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Elusive Quantum Interactions Tracked During Cooling

Over the past few decades, researchers have used ultracold atomic gases to simulate high-temperature superconductors and other materials in which electrons interact strongly. Frustratingly, these experiments have failed to uncover the temperature dependence of certain “p-wave” interactions relevant to some superconductors and superfluids. Now Kenta Nagase and his colleagues at the Institute of Science Tokyo have tracked how these interactions change as a cloud of lithium atoms is cooled toward absolute zero [1]. The results could help scientists better understand the behavior of certain exotic superconductors.

In a p-wave interaction, particles collide with each other in such a way that their interaction strength depends on their relative orientations. The inherent complexity of these interactions, such as their occurrence through three different scattering channels, meant that their predicted temperature dependence lacked experimental confirmation. To surmount this hurdle, Nagase and his colleagues isolated and analyzed the contributions to the interactions from each channel. They repeated their experiment at many temperatures, controlled by the strength of the optical trap confining the lithium cloud.

As they cooled the lithium cloud, Nagase and his colleagues saw that the strength of p-wave interactions increased, in agreement with predictions. These interactions caused the lithium atoms to briefly form fragile molecules, mimicking the pairing of electrons in a superconductor. The measured number, angular distribution, and behavior of such molecules were also consistent with expectations. These properties had been explored in the lab only partially, so the new work provides stronger support for current models of ultracold atomic gases.

Material Strength Doesn’t Follow the Rules

A textbook rule for the relationship between the structure and strength of a material breaks down for high-speed deformations, like those caused by strong impacts.

On the microscale, metallic materials are made of homogeneous crystalline regions—grains—separated by disordered boundaries. In general, materials with smaller grains are stronger because they have more grain boundaries, which impede deformation. But researchers have now demonstrated a radical departure from this rule: With rapid deformation, such as that from an explosive impact, finer grained metals are softer, not harder [1]. This new insight, the researchers hope, could be useful for engineers developing impact-resistant alloys for armor, aerospace structures, or hypersonic vehicles.

The yield strength of a material is the stress (force) at which it begins to deform permanently rather than springing back. At the atomic scale in crystalline materials, this deformation occurs when sections of the crystal slide past one another, facilitated by the motion of structural defects called dislocations. But at grain boundaries, dislocations are halted and can pile up, which translates into resistance to deformation and increased yield strength. Materials with smaller grains have more grain boundaries than those with larger grains, so smaller grains are associated with higher strength.

An ultra-fast quantum tunneling device for the 6G terahertz era

A research team affiliated with UNIST has unveiled a quantum device, capable of ultra-fast operation, a key step toward realizing technologies like 6G communications. This innovation overcomes a major hurdle that has long limited the durability of such devices under high electrical fields.

Professor Hyeong-Ryeol Park from the Department of Physics at UNIST, in collaboration with Professor Sang Woon Lee at Ajou University, has developed a terahertz quantum device that can operate reliably without suffering damage from intense electric fields—something that has been a challenge for existing technologies.

How does glass ‘shake’ and why does it start flowing when pushed hard enough?

Glassy materials are everywhere, with applications far exceeding windowpanes and drinking glasses. They range from bioactive glasses for bone repair and amorphous pharmaceuticals that boost drug solubility to ultra-pure silica optics used in gravitational-wave detectors. In principle, any substance can become glass if its hot liquid is cooled fast enough to avoid forming an ordered crystal.

A distinguishing feature of glass is that its atoms freeze into an irregular, disordered arrangement. This stands in contrast to crystals, where atoms sit in a regular pattern. This disorder gives glass many of its unique and useful properties, but scientists still struggle to understand how atomic-scale disorder produces the properties observed in everyday glasses.

Superconducting detector captures hot spots with submicron resolution

A research team from Osaka Metropolitan University proposed using a current-biased kinetic inductance detector with submicron 400 megapixels to image hot spots induced by a localized external stimulus over a 15 × 15 mm2 area. The team utilized a delay-line technique to trace the propagation of internal signals for a pair of signals arising from each hot spot.

