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Explaining the difference between brittle and ductile behavior in polymer glasses

Glasses are (mostly) brittle, metals can be ductile (plastic), and liquids flow easily. Polymers are interesting because they exhibit all three types of behavior, depending on their chemical nature, temperature, and deformation rate. If polymers are not able to crystallize, their low-temperature state is glassy, and they are hard and transparent. One example is poly(methylmethacrylate) [PMMA], which has been used as an artificial glass since the early 20th century.

Surprisingly, polymer glasses can be ductile at temperatures significantly below their glass transition temperature, Tg. For a typical laboratory strain rate (~10⁻³ s⁻¹), the brittle-ductile transition temperature (BDT or TBD) can be 50–100 K below Tg. This result is surprising—naively, one would expect a “glass” to be brittle—yet polymers can deform plastically well below Tg.

Slow-motion electron camera reveals light-driven quantum jumps in graphene

Using a new slow-motion electron camera, physicists from Regensburg, Marburg and Jülich revealed how intense electric fields drive electrons in graphene, causing them to jump across energy gaps in a seemingly paradoxical manner. This was made possible by a novel combination of laser technology and electron microscopy.

The electrons’ behavior is roughly equivalent to riding an elevator where the floor indicator suddenly jumps from “1,” “2,” and “3” to “20.” You never passed through the 17 floors in between, yet you arrive on the 20th floor. What sounds like an impossible leap is actually possible in the quantum world. Such processes are called Landau-Zener-Majorana transitions. It has long been suspected that these transitions could play an increasingly important role in high-speed semiconductor electronics.

A research team from the University of Regensburg, Philipps-Universität Marburg and the Forschungszentrum Jülich has succeeded in visualizing the ultrafast dynamics of such transitions in the material graphene. The team reports on this achievement in its latest study, published in the journal Nature.

When simulations fall short, this spectrometer learns for itself

An NMR spectrometer can reveal molecular structure down to the atomic level, but weak signals limit what it can see. Now, Aarhus University researchers have used AI to let the spectrometer learn the best pulse sequence directly from the sample.

Imagine trying to shepherd a group of sugar-fueled children through an amusement park. You cannot work out in advance exactly which combination of words, tone of voice, timing and body language will keep everyone moving in the right direction. The children react differently, they influence one another, and the larger the group, the harder it becomes to predict what will work.

At some point, the best strategy is simply to try something, see what happens and adjust.

Scientists uncover new way to control magnetism and topology using light in atomically thin materials

Envision a material whose magnetic properties and electronic topology can be toggled by exposure to light, paving the way for future electronic devices that do not rely on traditional electrical switching, which wastes energy by producing heat.

Researchers at Monash University have predicted that this kind of switching is possible in the two-dimensional magnetic topological material MnBi₂Te₄, through a type of hybrid light–matter excitation they call magnetophononic polaritons. The study is published in ACS Nano.

“Controlling magnetism and topology with light has long been a challenge in topological quantum materials research. Our calculations show a way to achieve both at once, which could enable ultrafast on–off switching of topological states,” said Dr. Enamul Haque, the study’s first author, who carried out the work during his Ph.D. at Monash University.

Decoding the loopy physics of hula hooping with high-tech earthquake sensors

Hula hooping may be literal child’s play, but as it turns out, the physics behind the gym-class staple is so complicated that scientists have spent decades trying to understand how the hula hoop defies gravity.

Multiple scientific papers have been devoted to this minor mystery: How do one’s hips and legs collude with friction and centrifugal forces to keep a simple toy spinning in midair? The still-unresolved question led a team of UC Berkeley-affiliated engineers to tackle the problem by using an innovative method to analyze motion-tracking data.

Their results, recently published in the journal Nonlinear Dynamics, challenge 20 years of conventional wisdom about hula hooping—and suggest a better way to model complex mechanical systems like the hula hoop’s twirl, which could be useful in fields like physical rehabilitation and robotics.

Identical vesicles, different behaviors: Model reveals how spontaneous asymmetry gives rise to lifelike behavior

In nonreciprocal active matter, agents act differently on each other, seemingly in violation of Newton’s third law. This principle can result in various active matter traits, such as self-propulsion, molecular regulation and collective motion.

