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Category: particle physics

A cryogenic winter for tomorrow’s accelerator

Behind every particle collision generated at the Large Hadron Collider is a multitude of technical feats. One of these is refrigeration on an industrial scale. To guide the particles, the thousands of superconducting magnets in the accelerator must be cooled to a temperature of close to absolute zero. This makes the LHC the largest cryogenic installation in the world: 23 of its 27 kilometers are maintained at 1.9 Kelvin (−271°C) using refrigerators in which superfluid helium circulates.

This unique cooling system needs to be further strengthened in preparation for the High-Luminosity LHC (HL-LHC), a major upgrade to the LHC that is scheduled to begin operation in 2030. On both sides of the two large experiments, ATLAS and CMS, more powerful focusing magnets and new types of cavities will considerably increase the number of collisions at each beam crossing or, in other words, the luminosity. This ultra-sophisticated equipment requires increased cooling power. Two new refrigerators are therefore being installed, in addition to the eight that are already needed for the existing accelerator.

The LHC’s refrigerators work on the same principle as the one in your kitchen, except that they are gigantic installations that occupy several buildings. Located on the surface, they include large compressors and an enormous cold box that contains the heat exchangers and the expansion turbines. These installations lower the helium temperature to 4.5 Kelvin (−268.6°C). Six compression units were installed in October.

A Long-Standing Spintronics Mystery May Finally Be Solved

A long-standing explanation for magnetoresistance may be incomplete. New evidence suggests a universal interfacial mechanism is at play. A major advance in spintronics came with the discovery of unusual magnetoresistance (UMR). In this effect, the electrical resistance of a heavy metal changes wh

Private donors pledge $1 billion for world’s largest particle accelerator

Europe’s physics lab CERN on Thursday said private donors had pledged $1 billion toward the construction of a new particle accelerator that would be by far the world’s biggest.

In a first, private individuals and philanthropic foundations have backed a flagship research project at CERN, the European Organization for Nuclear Research, which seeks to unravel what the universe is made of and how it works.

The donors include the Breakthrough Prize Foundation of billionaire Silicon Valley investor Yuri Milner; the Eric and Wendy Schmidt Fund for Strategic Innovation of former Google chief executive Eric Schmidt; plus Italian Agnelli family heir John Elkann, and French telecoms tycoon Xavier Niel.

Archimedean screw inspires new way to encode chirality into magnetic materials

In physics and materials science, the term “spin chirality” refers to an asymmetry in the arrangement of spins (i.e., the intrinsic angular momentum of particles) in magnetic materials. This asymmetry can give rise to unique electronic and magnetic behaviors that are desirable for the development of spintronics, devices that leverage the spin of electrons and electric charge to process or store information.

The creation of materials that exhibit desired spin chirality and associated physical effects on a large scale has so far proved challenging. In a recent paper published in Nature Nanotechnology, researchers at École Polytechnique Fédérale de Lausanne (EPFL), the Max Planck Institute for Chemical Physics of Solids and other institutes introduced a new approach to encode chirality directly into materials by engineering their geometry at a nanoscale.

“Dirk and myself were initially inspired by the elegance of the Archimedean screw and began wondering whether we could build a magnonic analog, something that could ‘pump’ magnons (i.e., collective electron spin excitations) in a similarly directional way,” Dr. Mingran Xu, first author of the paper, told Tech Xplore.

Physicists bring unruly molecules to the quantum party

Scientists have made leaps and bounds in bending atoms to their will, making them into everything from ultraprecise clocks to bits of quantum data. Translating these quantum technologies from obedient atoms to unruly molecules could offer greater possibilities. Molecules can rotate and vibrate. That makes molecules more sensitive to certain changes in the environment, like temperature.

“If you’re sensitive to something, it can be a curse, because you would like to not be sensitive, or it can be a blessing,” said NIST physicist Dietrich Leibfried. “You can use that sensitivity to your advantage.”

But that same sensitivity has made molecules difficult to control. Recently, physicists at the National Institute of Standards and Technology (NIST) achieved new levels of control over molecules. In a study published in Physical Review Letters, they were able to manipulate a calcium hydride molecular ion—made up of one atom of hydrogen and one atom of calcium, with one electron removed to make it a charged molecule—with almost perfect success. And this control opens possibilities for quantum technology, chemical research and exploring new physics.

