A free-falling video camera enabled researchers to observe a falling cloud of particles and infer the particles’ charges.
Category: particle physics
Using atomic nuclei could allow scientists to read time more precisely than ever
Most clocks, from wristwatches to the systems that run GPS and the internet, work by tracking regular, repeating motions.
To build a clock, you need something that ticks in a perfectly repeatable way. In a pendulum clock, that tick is the regular swinging of the pendulum: back and forth, back and forth, at nearly the same rate each time.
Our team of physicists studies whether an even better kind of clock could one day be built from the atomic nucleus. Today’s best clocks already use atoms to keep extraordinarily accurate time. But in principle, a clock based on a nucleus—the tiny, dense core at the center of an atom—rather than an atom’s electrons, could keep a steadier rhythm because it would be less sensitive to environmental disturbances such as temperature changes. In our research, published in the journal Nature, we measured and interpreted a unique nuclear property of thorium-229 in a crystal that could help make such nuclear clocks possible.
Next-generation atomic clock successfully tested at sea
Adelaide University researchers have successfully tested a new type of portable atomic clock at sea for the first time, using technology that could help power the next generation of navigation, communications and scientific systems. The research team, from the Institute for Photonics and Advanced Sensing (IPAS), developed the highly precise device and trialed it aboard a vessel provided by the Royal Australian Navy in July 2024. They have reported their findings in a new paper published in the journal Optica.
Atomic clocks are the world’s most accurate timekeepers and are essential for technologies such as GPS navigation, telecommunications networks and radio astronomy. However, most high-performance atomic clocks operate in carefully controlled laboratory environments and are not designed to be easily transported or used in challenging real-world conditions. The newly developed device changes that.
Photonics researchers created a portable optical atomic clock that uses laser-cooled atoms of the element ytterbium to keep time with extreme precision. By cooling the atoms with lasers and measuring a very specific atomic transition, the clock can track time far more accurately than conventional systems.
Copper blasted into a million-degree plasma strips away 22 electrons in a flash before atoms recover
When laser flashes hit matter, electrons are knocked off their orbits around the atomic nuclei. This can generate extremely hot plasmas composed of charged particles—ions and electrons. Researchers at HZDR have now observed this ionization process in more detail than ever before. To do so, they combined two state-of-the-art lasers: the X-ray free-electron laser and the high-intensity optical laser ReLaX at the HED-HiBEF experiment station at the European XFEL in Schenefeld, near Hamburg. Their findings, published in Nature Communications, deliver fundamental insights into the interaction of high-energy lasers and matter under extreme conditions.
Ionization takes place extremely quickly—in picoseconds, within a few trillionths of seconds. In order to monitor this process in detail, laser pulses must be significantly shorter. “These are exactly the conditions provided by the two lasers that have pulse durations of just 25 and 30 femtoseconds—that is, trillionths of a second,” explains Dr. Lingen Huang, head of experimentation in HZDR’s Division of High-Energy Density.
Initially, an extremely intense flash of light strikes a delicate copper wire that is only about one-seventh the thickness of a human hair. The pulse intensity is approximately 250 trillion megawatts per square centimeter—concentrated on a tiny surface for an extremely short time. Values like this are otherwise achieved only under exceptional conditions, such as in extreme astrophysical environments like the immediate vicinity of neutron stars or during gamma-ray bursts.
Torsion balances set strongest direct limits yet on ultralight dark matter
Dark matter is believed to make up a large fraction of the matter in the universe, yet its true nature remains unknown. Most past experiments have focused on heavier dark matter candidates, while much lighter dark matter, with masses closer to the mass of a neutrino, has been difficult to detect directly because its scattering signals are extremely weak.
An international team of researchers has found that torsion-balance experiments —precision instruments originally built to test the equivalence principle—can double as detectors for very light dark matter. The study, published in Physical Review Letters, provides the strongest direct detection limits to date on interactions between dark matter and nucleons in this mass range from about 0.01 to 1 eV.
The team of researchers, including The University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) Professor Shigeki Matsumoto and Kavli IPMU Todai Postdoctoral Research Fellow and JSPS Fellow Jie Sheng, focused on one key physical effect: when dark matter is sufficiently light, its number density in a galaxy becomes very high, and its scattering cross section with macroscopic objects can also be greatly enhanced by coherent effects.
