Category: Physics

A team of physicists has discovered an unusual form of matter—not a conventional metal, insulator, or magnet, for example, but something entirely different.

This phase, characterized by an unusual ordering of electrons, offers possibilities for new electronic device functionalities and could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity—the ability for some materials to conduct electricity without resistance, even at “high” temperatures approaching –100 degrees Celsius.

“The discovery of this phase was completely unexpected and not based on any prior theoretical prediction,” says David Hsieh, an assistant professor of physics at California Institute of Technology (Caltech), who previously was on a team that discovered another form of matter called a topological insulator.

“The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties.”

Hsieh and his colleagues describe their findings in Nature Physics. Liuyan Zhao, a postdoctoral scholar in Hsieh’s group, is lead author.

Above, an artist’s rendition of spatially segregated domains of multipolar order in the Sr₂IrO₄ crystal. The orientation of the multipolar order in each domain is depicted by the multi-lobed object. (Credit: Liuyan Zhao)

PICTURE ELECTRONS IN A CRYSTAL

The physicists made the discovery while testing a laser-based measurement technique that they recently developed to look for what is called multipolar order. To understand multipolar order, first consider a crystal with electrons moving around throughout its interior. Under certain conditions, it can be energetically favorable for these electrical charges to pile up in a regular, repeating fashion inside the crystal, forming what is called a charge-ordered phase. The building block of this type of order, namely charge, is simply a scalar quantity—that is, it can be described by just a numerical value, or magnitude.

In addition to charge, electrons also have a degree of freedom known as spin. When spins line up parallel to each other (in a crystal, for example), they form a ferromagnet—the type of magnet you might use on your refrigerator and that is used in the strip on your credit card. Because spin has both a magnitude and a direction, a spin-ordered phase is described by a vector.

Over the last several decades, physicists have developed sophisticated techniques to look for both of these types of phases. But what if the electrons in a material are not ordered in one of those ways? In other words, what if the order were described not by a scalar or vector but by something with more dimensionality, like a matrix?

This could happen, for example, if the building block of the ordered phase was a pair of oppositely pointing spins—one pointing north and one pointing south—described by what is known as a magnetic quadrupole. Such examples of multipolar-ordered phases of matter are difficult to detect using traditional experimental probes.

As it turns out, the new phase that the Hsieh group identified is precisely this type of multipolar order, they just had to figure out how to detect it. Find out how they approached that puzzle on the next page…

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In what can only be described as a happy accident, scientists at the University of Chicago and Penn State University have discovered a way to “paint” quantum circuits on a topological insulator grown on a particular substrate using a specific frequency of ultraviolet light. This new breakthrough enables scientists to draw – and erase – circuits on the topological insulators noninvasively, which makes working with the volatile material much simpler than ever before.

An amazing article on the Science Daily website reveals the details:

“This observation came as a complete surprise,” said David D. Awschalom, Liew Family Professor and deputy director in the Institute of Molecular Engineering at UChicago, and one of two lead researchers on the project. “It’s one of those rare moments in experimental science where a seemingly random event — turning on the room lights — generated unexpected effects with potentially important impacts in science and technology.”

The article continues:

“To be honest, we were trying to study something completely different,” said Andrew Yeats, a graduate student in Awschalom’s laboratory and the paper’s lead author. “There was a slow drift in our measurements that we traced to a particular type of fluorescent lights in our lab. At first we were glad to be rid of it, and then it struck us — our room lights were doing something that people work very hard to do in these materials.”

The researchers found that the surface of strontium titanate, the substrate material on which they had grown their samples, becomes electrically polarized when exposed to ultraviolet light, and their room lights happened to emit at just the right wavelength. The electric field from the polarized strontium titanate was leaking into the topological insulator layer, changing its electronic properties.

Awschalom and his colleagues found that by intentionally focusing beams of light on their samples, they could draw electronic structures that persisted long after the light was removed.

