Computers Math

An international team of physicists led by the University of Minnesota has discovered that a unique superconducting metal is more resilient when used as a very thin layer. The research is the first step toward a larger goal of understanding unconventional superconducting states in materials, which could possibly be used in quantum computing in the future.
The collaboration includes four faculty members in the University of Minnesota’s School of Physics and Astronomy — Associate Professor Vlad Pribiag, Professor Rafael Fernandes, and Assistant Professors Fiona Burnell and Ke Wang — along with physicists at Cornell University and several other institutions. The study is published in Nature Physics, a monthly, peer-reviewed scientific journal published by the Nature Research.
Niobium diselenide (NbSe2) is a superconducting metal, meaning that it can conduct electricity, or transport electrons from one atom to another, with no resistance. It is not uncommon for materials to behave differently when they are at a very small size, but NbSe2 has potentially beneficial properties. The researchers found that the material in 2D form (a very thin substrate only a few atomic layers thick) is a more resilient superconductor because it has a two-fold symmetry, which is very different from thicker samples of the same material.
Motivated by Fernandes and Burnell’s theoretical prediction of exotic superconductivity in this 2D material, Pribiag and Wang started to investigate atomically-thin 2D superconducting devices.
“We expected it to have a six-fold rotational pattern, like a snowflake.” Wang said. “Despite the six-fold structure, it only showed two-fold behavior in the experiment.”
“This was one of the first times [this phenomenon] was seen in a real material,” Pribiag said.
The researchers attributed the newly-discovered two-fold rotational symmetry of the superconducting state in NbSe2 to the mixing between two closely competing types of superconductivity, namely the conventional s-wave type — typical of bulk NbSe2 — and an unconventional d- or p-type mechanism that emerges in few-layer NbSe2. The two types of superconductivity have very similar energies in this system. Because of this, they interact and compete with each other.
Pribiag and Wang said they later became aware that physicists at Cornell University were reviewing the same physics using a different experimental technique, namely quantum tunneling measurements. They decided to combine their results with the Cornell research and publish a comprehensive study.
Burnell, Pribiag, and Wang plan to build on these initial results to further investigate the properties of atomically thin NbSe2 in combination with other exotic 2D materials, which could ultimately lead to the use of unconventional superconducting states, such as topological superconductivity, to build quantum computers.
“What we want is a completely flat interface on the atomic scale,” Pribiag said. “We believe this system will be able to give us a better platform to study materials to use them for quantum computing applications.”
In addition to Pribiag, Fernandes, Burnell, Wang, the collaboration included University of Minnesota physics graduate students Alex Hamill, Brett Heischmidt, Daniel Shaffer, Kan-Ting Tsai, and Xi Zhang; Cornell University faculty members Jie Shan and Kin Fai Mak and graduate student Egon Sohn; Helmuth Berger and László Forró, researchers at Ecole Polytechnique Fédérale de Lausanne in Switzerland; Alexey Suslov, a researcher at the National High Magnetic Field Laboratory in Tallahassee, Fla.; and Xiaoxiang Xi, a professor at Nanjing University in China.
The University of Minnesota research was supported primarily by the National Science Foundation (NSF) through the University of Minnesota Materials Research Science and Engineering Center (MRSEC). The research at Cornell was supported by the Office of Naval Research (ONR) and NSF. The work in Switzerland was supported by the Swiss National Science Foundation.
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Do you like the thick brush strokes and soft color palettes of an impressionist painting such as those by Claude Monet? Or do you prefer the bold colors and abstract shapes of a Rothko? Individual art tastes have a certain mystique to them, but now a new Caltech study shows that a simple computer program can accurately predict which paintings a person will like.
The new study, appearing in the journal Nature Human Behaviour, utilized Amazon’s crowdsourcing platform Mechanical Turk to enlist more than 1,500 volunteers to rate paintings in the genres of impressionism, cubism, abstract, and color field. The volunteers’ answers were fed into a computer program and then, after this training period, the computer could predict the volunteers’ art preferences much better than would happen by chance.
“I used to think the evaluation of art was personal and subjective, so I was surprised by this result,” says lead author Kiyohito Iigaya, a postdoctoral scholar who works in the laboratory of Caltech professor of psychology John O’Doherty.
The findings not only demonstrated that computers can make these predictions but also led to a new understanding about how people judge art.
“The main point is that we are gaining an insight into the mechanism that people use to make aesthetic judgments,” says O’Doherty. “That is, that people appear to use elementary image features and combine over them. That’s a first step to understanding how the process works.”
In the study, the team programmed the computer to break a painting’s visual attributes down into what they called low-level features — traits like contrast, saturation, and hue — as well as high-level features, which require human judgment and include traits such as whether the painting is dynamic or still. More

Magnetic-spin interactions that allow spin-manipulation by electrical control allow potential applications in energy-efficient spintronic devices.
