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Category: particle physics – Page 79

When ultrafast electrons are deflected, they emit light—synchrotron radiation. This is used in so-called storage rings in which magnets force the particles onto a closed path. This light is longitudinally incoherent and consists of a broad spectrum of wavelengths.

Its high brilliance makes it an excellent tool for . Monochromators can be used to pick out individual wavelengths from the spectrum, but this reduces the radiant power by many orders of magnitude to values of a few watts only.

But what if a were instead to deliver monochromatic, with outputs of several kilowatts, analogous to a ? Physicist Alexander Chao and his doctoral student Daniel Ratner found an answer to this challenge in 2010: if the orbiting in a storage ring become shorter than the wavelength of the light they emit, the emitted radiation becomes coherent and therefore millions of times more powerful.

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Advanced materials, including two-dimensional or atomically thin materials just a few atoms thick, are essential for the future of microelectronics technology. Now a team at Los Alamos National Laboratory has developed a way to directly measure such materials’ thermal expansion coefficient, the rate at which the material expands as it heats. That insight can help address heat-related performance issues of materials incorporated into microelectronics, such as computer chips.

The research has been published in ACS Nano (“Direct measurement of the thermal expansion coefficient of epitaxial WSe 2 by four-dimensional scanning transmission electron microscopy”).

“It’s well understood that heating a material usually results in expansion of the atoms arranged in the material’s structure,” said Theresa Kucinski, scientist with the Nuclear Materials Science Group at Los Alamos. “But things get weird when the material is only one to a few atoms thick.”

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With this measurement, the Large Hadron Collider again demonstrated its ability to provide very high-precision measurements and bring new insights into an old mystery.

The CMS collaboration revealed a groundbreaking measurement of the electroweak mixing angle, confirming Standard Model predictions and addressing previous discrepancies with the most precise collider-based measurement to date. This achievement highlights the potential for precision physics in hadron colliders and prepares for more advanced studies at the High-Luminosity LHC.

Electroweak Mixing Measurement

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Philosopher Wilfrid Sellars had a term for the world as it appears, the “manifest image.” This is the world as we perceive it. In it, an apple is an apple, something red or green with a certain shape, a range of sizes, a thing that we can eat, or throw.

The manifest image can be contrasted with the scientific image of the world. Where the manifest image has colors, the scientific one has electromagnetic radiation of certain wavelengths. Where the manifest image has solid objects, like apples, the scientific image has mostly empty space, with clusters of elementary particles, held together in configurations due to a small number of fundamental interactions.

The scientific image is often radically different from the manifest image, although how different it is depends on what level of organization is being examined. For many purposes, including scientific ones, the manifest image, which is itself a predictive theory of the world at a certain level or organization, works just fine. For example, an ethologist, someone who studies animal behavior, can generally do so without having to concern themselves about quantum fields and their interactions.

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Physicists at TU Graz have determined that certain molecules can be stimulated by pulses of infrared light to generate small magnetic fields. If experimental trials are also successful, this technique could potentially be applied in quantum computer circuits.

When molecules absorb infrared light, they start to vibrate as they receive energy. Andreas Hauser from the Institute of Experimental Physics at Graz University of Technology (TU Graz) used this well-understood process as a basis for exploring whether these vibrations could be harnessed to produce magnetic fields. Since atomic nuclei carry a positive charge, the movement of these charged particles results in the creation of a magnetic field.

Using the example of metal phthalocyanines – ring-shaped, planar dye molecules – Andreas Hauser and his team have now calculated that, due to their high symmetry, these molecules actually generate tiny magnetic fields in the nanometre range when infrared pulses act on them.

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Ontic structural realism argues that structure is all there is. In (French, 2014) I argued for an ‘eliminativist’ version of this view, according to which the world should be conceived, metaphysically, as structure, and objects, at both the fundamental and ‘everyday’ levels, should be eliminated. This paper is a response to a number of profound concerns that have been raised, such as how we might distinguish between the kind of structure invoked by this view and mathematical structure in general, how we should choose between eliminativist ontic structural realism and alternative metaphysical accounts such as dispositionalism, and how we should capture, in metaphysical terms, the relationship between structures and particles. In developing my response I shall touch on a number of broad issues, including the applicability of mathematics, the nature of representation and the relationship between metaphysics and science in general.

Keywords: Causation; Dependence; Disposition; Metaphysics; Object; Representation; Structure.

Copyright © 2018. Published by Elsevier Ltd.

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While solid-state spin qubits show promise as quantum information platforms, their qubit-to-qubit interactions extend over too short a distance to connect many of them together, posing a problem for complex computations. Now Frankie Fung and colleagues from Harvard University have devised a mechanical method—involving a vibrating nanobeam—to connect distant spin qubits, potentially overcoming this issue [1].

A popular solid-state spin qubit is the nitrogen-vacancy (NV) center, a single-atom defect in a diamond crystal. This system is attractive for quantum information applications, as it has both a light-sensitive electron spin state (which offers a knob for controlling the qubit) and a long-lived nuclear spin state (which acts as memory). But direct interactions between NV centers are limited to a few nanometers.

To lengthen the connections, Fung and his colleagues propose using a nanobeam fitted with a micromagnet as an intermediary between distant NV centers. The idea is then to place a line of NV centers along the length of a scanning-probe-microscope tip and move the tip over the micromagnet. When a particular NV center comes close to the micromagnet, the magnetic-field interaction should entangle the vibrational state of the nanobeam with the spin state of that NV center. This quantum information is then shared with the next NV center along the line.

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Dark energy—a mysterious force pushing the universe apart at an ever-increasing rate—was discovered 26 years ago, and ever since, scientists have been searching for a new and exotic particle causing the expansion.

Pushing the boundaries of this search, University of California, Berkeley physicists have now built the most precise experiment yet to look for minor deviations from the accepted theory of that could be evidence for such a particle, which theorists have dubbed a chameleon or symmetron. The results are published in the June 11, 2024, issue of Nature Physics.

The experiment, which combines an for precise gravity measurements with an to hold the atoms in place, allowed the researchers to immobilize free-falling atoms for seconds instead of milliseconds to look for gravitational effects, besting the current most precise measurement by a factor of five.

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Scientists at the University of Konstanz in Germany have advanced ultrafast electron microscopy to unprecedented time resolution. Reporting in Science Advances, the research team presents a method for the all-optical control, compression, and characterization of electron pulses within a transmission electron microscope using terahertz light. Additionally, the researchers have discovered substantial anti-correlations in the time domain for two-electron and three-electron states, providing deeper insight into the quantum physics of free electrons.

Ultrafast electron microscopy is a cutting-edge technique that combines the spatial resolution of traditional electron microscopy with the of ultrafast femtosecond laser pulses. This powerful combination allows researchers to observe atoms and electrons in motion, capturing dynamic processes in materials with unparalleled clarity. By visualizing these rapid events in space and time, scientists can gain deeper insights into the fundamental mechanisms that govern and transitions, helping to create advancements in research fields such as nanotechnology, optics, materials science, and .

Although ultrafast electron microscopy enables, in principle, the observation of atomic and electronic motions on fundamental spatial and temporal scales, capturing these rapid dynamics has remained challenging due to the limitations in electron pulse duration. The current standard electron pulses, lasting about 200 femtoseconds, are too long to resolve many fundamental reaction processes in materials and molecules. Pulses ten times shorter would be required to observe basic reaction paths and collective atomic motions, so-called phonon modes, in real time.

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