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Category: particle physics

New code connects microscopic insights to the macroscopic world

In inertial confinement fusion, a capsule of fuel begins at temperatures near zero and pressures close to vacuum. When lasers compress that fuel to trigger fusion, the material heats up to millions of degrees and reaches pressures similar to the core of the sun. That process happens within a miniscule amount of space and time.

To understand this process, scientists need to know about the large-scale conditions, like temperature and pressure, throughout the target chamber. But they also want detailed information about the material—and the atoms—contained within. Until now, computer models have struggled to bridge that gap across the wide range of conditions encountered in such experiments.

ATLAS confirms collective nature of quark soup’s radial expansion

Scientists analyzing data from heavy ion collisions at the Large Hadron Collider (LHC)—the world’s most powerful particle collider, located at CERN, the European Organization for Nuclear Research—have new evidence that a pattern of “flow” observed in particles streaming from these collisions reflects those particles’ collective behavior. The measurements reveal how the distribution of particles is driven by pressure gradients generated by the extreme conditions in these collisions, which mimic what the universe was like just after the Big Bang.

The research is described in a paper published in Physical Review Letters by the ATLAS Collaboration at the LHC. Scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University played leading roles in the analysis.

The international team used data from the LHC’s ATLAS experiment to analyze how particles flow outward in radial directions when two beams of lead ions—lead atoms stripped of their electrons—collide after circulating around the 17-mile circumference of the LHC at close to the speed of light. The findings offer new insight into the nature of the hot, dense matter generated in these collisions—with temperatures more than 250,000 times hotter than the sun’s core. These extreme conditions essentially melt the protons and neutrons that make up the colliding ions, setting free their innermost building blocks, quarks and gluons, to create a quark-gluon plasma (QGP).

Magnetic ‘sweet spots’ enable optimal operation of hole spin qubits

Quantum computers, systems that process information leveraging quantum mechanical effects, could reliably tackle various computational problems that cannot be solved by classical computers. These systems process information in the form of qubits, units of information that can exist in two states at once (0 and 1).

Hole spins, the intrinsic angular momentum of holes (i.e., missing electrons in semiconductors that can be trapped in nanoscale regions called quantum dots), have been widely used as qubits. These spins can be controlled using electric fields, as they are strongly influenced by a quantum effect known as spin-orbit coupling, which links the motion of particles to their magnetism.

Unfortunately, due to this spin-orbit coupling, hole spin qubits are also known to be highly vulnerable to noise, including random electrical disturbances that can prompt decoherence. This in turn can result in the loss of valuable quantum information.

Entangled Atoms Are Transforming How We Measure the World

Entangled atoms, separated in space, are giving scientists a powerful new way to measure the world with stunning precision.

Researchers from the University of Basel and the Laboratoire Kastler Brossel have shown that quantum entanglement can be used to measure multiple physical quantities at the same time with greater accuracy than previously possible.

What makes quantum entanglement so unusual.

Too much entanglement? Quantum networks can suffer from ‘selfish routing,’ study shows

Quantum technologies, systems that process, transfer or store information leveraging quantum mechanical effects, could tackle some real-world problems faster and more effectively than their classical counterparts. In recent years, some engineers have been focusing their efforts on the development of quantum communication systems, which could eventually enable the creation of a “quantum internet” (i.e., an equivalent of the internet in which information is shared via quantum physical effects).

Networks of quantum devices are typically established leveraging quantum entanglement, a correlation that ensures that the state of one particle or system instantly relates to the state of another distant particle or system. A key assumption in the field of quantum science is that greater entanglement would be linked to more reliable communications.

Researchers at Northwestern University recently published a paper in Physical Review Letters that challenges this assumption, showing that, in some realistic scenarios, more entanglement can adversely impact the quality of communications. Their study could inform efforts aimed at building reliable quantum communication networks, potentially also contributing to the future design of a quantum internet.

New insight into light-matter thermalization could advance neutral-atom quantum computing

Light and matter can remain at separate temperatures even while interacting with each other for long periods, according to new research that could help scale up an emerging quantum computing approach in which photons and atoms play a central role.

In a theoretical study published in Physical Review Letters, a University at Buffalo-led team reports that interacting photons and atoms don’t always rapidly reach thermal equilibrium as expected.

