A large and unexpected excess of top quark pairs has the physics community excited, but the interpretation is still up for debate.
Category: particle physics
Speed test of ‘tunneling’ electrons challenges alternative interpretation of quantum mechanics
As the photons traveled along the waveguide and tunneled into the barrier, they also tunneled into the secondary waveguide, jumping back and forth between the two at a consistent rate, allowing the research team to calculate their speed.
By combining this element of time with measurements of the photon’s rate of decay inside the barrier, the researchers were able to calculate dwell time, which was found to be finite.
The researchers write, “Our findings contribute to the ongoing tunneling time debate and can be viewed as a test of Bohmian trajectories in quantum mechanics. Regarding the latter, we find that the measured energy–speed relationship does not align with the particle dynamics postulated by the guiding equation in Bohmian mechanics.”
Carefully tuned laser beam protects quantum spins from noise
Researchers have discovered a simple yet powerful way to protect atoms from losing information—a key challenge in developing reliable quantum technologies.
By shining a single, carefully tuned laser beam on a gas of atoms, they managed to keep the atoms’ internal spins synchronized, dramatically reducing the rate at which information is lost. In quantum sensors and memory systems, atoms often lose their magnetic orientation —or “spin”—when they collide with each other or the walls of their container.
This phenomenon, known as spin relaxation, severely limits the performance and stability of such devices. Traditional methods to counteract it have required operating in extremely low magnetic fields and using bulky magnetic shielding.
Adding up Feynman diagrams to make predictions about real materials
Caltech scientists have found a fast and efficient way to add up large numbers of Feynman diagrams, the simple drawings physicists use to represent particle interactions. The new method has already enabled the researchers to solve a longstanding problem in the materials science and physics worlds known as the polaron problem, giving scientists and engineers a way to predict how electrons will flow in certain materials, both conventional and quantum.
In the 1940s, physicist Richard Feynman first proposed a way to represent the various interactions that take place between electrons, photons, and other fundamental particles using 2D drawings that involve straight and wavy lines intersecting at vertices. Though they look simple, these Feynman diagrams allow scientists to calculate the probability that a particular collision, or scattering, will take place between particles.
Since particles can interact in many ways, many different diagrams are needed to depict every possible interaction. And each diagram represents a mathematical expression. Therefore, by summing all the possible diagrams, scientists can arrive at quantitative values related to particular interactions and scattering probabilities.
Calculating the electron’s magnetic moment: State-dependent values emerge from Dirac equation
Quantum mechanics has a reputation that precedes it. Virtually everyone who has bumped up against the quantum realm, whether in a physics class, in the lab, or in popular science writing, is left thinking something like, “Now, that is really weird.” For some, this translates to weird and wonderful. For others it is more like weird and disturbing.
Chip Sebens, a professor of philosophy at Caltech who asks foundational questions about physics, is firmly in the latter camp. “Philosophers of physics generally get really frustrated when people just say, ‘OK, here’s quantum mechanics. It’s going to be weird. Don’t worry. You can make the right predictions with it. You don’t need to try to make too much sense out of it, just learn to use it.’ That kind of thing drives me up the wall,” Sebens says.
One particularly weird and disturbing area of physics for people like Sebens is quantum field theory. Quantum field theory goes beyond quantum mechanics, incorporating the special theory of relativity and allowing the number of particles to change over time (such as when an electron and positron annihilate each other and create two photons).
Studies offer new insights into production and structure of heavy hollow atoms
Hollow atoms are special atoms with multiple missing electrons in their inner shells, while their outer shells are still fully or partially filled with electrons. Studying the production mechanisms, internal structure, and de-excitation properties of these excited-state atoms provides insights into quantum electrodynamics and quantum many-body interactions, with applications in fields such as inner-shell ionization X-ray lasers, high-energy density physics, and molecular imaging.
Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences recently confirmed that the fully stripped heavy ion-atom collision is an effective way to produce heavy hollow atoms in high yield. They have also developed a high-resolution planar crystal spectrometer to measure the fine structure of inner-shell multi-ionization ion X-rays.
The results have been published in Spectrochimica Acta Part B: Atomic Spectroscopy and Physical Review A.
Stoichiometric crystal shows promise in quantum memory
For over two decades, physicists have been working toward implementing quantum light storage—also known as quantum memory—in various matter systems. These techniques allow for the controlled and reversible mapping of light particles called photons onto long-lived states of matter. But storing light for long periods without compromising its retrieval efficiency is a difficult task.
Nuclear mass measurement reveals new proton magic number
In nuclear physics, “magic numbers” identify specific numbers of protons or neutrons that lead to especially stable nuclei. Recognizing these numbers helps scientists better understand the structure of nuclei.
The magic numbers for stable, long-lived isotopes have long been known, but the magic numbers for exotic, short-lived isotopes are less well understood. By studying these rare cases, researchers can gain deeper insight into the nuclear “building code” under extreme conditions. This, in turn, improves our understanding of how elements formed in the universe and sheds light on the behavior of the nuclear force.
As part of this effort, researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences have precisely measured for the first time the mass of an extremely short-lived and neutron-deficient nucleus, silicon-22, revealing that the proton number 14 in silicon-22 is a new magic number.
New particle acceleration strategy uses cold atoms to unlock cosmic mysteries
Scientists have used ultracold atoms to successfully demonstrate a novel method of particle acceleration that could unlock a new understanding of how cosmic rays behave, a new study reveals.
More than 70 years after its formulation, researchers have observed the Fermi acceleration mechanism in a laboratory by colliding ultracold atoms against engineered movable potential barriers—delivering a significant milestone in high-energy astrophysics and beyond.
Fermi acceleration is the mechanism responsible for the generation of cosmic rays, as postulated by physicist Enrico Fermi in 1949. The process itself also features some universal properties that have spawned a wide range of mathematical models, such as the Fermi-Ulam model. Until now, however, it has been difficult to create a reliable Fermi accelerator on Earth.