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The Kondo effect influences the electrical resistance of metals at low temperatures and generates complex electronic and magnetic orders. Novel concepts for data storage and processing, such as using quantum dots, are based on this. In 1998, researchers from the United States published spectroscopic studies on the Kondo effect using scanning tunneling microscopy, which are considered ground-breaking and have triggered countless others of a similar kind. Many of these studies may have to be re-examined now that Jülich researchers have shown that the Kondo effect cannot be proven beyond doubt by this method. Instead, another phenomenon is creating precisely the spectroscopic ‘fingerprint’ that was previously attributed to the Kondo effect.

Normally the resistance of metals decreases as the temperature drops. The Kondo effect causes it to rise again below a threshold value typical to the material in question, the so-called Kondo temperature. This phenomenon occurs when magnetic foreign atoms, such as iron, contaminate non-magnetic host metals, such as copper. Simply put, when a current flows, the atomic nuclei are engulfed by electrons. The iron atoms have a quantum mechanical magnetic moment. This causes the electrons in the vicinity to align their spin antiparallel to the moment of the atom at low temperatures and to hang around the cobalt atom like a cloud on a mountaintop. This hinders the flow of the electrons—the electrical resistance then increases. In physics, this is known as entanglement, the strong coupling of the moment of the impurity with the spins of the surrounding electrons.

For mathematicians and computer scientists, 2020 was full of discipline-spanning discoveries and celebrations of creativity. We’d like to take a moment to recognize some of these achievements.

1. A landmark proof simply titled MIP = RE” establishes that quantum computers calculating with entangled qubits can theoretically verify the answers to an enormous set of problems. Along the way, the five computer scientists who authored the proof also answered two other major questions: Tsirelson’s problem in physics, about models of particle entanglement, and a problem in pure mathematics called the Connes embedding conjecture.

Continue reading “2020’s Biggest Breakthroughs in Math and Computer Science” »

They are as thin as a hair, only a hundred thousand times thinner—so-called two-dimensional materials, consisting of a single layer of atoms, have been booming in research for years. They became known to a wider audience when two Russian-British scientists were awarded the Nobel Prize in Physics in 2010 for the discovery of graphene, a building block of graphite. The special feature of such materials is that they possess novel properties that can only be explained with the help of the laws of quantum mechanics and that may be relevant for enhanced technologies. Researchers at the University of Bonn (Germany) have now used ultracold atoms to gain new insights into previously unknown quantum phenomena. They found out that the magnetic orders between two coupled thin films of atoms compete with each other. The study has been published in the journal Nature.

Quantum systems realize very unique states of matter originating from the world of nanostructures. They facilitate a wide variety of new technological applications, e.g. contributing to secure data encryption, introducing ever smaller and faster technical devices and even enabling the development of a quantum computer. In the future, such a computer could solve problems which conventional computers cannot solve at all or only over a long period of time.

How unusual quantum phenomena arise is still far from being fully understood. To shed light on this, a team of physicists led by Prof. Michael Köhl at the Matter and Light for Quantum Computing Cluster of Excellence at the University of Bonn are using so-called quantum simulators, which mimic the interaction of several quantum particles—something that cannot be done with conventional methods. Even state-of-the-art computer models cannot calculate complex processes such as magnetism and electricity down to the last detail.

A team working with Roland Fischer, Professor of Inorganic and Metal-Organic Chemistry at the Technical University Munich (TUM) has developed a highly efficient supercapacitor. The basis of the energy storage device is a novel, powerful and also sustainable graphene hybrid material that has comparable performance data to currently utilized batteries.

Usually, energy storage is associated with batteries and accumulators that provide energy for electronic devices. However, in laptops, cameras, cellphones or vehicles, so-called supercapacitors are increasingly installed these days.

Unlike batteries they can quickly store large amounts of energy and put it out just as fast. If, for instance, a train brakes when entering the station, supercapacitors are storing the energy and provide it again when the train needs a lot of energy very quickly while starting up.