An antisymmetric exchange known as Dzyaloshinskii-Moriya interactions (DMI) is vital to form various chiral spin textures, such as skyrmions, and permits their potential application in energy-efficient spintronic devices.
Published this week, a Chinese-Australia collaboration has for the first time illustrated that DMI can be induced in a layered material tantalum-sulfide (TaS2) by intercalating iron atoms, and can further be tuned by gate-induced proton intercalation.
REALIZING AND TUNING DMI IN VAN-DER-WAALS MATERIAL TaS2
Searching for layered materials that harbour chiral spin textures, such as skyrmions, chiral domain Walls is vital for further low-energy nanodevices, as those chiral spin textures are building blocks for topological spintronic devices and can be driven by ultra-low current density.
Generally, chiral spin textures are stabilized by DMI. Therefore, introducing and controlling DMI in materials is key in searching and manipulating the chiral spin textures. More

It is not the first time that spiders have served as biological models in the research field of soft robotics. The hydraulic actuation mechanisms they apply to move their limbs when weaving their web or hunting for prey give them powers many roboticists and engineers have drawn inspiration from.
A team of researchers at the Max Planck Institute for Intelligent Systems in Germany and at the University of Boulder in Colorado in the US has now found a new way to exploit the principles of spiders’ joints to drive articulated robots without any bulky components and connectors, which weigh down the robot and reduce portability and speed. Their slender and lightweight simple structures impress by enabling a robot to jump 10 times its height. At the end of May, the team’s work titled “Spider-inspired electrohydraulic actuators for fast, soft-actuated joints” was published in Advanced Science.
The high performance is enabled by Spider-inspired Electrohydraulic Soft-actuated joints — SES joints in short. The joints can be used in many different configurations — not just when creating an arachno-bot. In their paper, the scientists demonstrate a bidirectional joint, a multi-segmented artificial limb, and a three-fingered gripper, which can easily pick up delicate objects. All creations are lightweight, simple in their design, and exhibit high performance making them ideal for robotic systems that need to move rapidly and interact with many different environments.
The researchers developed their SES joints based on the HASEL technology which had previously been invented by the team to build artificial muscles. SES joints mimic a spider-inspired exoskeletal mechanism comprised of both rigid and softer elements, which function similarly to the animal’s leg extension through the use of hydraulic forces.
They built a flexible pouch made of thin plastic films (either polyester or polypropylene will do) which they filled with a liquid dielectric — a vegetable-based oil. They then placed electrodes on each side of the pouch. These liquid-filled pockets serve as actuators, in which the hydraulic power is generated through electrostatic forces. The pouch is attached to a rotary joint. When a high voltage is applied between the electrodes, the electrostatic forces cause the liquid dielectric to shift inside the pouch and the joint to flex. SES joints are capable of rotating up to 70 degrees, causing high torques, and can easily restore back to the starting position.
“The SES joints are very simple and light, as there are no peripheral components which weigh down the robot,” says Christoph Keplinger, Director of the Robotic Materials Department at the Max Planck Institute for Intelligence Systems. “Many applications for soft robots require versatile actuators. These spider-inspired joints allow for high functionality and consume only little power, they are easy and cheap to make — the plastics we are using are for food packaging — and their production is easily scalable. These are all qualities that are critical for the design of robots, which can move in many different ways and manipulate a variety of objects without breaking them.”
A three-fingered gripper was one application for which the team used SES joints to showcase their versatility. If the team had equipped the gripper with a muscle-like structure, it would have been in the way of the object that the gripper is grabbing. Using SES joints as the hinges of the gripper required much less space.
“The research stands out because we can use a wide variety of materials, even the plastic used to make chips bags to create the pouches,” the first author of the publication Nicholas Kellaris says. “That way we can implement SES in a wide variety of geometries with specifically tuned actuation characteristics.”
“The ultimate goal of our research was not to make a spider robot,” Philipp Rothemund, the second author of the publication, adds. “We wanted to develop a state-of-the-art, active joint that you can put in any type of robot.”
Especially for small-scale robotic systems of only a few centimeters in size, where the limited space severely restricts the choice of actuator technologies, the SES-joints will come in very useful. For the soft robotics community, this invention is truly a leap forward.
Video: https://www.youtube.com/watch?v=XtZSv7ZcoxY More

When someone bumps their elbow against a wall, they not only feel pain but also might experience bruising. Robots and prosthetic limbs don’t have these warning signs, which could lead to further injury. Now, researchers reporting in ACS Applied Materials & Interfaces have developed an artificial skin that senses force through ionic signals and also changes color from yellow to a bruise-like purple, providing a visual cue that damage has occurred.
