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Category: particle physics – Page 366

Spin valve uses coupled quantum dots and tiny magnetic fields

Researchers in Switzerland and Italy have developed a new method for generating currents of spin-polarized electrons without the need for large external magnetic fields. This could enable the development of devices that are compatible with superconducting electronic components, paving the way for the next generation of highly efficient electronics.

Emerging in the 1980s, “spintronics” is dedicated to creating practical devices that exploit electron spin. Semiconductor-based spintronics systems have garnered particular interest because semiconductors can be integrated within modern-day electronics with the aim of improving the efficiency and storage capacity of devices. But to make useful spintronics devices, researchers must control and detect the spin state of electrons with a high level of accuracy.

One way of controlling electron spin current is a “spin valve”, which usually consists of a non-magnetic material sandwiched between ferromagnetic materials. Electrons in one spin state (say up) can propagate through the device, while spin-down electrons are reflected or scattered away. The result is a “spin polarized current” in which all electrons are either spin-up or all spin-down) – at least in principle.

Tiny particles produce huge photon avalanches

Researchers in the US, Poland and Korea have observed photon avalanching – a chain-reaction-like process in which the absorption of a single photon triggers the emission of many – in tiny crystals just 25–30 nm in diameter. This highly nonlinear phenomenon had previously only been seen in bulk materials, and team leader James Schuck says that replicating it in nanoparticles could lead to “revolutionary new applications” in imaging, sensing and light detection (Nature 589 230).

Photon avalanching involves a process known as upconversion, whereby the energy of the emitted photons is higher than the energy of the photons that triggered the avalanche. Materials based on lanthanides (chemical elements with atomic numbers between 57 and 71) can support this process in part because their internal atomic structure enables them to store energy for long periods of time. Even so, achieving photon avalanching in lanthanide systems is difficult because high concentrations of lanthanide ions are needed to keep the avalanche going, and the relatively large volume of material required has previously restricted applications.

In the latest work, Schuck and colleagues at Columbia University, together with collaborators at Lawrence Berkeley National Laboratory, the Polish Academy of Sciences and Sungkyunkwan University, observed photon avalanching in lanthanide nanocrystals after exciting them with a laser at near-infrared wavelengths of either 1,064 or 1450 nm. The crystals are based on sodium yttrium fluoride in which 8% of the yttrium ions have been replaced with thulium. This doping fraction is much higher than the 0.2–1% typically found in previous work on photon avalanching.

Atomic quantum processors make their debut

Two research groups demonstrate quantum algorithms using neutral atoms as qubits. Tim Wogan reports.

The first quantum processors that use neutral atoms as qubits have been produced independently by two US-based groups. The result offers the possibility of building quantum computers that could be easier to scale up than current devices.

Two technologies have dominated quantum computing so far, but they are not without issues. Superconducting qubits must be constructed individually, making it nearly impossible to fabricate identical copies, so the probability of the output being correct is reduced – causing what is known as “gate fidelity”. Moreover, each qubit must be cooled close to absolute zero. Trapped ions, on the other hand, have the advantage that each ion is guaranteed to be indistinguishable by the laws of quantum mechanics. But while ions in a vacuum are relatively easy to isolate from thermal noise, they are strongly interacting and so require electric fields to move them around.

Time crystals: the search for a new phase of matter

Pedram Roushan, from Google’s Quantum AI team in California, describes this elusive form of matter – and how it could be simulated on the company’s Sycamore quantum processor.

With their enchanting beauty, crystalline solids have captivated us for centuries. Crystals, which range from snowflakes to diamonds, are made up of atoms or molecules that are regularly arranged in space. They have provided foundational insights that led to the development of the quantum theory of solids. Crystals have also helped develop a framework for understanding other spatially ordered phases, such as superconductors, liquid crystals and ferromagnets.

Periodic oscillations are another ubiquitous phenomenon. They appear at all scales, ranging from atomic oscillations to orbiting planets. For many years, we used them to mark the passage of time, and they even made us ponder the possibility of perpetual motion. What is common between these periodic patterns – either in space or time – is that they lead to systems with reduced symmetries. Without periodicity, any position in space, or any instance of time, is indistinguishable from any other. Periodicity breaks the translational symmetry of space or time.

