GTRI researchers have designed, fabricated, and demonstrated a number of ion traps and state-of-the-art components to support integrated quantum information systems. Among the technologies developed is the ability to precisely transport ions to where they are needed.

“We have very fine control of how the ions move, the speed at which they can be brought together, the potential they’re in when they are near one another, and the timing that’s necessary to do experiments like this,” said Fallek.

Other GTRI researchers involved in the project included Craig Clark, Holly Tinkey, John Gray, Ryan McGill and Vikram Sandhu. The research was done in collaboration with Los Alamos National Laboratory.

by UCLA Engineering Institute for Technology Advancement

While image denoising algorithms have undergone extensive research and advancements in the past decades, classical denoising techniques often necessitate numerous iterations for their inference, making them less suitable for real-time applications.

The advent of deep neural networks (DNNs) has ushered in a paradigm shift, enabling the development of non-iterative, feed-forward digital image denoising approaches.

These DNN-based methods exhibit remarkable efficacy, achieving real-time performance while maintaining high denoising accuracy. However, these deep learning-based digital denoisers incur a trade-off, demanding high-cost, resource- and power-intensive graphics processing units (GPUs) for operation.

In an article published in Light: Science & Applications, a team of researchers, led by Professors Aydogan Ozcan and Mona Jarrahi from University of California, Los Angeles (UCLA), U.S., and Professor Kaan Akşit from University College London (UCL), UK developed a physical image denoiser comprising spatially engineered diffractive layers to process noisy input images at the speed of light and synthesize denoised images at its output field-of-view without any digital computing.

Following a one-time training on a computer, the resulting visual processor with its passive diffractive layers is fabricated, forming a physical image denoiser that scatters out the optical modes associated with undesired noise or spatial artifacts of the input images.

Through its optimized design, this diffractive visual processor preserves the optical modes representing the desired spatial features of the input images with minimal distortions.

As a result, it instantly synthesizes denoised images within its output field-of-view without the need to digitize, store or transmit an image for a digital processor to act on it. The efficacy of this all-optical image denoising approach was validated by suppressing salt and pepper noise from both intensity- and phase-encoded input images.

Furthermore, this physical image denoising framework was experimentally demonstrated using terahertz radiation and a 3D-fabricated diffractive denoiser.

This all-optical image denoising framework offers several important advantages, such as low power consumption, ultra-high speed, and compact size.

The research team envisions that the success of these all-optical image denoisers can catalyze the development of all-optical visual processors tailored to address various inverse problems in imaging and sensing.

More information: Çağatay Işıl et al, All-optical image denoising using a diffractive visual processor, Light: Science & Applications (2024). DOI: 10.1038/s41377-024-01385-6

Provided by UCLA Engineering Institute for Technology Advancement 

by Tokyo Metropolitan University

Researchers from Tokyo Metropolitan University have created a new superconductor with a chiral crystalline structure by mixing two materials, one with superconductivity but no chirality, another with chirality but no superconductivity.

The new platinum-iridium-zirconium compound transitions to a bulk superconductor below 2.2 K and was observed to have chiral crystalline structure using X-ray diffraction. Their new solid solution approach promises to accelerate the discovery and understanding of new exotic superconducting materials.

Scientists studying superconductivity are on a mission to understand how the exotic nature of superconducting materials arises from their structure, and how we might control the structure to get desirable properties.

Of the many aspects of structure, an interesting recent development is the issue of chirality. Many structures have a “handedness,” that is, they do not look the same in a mirror. An effect of chirality in superconductors is to trigger something called asymmetric spin-orbit coupling (ASOC), an effect that can make superconductors more robust to high magnetic field exposure.

To understand chirality in more depth, however, scientists need more superconductors with a chiral structure to study. The usual route is to search out chiral compounds, check if they are superconducting or not, rinse and repeat: this is very inefficient.

That is why a team from Tokyo Metropolitan University led by Associate Professor Yoshikazu Mizuguchi has introduced an entirely new approach. Instead of combing through lists of compounds, they mixed two compounds with known physical properties, a platinum-zirconium compound with superconductivity but no chirality, and an iridium-zirconium compound with a chiral structure, but no reports of superconductivity. The work is published in the Journal of the American Chemical Society.

By combining elements in a ratio that matches a certain proportion of each compound, they were able to effectively “mix and match” physical properties, coming up with a new material that had both a chiral crystal structure and superconductivity.

• X-ray diffraction patterns at different temperatures (top), and the extracted fraction of chiral compound (bottom) show that the proportion of chiral compound increases at lower temperature. Credit: Tokyo Metropolitan University
• As the proportion of iridium is increased, the proportion of P6122, the chiral component, increases. Credit: Tokyo Metropolitan University
• Superconductivity can be confirmed below an iridium proportion of around x = 0.85 in (Pt_1-xIr_x)₃Zr₅. Credit: Tokyo Metropolitan University
• X-ray diffraction patterns at different temperatures (top), and the extracted fraction of chiral compound (bottom) show that the proportion of chiral compound increases at lower temperature. Credit: Tokyo Metropolitan University
• As the proportion of iridium is increased, the proportion of P6122, the chiral component, increases. Credit: Tokyo Metropolitan University

by US Department of Energy

Fixed numbers of protons and neutrons—the building blocks of nuclei—can rearrange themselves within a single nucleus. The products of this reshuffling include electromagnetic (gamma ray) transitions. These transitions connect excited energy levels called quantum levels, and the pattern in these connections provide a unique “fingerprint” for each isotope.

