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Category: particle physics – Page 7

Nobel Prize in Physics 2001

The matter surrounding us consists of atoms that obey the laws of quantum mechanics. At normal temperatures these often agree with classical conceptions, and a gas under these conditions behaves rather like a swarm of billiard balls bouncing against one another and the containing walls. When the temperature is lowered and the speed of the atoms is reduced, however, their properties will be increasingly dominated by the principles of quantum mechanics. The atoms rotate round their axes – they have spin – and this movement is described by a spin quantum number, which has to be an integer – a whole number – or a half-integer. Particles that have integer spin are called bosons, while those with half-integer spin are called fermions. Bosons show strong “social” behaviour and at low temperatures strive to gather in one and the same quantum state, the one with the lowest energy. Fermions on the other hand avoid one another. They cannot appear in exactly the same quantum state, so that states of higher energy must also be used. The arrangement of the elements in the periodic system may be understood on the basis of the fact that the electrons in the atomic shells are fermions.

As early as 1924 the Indian physicist S. N. Bose carried out a statistical calculation for the kind of particles which have since come to bear his name, bosons, and more specifically light particles later termed photons. Bose presented an alternative derivation for the radiation law earlier found by Planck. Bose sent his work to A. Einstein, who realised its importance. He translated it to German and had it published. Einstein rapidly extended the theory to cover Bose particles with mass and he himself published two articles in quick succession, predicting that when a given number of particles approach each other sufficiently closely and move sufficiently slowly they will together convert to the lowest energy state: what we now term Bose-Einstein condensation (BEC) occurs.

Ever since publication of this pioneering work, physicists have wished to be able to achieve this new fundamental state of matter, which was expected to have many interesting and useful properties. Seventy years were to pass before this year’s laureates, Eric A. Cornell, Wolfgang Ketterle and Carl E. Wieman, using very advanced methods, finally managed to do this in 1995. The state was achieved in alkali atom gases, in which the phenomenon can be studied in a very pure manner. Nowhere else in the universe can one find the extreme conditions which BEC in dilute gases represents. Manifestations of Bose-Einstein condensation have earlier been observed in more complicated systems: condensation of paired electrons in superconductors (loss of all electrical resistance) and suprafluidity (loss of internal friction in fluids). Here, too, low temperatures are required. Research in these areas has been rewarded with several Nobel Prizes. As opposed to alkali-atom vapours these quantum-mechanical systems are not simple since the condensation phenomenon concerns only a part of the systems and the strong interactions involved tend to hide the BEC phenomenon.

Electric field reverses phonon chirality and spin direction in ferroelectric crystal

Chiral phonons are groups of atoms that move in a circular direction when excited by an energy source, such as heat. As the phonons move through a material, they propagate that circular motion, or angular momentum, through the material. The angular momentum serves as the source of spin, and the chirality dictates the direction of the spin, enabling spin control in spintronics.

Chirality, in simple terms, means that a molecule or material cannot be superimposed on its mirror image—think of your left and right hands, for example. A left-handed glove does not fit on your right hand, and vice versa.

In a new study, researchers used an electric field to switch the chirality of phonons within a ferroelectric crystal. The work could lead to the creation of faster and more energy-efficient spintronic devices.

Miniaturized laser technology paves the way for fundamental physics experiments in space

An international team of researchers has succeeded in producing atomic quantum gas mixtures with an unprecedented particle flux. In the journal Nature Communications, the scientists report on experiments conducted with the MAIUS-B apparatus, in which Bose–Einstein condensates (BECs) consisting of two different atomic species—rubidium and potassium—were generated and studied under microgravity conditions in the Einstein Elevator at Leibniz University Hannover in Germany.

A key contribution to this achievement came from a technological development at Johannes Gutenberg University Mainz (JGU): the highly sophisticated and compact optical system used to control the atoms.

Air-stable, ultrathin superconductors developed for more scalable quantum devices

Super-thin superconducting materials, which are only one or a few atoms thick, have unique properties scientists can leverage to produce more compact, scalable, and efficient quantum devices. But these fragile materials degrade so rapidly in air that they are difficult to study or manufacture.

Now, researchers from MIT and elsewhere have discovered and harnessed a method to generate a large, uniform area of ultrathin superconducting material that remains stable in air.

They “grow” the superconducting material, called niobium diselenide, underneath another atomically thin material, carbon-based graphene. The graphene layer protects the fragile superconductor from oxidation, while guiding it to grow in a smooth layer over a large wafer-scale area.

Using the Earth’s magnetic field to hunt for axions and dark photons

Dark matter’s existence is all but certain—astronomers believe it makes up about a quarter of the universe’s total energy content—yet its true identity has eluded us for decades. Two of the leading candidates for dark matter are the hypothetical particles ultralight axions and dark photons, which in the range studied here would be some 19 to 21 orders of magnitude lighter than the electron.

