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Category: particle physics – Page 276

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.

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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 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.

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‘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.

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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.

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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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Year 2017 face_with_colon_three

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.

The situation may be briefly explained as follows. Ferrari and co-workers have shown [11], [12], [13], [14] that, simply for reasons of internal mathematical consistency, a string-theoretic bulk spacetime with a holographic dual must satisfy certain fundamental relations between the Euclidean spacetime action and the action of probes (such as branes). This has been explicitly confirmed in a large number of concrete cases [14].

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In a new study, scientists say that a particle that links to a fifth dimension can explain dark matter.

The “warped extra dimension” (WED) is a trademark of a popular physics model that was first introduced in 1999. This research, which was published in The European Physical Journal C, is the first to use the theory to explain the long-standing dark matter problem in particle physics. Gravity portals' could morph dark matter into ordinary matter, astrophysicists propose | Live Science

The idea of dark matter, which makes up most of the matter in the universe, is the basis for what we know about how the universe works. Dark matter is like a pinch-hitter that helps scientists figure out how gravity works. Without a “x factor” of dark matter, many things would dissolve or fall apart. Even so, dark matter doesn’t change the particles we can see and “feel,” so it must have other special qualities as well.

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Scientists how now developed a mini tractor beam that can pull atoms and nanoparticles. Scientists have built a real working tractor beam, albeit at a very small scale. The device, which attracts one object to another from a distance, originates in fiction. The term was coined by E. E. Smith who mentioned the technology in his 1931 novel Spacehounds of IPC, and since the 1990s, researchers have worked to make it a reality.

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The standard model of particle physics tells us that most particles we observe are made up of combinations of just six types of fundamental entities called quarks. However, there are still many mysteries, one of which is an exotic, but very short-lived, Lambda resonance known as Λ(1405). For a long time, it was thought to be a particular excited state of three quarks—up, down, and strange—and understanding its internal structure may help us learn more about the extremely dense matter that exists in neutron stars.

Investigators from Osaka University were part of a team that has now succeeded in synthesizing Λ(1405) for the first time by combining a K- meson and a proton and determining its complex mass (mass and width). The K− meson is a negatively charged particle containing a strange and an up antiquark. The much more familiar proton that makes up the matter that we are used to has two up quarks and a down quark. The researchers showed that Λ(1405) is best thought of as a temporary bound state of the K- meson and the proton, as opposed to a three-quark .

In their study published recently in Physics Letters B, the group describes the experiment they carried out at the J-PARC accelerator. K− mesons were shot at a deuterium target, each of which had one proton and one neutron. In a successful reaction, a K− meson kicked out the neutron, and then merged with the proton to produce the desired Λ(1405).

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Starting with the emergence of quantum mechanics, the world of physics has been divided between classical and quantum physics. Classical physics deals with the motions of objects we typically see every day in the macroscopic world, while quantum physics explains the exotic behaviors of elementary particles in the microscopic world.

Many solids or liquids are composed of particles interacting with one another at close distances, which sometimes results in the rise of “quasiparticles.” Quasiparticles are long-lived excitations that behave effectively as weakly interacting particles. The idea of quasiparticles was introduced by the Soviet physicist Lev Landau in 1941, and ever since has been highly fruitful in quantum matter research. Some examples of quasiparticles include Bogoliubov quasiparticles (i.e. “broken Cooper pairs”) in superconductivity, excitons in semiconductors, and phonons.

Examining emergent collective phenomena in terms of quasiparticles provided insight into a wide variety of physical settings, most notably in superconductivity and superfluidity, and recently in the famous example of Dirac quasiparticles in graphene. But so far, the observation and use of quasiparticles have been limited to : in classical condensed matter, the collision rate is typically much too high to allow long-lived particle-like excitations.

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