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Category: particle physics

Attosecond interferometry meets quantum optics

Experimental attosecond science is built around the ability to generate and control light flashes lasting billionths of a billionth of a second. Such extreme pulses can be created through high harmonic generation (HHG), where an intense laser field drives electrons out of atoms or solids and then forces them back, releasing bursts of extreme ultraviolet radiation. Techniques like this have transformed our ability to observe electron motion on its natural timescale.

To extract information from such ultrafast processes, physicists often rely on attosecond interferometry. By combining a strong laser field with a weaker second colour, different electron trajectories are made to interfere, imprinting timing and phase information onto the emitted harmonics. Over recent years, these schemes have become standard tools for attosecond metrology and spectroscopy.

To discover new physics, AI may need to ‘unlearn’ the old one

A study in the Journal of Cosmology and Astroparticle Physics explores how a machine-learning strategy known as transfer learning could dramatically reduce the computational cost of searching for new physics beyond the standard cosmological model—while also revealing an unexpected risk: Sometimes AI systems can become too reliant on what they already know.

Artificial intelligence is widely used in cosmology to analyze the universe. But testing theories beyond the standard cosmological model, known as ΛCDM, remains extremely computationally demanding.

Although ΛCDM successfully describes many properties of the universe—from its expansion to the distribution of galaxies—physicists know it is probably incomplete. Recent observations hint that phenomena such as massive neutrinos, modified gravity or evolving dark energy could point toward new physics beyond the current model.

Monolayer WSe₂ unlocks high-performance p-type transistors that could change how future chips balance speed and power

Transistors, small devices that can amplify or switch electrical signals, are central components of all modern computer chips and digital devices. There are two main types of transistors, known as n-type and p-type transistors.

N-type transistors conduct current using electrons (i.e., negatively charged particles), while p-type transistors utilize electron holes (i.e., positively charged spaces in a crystal lattice without electrons).

Electronics engineers worldwide have been exploring different solutions that could help reduce the size of existing transistors without compromising their performance, which could enable the further miniaturization of electronic devices. One promising route is to fabricate transistors using two-dimensional (2D) semiconductors, semiconducting materials that are just a single atom or a few atoms thick.

Neutron-rich nuclei yield beta-decay clues that could refine heavy-element origin models

How are heavy elements formed in the universe? Extremely neutron-rich atomic nuclei and their beta-decay rates play an important role in this process. Until now, it has been very difficult to determine these rates experimentally. Researchers at TU Darmstadt have developed theoretical predictions for such processes and successfully compared them with experimental data, where they exist. The results were published in Physical Review Letters.

The study focuses on beta-decay rates of neutron-rich nuclei, which are of great importance for element synthesis in the universe. To better understand and predict these decay rates, the team developed modern “ab initio” methods in nuclear physics for these systems. These methods calculate the properties of atomic nuclei directly from the fundamental interactions between their constituents, without making empirical adjustments to known measured values.

The researchers combined modern nuclear forces and decay operators with many-particle methods to precisely determine the structure of nuclei and, from this, the decay rates. A key finding of the work is that the theoretical predictions agree very well with experimental data—in the range where such extremely neutron-rich nuclei can currently be studied at accelerator facilities. The latest experiments on these nuclei took place at the RIKEN research center in Japan.

Scientists identify the origin of noise in spin qubit quantum processors

A spin qubit, in which quantum information is encoded in the spin state of an electron, is one of the most promising platforms for quantum computing. Spin qubits exhibit long coherence times and are compatible with advanced semiconductor manufacturing technologies. The leading implementation of spin qubits involves confined electrons inside quantum dots, a nanoscale semiconductor architecture that behaves like a controllable artificial atom. Recent advances have enabled high-fidelity operation of single- and two-qubit gates, exceeding the threshold required for certain surface code quantum error correction techniques.

Physicists create new family of Schrödinger-cat states

Quantum mechanics, unlike classical physics, allows objects to exist in more than one state at the same time. This idea is often illustrated by Schrödinger’s cat, imagined as being both alive and dead until it is observed. In the laboratory, physicists can create less dramatic but very real versions of this effect by placing atoms, light or motion into two distinct quantum states at once. Creating and controlling these superpositions is essential for applications ranging from quantum computing to precision timekeeping.

A simple example is a quantum bit, or qubit, in a superposition of both 0 and 1. But quantum systems are not limited to just two states. In a quantum harmonic oscillator, which can occupy many different energy levels, there is a much richer set of possibilities. Quantum harmonic oscillators describe many physical systems, including light, vibrations and the motion of trapped particles, and have been used to create a wide variety of quantum superpositions. One well-known example is a “cat state,” in which an oscillator is placed in a superposition of two wave packets displaced in opposite directions. These wave packets, known as coherent states, resemble classical motion as closely as quantum mechanics allows.

Researchers at the University of Oxford have now demonstrated a new family of quantum superpositions. Instead of building catlike states from coherent-state wave packets, they developed a method for creating superpositions from a broad range of components that are themselves highly nonclassical. In examples such as squeezed-state superpositions, quantum uncertainty is redistributed differently in each part of the state. The research is published in the journal Physical Review X.

Tabletop experiment helps reconcile fundamental physics

Assistant Professor Haocun Yu is something of a scientific diplomat. In a recent Physical Review Letters publication, she and her colleagues show how a tabletop experiment can bring together two bedrock physics theories that have never been fully reconciled.

More than a century ago, Albert Einstein gave us the theory of general relativity, describing gravity in relation to space and time on a large scale. Within a decade, physicists were developing a deeper knowledge of quantum mechanics, the laws that govern the subatomic world, including atoms, photons and other microscopic systems.

“Quantum mechanics and general relativity are two of the most successful theories in physics, but they describe nature in very different ways,” Yu explained.

Research uncovers novel electronic properties in quantum material

Florida State University physicists are part of a team that has discovered unusual superconducting states in parts of graphene, with the potential to drive unexpected quantum technologies.

Assistant Professor of Physics Cyprian Lewandowski and postdoctoral researcher Phong Võ Tiến are part of an international collaboration that has uncovered new aspects of superconductivity and topology in rhombohedral graphene, a system comprising just a few layers of carbon atoms stacked like the treads of a staircase in a shape known as chiral stacking. The work is published in Nature Physics.

“The rhombohedral graphene system seems to capture many of the intriguing electronic phenomena that scientists have seen previously in other atomically thin systems, but they were previously not as ideal for technical applications because of the intrinsic complexity of the devices or replicability issues,” Lewandowski said.

Achiral crystal reveals Raman optical activity through ferroaxial order

Raman optical activity, long thought to require chiral molecules or magnetic order, has been demonstrated in an achiral, nonmagnetic crystal by researchers at the Institute of Science Tokyo. The effect arises through ferroaxial order, a coordinated rotation of atoms within the lattice, and is detected using circularly polarized Raman spectroscopy. The findings show that optically inactive materials can also display chirality-like optical responses and expand the scope of optical techniques for discovering new materials.

In nature, molecules can be divided into two categories based on their symmetry: chiral and achiral. Chiral molecules are not identical to their mirror images, much like left and right hands. Achiral molecules, by contrast, are identical to their mirror images and therefore do not possess a definite handedness.

Light offers a way to distinguish between these two types. When light interacts with a chiral molecule, the response depends on its handedness. For example, chiral molecules absorb left-and right-circularly polarized light to different extents, a phenomenon known as circular dichroism. They also scatter these two types of light with different intensities, an effect called Raman optical activity (ROA), which is widely used to identify chirality. ROA has long been associated only with chiral molecules or with materials that have magnetic order, where inversion or time-reversal symmetry is broken.

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