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Category: quantum physics

Quantum magnetism: Spin-flip process in atomic nucleus does not account for all magnetic behavior

In the air people breathe, the water on Earth, the stars in the sky and more, atoms are the building blocks that make up the universe. Understanding the structure of the atomic nucleus is crucial for research with implications for astrophysics and in applications such as medical imaging and data storage.

A new study conducted by Department of Physics researchers using the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University examined titanium-50 nuclei and showed that a long-standing explanation for where magnetism in atomic nuclei comes from does not fully work for titanium-50. The research, which was published in Physical Review Letters, suggests that scientists may need to rethink how they explain nuclear magnetism.

“What current models propose is that magnetic strength is largely generated by spin-flip excitations, that means when flipping proton or neutron spins from up to down between so-called spin-orbit partner orbitals,” said Associate Professor Mark Spieker, a co-author on the multi-institution study. “For the first time, we showed that this type of spin-flip cannot be the only mechanism that generates nuclear magnetism.”

Racetrack-shaped lasers developed for bright, stable frequency combs

A new, miniature laser source developed by applied physicists in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Technical University of Vienna (TU Wien) could soon pack the power of a laboratory-based spectrometer—an important workhorse tool for precision environmental gas analysis—onto a single microchip.

The device, a ring-shaped, “racetrack” quantum cascade laser, generates a specific type of light source, called a frequency comb, in the difficult-to-access mid-infrared region of the electromagnetic spectrum. It was developed in the lab of Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, in collaboration with co-senior author Benedikt Schwarz and colleagues at TU Wien.

The research was co-led by first author Ted Letsou, a postdoctoral researcher in the Capasso group, and Johannes Fuchsberger, a graduate student at TU Wien, and is published in Optica.

Chiral metasurfaces guide twisted light into free space

Light can carry angular momentum in two distinct ways. One comes from polarization, which describes how the electric field rotates. The other comes from the shape of the wavefront itself, which can twist like a corkscrew as it travels. This second form, known as orbital angular momentum, has attracted wide interest because it allows light to encode information, interact with matter in new ways, and probe physical and biological systems. Despite this promise, producing well-defined twisted light in free space remains technically challenging, especially when the light originates from small or localized sources.

Recent research reported in Advanced Photonics Nexus demonstrates a route to generating twisted light beams by combining a dielectric multilayer with a patterned metallic surface. The work shows that surface-bound light waves can be converted into free-space beams with controlled angular momentum and polarization. Importantly, the approach avoids several limitations of earlier designs and points toward future integration with single-photon emitters.

Many existing methods for generating orbital angular momentum rely on reshaping a laser beam using holograms, liquid-crystal plates, or patterned films known as metasurfaces. While effective for large, externally illuminated beams, these approaches struggle when light must be generated directly on a chip or from nanoscale emitters such as quantum dots or single molecules. Such sources cannot uniformly illuminate a structure or arrive at a precisely defined angle, making efficient beam shaping difficult.

Google Warns Quantum Computers Could Break Bitcoin and Ethereum Encryption in 9 Minutes — Are Your BTC and ETH at Risk?

In short: The “lock” on the vault hasn’t been broken yet, but Google just published the blueprint for the bolt cutters, and they are much smaller than we imagined.

Google’s latest research warns quantum computers could break Bitcoin and Ethereum encryption faster than expected.

Symmetry Keeps Fermions Pure in a Noisy World

A theoretical study reveals how to control and drive a quantum system without causing its decoherence.

Quantumness is famously fragile. Decoherence, particle loss, and other dissipative processes typically destroy delicate quantum superpositions, causing open quantum systems to behave classically. This universal, inevitable fate suggests that, even when a system’s constituents are fully quantum, its nonequilibrium critical points could be described by classical universality classes. That is, the system could belong to a group whose behavior near a critical point is identical and scale invariant regardless of microscopic details. In a new theoretical study, Rohan Mittal and his collaborators at the University of Cologne in Germany have overturned this expectation for open systems of fermions [1]. They identified a particular symmetry, which, if present, blocks most of the noise channels that would ordinarily wash out quantum behavior at large scales.

Quantum twisting microscope reveals electron-electron interactions in graphene at room temperature

An international team of researchers built a highly sensitive quantum microscope and used it to directly observe, for the first time at room temperature, how electrons subtly interact with each other in graphene—confirming a decades-old theoretical prediction with remarkable precision. The research is published in the journal Nano Letters. The team was led by Dmitri Efetov, Professor of Experimental Solid State Physics at LMU München’s Faculty of Physics and MCQST co-coordinator for Research Area Quantum Matter.

