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Particles can carry information securely because intercepting them would alter the message and alert the receiver or sender.

The device uses lasers to accelerate electrons along an etched channel.

A 2017 report of the discovery of a particular kind of Majorana fermion — the chiral Majorana fermion, referred to as the “angel particle” — is likely a false alarm, according to new research. Majorana fermions are enigmatic particles that act as their own antiparticle and were first hypothesized to exist in 1937. They are of immense interest to physicists because their unique properties could allow them to be used in the construction of a topological quantum computer.

A team of physicists at Penn State and the University of Wurzburg in Germany led by Cui-Zu Chang, an assistant professor of physics at Penn State studied over three dozen devices similar to the one used to produce the angel particle in the 2017 report. They found that the feature that was claimed to be the manifestation of the angel particle was unlikely to be induced by the existence of the angel particle. A paper describing the research appears on January 3, 2020 in the journal Science.

“When the Italian physicist Ettore Majorana predicted the possibility of a new fundamental particle which is its own antiparticle, little could he have envisioned the long-lasting implications of his imaginative idea.”

Nothing lasts forever. Humans, planets, stars, galaxies, maybe even the Universe itself, everything has an expiration date. But things in the quantum realm don’t always follow the rules. Scientists have found that quasiparticles in quantum systems could be effectively immortal.

That doesn’t mean they don’t decay, which is reassuring. But once these quasiparticles have decayed, they are able to reorganise themselves back into existence, possibly ad infinitum.

This seemingly flies right in the face of the second law of thermodynamics, which asserts that entropy in an isolated system can only move in an increasing direction: things can only break down, not build back up again.

Clusters composed of a few atoms tend to be spherical. They are usually organized in shells of atoms around a central atom. This is the case for many elements, but not for gold! Experiments and advanced computations have shown that freestanding clusters of twenty gold atoms take on a pyramidal shape. They have a triangular ground plane made up of ten neatly arranged atoms, with additional triangles of six and three atoms, topped by a single atom.

The remarkable tetrahedral structure has now been imaged for the first time with a scanning tunnelling microscope. This high-tech microscope can visualise single atoms. It operates at extremely low temperatures (269 degrees below zero) and uses quantum tunnelling of an electrical current from a sharp scanning metallic tip through the cluster and into the support. Quantum tunnelling is a process where electrical current flows between two conductors without any physical contact between them.

The researchers used intense plasmas in a complex vacuum chamber setup to sputter gold atoms from a macroscopic piece of gold. “Part of the sputtered atoms grow together to small particles of a few up to a few tens of atoms, due to a process comparable with condensation of water molecules to droplets,” says Zhe Li, the main author of the paper, currently at the Harbin Institute of Technology, Shenzhen. “We selected a beam of clusters consisting of exactly twenty gold atoms. We landed these species with one of the triangular facets onto a substrate covered with a very thin layer of kitchen salt (NaCl), precisely three atom layers thick.”

The study also revealed the peculiar electronic structure of the small gold pyramid. Similar to noble gas atoms or aromatic molecules, the cluster only has completely filled electron orbitals, which makes them much less reactive than clusters with one or a few atoms more or less.

Continue reading “Clusters of gold atoms form peculiar pyramidal shape” »

No one really knows what happens inside an atom. But two competing groups of scientists think they’ve figured it out. And both are racing to prove that their own vision is correct.

Here’s what we know for sure: Electrons whiz around “orbitals” in an atom’s outer shell. Then there’s a whole lot of empty space. And then, right in the center of that space, there’s a tiny nucleus — a dense knot of protons and neutrons that give the atom most of its mass. Those protons and neutrons cluster together, bound by what’s called the strong force. And the numbers of those protons and neutrons determine whether the atom is iron or oxygen or xenon, and whether it’s radioactive or stable.

During one of these phase transitions (which happened when the universe was less than a second old), the axions of string theory didn’t appear as particles. Instead, they looked like loops and lines — a network of lightweight, nearly invisible strings crisscrossing the cosmos.

This hypothetical axiverse, filled with a variety of lightweight axion strings, is predicted by no other theory of physics but string theory. So, if we determine that we live in an axiverse, it would be a major boon for string theory.

How can we search for these axion strings? Models predict that axion strings have very low mass, so light won’t bump into an axion and bend, or axions likely wouldn’t mingle with other particles. There could be millions of axion strings floating through the Milky Way right now, and we wouldn’t see them.

Nuclear fusion, the process that powers our sun, happens when nuclear reactions between light elements produce heavier ones. It’s also happening — at a smaller scale — in a Colorado State University laboratory.

Using a compact but powerful laser to heat arrays of ordered nanowires, CSU scientists and collaborators have demonstrated micro-scale nuclear fusion in the lab. They have achieved record-setting efficiency for the generation of neutrons — chargeless sub-atomic particles resulting from the fusion process.

Their work is detailed in a paper published in Nature Communications (“Micro-scale fusion in dense relativistic nanowire array plasmas”), and is led by Jorge Rocca, University Distinguished Professor in electrical and computer engineering and physics. The paper’s first author is Alden Curtis, a CSU graduate student.

As 2019 winds to a close, the journey towards fully realised quantum computing continues: physicists have been able to demonstrate quantum teleportation between two computer chips for the first time.

Put simply, this breakthrough means that information was passed between the chips not by physical electronic connections, but through quantum entanglement – by linking two particles across a gap using the principles of quantum physics.

We don’t yet understand everything about quantum entanglement (it’s the same phenomenon Albert Einstein famously called “spooky action”), but being able to use it to send information between computer chips is significant, even if so far we’re confined to a tightly controlled lab environment.