Scientists have developed many different types of electronic skins, or e-skins, that can sense stimuli through electron transmission. However, these electrical conductors are not always biocompatible, which could limit their use in some types of prosthetics. In contrast, ionic skins, or I-skins, use ions as charge carriers, similar to human skin. These ionically conductive hydrogels have superior transparency, stretchability and biocompatibility compared with e-skins. Qi Zhang, Shiping Zhu and colleagues wanted to develop an I-skin that, in addition to registering changes in electrical signal with an applied force, could also change color to mimic human bruising.
The researchers made an ionic organohydrogel that contained a molecule, called spiropyran, that changes color from pale yellow to bluish-purple under mechanical stress. In testing, the gel showed changes in color and electrical conductivity when stretched or compressed, and the purple color remained for 2-5 hours before fading back to yellow. Then, the team taped the I-skin to different body parts of volunteers, such as the finger, hand and knee. Bending or stretching caused a change in the electrical signal but not bruising, just like human skin. However, forceful and repeated pressing, hitting and pinching produced a color change. The I-skin, which responds like human skin in terms of electrical and optical signaling, opens up new opportunities for detecting damage in prosthetic devices and robotics, the researchers say.
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Quantum computers could outperform classical computers at many tasks, but only if the errors that are an inevitable part of computational tasks are isolated rather than widespread events. Now, researchers at the University of Wisconsin-Madison have found evidence that errors are correlated across an entire superconducting quantum computing chip — highlighting a problem that must be acknowledged and addressed in the quest for fault-tolerant quantum computers.
The researchers report their findings in a study published June 16 in the journal Nature, Importantly, their work also points to mitigation strategies.
“I think people have been approaching the problem of error correction in an overly optimistic way, blindly making the assumption that errors are not correlated,” says UW-Madison physics Professor Robert McDermott, senior author of the study. “Our experiments show absolutely that errors are correlated, but as we identify problems and develop a deep physical understanding, we’re going to find ways to work around them.”
The bits in a classical computer can either be a 1 or a 0, but the qubits in a quantum computer can be 1, 0, or an arbitrary mixture — a superposition — of 1 and 0. Classical bits, then, can only make bit flip errors, such as when a 1 flips to 0. Qubits, however, can make two types of error: bit flips or phase flips, where a quantum superposition state changes.
To fix errors, computers must monitor them as they happen. But the laws of quantum physics say that only one error type can be monitored at a time in a single qubit, so a clever error correction protocol called the surface code has been proposed. The surface code involves a large array of connected qubits — some do the computational work, while others are monitored to infer errors in the computational qubits. However, the surface code protocol works reliably only if events that cause errors are isolated, affecting at most a few qubits.
In earlier experiments, McDermott’s group had seen hints that something was causing multiple qubits to flip at the same time. In this new study, they directly asked: are these flips independent, or are they correlated? More

The phenomenon of quantum nonlocality defies our everyday intuition. It shows the strong correlations between several quantum particles some of which change their state instantaneously when the others are measured, regardless of the distance between them. While this phenomenon has been confirmed for slow moving particles, it has been debated whether nonlocality is preserved when particles move very fast at velocities close to the speed of light, and even more so when those velocities are quantum mechanically indefinite. Now, researchers from the University of Vienna, the Austrian Academy of Sciences and the Perimeter Institute report in the latest issue of Physical Review Letters that nonlocality is a universal property of the world, regardless of how and at what speed quantum particles move.
It is easy to illustrate how correlations can arise in everyday life. Imagine that each day of the month you send two of your friends, Alice and Bob, a toy engine of a set of two for their collection. You can choose each of the engines to be either red or blue or either electric or steam. Your friends are separated by a large distance and do not know about your choice. Once their parcels arrive, they can check the colour of their engine with a device that can distinguish between red and blue or check whether the engine is electric or steam using another device. They compare the measurements made over time to look for particular correlations. In our everyday world, such correlations obey two principles — “realism” and “locality.” “Realism” means that Alice and Bob reveal only what colour or the mechanism of the engine you had chosen in the past, and “locality” means that Alice’s measurement cannot change the colour or the mechanism of Bob’s engine (or vice versa). Bell’s theorem, published in 1964 and considered by some to be one of the most profound discoveries in the foundations of physics, showed that correlations in the quantum world are incompatible with the two principles — a phenomenon known as quantum non-locality.
Quantum nonlocality has been confirmed in numerous experiments, the so-called Bell tests, on atoms, ions and electrons. It not only has deep philosophical implications, but also underpins many of the applications such as quantum computation and quantum satellite communications. However, in all of these experiments, the particles were either at rest or moving at low velocities (scientists call this regime “non-relativistic”). One of the unsolved problems in this field, which still puzzles physicists, is whether nonlocality is preserved when particles are moving extremely fast, close to the speed of light (i.e., in the relativistic regime), or when they are not even moving at a well-defined speed.