“It’s like having a sort of quantum etch-a-sketch in our lab,” he said. They also found that bright red light counteracted the effect of the ultraviolet light, allowing them to both write and erase. “Instead of spending weeks in the cleanroom and potentially contaminating our materials,” said Awschalom, “now we can sketch and measure devices for our experiments in real time. When we’re done, we just erase it and make something else. We can do this in less than a second.”

Interestingly, the effect is not limited to topological insulators, but extends to other materials that are grown on the same substrate:

“In a way, the most exciting aspect of this work is that it should be applicable to a wide range of nanoscale materials such as complex oxides, graphene, and transition metal dichalcogenides,” said Awschalom

We’re looking forward to what this accidental breakthrough in quantum computing will enable. In the meantime, you can learn more about it via Science Daily’s excellent article.

 

Source: ScienceDaily.com – “Scientists paint quantum electronics with beams of light“

Featured Image Source: Peter Allen

Ryan Wilkinson, Durham University and Celine Boehm, Durham University

Canada’s Arthur B McDonald and Japan’s Takaaki Kajita have won this year’s
Nobel Prize in Physics for their surprising discovery that tiny, subatomic particles called neutrinos have mass.

Their experimental results forced scientists to rethink the “Standard Model” of particle physics that had successfully explained all observations of the subatomic world for decades.

What are neutrinos?

Neutrinos are produced when radioactive isotopes decay and have been shrouded in mystery ever since Wolfgang Pauli first proposed them in 1930. In the Standard Model, they were assumed to have no mass (like particles of light, photons) and be neutral (lacking electric charge). This would also explain why neutrinos usually pass straight through matter without interacting, making them extremely difficult to detect. Enormous instruments are required to observe them in sufficient numbers to study their properties.

Neutrinos were first directly observed by the Cowan-Reines experiment in 1956, using neutrinos from a nuclear reactor and two large tanks of water. If a neutrino interacted with a nucleus in the detector, this would result in a flash of light that could be picked up by photomultiplier tubes that were sandwiched between the tanks. Frederick Reines was awarded the Nobel Prize in 1995 for this work.

Where the neutrino fits in the subatomic family.
MissMJ – Own work by uploader, PBS NOVA, Fermilab, Office of Science, United States Department of Energy, Particle Data Group, CC BY

However, when detectors became sensitive enough to observe neutrinos created in nuclear reactions in the Sun, scientists faced a big problem.
They had calculated the amount of neutrinos from the Sun that should be hitting the Earth, but observed only a third of this number in their experiments. A further Nobel Prize was presented to Ray Davis in 2002 for this discovery. The mystery of these missing neutrinos was coined the “solar neutrino problem” and remained a puzzle for forty years, until the collaborations led by Kajita and McDonald made their exciting discovery.

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There’s a good chance that at some point in your life you’ve yearned for the technology that could teleport you from wherever you were to the place you wanted to be. It turns out that teleportation tech may be closer to reality that you might have thought.

For many people the word “teleportation” conjures up “Beam me up, Scotty” images from Star Trek. But in the last two decades, quantum teleportation—transferring the quantum structure of an object from one place to another without physical transmission—has moved from the realms of science fiction to tangible reality.

Quantum teleportation is an important building block for quantum computing, quantum communication, and quantum network and, eventually, a quantum internet. While theoretical proposals for a quantum internet already exist, the problem for scientists is that there is still debate over which technology provides the most efficient and reliable teleportation system.

In a new paper, published in Nature Photonics, scientists reviewed the theoretical ideas around quantum teleportation focusing on the main experimental approaches and their associated advantages and disadvantages.

None of the technologies alone provide a perfect solution—the scientists say a hybridization of the various protocols and underlying structures offer the most fruitful approach.

For instance, systems using photonic qubits work over distances up to 143 kilometers, but they are probabilistic in that only 50 percent of the information can be transported. To resolve this, such photon systems may be used in conjunction with continuous variable systems, which are 100 percent effective but currently limited to short distances.

Most importantly, teleportation-based optical communication needs an interface with suitable matter-based quantum memories where quantum information can be stored and further processed.