Astronomers Radically Reimagine the Making of the Planets

Now look out past the sun, way beyond. Most of the stars harbor planets of their own. Astronomers have spotted thousands of these distant star-and-planet systems. But strangely, they have so far found none that remotely resemble ours. So the puzzle has grown harder: Why these, and why those?

The swelling catalog of extrasolar planets, along with observations of distant, dusty planet nurseries and even new data from our own solar system, no longer matches classic theories about how planets are made. Planetary scientists, forced to abandon decades-old models, now realize there may not be a grand unified theory of world-making—no single story that explains every planet around every star, or even the wildly divergent orbs orbiting our sun. “The laws of physics are the same everywhere, but the process of building planets is sufficiently complicated that the system becomes chaotic,” said Alessandro Morbidelli, a leading figure in planetary formation and migration theories and an astronomer at the Côte d’Azur Observatory in Nice, France.

Still, the findings are animating new research. Amid the chaos of world-building, patterns have emerged, leading astronomers toward powerful new ideas. Teams of researchers are working out the rules of dust and pebble assembly and how planets move once they coalesce. Fierce debate rages over the timing of each step, and over which factors determine a budding planet’s destiny. At the nexus of these debates are some of the oldest questions humans have asked ourselves: How did we get here? Is there anywhere else like here?

Scientists Are Getting Better and Better at Levitating Objects With Sound Waves

Researchers have come up with a new and improved way to levitate objects using sound waves alone, an impressive feat of mixed-reality technology that could pave the way for some seriously futuristic hologram-like displays.

As seen in a new video, the researchers were able to levitate individual polystyrene beads and water particles inside a special enclosure, making them move in three dimensions by adjusting the output of hundreds of small speakers, set up in a grid.

In one demonstration, they were even able to float a tiny piece of fabric in midair, on which they projected a movie of a leaping rabbit.

Silicon Quantum Computing announces world’s first quantum integrated circuit

After a Sydney-based firm built the world’s first atomic-scale quantum integrated circuit.

Sydney-based firm Silicon Quantum Computing (SQC) built the first integrated silicon quantum computer circuit manufactured at the atomic scale, in what has been touted as a “major breakthrough” on the road to quantum supremacy, a press statement reveals.

The atomic-scale integrated circuit, which functions as an analog quantum processor, may be SQC’s biggest milestone since it announced in 2012 that it had built the world’s first single-atom transistor.

Tiny fish-shaped robot ‘swims’ around picking up microplastics

Microplastics are found nearly everywhere on Earth and can be harmful to animals if they’re ingested. But it’s hard to remove such tiny particles from the environment, especially once they settle into nooks and crannies at the bottom of waterways. Now, researchers in ACS’ Nano Letters have created a light-activated fish robot that “swims” around quickly, picking up and removing microplastics from the environment.

Because microplastics can fall into cracks and crevices, they’ve been hard to remove from aquatic environments. One that’s been proposed is using small, flexible and self-propelled robots to reach these pollutants and clean them up. But the used for soft robots are hydrogels and elastomers, and they can be damaged easily in aquatic environments. Another material called mother-of-pearl, also known as nacre, is strong and flexible, and is found on the inside surface of clam shells. Nacre layers have a microscopic gradient, going from one side with lots of calcium carbonate mineral-polymer composites to the other side with mostly a silk protein filler. Inspired by this , Xinxing Zhang and colleagues wanted to try a similar type of gradient structure to create a durable and bendable material for .

The researchers linked β-cyclodextrin molecules to sulfonated graphene, creating composite nanosheets. Then solutions of the nanosheets were incorporated with different concentrations into polyurethane latex mixtures. A layer-by-layer assembly method created an ordered concentration gradient of the nanocomposites through the material from which the team formed a tiny fish robot that was 15-mm (about half-an-inch) long. Rapidly turning a near-infrared light laser on and off at a fish’s tail caused it to flap, propelling the robot forward. The robot could move 2.67 body lengths per second—a that’s faster than previously reported for other soft swimming robots and that is about the same speed as active phytoplankton moving in water. The researchers showed that the swimming fish robot could repeatedly adsorb nearby polystyrene microplastics and transport them elsewhere. The material could also heal itself after being cut, still maintaining its ability to adsorb microplastics.