Thermal equilibrium is the process by which interacting particles exchange energy before settling at the same temperature, and it typically happens quickly when trapped light repeatedly interacts with matter. Under the right circumstances, however, physicists found that photons and atoms can instead settle at different—and in some cases opposite—temperatures for extended periods.

Innovative optical atomic clock could combine single-ion accuracy with multi-ion stability

For many years, cesium atomic clocks have been reliably keeping time around the world. But the future belongs to even more accurate clocks: optical atomic clocks. In a few years’ time, they could change the definition of the base unit second in the International System of Units (SI). It is still completely open, which of the various optical clocks will serve as the basis for this.

The large number of optical clocks that the Physikalisch-Technische Bundesanstalt (PTB), as a leading institute in this field, has realized could be joined by another type: an optical multi-ion clock with ytterbium-173 ions. It could combine the high accuracy of individual ions with the improved stability of several ions. This is the result of a cooperation between PTB and the Thai metrology institute NIMT.

The team led by Tanja Mehlstäubler reports on this in the current issue of the journal Physical Review Letters. The results are also interesting for quantum computing and, with a new look inside the atom, for fundamental research.

Optical technique reveals hidden magnetic states in antiferromagnets

Imagine computer hardware that is blazing fast and stores more data in less space. That’s the promise of antiferromagnets, magnetic materials that do not interfere with each other and can switch states at high speed, opening the door to advanced computing and quantum applications.

Magnetism comes from unpaired electrons, tiny particles that orbit an atom’s nucleus. Each electron has a property called spin, which can point up or down. In standard ferromagnets, the atomic spins point in the same direction, creating a strong magnetic field. In antiferromagnets, neighboring spins point in opposite directions, canceling each other out and yielding no net magnetism.

Flipping individual spins in an antiferromagnet requires very little movement of magnetization, which allows ultrafast processing. Antiferromagnets can switch states trillions of times per second, compared with billions for ferromagnets. With net zero magnetism, antiferromagnets can be placed very close together without repelling or attracting each other, allowing more data to be stored in a small space.

Metal clumps in a quantum state: Physicists place thousands of sodium atoms in a ‘Schrödinger’s cat state’

Can a small lump of metal be in a quantum state that extends over distant locations? A research team at the University of Vienna answers this question with a resounding yes. In the journal Nature, physicists from the University of Vienna and the University of Duisburg-Essen show that even massive nanoparticles consisting of thousands of sodium atoms follow the rules of quantum mechanics. The experiment is currently one of the best tests of quantum mechanics on a macroscopic scale.

In quantum mechanics, not only light but also matter can behave both as a particle and as a wave. This has been proven many times for electrons, atoms, and small molecules through double-slit diffraction or interference experiments. However, we do not see this in everyday life: marbles, stones, and dust particles have a well-defined location and a predictable trajectory; they follow the rules of classical physics.

At the University of Vienna, the team led by Markus Arndt and Stefan Gerlich has now demonstrated for the first time that the wave nature of matter is also preserved in massive metallic nanoparticles. The scale of the particles is impressive: the clusters have a diameter of around 8 nanometers, which is comparable to the size of modern transistor structures.

Velocity gradients prove key to explaining large-scale magnetic field structure

All celestial bodies—planets, suns, even entire galaxies—produce magnetic fields, affecting such cosmic processes as the solar wind, high-energy particle transport, and galaxy formation. Small-scale magnetic fields are generally turbulent and chaotic, yet large-scale fields are organized, a phenomenon that plasma astrophysicists have tried explaining for decades, unsuccessfully.

In a paper published January 21 in Nature, a team led by scientists at the University of Wisconsin–Madison have run complex numerical simulations of plasma flows that, while leading to turbulence, also develop structured flows due to the formation of large-scale jets. From their simulations, the team has identified a new mechanism to describe the generation of magnetic fields that can be broadly applied, and has implications ranging from space weather to multimessenger astrophysics.

“Magnetic fields across the cosmos are large-scale and ordered, but our understanding of how these fields are generated is that they come from some kind of turbulent motion,” says the study’s lead author Bindesh Tripathi, a former UW–Madison physics graduate student and current postdoctoral researcher at Columbia University.

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