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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.

EAST achieves new plasma confinement regime using small 3D magnetic perturbations

A research group has achieved a new plasma confinement regime using small 3D magnetic perturbations that simultaneously suppress edge instabilities and enhance core plasma confinement in the Experimental Advanced Superconducting Tokamak (EAST). The research results are published in PRX Energy.

Sustained high plasma confinement at both the core and the edge without edge crash events due to edge instabilities is critical for efficient fusion energy production in tokamaks. However, achieving stable, high-core confinement with an internal transport barrier (ITB) is extremely challenging, especially in tungsten-wall devices where tungsten impurity accumulation must be controlled. Furthermore, controlling edge instabilities usually results in degraded core plasma confinement.

In this study, the researchers applied small 3D magnetic perturbations localized at the plasma edge. This method achieved the suppression of edge instabilities and control of tungsten impurities. For the first time, it also enabled the induction and sustained confinement of high-core plasma with an ITB.

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.

Making Hidden States Visible

Experiments with programmable electroacoustic cavities reveal that a multistable system can be steered into states that are unreachable with conventional control methods.

Many physical systems can be in more than one stable state: A laser can be on or off, and a magnetic bit up or down. This multistability can appear in nonlinear resonators—such as ferromagnets and genetic toggle switches in cells—that are driven into different steady states, or “branches,” by ramping up and down the driving parameter [1]. This behavior is often pictured using a familiar hysteresis loop that traces the system’s trajectory between a lower branch and higher branch (Fig. 1). It is easy to imagine that additional steady states might coexist with those sampled, but experiments have largely ignored that possibility, assuming instead that slow, quasistatic parameter sweeps reveal all “physically relevant” behavior.

In a new acoustic experiment, Kun Zhang from the Wuhan University in China and colleagues challenge that assumption [2]. They show that a pair of coupled acoustic cavities can host a fully “folded” steady state that is perfectly stable yet invisible to conventional sweeps. This hidden branch can, however, be reached with carefully designed sound pulses, the team shows. These results—combined with those from another recent study [3]—turn the abstract idea of hidden multistability into a concrete and controllable feature of nonlinear resonator networks, which might one day be used to securely store sensitive information.

A Very Stable Mirror

To make an ultrastable laser beam for applications such as gravitational-wave detectors, the frequency of a beam confined within an optical cavity is locked to the cavity’s resonant frequency. This frequency is determined by the cavity’s length. The stability of the laser beam’s frequency and the quality of the cavity’s resonance depend on the thermal noise of the mirrors that define that length. Dahyeon Lee at JILA and the University of Colorado Boulder and his colleagues have now demonstrated a crystalline mirror coating with superior thermomechanical properties compared to conventional coatings [1]. The new coating could lead to ultrastable cavities for optical clocks and next-generation interferometers.

Recently, mirrors coated with crystalline alloys of gallium arsenide (GaAs) have emerged as promising candidates to replace those with conventional amorphous dielectric coatings. GaAs-coated mirrors have excellent optical qualities and exhibit low thermal noise at room temperature. But previous studies found that these crystalline coatings suffer from additional noise contributions, which undermine their potential usefulness.

The origins of some of those noise contributions remain unclear. Nevertheless, Lee and colleagues have demonstrated that crystalline GaAs-based coatings can still be superior at cryogenic temperatures. The researchers constructed a 6-cm-long cavity bounded by two mirrors made of alternating layers of GaAs and aluminum gallium arsenide on silicon substrates. They used more layers compared to previous experiments, which reduced photon loss. Operating the cavity at 17 K, where the thermal expansion coefficient of the silicon substrate is zero, they achieved a frequency stability of 2.5 × 10−17. This stability is 4 times better than the expected limit for conventional coatings and sets a new record for cavity-stabilized lasers.

2.8 Days to Disaster: Low Earth Orbit Could Collapse Without Warning

A new analysis suggests modern satellite networks could suffer catastrophic collisions within days of losing control during a major solar storm. The phrase “House of Cards” is often associated today with a Netflix political drama, but its original meaning refers to a structure that is inherently

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