The odd, wavy pattern that results from viewing certain phone or computer screens through polarized glasses has led researchers to take a step toward thinner, lighter-weight lenses. Called moiré, the pattern is made by laying one material with opaque and translucent parts at an angle over another material of similar contrast.

A team of researchers from Tokyo University of Agriculture and Technology, TUAT, in Japan have demonstrated that moiré metalenses—tiny, patterned lenses composed of artificial ‘meta’ atoms—can tune focal length along a wider range than previously seen. They published their results on November 23 in Optics Express.

“Metalenses have attracted a lot of interest because they are so thin and lightweight, and could be used in ultra-compact imaging systems, like future smart phones, virtual reality goggles, drones or microbots,” said paper author Kentaro Iwami, associate professor in the TUAT Department of Mechanical Systems Engineering.

The enormous impact of the recent COVID-19 pandemic, together with other diseases or chronic health risks, has significantly prompted the development and application of bioelectronics and medical devices for real-time monitoring and diagnosing health status. Among all these devices, smart contact lenses attract extensive interests due to their capability of directly monitoring physiological and ambient information. Smart contact lenses equipped with high sensitivity sensors would open the possibility of a non-invasive method to continuously detect biomarkers in tears. They could also be equipped with application-specific integrated circuit chips to further enrich their functionality to obtain, process and transmit physiological properties, manage illnesses and health risks, and finally promote health and wellbeing. Despite significant efforts, previous demonstrations still need multistep integration processes with limited detection sensitivity and mechanical biocompatibility.

Recently, researchers from the University of Surrey, National Physical Laboratory (NPL), Harvard University, University of Science and Technology of China, Zhejiang University Ningbo Research Institute, etc. have developed a multifunctional ultrathin contact lens sensor system. The sensor systems contain a photodetector for receiving optical information, imaging and vision assistance, a temperature sensor for diagnosing potential corneal disease, and a glucose sensor for monitoring glucose level directly from the tear fluid.

Dr. Yunlong Zhao, Lecturer in Energy Storage and Bioelectronics at the Advanced Technology Institute (ATI), University of Surrey and Senior Research Scientist at the UK National Physical Laboratory (NPL), who led this research stated, “These results provide not only a novel and easy-to-make method for manufacturing advanced smart contact lenses but also a novel insight of designing other multifunctional electronics for Internet of Things, human machine interface, etc.” Dr. Zhao added, “our ultrathin transistors-based serpentine mesh sensor system and fabrication strategy allow for further incorporation of other functional components, such as electrode array for electrophysiology, antennas for wireless communication, and the power modules, e.g. thin-film batteries and enzymatic biofuel cell for future in vivo exploration and practical application. Our research team at ATI, University of Surrey and NPL are currently working on these fields.”

Two teams found different ways for quantum computers to process nonlinear systems by first disguising them as linear ones.

Researchers demonstrate a new technique for suppressing back reflections of light—better signal quality for sensing and information technology.

Microresonators are small glass structures in which light can circulate and build up in intensity. Due to material imperfections, some amount of light is reflected backwards, which is disturbing their function.

Continue reading “Trapping light without back reflections” »

The U.S. Navy is testing out a new solution to the age-old problem of prepping for painting. Instead of chipping, sandblasting or hydroblasting, it is adopting technology from the aerospace sector: laser ablation.

Teams at Puget Sound Naval Shipyard are already using a laser paint stripping system that was originally developed by Missouri-based tech company Adapt Laser for use on aircraft components. The device peels off rust, paint, oil and other contaminants without leaving any residue or damaging the substrate. Instead of a dust of chips, rust and blasting grit on the surface, it leaves clean and ready-to-paint bare steel, according to the Navy.

7th Fleet’s shipyard at Yokosuka (Ship Repair Facility and Japan Regional Maintenance Center, or SRF-JRMC) is looking at bringing laser ablation into its yard in order to improve conditions for its workforce and accelerate its workflow. When considering prep time, the stripping process and post-stripping cleanup, laser ablation may be faster than some traditional surface preparation processes, according to Naval Sea Systems Command (NAVSEA).