For two quantum particles in a Bell’s test which move at high speeds researchers predict that the correlations between the particles are, in principle, reduced. However, if Alice and Bob adapt their measurements in a way that depends on the speed of the particles the correlations between the results of their measurements are still nonlocal. Now imagine that not only are the particles moving very fast, but their velocity is also indefinite: each particle moves in a so-called superposition of different velocities simultaneously, just as the infamous Schrödinger’s cat is simultaneously dead and alive. In such a case, is their description of the world still non-local?
Researchers, led by ?aslav Brukner at the University of Vienna and the Austrian Academy of Sciences, have shown that Alice and Bob can indeed design an experiment which would prove that the world is nonlocal. For this they used one of the most fundamental principles of physics namely that physical phenomena do not depend on the frame of reference from which we observe them. For example, according to this principle, any observer, whether moving or not, will see that an apple falling from a tree will touch the ground. The researchers went a step further and extended this principle to reference frames “attached” to quantum particles. These are called “quantum reference frames.” The key insight is that if Alice and Bob could move with the quantum reference frames along with their respective particles, they could perform the usual Bell test, since for them the particles would be at rest. In this way, they can prove quantum nonlocality for any quantum particle, regardless of whether the velocity is indefinite or close to that of light.
Flaminia Giacomini, one of the study’s authors, says, “Our result proves that it is possible to design a Bell experiment for particles moving in a quantum superposition at very high speeds.” The co-author, Lucas Streiter, concludes, “We have shown that nonlocality is a universal property of our world.” Their discovery is expected to open applications in quantum technologies, such as quantum satellite communications and quantum computation, using relativistic particles.
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In a new study, North Carolina State University researchers demonstrated they could print layers of electrically conductive ink on polyester fabric to make an e-textile that could be used in the design of future wearable devices.
Since the printing method can be completed at room temperature and in normal atmospheric conditions, researchers believe inkjet printing could offer a simpler and more effective method of manufacturing electronic textiles, also known as e-textiles. In addition, researchers said the findings suggest they could extend techniques common in the flexible electronic industry to textile manufacturing. They reported their findings in the journal ACS Applied Materials & Interfaces.
“Inkjet printing is a rapidly advancing new technology that’s used in flexible electronics to make films used in cellphone displays and other devices,” said the study’s corresponding author Jesse S. Jur, professor of textile engineering, chemistry and science at NC State. “We think this printing method, which uses materials and processes that are common in both the electronics and textiles industries, also shows promise for making e-textiles for wearable devices.”
In the study, researchers described how they used a FUJIFILM Dimatix inkjet printer to create a durable and flexible e-textile material, what they did to reliably create the e-textile, and its properties. Part of their challenge was to find the right composition of materials so the liquid ink would not seep through the porous surface of the textile materials and lose its ability to conduct electricity.
“Printing e-textiles has been a very big challenge for the e-textile industry,” said the study’s first author Inhwan Kim, a former graduate student at NC State. “We wanted to build a structure layer by layer, which has not been done on a textile layer with inkjet printing. It was a big struggle for us to find the right material composition.”
They created the e-textile by printing layers of electrically conductive silver ink like a sandwich around layers of two liquid materials, which acted as insulators. They printed those sandwich layers on top of a woven polyester fabric. After they printed the layers of silver ink and insulating materials — made of urethane-acrylate, and poly(4-vinylphenol) — they monitored the surface of the material using a microscope. They found that the chemical properties of the insulating materials, as well as of the textile yarns, were important to maintaining the ability of the liquid silver ink to conduct electricity, and prevent it from penetrating through the porous fabric.
“We wanted a robust insulation layer in the middle, but we wanted to keep it as thin as possible to have the entire structure thin, and have the electric performance as high as possible,” Kim said. “Also, if they are too bulky, people will not want to wear them.”
The researchers evaluated the electrical performance of the e-textile after they bent the material multiple times. They tested more than 100 cycles of bending, finding the e-textile didn’t lose its electrical performance. In future work, they want to improve the materials’ electrical performance compared to e-textiles created using methods that require special facilities and atmospheric conditions, as well as increase the material’s breathability.
Eventually, they want to use the printing method to create an e-textile that could be used in wearable electronics such as biomedical devices that could track heart rate, or used as a battery to store power for electronic devices.
“We were able to coat the ink on the fabric in a multi-layer material that’s both durable and flexible,” Kim said. “The beauty of this is, we did everything with an inkjet printer — we didn’t use any lamination or other methodologies.”
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