A new model describes how such nonreciprocal interactions can emerge spontaneously between chemically active vesicles. Physicists from the Department of Living Matter Physics at the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) found that such vesicles can dynamically switch between ignoring, attracting, repelling and chasing each other.

The study is published in the journal Newton.

SPINE: A machine-learning program is on the trail of ghost particles

Neutrinos are among the most abundant particles in the universe, but they are also among the most elusive. Nearly massless, they are produced by nuclear reactions in the sun, exploding stars, particle accelerators and even the decay of radioactive elements on Earth. They interact so weakly with ordinary matter that trillions pass through each person every second without leaving a trace. Studying these ghostly particles could help answer some of the biggest questions in physics, from the nature of dark matter to why matter exists at all.

Because neutrinos are so elusive, scientists build enormous detectors and intense particle beams to catch even a small number of them in action. But capturing a neutrino interaction is only the beginning. Scientists must then reconstruct what happened from an extraordinarily complicated picture of particle tracks, overlapping signals and background activity. Researchers at the Department of Energy’s (DOE) SLAC National Accelerator Laboratory have developed a machine-learning program called SPINE to tackle this challenge.

SPINE, which stands for Scalable Particle Imaging with Neural Embeddings, analyzes data from liquid argon time-projection chambers, the detector technology used by experiments including the Short-Baseline Neutrino program at the DOE’s Fermi National Accelerator Laboratory in Illinois and the Deep Underground Neutrino Experiment (DUNE), currently under construction in Illinois and South Dakota and expected to start taking data in 2030. SPINE learns from simulated detector images to identify particles, trace their paths and piece together the interactions that produced them.

Quantum gates set speed record at 6.8 nanoseconds with over 99.98% accuracy

Researchers from Jülich, Aachen and Cologne have performed a quantum operation on a qubit in just 6.8 nanoseconds—with more than 99.98% accuracy. Such operations typically take several tens of nanoseconds in superconducting quantum computers. The paper was published in Nature Communications.

6.8 nanoseconds—that’s how long it takes light to travel a distance of around two meters (6.6 feet) in a vacuum. In this tiny fraction of a second, researchers at the Peter Grünberg Institute for Functional Quantum Systems (PGI-13) and Quantum Control (PGI-8) at Forschungszentrum Jülich have succeeded in performing elementary computing operations on a quantum bit, or qubit for short.

Switching speed is a critical factor in quantum computing. This is because qubits are sensitive and retain their quantum states for only a limited time. The faster individual operations can be performed, the more can fit into this time window. This is important for complex algorithms and for resource-intensive error correction.

Quantum sensor loop design could improve magnetic measurements for medicine and communications

Adelaide University quantum engineers have found a new way to improve some of the world’s most sensitive sensors of electromagnetic fields, a breakthrough that could help advance brain imaging, medical diagnostics, communications technology and next-generation quantum devices.

The research, published today in Physical Review Applied, is led by the university’s Quantum and Nano Technology Group (QuaNTeG) and solves a long-standing problem that has limited the performance of superconducting quantum interference devices, known as SQUIDs.

SQUIDs are among the most sensitive magnetic field detectors ever created. They are used in specialized applications including brain imaging systems, scientific instruments and advanced radio-frequency sensors. However, while they can detect incredibly small changes in magnetic fields, they have struggled to accurately identify when a magnetic field is exactly zero.

Against all expectations, researchers control the magnetic core of a single atom

Researchers at Delft University of Technology (the Netherlands) have succeeded in controlling the magnetism in the nucleus of a single atom with radio waves. This came as a surprise: until now, physicists believed that this nuclear spin could not be manipulated directly. The discovery could open up new possibilities for storing and reading quantum information. The research is published in the journal Nature Communications.

In metals such as iron and nickel, every atom is slightly magnetic. But inside the atom, different magnetic “compass needles,” known in quantum mechanics as spins, are also at work. “By far the strongest magnetism comes from the electrons,” says lead researcher Sander Otte. “But in some atoms, the nucleus also carries a spin. That spin is much weaker, but it is also much better shielded from the outside world.”

Otte’s group studies spins using a converted scanning tunneling microscope. This enables electrical signals to be directed with extreme precision at a single atom. In the past, the researchers mainly focused on the electron spin, which is the easiest to read out. The nuclear spin appeared only indirectly, through the so-called hyperfine interaction. This causes the spins of the nucleus and the electron to become slightly entangled.