Further, they used the timestamps of signal arrivals at the electrodes to determine the position of each hot spot (x, y). Because the signal velocity inside the detector is ultrafast at about 20% the speed of light, a readout circuit with a temporal resolution faster than 250 ps is necessary to resolve the position of a hot spot with a precision of 1.5 μm, which is the size of a meander pitch.

The research is published in the journal AIP Advances.

Engines of light: New study suggests we could increase useful energy obtained from sunlight

Physicists from Trinity College Dublin believe new insights into the behavior of light may offer a new means of solving one of science’s oldest challenges—how to turn heat into useful energy.

Their theoretical leap forwards, which will now be tested in the lab, could influence the development of specialized devices that would ultimately increase the amount of energy we can capture from sunlight (and lamps and LEDs) and then repurpose to perform useful tasks.

The work has just been published in the journal, Physical Review A.

Laser pulse ‘sculpting’ unlocks new control over particle acceleration

In high-intensity laser–matter interactions, including laser-induced particle acceleration, physicists generally want to work with the highest possible focused laser peak power, which is the ratio of energy per unit area to pulse duration. Therefore, for the same pulse energy and focus, the highest peak intensity can be achieved with the shortest pulse duration.

According to Károly Osvay, head of the National Laser-Initiated Transmutation Laboratory (SZTE NLTL) at the University of Szeged, it has long been known that by changing the so-called spectral phase in a laser pulse, it is possible to ensure that the components of the pulse reach the target in a specific temporal sequence. This ultimately allows the temporal shape of the pulse to be influenced.

“We looked at what happens when we change the relative timing of the frequency components. We confirmed that the order of the components influences which particles we can accelerate best and to what extent. In the case of deuterated solid-state foils, for example, we can change the ratio of accelerated proton and deuteron ions, as well as the ratio of the forward and backward accelerated species. All this is fundamentally influenced by the complex temporal shape of the laser pulse,” said the researcher.

How your brain keeps time: Consistent probability calculations help you react rapidly

Humans respond to environments that change at many different speeds. A video game player, for example, reacts to on-screen events unfolding within hundreds of milliseconds or over several seconds. A boxer anticipates an opponent’s moves—even when their timing differs from that of previous opponents. In each case, the brain predicts when events occur, prepares for what comes next and flexibly adapts to the demands of the situation.

A study by neuroscientists from the Ernst Strüngmann Institute of the Max Planck Society, Goethe University Frankfurt, the Max Planck Institute for Empirical Aesthetics, and New York University, explains how the human brain predicts the timing of future events.

The research, published in the journal Proceedings of the National Academy of Sciences, shows that the brain continuously estimates how likely something is to happen within the next three seconds—and uses this estimate to prepare fast and accurate reactions.

‘Motivation brake’ may explain why it’s so hard to get started on an unpleasant task

Most of us know the feeling: maybe it is making a difficult phone call, starting a report you fear will be criticized, or preparing a presentation that’s stressful just to think about. You understand what needs to be done, yet taking that very first step feels surprisingly hard.

When this difficulty becomes severe, it is known medically as avolition. People with avolition are not lazy or unaware: they know what they need to do, but their brain seems unable to push the “go” button.

Avolition is commonly seen in conditions such as depression, schizophrenia, and Parkinson’s disease, and it seriously disrupts a person’s ability to manage daily life and maintain social functions.

OLED lighting: Corrugated panel design extends longevity and efficiency

The organic light emitting diodes—known widely as OLEDs—that create vibrant smartphone displays could illuminate rooms, but current designs burn out too quickly at the high brightness needed for room lighting. A new approach overcomes this tradeoff by building OLEDs on a corrugated surface, packing more emitting material into a given lighting panel area to produce the same amount of light while operating the OLED itself at lower brightness.

This corrugated panel strategy increased device lifespan by a factor of 2.7 compared to flat panels operated at the same current, according to a study led by the University of Michigan in collaboration with OLEDWorks and The Pennsylvania State University.

“While the problems we solved along the way were daunting, in the end the new device performed tremendously better than predecessors. It’s rewarding to see our ideas point towards a valid path to improve the efficiency and lifetime of OLED lighting,” said Max Shtein, a professor of materials science and engineering and chemical engineering at U-M and co-corresponding author of the study published in Nature Communications.

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