In recent years, “moiré materials”—atomically thin, two-dimensional layered structures such as graphene—have emerged as one of the most exciting frontiers in condensed matter physics. By stacking these atomic layers with a slight rotational misalignment, researchers create interference patterns that fundamentally reshape how electrons move. This simple twist can unlock entirely new quantum phases, including superconductivity and correlated insulating states, making moiré systems a powerful platform for exploring emergent physical phenomena.

Studying these systems, however, has traditionally come with significant technical hurdles. Conventional devices must be assembled with extreme precision, relying on fixed twist angles, painstakingly assembled with precision often better than a tenth of a degree. Even then, imperfections such as strain and disorder can obscure the underlying physics.

Pairs of atoms observed existing in two places at once for the first time

Quantum physicists at ANU have observed atoms entangled in motion. “It’s really weird for us to think that this is how the universe works,” says Dr. Sean Hodgman from the ANU Research School of Physics. “You can read about it in a textbook, but it’s really weird to think that a particle can be in two places at once.”

Their experiment using helium atoms represents a major advancement over similar experiments using photons, which are particles of light. Unlike photons, helium atoms have mass and experience gravity. The research is published in Nature Communications.

“Experimentally, it’s extremely hard to demonstrate this,” says lead author and Ph.D. researcher, Yogesh Sridhar. “Several people have tried in the past to show these effects, and they have always come short.”

Silicon quantum computer performs logical operations for the first time

Silicon is ubiquitous in modern electronics, and now it is becoming increasingly useful in quantum computing. In particular, silicon’s compatibility with existing chip technology and its long coherence times in silicon-based spin qubits make it a promising material for scalable quantum computing. A new study, published in Nature Nanotechnology, has demonstrated silicon’s use in a logical quantum processor, representing the first of its kind.

Quantum computers are highly sensitive to errors from environmental noise, creating hurdles for practical quantum computation. To help suppress these errors, information can be encoded in logical qubits using fault-tolerant quantum computation (FTQC). Prior to this study, silicon had not been used for logical operations in FTQC.

“In silicon-based quantum processors, frequency crowding and cross-talk further exacerbate the errors as the system scales. To address these errors, logical encoding stands as the only viable solution by redundantly storing quantum information across multiple physical qubits. While logical qubits and operations have been successfully demonstrated in platforms such as superconducting circuits, neutral atoms, nitrogen-vacancy centers and trapped ions, their implementation in silicon-based spin qubits poses notable technical challenges,” the study authors write.

Framework unifies the classical and quantum Mpemba effects

Physicists have developed a new theoretical framework which unifies a wide array of seemingly unrelated “Mpemba effects”: counterintuitive cases where systems driven further from equilibrium relax faster than those closer to it. Reporting their results in Physical Review X, researchers led by John Goold at Trinity College Dublin show that both classical and quantum versions of the effect can be understood using the same underlying logic—resolving a long-standing conceptual puzzle.

In 1963, 13-year-old Tanzanian student Erasto Mpemba noticed that when he placed an ice cream mixture in the freezer while it was still hot, it froze faster than the other, initially cooler mixtures in the freezer. His observation was later confirmed in 1969 through a study involving Mpemba, together with physicist Denis Osborne.

Since then, effects analogous to the Mpemba effect have been observed in transitions ranging from crystallizing polymers to transitions in magnetic materials. Yet despite close experimental scrutiny, the mechanisms underlying the effect remained elusive.

Next-generation optical sensor can read photon spin across UV-to-infrared wavelengths

A research team led by Professor Jiwoong Yang of the Department of Energy Science and Engineering at DGIST has developed next-generation optical sensor technology capable of precisely detecting not only the intensity and wavelength of light but also its rotational direction—the spin information of photons. The team successfully implemented a quantum-dot-based optical sensor that can detect circularly polarized light (CPL) across an ultra-wide spectral range—from ultraviolet to short-wave infrared—demonstrating photodetection performance comparable to that of commercial silicon optical sensors. The paper is published in Advanced Materials.

CPL refers to light in which the electric field rotates helically as it propagates. This is directly linked to the spin information of photons—the fundamental particles of light. This polarization information serves as a crucial signal in next-generation security and communication technologies, such as quantum communication, quantum cryptography, and photonic quantum information processing, which is why related optical sensor technologies are attracting significant worldwide attention.

Conventional circularly polarized light sensors typically require the light-absorbing material itself to possess a specific helical orientation, known as a chiral structure. This approach not only limits the range of usable materials but also confines detection to narrow spectral regions, such as ultraviolet or visible light. Extending this technology into the infrared region, which is essential for quantum communication and optical sensing, has previously posed a major technical challenge.

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