“We don’t have an ideal or universal technology for quantum teleportation,” says Stefano Pirandola of the computer science department at the University of York. “The field has developed a lot but we seem to need to rely on a hybrid approach to get the best from each available technology.

“The use of quantum teleportation as a building block for a quantum network depends on its integration with quantum memories. The development of good quantum memories would allow us to build quantum repeaters, therefore extending the range of teleportation. They would also give us the ability to store and process the transmitted quantum information at local quantum computers.

“This could ultimately form the backbone of a quantum internet. The revised hybrid architecture will likely rely on teleportation-based long-distance quantum optical communication, interfaced with solid state devices for quantum information processing.”

Researchers from the University of Toronto, the Freie Universität Berlin, and the University of Tokyo coauthored the study.

 

Source: Reproduced from Futurity.org with a new title and minor additions to the original by David Garner under the Creative Commons Attribution 4.0 International license.

Feature Image Credit:  JD Hancock/Flickr

Spin wins tennis matches. Period. The ability to put spin on the ball and ace your opponent is key. But who figured that out first?  A fascinating article on Wired’s website delves into the details.

First of all, how does a player generate spin with their racquet?

In order to generate spin, you have to brush your racquet up across the ball, rather than strike it dead on. The motion looks kind of like you are giving the ball a weird high five. Starting low, with the racquet at your waist, you bring it up and forward, twisting with your hips and elbow so the racquet’s head finishes high above your opposite shoulder.

And that’s not all. “For a good topspin, you have to tilt the racquet at a good angle, too,” says Crawford Lindsey, head tester at the Tennis Warehouse University, a tennis testing website (with some seriouslyawesomestudies). “You don’t present much face to the ball, because everything is slanted.”

The best angle for your racquet’s forward face is around 50 degrees, or less, relative to the surface of the ground. This puts spin on the ball, but also makes it a lot easier to ding the ball with the rim. “Bigger racquets give you more surface area, and therefore safety, so you can swing faster and at a greater angle,” says Lindsey.

However, the technique can be greatly enhanced by the technology, so you may wonder: who thought about that first?  The article continues:

The modern, spin-dominated game of tennis owes everything to an inventor named Howard Head. In the late 1940s, Head was an airplane mechanic, and he was learning to ski. He liked the sport, but didn’t like lugging the heavy wooden planks up the hill between each run. His frustration became the first aluminum skis, which he patented and used to form the Head Ski Company.

What’s that got to do with tennis? A few decades later, Head sold his company, retired, and took up tennis. Like, he went all in: built a court at his house, hired a coach, bought a newfangled ball machine. But again, he found a sport that wasn’t quite designed right. First of all, his ball machine was wack. So he bought the company the made it—Prince—and invented a better version.

Then he went after the personal gear. Like with skiing, tennis was dominated by wood. But that medium restricted the racquets’ head area to about 60 square inches—the frame would break if it got any bigger. “There just wasn’t enough margin of error with a racquet that size,” says Rod Cross, a retired physicist in Australia who studies tennis physics. So Head brought his aluminum expertise to bear on the problem, and invented the sturdier aluminum Prince Classic. His patent covered tennis racquets with heads up to 125 square inches.

Howard Head’s big headed racquets let players attack the ball with more angle on their swings. (He later introduced graphite frames, which are even lighter and stronger.) But frame size is only part of the racquet design equation.

Read on, as we explore what else influences that critical equation…

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Eugene Lim, King’s College London
The existence of parallel universes may seem like something cooked up by science fiction writers, with little relevance to modern theoretical physics. But the idea that we live in a “multiverse” made up of an infinite number of parallel universes has long been considered a scientific possibility – although it is still a matter of vigorous debate among physicists. The race is now on to find a way to test the theory, including searching the sky for signs of collisions with other universes.

It is important to keep in mind that the multiverse view is not actually a theory, it is rather a consequence of our current understanding of theoretical physics. This distinction is crucial. We have not waved our hands and said: “Let there be a multiverse”. Instead the idea that the universe is perhaps one of infinitely many is derived from current theories like quantum mechanics and string theory.

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