Conventional axion searches tend to involve converting them into photons with the help of strong laboratory magnets. However, research in a laboratory inherently limits the space over which such a field can be applied.

A collaborative team of researchers from Kyoto University, Hiroshima University and Nihon University realized that, by contrast, Earth’s own magnetic field spans a scale no laboratory could match. Their paper is published in the journal Progress of Theoretical and Experimental Physics.

Attosecond X-ray method maps early electron motions that trigger chemical reactions

All chemistry starts with a push from electrons. In the early moments of a chemical reaction, it’s the movement of electrons that initiates the breaking of old chemical bonds and forging of new ones, transforming one molecule into another.

When an electron is removed from a molecule faster than the molecule can react—called “impulsive ionization”—the other electrons in the molecule enter excited quantum states that evolve on ultrafast timescales. Scientists have long sought to map the ultrasmall, ultrafast electronic motions behind chemical reactions on their natural timescales.

Now, researchers at the Department of Energy’s SLAC National Accelerator Laboratory have created a movie of early electron motion in an impulsively excited molecule. Each frame captures changes happening in mere attoseconds, just billionths of a billionth of a second.

‘Spooky’ particles transit DC suburbs, a step toward a quantum network

In early 2025, special signals wended their way through a fiber-optic highway strung above the streets and sidewalks of the Maryland suburbs. The arrival of those signals at their destination marks a significant step toward a long-held dream of building a “quantum network.” Researchers believe that this emerging technology could someday link quantum devices in ways that supercharge scientific research, enable ultrasecure communications and boost the power of future quantum computers.

National Institute of Standards and Technology (NIST) researchers and collaborators reported this advance in the Journal of Optical Communications and Networking.

A temperature dial for more realistic quantum simulations

Scientists from Rice University in the U.S. have developed a way to precisely tune the temperature inside a trapped-ion simulator. The breakthrough means they will be able to run quantum simulations at precise temperatures that better reflect real-world conditions.

Trapped-ion simulators are quantum devices that isolate charged particles inside a sealed vacuum chamber, using electric fields to hold them in place. They mimic and study complex quantum systems, such as chemical reactions or exotic materials, that are too difficult for ordinary computers to calculate.

Temperatures inside these devices are typically kept as close as possible to absolute zero so that thermal motion does not disrupt calculations or cause errors. But researchers lacked a suitable way to set the temperature without accidentally changing how fast the system loses energy. This meant that studies were mostly stuck using absolute zero or uncontrolled high temperatures.

New approach to cleaning the inner walls of a fusion system removes another obstacle to near-endless energy

Fusion systems need inner walls that can withstand extreme heat. One promising solution uses liquid lithium to protect the walls, held like water in a sponge made of the exceptionally strong metal tungsten. An advanced manufacturing process can be used to make tungsten into sponge-like wall tiles with lots of pores for flowing liquid lithium. But this process also leaves the tungsten contaminated with other materials, such as carbon, oxygen or nitrogen.

When exposed to liquid lithium, the carbon and oxygen react to form solids that can plug the holes in the tungsten, preventing the lithium from flowing properly. Even if the tungsten were cleaned at the end of the manufacturing process, it would become recontaminated when the tiles are exposed to air during installation.

Now researchers from the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), Princeton University and Pennsylvania State University have found a clever way to clean those tiles after they are installed and sealed inside the fusion system—in vacuum chambers from which the air has been removed. The advance, which uses heat combined with particles from a neon plasma to knock contaminants out of tiles, could help future fusion systems run better with liquid lithium.

Molecular orbitals imaged in 3D, opening path to femtosecond videos

One of the most famous and intriguing results of quantum mechanics is the finding that fundamental particles, such as electrons, cannot be pinned down to one single location. Instead, a particle is described by its “wavefunction,” which allows researchers to derive probability distributions—a sort of mathematical map that shows the possibilities—of fundamental properties such as its position and momentum. In particular, the electron wavefunctions within a molecule, known as “molecular orbitals,” carry information about how the molecule interacts with its surroundings. For example, they show how it may absorb light or how a chemical reaction might take place.

As a consequence, knowledge of the complete three-dimensional wavefunction is highly desirable, but imaging the wavefunction has proven to be a major experimental challenge. An interdisciplinary research team at the University of Göttingen has now managed to image the three-dimensional wavefunction of a nanometer-sized organic molecule. They overcame the limitations by combining state-of-the-art photoelectron spectroscopy with powerful mathematical algorithms. The results are published in Nature Communications.

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