Mirror-positioning method could make quantum gravity tests possible
In quantum physics, objects can exist in multiple states at the same time—a phenomenon known as quantum superposition, where a particle does not have a single definite value of position or momentum until it is measured. A major open question is whether gravity, one of the fundamental forces, also follows the quantum rule. One way to examine this is through gravity-induced entanglement, in which two objects that interact only via gravity become quantum mechanically linked.
Now, researchers led by Professor Kazuhiro Yamamoto at the Faculty of Science and Quantum and Spacetime Research Institute, Kyushu University, have proposed a way to enhance the quantum superposition of a mirror’s position in systems in which two mirrors interact via gravity, thereby making the resulting entanglement signal easier to detect. Their findings, published in the journal Physical Review Research on April 13, 2026, represent a crucial step toward experimentally testing whether gravity is fundamentally quantum.
Gravity-induced entanglement suggests that if gravity follows quantum mechanics, then two objects interacting only through gravity should become entangled. This is a natural prediction of the quantum nature of gravity. Detecting this effect, however, is challenging as gravity is weak at small scales.
Graphene as a charge mirror: Why water droplets ‘see’ graphene—but don’t show it
Research on graphene has made great strides in recent years. However, to fully harness its potential in applications such as desalination membranes, sensors, and energy storage and conversion, a deeper understanding of the interaction between graphene and water is required.
Until now, it was widely thought that graphene, when supported on a substrate, largely inherits the wetting properties of the underlying material, a phenomenon known as “wetting transparency.” An international research team led by Yongkang Wang and Yair Litman has now shown that, while graphene appears transparent on large scales, it exerts a subtle but significant influence on nearby water molecules at the nanoscale. The study is published in the journal Chem.
Graphene, a carbon layer just one atom thick, is considered a wonder material: extremely stable, highly conductive, and optically transparent. For a long time, it appeared just as transparent to water: measurements of the water contact angle—a measure of wettability—showed that graphene on a substrate lets through the substrates wettability virtually unchanged. This phenomenon of wetting transparency, observed for years, seemed to contradict the fact that graphene is highly polarizable and therefore reacts sensitively to charges in the substrate.
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The once-theoretical skyrmion could unlock supercomputing memory
When looking to the future of information technology, researchers have pinpointed a once-theoretical particle-like structure: the skyrmion. Magnetic skyrmions are very stable structures found on micromagnetic materials that have a vortex-like spin. Because they can be moved with minimal electrical current, these structures could help develop memory to power the next generation of computing without consuming a lot of power.
But until recently, the fundamental properties of the skyrmion remained a mystery to researchers. In a paper published in Nature Communications, researchers shared new details and properties about these structures.
“Skyrmions are highly stable and move with minimal electrical current, paving the way for next-generation memory with extremely low power consumption. It’s the ultimate miniaturization, utilizing ‘world-class’ 2-nanometer structures that will allow ultra-high-density data storage and much smaller electronic devices,” said Kosuke Nakayama, a professor at Tohoku University in Sendai, Japan.
Cracking a 16-year proton mystery as ultra-precise hydrogen measurements confirm a smaller-than-expected core
The simplicity of a hydrogen atom makes it an ideal model for studying atomic structure and interactions. Yet, despite the fact that its simplest form consists of only one proton and one electron, physicists have had a hard time pinning down the exact charge radius of the proton. But a new study, published in the journal Physical Review Letters, outlines a method of measurement that helps to resolve some past discrepancies.
In the quest to better understand one of the universe’s most important building blocks, several research teams have focused on measuring the proton’s charge radius—a measure of the spatial distribution of electric charge from a proton—using hydrogen spectroscopy. Some research teams did these experiments with normal hydrogen atoms and some with a form of hydrogen called muonic hydrogen. Muonic hydrogen is an exotic hydrogen atom consisting of a negatively charged muon bound to a proton, instead of an electron bound to a proton.
Theoretically, the protons in both regular and muonic hydrogen should have the same proton charge radius. However, some experimental results have shown disagreements regarding the rather precise measurements of muonic hydrogen’s charge radius, which gave a smaller value. This discrepancy is referred to as the “proton radius puzzle,” and it has plagued physicists since 2010, when the first results from a highly precise muonic hydrogen spectroscopy experiment came out.