Determining these fingerprints provides a sensitive test of scientists’ ability to describe one of the fundamental forces, the strong (nuclear) force that holds protons and neutrons together.

In the laboratory, scientists can initiate the movement of protons and neutrons through an injection of excess energy using a nuclear reaction.

In a paper, published in Physical Review C, researchers successfully used this approach to study the fingerprint of sulfur-38. They also used machine learning and other cutting-edge tools to analyze the data.

The results provide new empirical information on the “fingerprint” of quantum energy levels in the sulfur-38 nucleus. Comparisons with theoretical models may lead to important new insights. For example, one of the calculations highlighted the key role played by a particular nucleon orbital in the model’s ability to reproduce the fingerprints of sulfur-38 as well as neighboring nuclei.

The study is also important for its first successful implementation of a specific machine learning-based approach to classifying data. Scientists are adopting this approach to other challenges in experimental design.

Researchers used a measurement that included a machine learning (ML) assisted analysis of the collected data to better determine the unique quantum energy levels—a “fingerprint” formed through the rearrangement of the protons and neutrons—in the neutron-rich nucleus sulfur-38.

The results doubled the amount of empirical information on this particular fingerprint. They used a nuclear reaction involving the fusion of two nuclei, one from a heavy-ion beam and the second from a target, to produce the isotope and introduce the energy needed to excite it into higher quantum levels.

The reaction and measurement leveraged a heavy-ion beam produced by the ATLAS Facility (a Department of Energy user facility), a target produced by the Center for Accelerator and Target Science (CATS), the detection of electromagnetic decays (gamma-rays) using the Gamma-Ray Energy Tracking Array (GRETINA), and the detection of the nuclei produced using the Fragment Mass Analyzer (FMA).

Due to complexities in the experimental parameters—which hinged between the production yields of the sulfur-38 nuclei in the reaction and the optimal settings for detection—the research adapted and implemented ML techniques throughout the data reduction.

These techniques achieved significant improvements over other techniques. The ML-framework itself consisted of a fully connected neural network that was trained under supervision to classify sulfur-38 nuclei against all other isotopes produced by the nuclear reaction.

by Daegu Gyeongbuk Institute of Science and Technology (DGIST)

Programmable photonic integrated circuits (PPICs) process light waves for computation, sensing, and signaling in ways that can be programmed to suit diverse requirements. Researchers at Daegu Gyeongbuk Institute of Science and Technology (DGIST), in South Korea, with collaborators at Korea Advanced Institute of Science and Technology (KAIST), have achieved a major advance in incorporating microelectromechanical systems into PPICs.

Their research has been published in the journal Nature Photonics.

“Programmable photonic processors promise to outperform conventional supercomputers, offering faster, more efficient and massively parallel computing capabilities,” says Sangyoon Han of the DGIST team. He emphasizes that, in addition to the increased speeds achieved by using light instead of electric current, the significant reduction in power consumption and size of PPICs could lead to major advances in artificial intelligence, neural networks, quantum computing, and communications.

The microelectromechanical systems (MEMS) at the heart of the new advance are tiny components that can interconvert optical, electronic, and mechanical changes to perform the variety of communication and mechanical functions needed by an integrated circuit.

The researchers believe they are the first to integrate silicon-based photonic MEMS technologies onto PPIC chips that operate with extremely low power requirements.

“Our innovation has dramatically reduced the power consumption to femtowatt levels, which is over a million times an improvement compared to the previous state of the art,” says Han. The technology can also be built onto chips up to five times smaller than existing options.

One key to the dramatic reduction in power requirements was to move away from the dependence on temperature changes required by the dominant “thermo-optic” systems currently in use. The required tiny mechanical movements are powered by electrostatic forces—the attractions and repulsions between fluctuating electric charges.

The components integrated onto the team’s chips can manipulate a feature of light waves called “phase” and control the coupling between different parallel waveguides, which guide and constrain the light. These are the two most fundamental requirements for building PPICs. These features interact with micromechanical “actuators” (essentially switches) to complete the programmable integrated circuit.

The key to the advance has been to apply innovative concepts to the fabrication of the required silicon-based parts. Crucially, the manufacturing process can be used with conventional silicon wafer technology. This makes it compatible with the large-scale production of photonic chips essential to commercial applications.

The team now plans to refine their technology to build and commercialize a photonic computer that will outperform conventional electronic computers in a wide variety of applications. Han says that examples of specific uses include the crucial inference tasks in artificial intelligence, advanced image processing, and high-bandwidth data transmission.

“We expect to continue to push the boundaries of computational technology, contributing further to the field of photonics and its practical applications in modern technology,” Han concludes.

More information: Dong Uk Kim et al, Programmable photonic arrays based on microelectromechanical elements with femtowatt-level standby power consumption, Nature Photonics (2023). DOI: 10.1038/s41566-023-01327-5