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Category: particle physics – Page 14

Physics-aware benchmark reveals why similar materials AI models can predict thermal conductivity differently

Material properties such as sound insulation, resistance to extreme heat and thermal expansion originate from how the zillions of microscopic building blocks (nuclei and electrons) interact at equilibrium and respond to perturbations. Atoms are typically about one ten-billionth of a meter across, so there can be a lot of parts to keep track of—a task that is complicated at the quantum-mechanical level, where particles are neither here nor there until observed.

In recent years, researchers have turned to machine learning (ML) to overcome the challenges of tracking countless quantum particles while connecting these atomic-level details to observable physical properties. Models abound, but can they be trusted?

In a new paper published in Nature Communications, Michele Simoncelli, assistant professor of applied physics at Columbia, sets a benchmark for evaluating ML models that aim to predict the thermal and mechanical properties of different materials.

To Lase or Not to Lase: The Question of Neutrino Superradiance

Two studies find that fundamental quantum constraints rule out a previously proposed neutrino-laser scheme.

One of the most striking demonstrations of collective quantum behavior is superradiance. When photons emitted by many particles carry no information about which particle produced them, the different emission pathways interfere constructively, and the ensemble radiates far more intensely than independent emitters would. Last year, scientists proposed that this principle could extend from photons to neutrinos, potentially enabling the first neutrino laser (see Viewpoint: Envisioning a Neutrino Laser) [1]. The idea was especially appealing because neutrinos are otherwise extremely difficult to control and detect, owing to their weak interactions with matter. Now Wolfgang Ketterle and his colleagues at MIT have demonstrated that this vision of neutrino superradiance runs up against fundamental constraints—ones imposed not by engineering challenges but by quantum mechanics itself [2, 3].

Superradiance is a collective enhancement of spontaneous emission [4]. An isolated atom emits at its natural rate γ so N independent atoms radiate at a total rate N γ But when all the atoms radiate into the same mode, constructive interference of the different emission pathways can cause the maximum emission rate to scale as N2 γ This superradiant regime can occur when the atoms occupy a region much smaller than the radiation’s wavelength or when an optical cavity forces them to couple to a common mode [5–7]. Such collective emission can also arise in extended atomic systems, where it becomes directional and is shaped by propagation effects. This extended-ensemble superradiance has been observed in free space [8] and in waveguides [9].

A photon that challenges Einstein: According to current physics, it should never have reached Earth

How did a photon survive a journey of more than 2 billion light-years when, according to known physics, it should have been absorbed long before reaching Earth? This is the question at the heart of a new study by Giorgio Galanti (INAF) and Marco Roncadelli (INFN), accepted for publication in Physical Review Letters.

The research addresses one of the most fascinating puzzles in contemporary astrophysics. It proposes a possible explanation for the highest-energy photon ever observed from a gamma-ray burst, suggesting that under extreme conditions spacetime may behave differently from what Einstein’s theory of relativity predicts.

At the center of the story is the brightest gamma-ray burst ever observed, GRB 221009A, nicknamed BOAT by astronomers—the Brightest Of All Time. The explosion, which occurred about 2 billion light-years from Earth and was observed on Oct. 9, 2022, reached our planet as an enormous shower of photons, the elementary particles of light.

Fast radio bursts could help disentangle galactic feedback from dark matter effects

Intense, brief flashes of radio light called fast radio bursts (FRBs) travel across billions of light-years to reach Earth, passing through a fog of matter along the way. The bursts’ origins are unclear but may originate from highly magnetized dead stars called magnetars. The denser the fog through which FRBs travel, the more dispersed their signals become—similar to the way a prism splits white light into a rainbow of colors.

Thanks to this dispersive property, FRBs make excellent tracers of how ordinary matter is distributed in the universe; ordinary matter is the same stuff that makes up people, planets, stars and anything made of subatomic particles called baryons. As the FRB radio beams pass through this matter in our universe, they can essentially map out how much is present and how clumpy it is.

In a new Nature Astronomy study, researchers show how these FRB measurements can help solve some of the biggest questions in cosmology.

Curved nanographene with five-, six- and seven-membered rings synthesized in two steps

Nanographenes can be considered molecular fragments of graphene, a 2D conductive material in which carbon atoms are connected in a honeycomb pattern. Because their electronic and photophysical properties vary depending on the size and shape of the molecule, nanographenes are expected to find applications in OLEDs, organic solar cells, organic field-effect transistors and more.

For this, simple methods for synthesizing nanographenes that avoid complex multistep processes are desired. Now, a team of scientists from WPI-ITbM at Nagoya University and RIKEN has established a new two-step annulative π-extension (APEX) method that generates structurally diverse nanographenes. This research is published in the journal Angewandte Chemie International Edition.

Princeton AI Tames Fusion Plasma Hotter Than the Sun

Princeton’s PACMAN AI can control fusion plasma in milliseconds and predict dangerous instabilities before they start.

In some fusion energy systems, particles can reach temperatures hotter than the center of the Sun. The challenge is keeping that extreme plasma under control, because disturbances can develop within just a few thousandths of a second, much faster than a person could respond.

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University have developed a new software framework that uses artificial intelligence (AI) to make those rapid control decisions. The system is designed to respond at machine speed while maintaining strict safety protections and leaving the overall goals in human hands.

Physicists Find Useful Energy Hiding in Quantum “Waste Heat”

A new theoretical approach helps connect quantum physics with classical thermodynamics by clarifying what counts as heat and useful work in tiny quantum machines.

When a machine is reduced to a single atom and particles of light, even basic concepts such as heat and useful work become difficult to define. This problem sits at the intersection of thermodynamics and quantum physics, and researchers at the University of Basel in Switzerland have developed a theoretical framework that brings the two descriptions into agreement.

Thermodynamics and quantum physics emerged to explain very different scales of nature. Thermodynamics took shape in the 19th century to describe machines such as steam engines, while quantum physics arose in the early 20th century to explain atoms and subatomic particles. Modern quantum technologies now bring those worlds together because tiny systems built from atoms and light particles (photons) can absorb, transform, and release energy, effectively operating as miniature quantum machines.

Scientists observe Einstein’s gravity in the quantum world for the first time

Physicists have directly observed a long-predicted quantum effect of gravity, putting one of Einstein’s foundational ideas to a striking new test. Using ultracold atoms, researchers split an atom’s quantum wave so that one part was held in place while the other fell freely under gravity, then reunited the two to measure the tiny difference that emerged.

Reversible electric control unlocks persistent chiral phonon states

Atoms in a material are rarely still. They jiggle back and forth in collective lattice vibrations known as phonons. Their motion can also carry a rotational element: In 2023, scientists at PSI experimentally proved the existence of chiral phonons, which exhibit handedness depending on which way they rotate.

Now, the same team of researchers has shown that an applied electric field can control the handedness of these phonons. The research is published in the journal Nature Materials.