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Category: particle physics – Page 5

Quantum geometry provides theoretical limits on measurable properties of solids

Two RIKEN physicists have established new theoretical limits for experimentally measurable quantities by viewing solids through a lens of quantum geometry. Their results shed light both on the physics of solids and on quantum mechanics.

The usual approach to studying a solid in physics is to consider all the interactions acting between its atoms or molecules and then use the laws of quantum mechanics to determine the solid’s properties. But a new methodology involves considering the “quantum geometry” of a solid. It entails studying the geometric structures that arise not in physical space, but in the space of quantum states.

One of the key concepts in this approach is the quantum geometric tensor—a matrix that contains information about the distances and curvatures of quantum states.

3D atomic rearrangement creates 40,000 quantum defects in 40 minutes

It’s been 37 years since scientists first demonstrated the ability to move single atoms, suggesting the possibility of designing materials atom by atom to customize their properties. Today there are several techniques that allow researchers to move individual atoms in order to give materials exotic quantum properties and improve our understanding of quantum behavior.

But existing techniques can only move atoms across the surface of materials in two dimensions. Most also require painstakingly slow processes and high-vacuum, ultracold lab conditions.

Now a team of researchers at MIT, the Department of Energy’s Oak Ridge National Laboratory, and other institutions has created a way to precisely move tens of thousands of individual atoms within a material in minutes at room temperature. The approach uses a set of algorithms to carefully position an electron beam at specific locations of a material, then scan the beam to drive atomic motions.

AI surrogate accelerates nonlinear optics simulations by orders of magnitude

Simulating the nonlinear optical physics that underlies ultrafast laser systems is computationally demanding—a practical bottleneck in settings that require rapid feedback. A study by researchers at Stanford University, University of California, Los Angeles (UCLA), and SLAC National Accelerator Laboratory introduces a deep learning surrogate that delivers orders-of-magnitude acceleration over conventional simulation methods, while maintaining high fidelity across a challenging range of pulse shapes.

The work centers on second-order nonlinear optics (χ² processes), in which light waves exchange energy inside specially engineered crystals to generate new frequencies and tailored pulse shapes. In particle accelerator facilities, these processes play a key role. At SLAC’s upgraded Linac Coherent Light Source (LCLS-II), infrared laser pulses are first to green light and then to ultraviolet (UV). The UV pulse strikes a cathode to liberate an electron bunch that is subsequently accelerated and modulated to produce intense X-ray pulses. The temporal shape of the UV pulse directly influences the properties of that electron bunch—and ultimately the quality of the X-rays available for science.

A surrogate model for the nonlinear χ² frequency conversion step at the heart of this process is reported in Advanced Photonics.

Atoms vibrate on circular paths—with an unexpected twist

An international team of researchers, including scientists from HZDR and Fritz Haber Institute of the Max Planck Society, for the first time directly observed how angular momentum is transferred and conserved within a crystal lattice. Using intense terahertz laser pulses, the researchers were able to selectively control these processes, which unveiled a surprising effect: During the angular momentum transfer, the direction of rotation reverses—caused by the rotational symmetry of the material.

The results, published in Nature Physics, provide new insights into the foundation of magnetism and open up possibilities for tailored control of quantum materials.

Conserved quantities such as energy, momentum, and angular momentum determine the fundamental laws of nature. In a closed system, these quantities are always conserved: they cannot be created or destroyed, only transformed or transferred. While angular momentum is familiar in everyday life through rotating carousels or riding a bicycle, it plays a central role at the quantum level—for example, as the fundamental origin of magnetism.

How temperature changes light: New model could guide smarter LEDs, sensors and photonic devices

Technion researchers have developed, for the first time, a comprehensive physical model explaining how the properties of a radiating material, including absorption, emission, and quantum efficiency, affect the fundamental characteristics of the light it emits as a function of temperature. In essence, the emitted light changes its color, intensity, and randomness according to the material’s properties and its temperature. The discovery was published in Optica and opens new possibilities for designing advanced light sources, optical sensors, and thermally based photonic systems.

The research was led by M.Sc. student Tomer Bar-Lev and Prof. Carmel Rotschild from the Faculty of Mechanical Engineering and the Russell Berrie Nanotechnology Institute at the Technion. According to the researchers, the central phenomenon examined in this work is photoluminescence, a process in which a material emits light in response to incident illumination. In this phenomenon, light particles (photons) are absorbed by the material and re-emitted, forming the basis of many technologies, including LED lighting and optical sensors.

The Technion researchers demonstrated that the influence of fundamental physical laws formulated more than a century ago is far broader than previously thought.