A simple spin swap reveals exotic anyons

Researchers from the University of Innsbruck, the Collège de France, and the Université Libre de Bruxelles have developed a simple yet powerful method to reveal anyons—exotic quantum particles that are neither bosons nor fermions—in one-dimensional systems. Their paper is published in Physical Review Letters.

In conventional three-dimensional space, particles belong to one of two categories: fermions or bosons. In low-dimensional settings, however, quantum mechanics allows for more exotic behavior. Here, anyons can emerge—quasi-particles whose exchange properties continuously interpolate between those of bosons and fermions, leading to fractional statistics. Detecting and engineering such particles in one dimension has long been a central challenge, typically requiring, as theory proposals suggest, intricate scattering schemes or density-dependent tunneling processes.

The new study by teams led by Hanns-Christoph Nägerl at the University of Innsbruck and Nathan Goldman at the Université Libre de Bruxelles and Collège de France (CNRS) now introduces a remarkably simple yet powerful approach. The researchers propose an effective “swap” model that leverages the spin degree of freedom of ultracold atoms. By assigning a complex phase to the exchange—or “swap”—of two spins, the system naturally acquires the fractional statistical behavior characteristic of anyons.

Bazinga! Physicists crack a ‘Big Bang Theory’ problem that could help explain dark matter

A professor at the University of Cincinnati and his colleagues have figured out something two of America’s most famous fictional physicists couldn’t: how to theoretically produce subatomic particles called axions in fusion reactors.

Particle physicists Sheldon Cooper and Leonard Hofstadter, roommates in the sitcom “The Big Bang Theory,” worked on the problem in three episodes of Season 5, but couldn’t crack it.

Now UC physics Professor Jure Zupan and his theoretical physicist co-authors at the Fermi National Laboratory, MIT and Technion–Israel Institute of Technology think they have one solution in a study published in the Journal of High Energy Physics.

Silicon atom processor links 11 qubits with more than 99% fidelity

In order to scale quantum computers, more qubits must be added and interconnected. However, prior attempts to do this have resulted in a loss of connection quality, or fidelity. But, a new study published in Nature details the design of a new kind of processor that overcomes this problem. The processor, developed by the company Silicon Quantum Computing, uses silicon—the main material used in classical computers—along with phosphorus atoms to link 11 qubits.

The new design uses precision-placed phosphorus atoms in isotopically purified silicon-28, which are arranged into two multi-nuclear spin registers. One register contains four phosphorus atoms, while the other contains five, and each register shares an electron spin. The two registers are linked by electron exchange interaction, allowing for non-local connectivity across the registers and 11 linked qubits.

Because of the placement of silicon and phosphorus in the periodic table, the design is referred to as the “14|15 platform.” This 11-qubit atom processor in silicon is the largest of its kind to date, marking a major accomplishment for quantum computing.

Scientists build a quantum computer that can repair itself using recycled atoms

Like their conventional counterparts, quantum computers can also break down. They can sometimes lose the atoms they manipulate to function, which can stop calculations dead in their tracks. But scientists at the US-based firm Atom Computing have demonstrated a solution that allows a quantum computer to repair itself while it’s still running.

The team zeroed in on quantum computers that use neutral atoms (atoms with equal numbers of protons and electrons). These individual atoms are the qubits, or the basic building blocks of a quantum computer’s memory. They are held in place by laser beams called optical tweezers, but the setup is not foolproof.

Occasionally, an atom slips out of its trap and disappears. When this happens mid-calculation, the whole process can grind to a halt because the computer can’t function with a missing part.

Flat Fermi surface in altermagnets enables quantum limit spin currents

The key feature of spintronic devices is their ability to use spin currents to transfer momentum, enabling low-energy, high-speed storage and logical signal control. These devices are usually manipulated by electric currents and fields. The charge-to-spin conversion efficiency (CSE) is a key metric for evaluating their performance.

Now, scientists from the Institute of Metal Research (IMR) of the Chinese Academy of Sciences have proposed a new deep correlation between the spin splitting torque (SST) and the Fermi surface geometry, achieving a quantum limit of 100% in a system with a flat Fermi surface. These results were published in Physical Review Letters on December 16.

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