Lifeboat Foundation

An international team of space scientists reports that the moon exerts a tidal impact on the plasmasphere. For their paper published in the journal Nature Physics, the group used data from multiple spacecraft over a nearly 40-year period to measure tidal perturbations in the plasmapause. Balázs Heilig, with the Institute of Earth Physics and Space Science, in Hungary, has published a News & Views piece in the same journal issue, explaining the nature of the plasmasphere and outlining the work in this new effort.

Early scientists found a connection between the tides and the movement of the moon thousands of years ago. More recent evidence suggests the moon’s pull acts on the ionosphere as well. In this new study, the researchers wondered if the moon might also have an impact on the plasmasphere.

The plasmasphere is a toroidal mass of plasma that surrounds the Earth. It lies beyond the ionosphere and is made up mostly of electrons and protons. Its particles are charged by the ionosphere, and its outer boundary is known as the plasmapause.

Neutrinos are one of the most abundant particles in our universe, but they are notoriously difficult to detect and study: they don’t have an electrical charge and have nearly no mass. They are often referred to as “ghost particles” because they rarely interact with atoms.

But because they are so abundant, they play a large role in helping scientists answer fundamental questions about the universe.

In groundbreaking research described in Nature —led by researchers from the University of Rochester—scientists from the international collaboration MINERvA have, for the first time, used a beam of neutrinos at the Fermi National Accelerator Laboratory, or Fermilab, to investigate the structure of protons.

With some careful twisting and stacking, MIT physicists have revealed a new and exotic property in “magic-angle” graphene: superconductivity that can be turned on and off with an electric pulse, much like a light switch.

The discovery could lead to ultrafast, energy-efficient superconducting transistors for neuromorphic devices—electronics designed to operate in a way similar to the rapid on/off firing of neurons in the human brain.

Magic-angle graphene refers to a very particular stacking of graphene—an atom-thin material made from carbon atoms that are linked in a hexagonal pattern resembling chicken wire. When one sheet of graphene is stacked atop a second sheet at a precise “magic” angle, the twisted structure creates a slightly offset “moiré” pattern, or superlattice, that is able to support a host of surprising electronic behaviors.

For the first time, physicists have achieved quantum mechanical entanglement of two stable light sources.

Called “spooky action at a distance” by Einstein, quantum entanglement is a seemingly magical phenomenon. Entangled particles, for example light particles called “photons”, share a physical state. Changes to the physical state of one particle in an entangled pair instantaneously causes the same change to occur in its partner – no matter how far apart they are separated.

While quantum mechanical theory is clear on the existence of this effect in the universe, creating entangled pairs of particles is no trivial feat.

When it comes to creating ever more intriguing quantum systems, a constant need is finding new ways to observe them in a wide range of physical scenarios. JILA Fellow Cindy Regal and JILA and NIST Fellow Ana Maria Rey have teamed up with Oriol Romero-Isart from the University of Innsbruck and IQOQI to show that a trapped particle in the form of an atom readily reveals its full quantum state with quite simple ingredients, opening up opportunities for studies of the quantum state of ever larger particles.

In the quantum realm an atom does not behave as a point particle; instead it behaves more as a wave. Its properties (e.g., its position and velocity) are described in terms of what is referred to as the wavefunction of the atom. One way to learn about the wavefunction of a particle is to let the atom fly and then capture its location with a camera.

And with the right tricks, pictures can be taken of the particle’s quantum state from many vantage points, resulting in what is known as quantum tomography (“tomo” being Greek for slice or section, and “graphy” meaning describing or recording). In the work published in Nature Physics, the authors used a rubidium atom placed carefully in a specific state of its motion in a tightly focused laser beam, known as an optical tweezer. And they were able to observe it from many vantage points by letting it evolve in the optical tweezer in time. Like a ball rolling in a bowl, at different times the velocity and location of the particle interchange, and by snapping pictures at the right time during a video reel of the ball, many vantages of the particle’s state can be revealed.

‘Spin’ is a fundamental quality of fundamental particles like the electron, invoking images of a tiny sphere revolving rapidly on its axis like a planet in a shrunken solar system.

Only it isn’t. It can’t. For one thing, electrons aren’t spheres of matter but points described by the mathematics of probability.

But California Institute of Technology philosopher of physics Charles T. Sebens argues such a particle-based approach to one of the most accurate theories in physics might be misleading us.

The dynamics of electrons submitted to voltage pulses in a thin semiconductor layer is investigated using a kinetic approach based on the solution of the electron Boltzmann equation using particle-in-cell/Monte Carlo collision simulations. The results showed that due to the fairly high plasma density, oscillations emerge from a highly nonlinear interaction between the space-charge field and the electrons. The voltage pulse excites electron waves with dynamics and phase-space trajectories that depend on the doping level. High-amplitude oscillations take place during the relaxation phase and are subsequently damped over time-scales in the range 100 – 400 fs and decrease with the doping level. The power spectra of these oscillations show a high-energy band and a low-energy peak that were attributed to bounded plasma resonances and to a sheath effect. The high-energy THz domain reduces to sharp and well-defined peaks for the high doping case. The radiative power that would be emitted by the thin semiconductor layer strongly depends on the competition between damping and radiative decay in the electron dynamics. Simulations showed that higher doping level favor enhanced magnitude and much slower damping for the high-frequency current, which would strongly enhance the emitted level of THz radiation.

Laser interaction with foam targets is of interest for applications in the inertial confinement fusion studies and for the creation of secondary sources of energetic particles and radiation. Numerical modeling of such an interaction presents difficulties related to the sub-wavelength dimension of solid elements and high density contrast. Here, we present an analysis of laser interaction with thin wires based on the Mie theory, which demonstrates an enhanced laser absorption due to plasma resonance, and confirm this conclusion with detailed kinetic simulations. Numerical simulations also provide the characteristic time of the solid element transformation in a plasma and the energy partition between electrons and ions.

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A basic question [1] in the study of the gauge-gravity duality is this: which field theories have a gravity dual? In the case of applications to actual strongly coupled systems such as the Quark–Gluon Plasma [2], [3], [4], [5], [6], this question becomes: does every realistic strongly coupled system have such a dual? To settle this, one needs to examine the most extreme cases. The most extreme strongly-coupled systems currently accessible to experiment are probably (see below) the plasmas produced by collisions of heavy ions at the LHC [7], [8] ; so one needs to consider whether holography works in this case.

In [9] we adduced evidence suggesting that it does not. The problem is a very fundamental one: it appears that the purported gravity dual in some cases does not exist when one attempts to interpret it (as one ultimately must [10]) as a string-theoretic system.

Continue reading “On the existence of a holographic description of the LHC quark–gluon plasmas” »