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Category: particle physics

What if dark matter came in two states?

The absence of a signal could itself be a signal. This is the idea behind a new study published in the Journal of Cosmology and Astroparticle Physics, which aims to redefine how we search for dark matter, showing that it may not be necessary to find the same “clues” everywhere in order to interpret it.

In particular, the study suggests that even if we observe a certain type of signal at the center of our galaxy—an excess of gamma radiation that could result from the annihilation of dark matter particles—failing to detect the same signal in other systems, such as dwarf galaxies, is not enough to rule out this explanation.

Dark matter, in fact, may not consist of a single particle, but of multiple slightly different components, whose behavior varies depending on the cosmic environment.

Physicists zero in on the mass of the fundamental W boson particle

When fundamental particles are heavier or lighter than expected, physicists’ understanding of the universe can tip into the unknown. A particle that is just beyond its predicted mass can unravel scientists’ assumptions about the forces that make up all of matter and space. But now, a new precision measurement has reset the balance and confirmed scientists’ theories, at least for one of the universe’s core building blocks.

In a paper appearing in the journal Nature, an international team including MIT physicists reports a new, ultraprecise measurement of the mass of the W boson.

The W boson is one of two elementary particles that embody the weak force, which is one of the four fundamental forces of nature. The weak force enables certain particles to change identities, such as from protons to neutrons and vice versa. This morphing is what drives radioactive decay, as well as nuclear fusion, which powers the sun.

AI trained like a Rubik’s Cube solver simplifies particle physics equations

For years, Rutgers physicist David Shih solved Rubik’s Cubes with his children, twisting the colorful squares until the scrambled puzzle returned to order. He didn’t expect the toy to connect to his research, but recently he realized the logic behind the puzzle was exactly what he needed to solve a problem involving particle physics.

That idea led to a new artificial intelligence (AI) method that can simplify some of the extremely complex equations used in particle physics. Shih described the method in a study posted to the arXiv preprint server, a widely used site where scientists share new research.

“In reaching our solutions, we found that an analogy between mathematical simplification and solving Rubik’s Cubes was key,” said Shih, a professor in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences. “Both can be viewed as scrambling and unscrambling problems.”

Robust against noise, geometric-phase swap gates bring stability to quantum operations

Researchers at ETH Zurich have realized particularly stable quantum logical operations with qubits made of neutral atoms. Since these operations, called quantum gates, are based on geometric phases, they are extremely robust against experimental noise and can be used in quantum computers in the future.

Quantum bits, or qubits, which are required for building quantum computers, come in different kinds. In recent years, many research institutes and companies have focused on superconducting circuits and trapped ions. However, neutral atoms trapped with laser light also have a lot going for them: since they carry no electric charge, they are less sensitive to disturbances. Moreover, trapping with laser light makes it easy to realize several thousand qubits in a single system—using superconductors or ions this is much more difficult.

Nevertheless, neutral atoms have their own problems. In quantum computers, qubits exist in superposition states of the logic values 0 and 1. To perform calculations with them, one needs to execute quantum logic operations, also known as quantum gates.

Electron–atom scattering encodes the quantum state of electron wave packets

A new analysis reveals what happens when very short or narrow electron beams encounter a particle. The research is published in the New Journal of Physics. Scientists should be able to achieve a new level of control over high-energy electrons interacting with a particle, according to the theoretical analysis by a RIKEN physicist and two colleagues.

Electrons are particles, but according to quantum mechanics they also behave like waves under certain circumstances.

Electron microscopes exploit this wave-like nature of electrons to obtain high-resolution images of objects by imaging how an electron beam is scattered from an object.

Giant Atoms for Measuring Radiation

The invention of the radio just over a century ago transformed people’s ability to communicate. Suddenly, people could send and receive light-speed messages from thousands of miles away — a capability that continues to transform the world.

Soon, quantum scientists could usher in the next big advance in radio communication: compact, highly sensitive receivers based on atoms.

Atoms are typically far too small to interact with radio waves. But one of quantum theory’s stranger predictions is the possibility of gargantuan atoms with diameters up to the width of a human hair.

How a century-long argument over light’s true nature came to an end

Two of the forefathers of quantum theory, Albert Einstein and Niels Bohr, had a famous argument over whether light is a wave or a particle. Columnist Karmela Padavic-Callaghan finds that the matter has been settled once and for all.

By Karmela Padavic-Callaghan

Experiment indicates new type of mesic nuclei that could reveal how matter acquires mass

Nearly every object we interact with in our lives has a mass, but where does this mass come from? Modern physics says matter acquires its mass from interaction with a physical vacuum—it is not an empty space, but contains a complex structure. Investigating the system of a meson—a composite particle made of a quark, an elementary particle, and its anti-matter, anti-quark—bound to an atomic nucleus, a mesic nucleus, provides precious insight into the vacuum structure, or mass generation mechanism. Scientists are now one step closer to further understanding the origin of mass thanks to new experimental results on a completely new type of mesic nucleus.

The researchers, as part of a major international collaboration, have reported evidence hinting at the existence of a never-before-seen but predicted exotic bound state known as an η′-mesic nucleus. The findings are published in Physical Review Letters.

Physicists have theorized that under certain conditions, short-lived particles called mesons—which only exist for less than a ten-millionth of a second—can become temporarily trapped inside a nucleus, forming an exotic bound system. Measuring mesic nuclei could help scientists understand how the strong nuclear force, which binds atomic nuclei together, behaves and how the vacuum structure changes in extremely high-density environments.

Watching Atoms Make Waves

A new microscope captures how atoms rearrange themselves when they are illuminated inside an optical cavity.

When light hits an atom, it exerts a force on the atom. As weak as these light-induced forces may be, understanding them allows scientists to levitate particles, create the coldest atomic gases in the Universe, operate solar sails, and observe gravitational waves. More exotic phenomena occur when light is confined between a pair of mirrors known as an optical cavity. When a gas of atoms is placed inside such a cavity, light emitted by one atom can be absorbed by another atom. Through the exchange of photons, each atom simultaneously tugs on all the other atoms, causing the ensemble to autonomously rearrange itself into a periodic pattern called a density wave. Now Jean-Philippe Brantut and his colleagues at the Swiss Federal Institute of Technology in Lausanne (EPFL) have built a microscope to, for the first time, image this light-induced density wave in an ultracold atomic gas [1].

Quantum ground state of rotation achieved for the first time in two dimensions

Quantum mechanics tells us that a particle can never be perfectly still. But how precisely can it be oriented? A research team at the University of Vienna, together with colleagues at TU Wien and Ulm University, has now cooled the rotational motion of a levitated silica nanorotor all the way to its quantum ground state—in two orientational degrees of freedom.

Reporting in Nature Physics, they show how optical cooling confines the nanoparticle’s orientation to within the bounds of quantum zero-point fluctuations, the unavoidable orientational uncertainty imposed by Heisenberg’s uncertainty principle. Such quantum-limited alignment is an important milestone towards rotational matter-wave interferometry and ultra-sensitive quantum torque sensing.

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