In Quantum Gravity, the Cosmological Constant May Behave Similar To The Quantum Hall Effect

So why not do the same thing for a gravitational field? Well, it turns out that quantum renormalization only works for Euclidean space. In general relativity, the mass-energy of a system warps space and time. So all those quantum fluctuations curve spacetime, and curved spacetime induces even more virtual particles, which warp space even more… oh no! It all breaks down, and we can’t quantize gravitational fields the way we quantize the other fundamental forces.

Problems like these have led some researchers to develop a model known as loop quantum gravity. Rather than trying to calculate the behavior of quantum particles in a timey-wimey background, why not treat the entire mass-energy-spacetime structure as a single quantum system? It’s like imagining the Universe within an unseen background that is Euclidean. This way the problem of renormalization can be overcome in many cases. One case where it doesn’t work well is the cosmological constant. In most cosmological models, the cosmological constant is what drives cosmic expansion. Since it is a universal dark energy field, it amplifies the loop quantum gravity sums, and once again the whole thing diverges. You can handle this by fixing the cosmological constant to a specific value, but that isn’t really a solution to the problem. It’s the cosmology equivalent of ignoring the engine light in your car…

A new study finds this might not be too bad after all. In it, the authors demonstrate an interesting similarity between the cosmological constant in loop quantum gravity and the quantum Hall effect in standard quantum theory.

How Neutrino Oscillations Affect Supernovae

Numerical models of core-collapse supernovae have matured greatly over the past few decades. With impressive accuracy, they now couple relativistic gravity, magnetohydrodynamics, nuclear physics, and neutrino transport. Neutrinos, copiously produced in the collapsed core, are the main driver of most of these supernovae. Neutrino oscillations are probably the most crucial ingredient that is still missing from the majority of models, even though their presence and possible importance have long been suggested. The reason for this gap in modeling is twofold: Many relevant physical parameters are poorly known, and the most important oscillation processes are very difficult to simulate. Now Ryuichiro Akaho at Waseda University in Japan and colleagues have made a key step toward a self-consistent model and revealed some complexities that arise when incorporating neutrino oscillations [1].

Stars are supported against their own gravity primarily by gas pressure, which is maintained by exothermic nuclear reactions. In high-mass stars, nuclear burning starts with the fusion of hydrogen into helium and continues through progressively heavier elements until the core is dominated by iron-group nuclei, at which point fusion no longer releases energy. Pressure support then no longer suffices to stabilize the core, and it collapses to a protoneutron star, a hot compact object with about 1.5 solar masses concentrated in a radius of a few tens of kilometers. During the collapse, a shock wave forms at this object’s surface and stalls after propagating outward for only about 100 km (Fig. 1). Neutrinos generated in and around the protoneutron star can heat the surrounding gas, increasing its energy.

Quantum dot emitter delivers near-identical telecom photons at 40 million per second

Quantum technologies, devices that perform specific functions leveraging quantum mechanical effects, could soon outperform their classical counterparts on some tasks. Quantum emitters, devices that release individual particles of light (i.e., photons), are central components of many of these technologies, including quantum communication systems and quantum computers.

To enable the reliable operation of quantum technologies, emitters should emit photons with high consistency and coherence. In other words, they should ensure that the quantum properties of emitted photons remain stable and predictable.

Researchers at University of Copenhagen’s Niels Bohr Institute, Ruhr-University Bochum, University of Basel and Sparrow Quantum ApS recently developed a new photon emitter based on quantum dots, tiny structures that can trap electrons in confined regions and enable the controlled emission of individual photons.

Light reshapes metal-organic framework to harvest airborne water

Chemists at the University of Iowa have created a three-dimensional lattice that captures water from the air and stores it. In a new study appearing in the Journal of the American Chemical Society, researchers describe a millimeter-scale structure made of metal atoms connected by two types of organic molecules. When exposed to ultraviolet light, the material undergoes a chemical reaction that changes its shape, creating cavities throughout the lattice. Those cavities attract water molecules from the air and store them—like a multitude of tiny canteens.

The results, which would need to be tested at larger scales, show promise as a method to help provide drinking water to people and areas with limited access. Water stress or scarcity will affect nearly five billion people—half the world’s projected population—by 2050, according to the United Nations.

“We have found and validated a way to capture and to store water that would require only sunlight,” says Leonard MacGillivray, adjunct professor in the Department of Chemistry and former professor and department chair. “You can transport the crystal lattice and eventually release the water on demand. That’s why it’s such an advance.”

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