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Category: particle physics

Symmetry Keeps Fermions Pure in a Noisy World

A theoretical study reveals how to control and drive a quantum system without causing its decoherence.

Quantumness is famously fragile. Decoherence, particle loss, and other dissipative processes typically destroy delicate quantum superpositions, causing open quantum systems to behave classically. This universal, inevitable fate suggests that, even when a system’s constituents are fully quantum, its nonequilibrium critical points could be described by classical universality classes. That is, the system could belong to a group whose behavior near a critical point is identical and scale invariant regardless of microscopic details. In a new theoretical study, Rohan Mittal and his collaborators at the University of Cologne in Germany have overturned this expectation for open systems of fermions [1]. They identified a particular symmetry, which, if present, blocks most of the noise channels that would ordinarily wash out quantum behavior at large scales.

Pairs of atoms observed existing in two places at once for the first time

Quantum physicists at ANU have observed atoms entangled in motion. “It’s really weird for us to think that this is how the universe works,” says Dr. Sean Hodgman from the ANU Research School of Physics. “You can read about it in a textbook, but it’s really weird to think that a particle can be in two places at once.”

Their experiment using helium atoms represents a major advancement over similar experiments using photons, which are particles of light. Unlike photons, helium atoms have mass and experience gravity. The research is published in Nature Communications.

“Experimentally, it’s extremely hard to demonstrate this,” says lead author and Ph.D. researcher, Yogesh Sridhar. “Several people have tried in the past to show these effects, and they have always come short.”

Silicon quantum computer performs logical operations for the first time

Silicon is ubiquitous in modern electronics, and now it is becoming increasingly useful in quantum computing. In particular, silicon’s compatibility with existing chip technology and its long coherence times in silicon-based spin qubits make it a promising material for scalable quantum computing. A new study, published in Nature Nanotechnology, has demonstrated silicon’s use in a logical quantum processor, representing the first of its kind.

Quantum computers are highly sensitive to errors from environmental noise, creating hurdles for practical quantum computation. To help suppress these errors, information can be encoded in logical qubits using fault-tolerant quantum computation (FTQC). Prior to this study, silicon had not been used for logical operations in FTQC.

“In silicon-based quantum processors, frequency crowding and cross-talk further exacerbate the errors as the system scales. To address these errors, logical encoding stands as the only viable solution by redundantly storing quantum information across multiple physical qubits. While logical qubits and operations have been successfully demonstrated in platforms such as superconducting circuits, neutral atoms, nitrogen-vacancy centers and trapped ions, their implementation in silicon-based spin qubits poses notable technical challenges,” the study authors write.

Earth formed from material exclusively from the inner solar system, planetary scientists show

Planetary scientists have long debated where the material that formed Earth comes from. Despite its location in the inner solar system, they consider it likely that 6–40% of this material must have come from the outer solar system, i.e., beyond Jupiter. For a long time, material from the outer solar system was considered necessary to bring volatile components such as water to Earth. Accordingly, there must also have been an exchange of material between the outer and inner solar systems during the formation of Earth. But is that really true?

Planetary scientists Paolo Sossi and Dan Bower, from ETH Zurich, compared existing data on the isotopic ratios of a wide range of meteorites, including those from Mars and the asteroid Vesta, with those of Earth. Isotopes are sibling atoms of the same element (same number of protons) that have a different mass (different number of neutrons).

The researchers analyzed this data in a new way and arrived at a surprising conclusion: the material that makes up Earth originates entirely from the inner region of the solar system.

Quadratic gravity theory reshapes quantum view of Big Bang

Waterloo scientists have developed a new way to understand how the universe began, and it could change what we know about the Big Bang and the earliest moments of cosmic history. Their work suggests that the universe’s rapid early expansion could have arisen naturally from a deeper, more complete theory of quantum gravity. The paper, “Ultraviolet completion of the Big Bang in quadratic gravity,” appears in Physical Review Letters.

