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Category: particle physics

Superconductor Theory Under Cold-Atom Scrutiny

Snapshot measurements of cold-atom gases reveal hidden spin correlations that could force an update of some superconductivity theories.

Our understanding of nature is inherently bound to the experimental tools we build to observe the world. Superconductivity, for example, has been traditionally studied using current and voltage meters under a variety of temperatures and other environmental conditions. From these observations, theorists have developed models—notably the Bardeen-Cooper-Schrieffer (BCS) theory, which assumes that the zero-resistance flow in a superconductor arises from electrons forming so-called Cooper pairs. This theory has been successful in explaining a large class of superconductors, but Tarik Yefsah from the Ecole Normale Supérieure in Paris and colleagues have now observed behavior that contradicts BCS predictions [1]. Using a recently developed technique called atom-resolved continuum quantum gas microscopy, the researchers directly observed spatial correlations in cold atoms that mimic superconducting electrons.

Astronomers crack a decades-old mystery, catching gas morphing into planet-building disks around newborn stars

An international team led by Dr. Indrani Das of Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has shown, for the first time, how infalling gas from star-forming cores gradually transitions into planet-forming disks. Their findings, combining numerical simulations with Atacama Large Millimeter/submillimeter Array (ALMA) observations, are published today in The Astrophysical Journal.

Protoplanetary disks form around young stars when dense molecular cloud cores collapse under their own gravity. An outer shroud of gas and dust, known as the envelope, surrounds and feeds both the young star and the forming disk. While it is well understood that planets eventually form within these disks and follow Keplerian orbits, the mechanism that transforms rapid infalling gas motion from the envelope into ordered Keplerian motion within the disk has remained a mystery for decades.

Based on both theoretical and observational evidence, the recent study discovered that there exists a distinct transition zone at the envelope-disk interface of a young star-disk system, which Das named ENDTRANZ (Envelope Disk Transition Zone). The findings have established that infalling gas motions gradually transition into Keplerian motions across this transition zone. Crucially, this transition is far from abrupt and contradicts earlier infall models that are based on classical test-particle dynamics.

Dark matter could explain the earliest supermassive black holes

A growing mystery in astronomy is the presence of gargantuan black holes—some weighing as much as a billion suns—existing less than a billion years after the Big Bang. According to the standard theory of black hole formation, these black holes simply should not have had enough time to grow so large. A study led by University of California, Riverside graduate student Yash Aggarwal shows that dark matter decays could be the key to understanding the origin of these cosmic behemoths. Published in the Journal of Cosmology and Astroparticle Physics, the research shows that the energy released from dark matter decay could alter the chemistry of early galaxies enough to cause some of them to directly collapse into black holes rather than forming stars.

The result is timely, since NASA’s James Webb Space Telescope continues to observe unusually large black holes in the early universe that could have formed by direct collapse. Astronomers had believed this process requires a coincidence of nearby stars shining onto pre-stellar gas and so expected it to be rare.

Aggarwal’s team goes beyond the standard approach by using dark matter—the unknown 85% of the matter in the universe that helps form galaxies. They show that if dark matter decays, it can leak a small amount of its energy into the gas and supercharge the direct collapse rate. Each decaying dark matter particle would only need to inject an amount of energy that is a billion trillionths of the energy of a single AA battery.

Scientists capture superconductivity’s ‘dancing pairs’ for first time, revealing missing pieces in a decades-old theory

For the first time, scientists have directly imaged the quantum process underlying superconductivity, a phenomenon in which paired electrons cause electric current to flow without resistance at sufficiently low temperatures. The results weren’t quite what they expected.

In the study, published April 15 in Physical Review Letters, the scientists directly imaged individual atoms pairing up in a special gas cooled nearly to absolute zero—the unreachable limit to how cold things can get. The type of gas, called a Fermi gas, allows scientists to substitute electrons with atoms and probe the physics of superconductors in a controlled way.

Surprisingly, the scientists found that after pairing up, the atoms moved in a synchronized dance, with their positions dependent on those of other pairs—a phenomenon not predicted by the 70-year-old, Nobel-prize-winning theory of superconductivity.

Multitasking quantum sensors can measure several properties at once

A special class of sensors leverages quantum properties to measure tiny signals at levels that would be impossible using classical sensors alone. Such quantum sensors are currently being used to study the inner workings of cells and the outer depths of our universe.

Particularly promising are solid-state quantum sensors, which can operate at room temperature. Unfortunately, most solid-state quantum sensors today only measure one physical quantity at a time—such as the magnetic field, temperature, or strain in a material. Trying to measure both the magnetic field and temperature of a material at the same time causes their signals to get mixed up and measurements to become unreliable.

Now, MIT researchers have created a way to simultaneously measure multiple physical quantities with a solid-state quantum sensor. They achieved this by exploiting entanglement, where particles become correlated into a single quantum state. In a new paper, the team demonstrated its approach in a commonly used quantum sensor at room temperature, measuring the amplitude, frequency, and phase of a microwave field in a single measurement. They also showed the approach works better than sequentially measuring each property or using traditional sensors.

Inside a Neutron Star, Matter Starts Breaking Down

What happens to matter when gravity crushes it beyond the breaking point? Inside a neutron star, atoms are destroyed. Electrons are forced into protons. Nuclei dissolve into a sea of neutrons. And at the very center, even neutrons themselves may break apart into quarks — forming exotic states of matter that physicists still can’t fully explain.

In this video, we go inside a neutron star layer by layer. From the crystalline outer crust where neutron-rich nuclei sit in a lattice denser than anything on Earth, through the bizarre nuclear pasta phases where matter forms sheets, tubes, and bubbles of nuclear material, into the superfluid outer core where neutrons flow without friction and protons conduct without resistance, and finally into the mysterious inner core where densities reach five to ten times that of an atomic nucleus and the very concept of a \.

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Earth’s magnetic field creates a previously undetected pocket of protection from radiation on the moon

High-energy particles called galactic cosmic rays (GCRs) bombard unprotected objects in space, often causing damage. Earth, however, is protected by its magnetic field, which creates a protective shell around the planet that can deflect dangerous charged particles, like GCRs.

The moon is known to pass through the tail-like part of Earth’s magnetosphere, but a new study, published in Science Advances, suggests the moon might experience additional protection at another point in its orbit. Although this pocket of protection exists when the moon is outside of the magnetosphere, researchers believe the effects are still due to Earth’s magnetic field.

An anomalous dip in particle counts When the research team analyzed data taken from the Lunar Lander Neutron and Dosimetry (LND), onboard China’s Chang’E-4 lander, they were surprised to find that the LND experienced a 20% dip in GCR particles hitting detectors while the lander was on the moon’s far side. This occurred at a specific time during the lunar “morning” and only for about 2 days each lunar cycle. Since the LND took data over 31 cycles, the team could see that this was not just a one-off occurrence. This was unexpected because it was previously assumed that GCRs are evenly distributed in the space between Earth and the moon, outside Earth’s magnetosphere.

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