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Cosmic lockdown: How the environment can isolate quantum fields
A simplified cosmological model suggests that decoherence can suppress quantum tunneling, effectively locking fields into the vacuum state they have reached.
The vacuum is not always so empty. “When we talk about a vacuum in cosmology, we do not mean completely devoid of energy,” explains David Wands, Professor at the Institute of Cosmology & Gravitation at the University of Portsmouth. “A vacuum is rather a state in which a field sits at a minimum of its energy. The true vacuum is the lowest possible minimum, but there can also be local minima, which we call false vacua.” We can picture this as a landscape made up of valleys of different depths: the true vacuum is the deepest one, while the others are false vacua.
Something sitting in one of these depressions can remain “trapped” there even if, somewhere else, a lower-energy state exists. This is exactly what can happen to quantum fields, fundamental physical objects that permeate the universe. A classical field is something that has a value at every position in space, like a magnetic field, whose strength changes from point to point. Quantum fields behave in a similar way, and their excitations appear as particles.
Whirlpool in a water tank reveals long-predicted wave turbulence
When water drains from a bathtub, a whirlpool often forms above the drain, and its narrow core can start to wobble and twist. For almost 150 years, physicists have predicted that these wobbles can become turbulent, passing energy from large ripples down to ever smaller ones. Until now, however, this “Kelvin-wave turbulence” had never been seen directly in an experiment.
In new research published in Physical Review Letters, a team led by Eric Falcon at Université Paris Cité has observed the effect using a carefully controlled whirlpool in a tank of water.
Faint young stars reveal spiral galaxy Messier 74 may be twice as large as thought
Astronomers have discovered a faint population of young stars extending far beyond the known edge of the nearby spiral galaxy Messier 74. The finding suggests the galaxy is nearly twice as large as previously measured. The new study was published Sept. 4 in Astronomy & Astrophysics.
Over time, galaxies grow by accumulating gas from their surroundings. Because this newer gas spins faster relative to the center, it cannot collapse all the way to the core. Instead, it settles into the outer disk, where it eventually sparks the formation of new stars. Astronomers have observed this growth, but whether it is smooth and gradual or occurs in fast, episodic bursts remains unclear. Mergers or interactions with satellite galaxies can also trigger bursts of star formation in the outskirts of galactic disks, making them grow bigger.
One way to identify such growth is the “extended ultraviolet disk” (XUV disk): UV light tracing young stars beyond a galaxy’s traditional boundary as seen in optical light. But astronomers are still debating how to define this “optical boundary,” making XUV disks difficult to classify.
Vertical quantum sensor could reveal nanoscale magnetic patterns in quantum materials
Quantum materials do things ordinary materials cannot. They carry current without any loss, or conduct only along their outer edge while the inside insulates. Future quantum computers and quantum sensors will run on materials like these. To improve them, researchers need to see exactly where currents and magnetic fields run at the nanoscale.
A SQUID, a superconducting ring that registers even the smallest magnetic changes, is sensitive enough for the task. The problem is distance. Magnetic fields weaken quickly with distance, so the sensor must get close to the material. If the ring lies flat in the plane of a chip, the rest of the chip holds it several micrometers away from the material. That is where the detail is lost. The University of Twente has worked on scanning SQUID microscopy for years, mapping the magnetism of a surface.
“That is why we put the sensor on a pyramid,” says Hans Hilgenkamp. “On top of that pyramid the sensor can be brought right up to the material we want to look at, with nothing else in the way. That lets us image magnetism at the scale where quantum materials do their work.” This opens the door to new materials with unusual functionality. Within the Gravitation program QuMat, Twente builds instruments that it and its partners can use to measure quantum materials and develop them further.
Physicists define new material blueprint for next-generation microchip encryption
Behind every secure online transaction or encrypted message lies a string of completely unpredictable numbers. A team of physicists has now proposed a theoretical way around a long-standing roadblock, opening the door to next-generation security chips that protect everyday data without slowing performance.
In a study published in Physical Review Letters, a research team co-led by Rice University’s Jun-Jie Zhang and Boris Yakobson describes a new class of materials. The research was conducted in collaboration with Shuai Dong, chair of the School of Physics at Southeast University in China.
These materials, called autferroics, could speed up physical true random number generators (TRNG) thousands of times while keeping signals clear.
Unlocking sulfur’s third electron boosts lithium-sulfur battery voltage and capacity
While lithium-ion batteries (LIBs) remain the most widely used rechargeable batteries worldwide, energy engineers have been testing various alternatives with different underlying chemistries. These include lithium-sulfur batteries, which store and release energy by moving lithium ions between two electrodes on opposite sides of a cell, while sulfur undergoes reactions in the cathode (i.e., positive electrode).
Lithium-sulfur batteries could offer several advantages, including high energy densities and lower production costs, because sulfur is abundant and can store significant charge relative to its mass. Despite their potential, these batteries often exhibit low operating voltages (i.e., the pressure driving current), slow electron-transfer reactions, and energy losses caused by the migration of sulfur compounds between electrodes.
Researchers at the University of Maryland, Vanderbilt University, the Brookhaven National Laboratory, and other institutes recently introduced a new ionic liquid electrolyte that could improve the performance of lithium-sulfur batteries. This electrolyte, presented in a paper published in Nature Energy, was found to increase both the voltage and energy storage of lithium-sulfur batteries.
Higher-dimensional black holes hide an exact symmetry in their ringing, and string-inspired gravity breaks it
Strike a bell, and it rings with a pitch and a fading that tell you about the bell: its size, its shape, the metal it is made of. Black holes ring too. When two merge, the newborn black hole shivers and sheds gravitational waves in a brief, dying chord, and since 2015, gravitational-wave detectors have been listening. The notes of that chord, which physicists call quasinormal modes, depend only on the black hole’s mass and spin and on the law of gravity itself. Change the law, and the chord changes.
My colleague Davide Batić and I, both mathematicians at Khalifa University in Abu Dhabi, wanted to know how the chord changes when space has more dimensions than the three we see, and when Einstein’s equations receive a correction suggested by string theory. We report the answer in a paper published in Physical Review D. Along the way, we met something we had not been looking for: two quite different kinds of waves that ring at exactly the same notes.
Several attempts to unite gravity with quantum physics, string theory first among them, need extra dimensions of space. At low energies, some string theories add a term to Einstein’s equations built from the curvature of spacetime, called the Gauss–Bonnet term. In our four-dimensional spacetime, this term leaves the gravity equations unchanged; it only comes alive when there are more dimensions.