Dr. Niayesh Afshordi, professor of physics and astronomy at the University of Waterloo and Perimeter Institute (PI), led the research team that explored a novel method of combining gravity with quantum physics, the rules that govern how the smallest particles in the universe behave. While general relativity has been successful for more than a century, it breaks down at the extreme conditions that existed at the birth of the universe. To address this problem, the team used Quadratic Quantum Gravity, which remains mathematically consistent even at extremely high energies—similar to the kind present during the Big Bang.

Most existing explanations for the Big Bang rely on Einstein’s theory of gravity, plus additional components added by hand. This new approach offers a more unified picture that connects the earliest moments of the universe to the well-tested cosmology scientists observe today.

In world first, antimatter taken on test drive at CERN

CERN scientists on Tuesday pulled off the unprecedented feat of transporting antiprotons by road, successfully test-driving the world’s first antimatter delivery system, with an eye to one day supplying research labs across Europe.

“The particles returned… so this was a success,” CERN physicist Stefan Ulmer told reporters after the large truck came back from a 10-kilometer drive around the campus of Europe’s main physics laboratory.

While that might not sound like a big distance, Ulmer, a spokesman for CERN’s BASE experiment probing the asymmetry between matter and antimatter in the universe, said it marked the “starting point to a new era.”

Astrophysicists trace the origin of valuable metals in space, from colliding stars to merging galaxies

Billions of light years away in a remote part of the universe, two neutron stars—the ultradense remnants of dead stars—collided. The catastrophic cosmic event sent light and particles, including a sudden flash of gamma rays, streaming through the universe. These gamma rays traveled for 8.5 billion years before reaching Earth.

In a new study, our team of astrophysicists examined this gamma-ray signal. We learned that the stellar collision it came from was likely caused by an even more catastrophic encounter—a merger between two galaxies.

This is the first time astronomers associated this type of signal with such a large-scale galactic interaction. Our finding offers new insight into how stellar collisions spread metals across the universe.

Piezoelectric materials enable a new approach to searching for axions

Dark matter, a type of matter that does not emit, reflect or absorb light, is predicted to account for most of the matter in the universe. As it eludes common experimental techniques for studying ordinary matter, understanding the nature and composition of dark matter has so far proved very challenging. One hypothesis is that it is made up of hypothetical particles known as quantum chromodynamics (QCD) axions. These are theoretical elementary particles that would interact very weakly with ordinary matter and are predicted to be extremely light, highly stable and electrically neutral.

While several large-scale studies have searched for small signals or effects that would indicate the presence of these particles or their interaction with ordinary matter, their existence has not yet been confirmed experimentally. In a paper recently published in Physical Review Letters, researchers at Perimeter Institute, University of North Carolina, Kavli Institute and New York University have introduced a new approach to search for QCD axions using a class of materials that generate electric fields when deformed, called piezoelectric materials.

“The axion was proposed in the late 1970s by Weinberg and Wilczek, as a solution to the strong CP (Charge-Parity) problem, a long-standing puzzle in the theory of the strong nuclear force,” Amalia Madden, co-senior author of the paper, told Phys.org.

Physicists create optical phenomenon inspired by the quantum Hall and spin Hall effects

Researchers at the Würzburg site of the Cluster of Excellence ctd.qmat have succeeded in transferring the topological quantum Hall and spin Hall effects to a hybrid light-matter system by harnessing targeted material design. The team led by Professor Sebastian Klembt generated this optical quantum phenomenon by using polaritons—hybrid light-matter particles. This advance paves the way for optical information processing. The results have been published in Nature Communications.

Back in 1980, Nobel laureate Klaus von Klitzing, then working in Würzburg, first demonstrated topological charge transport with the quantum Hall effect.

In 2006, Professor Laurens Molenkamp at JMU Würzburg provided the world’s first experimental evidence of the quantum spin Hall effect as an intrinsic property of a topological insulator. Both phenomena protect electrons from scattering.

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