How can the mindless microscopic particles that compose our brains ‘experience’ the setting sun, the Mozart Requiem, and romantic love?
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Category: particle physics – Page 372
Catching neutrinos at the LHC
CERN physicist Jamie Boyd enters a tunnel close to the ATLAS detector, an experiment at the largest particle accelerator in the world. From there, he turns into an underground space labeled TI12.
“This is a very special tunnel,” Boyd says, “because this is where the old transfer line used to exist for the Large Electron-Positron Collider, before the Large Hadron Collider.” After the LHC was built, a new transfer line was added, “and this tunnel was then abandoned.”
The tunnel is abandoned no more. Its new resident is an experiment much humbler in size than the neighboring ATLAS detector. Five meters in length, the ForwArd Search ExpeRiment, or FASER, detector sits in a shallow excavated trench in the floor, surrounded by low railings and cables.
A Jiggling Ultracold Atomic Gas Simulates Spin Dynamics
Researchers produce analogues of hard-to-study quantum phenomena in a gas of strontium atoms near absolute zero.
Recently, researchers have begun using ultracold atomic gases to simulate phenomena that are difficult to study in their natural environments. Using electromagnetic fields, for example, they can orchestrate interatomic interactions that are analogous to interactions in condensed-matter systems, which they can then study with greater experimental control than the real examples allow. Now David Wilkowski of Nanyang Technological University in Singapore and colleagues use an ultracold atomic gas to simulate a condensed-matter system’s spin dynamics [1].
Wilkowski’s team cools a gas of strontium-87 atoms to 30 nK. Then, using three convergent laser beams, they drive the gas through various transitions until the atoms populate two so-called dark states, in which quantum mechanics forbids the atoms from undergoing spontaneous emission.
A Solid Observation of Strong Kerr Nonlinearity
Researchers have demonstrated that a solid can exhibit an enhanced nonlinear optical phenomenon usually seen only in cold atomic gases.
Among the benefits brought about by the invention of the laser in the 1960s is the ability to generate light at an intensity great enough to produce nonlinear optical effects. Such nonlinear effects have entered daily use in applications that include infrared-to-visible-light wavelength conversion (in a green laser pointer, for example) and two-photon excitation (in fluorescence microscopes for observing biological living tissue). Now Corentin Morin of the École Normale Supérieure in Paris and colleagues address a third-order nonlinear process called the Kerr effect, which manifests as a change in a material’s refractive index when it is illuminated with light of different intensities [1]. The researchers demonstrate a giant Kerr nonlinearity in a solid, a state of matter that has, until now, exhibited only a weak Kerr effect. The result implies the possibility of scalable nonlinear quantum optics without the need of cold atoms in high vacuum.
The key to the discovery by Morin and colleagues is a quasiparticle called a Rydberg exciton, the understanding of which rests on two concepts. The first concept is the Rydberg series, which is the discrete energy-level structure available to an atom’s outermost electron, and which is indexed by the principal quantum number n. A high-lying Rydberg state has a large n and exhibits properties such as a large electron orbital radius, a long lifetime, and a large dipole moment, all of which are missing in the ground state. The second concept is a hydrogen-atom-like quasiparticle called an exciton—a negatively charged electron, photoexcited across a semiconductor’s band gap, Coulomb-bound to a positively charged hole left in the valence band.
Differentiating right- and left-handed particles using the force exerted
Researchers investigated the polarization-dependence of the force exerted by circularly polarized light (CPL) by performing optical trapping of chiral nanoparticles. They found that left-and right-handed CPL exerted different strengths of the optical gradient force on the nanoparticles, and the D-and L-form particles are subject to different gradient force by CPL. The present results suggest that separation of materials according to their handedness of chirality can be realized by the optical force.
Chirality is the property that the structure is not superimposable on its mirrored image. Chiral materials exhibit the characteristic feature that they respond differently to left-and right-circularly polarized light. When matter is irradiated with strong laser light, optical force is exerted on it. It has been expected theoretically that the optical force exerted on chiral materials by left-and right-circularly polarized light would also be different.
The research group at Institute for Molecular Science and three other universities used an experimental technique of optical trapping to observe the circular-polarization dependent optical gradient force exerted on chiral gold nanoparticles. Chiral gold nanoparticles have either D-form (right-handed) or L-form (left-handed) structure, and the experiment was performed using both.
Designing new quantum materials on the computer
How do you find novel materials with very specific properties—for example, special electronic properties which are needed for quantum computers? This is usually a very complicated task: various compounds are created, in which potentially promising atoms are arranged in certain crystal structures, and then the material is examined, for example in the low-temperature laboratory of TU Wien.
Now, a cooperation between Rice University (Texas), TU Wien and other international research institutions has succeeded in tracking down suitable materials on the computer. New theoretical methods are used to identify particularly promising candidates from the vast number of possible materials. Measurements at TU Wien have shown the materials do indeed have the required properties and the method works. This is an important step forward for research on quantum materials. The results have now been published in the journal Nature Physics.
The Schwinger Effect: Scientists Finally Created Matter From Nothing Just by Using Electromagnetic Fields [Research Study]
Wait, what? really?
For the first time, scientists were able to create particles without precursor particles or colliding two quanta together. Using the Schwinger effect, they could create matter with the aid of electromagnetic fields.
What Is a Schwinger Effect?
According to Wikipedia, a powerful electric field is thought to form matter due to the Schwinger effect. It is a quantum electrodynamics (QED) prediction that, in the presence of an electric field, electron-positron pairs spontaneously form, leading to the decay of the electric field.
Astronomers discover how naughty baby stars steal each others’ planets
Stellar nurseries are a hotbed for heists.
These stellar nurseries are densely populated places, where hundreds of thousands of stars often reside in the same volume of space that the Sun inhabits on its own. Violent interactions, in which stars exchange energy, occur frequently, but not for long. After a few million years, the groups of stars dissipate, populating the Milky Way with more stars.
Our new paper, published in the Monthly Notices of the Royal Astronomical Society, shows how massive stars in such stellar nurseries can steal planets away from each other — and what the signs of such theft are.
Almost immediately after young stars are born, planetary systems begin to form around them. We have had indirect evidence of this for more than 30 years. Observations of the light from young stars display an unexpected excess of infrared radiation. This was (and still is) explained as originating from small dust particles (100th of a centimeter) orbiting the star in a disc of material. It is from these dust particles that planets are (eventually) formed.
Strange Hexagonal Diamonds Found on Earth Came From Another World
Four meteorites in northwest Africa were found to contain mysterious hexagonal diamonds that don’t naturally occur on Earth. Essentially, scientists exploring the contents of the space rocks discovered extraterrestrial materials, if you will, alien diamonds. According to Alan Salek, a member of the team that discovered the materials, “some people in the field doubted the existence of this material.” As with regular diamonds, hexagonal diamonds are made of carbon, but their atoms are arranged hexagonally rather than cubically.
The first hexagonal diamonds were recorded in meteorites in the United States and India in the 1960s and were dubbed lonsdaleite. The previously discovered crystals, however, were so small – only nanometres wide – that their hexagonality could not be confirmed. A powerful electron microscope was used by Salek and his colleagues to examine 18 meteorite samples in search of larger crystals. One of them was from Australia, and the other three were from northwestern Africa. It was found that four of the African meteorites contained hexagonal diamonds, some measuring up to a micrometer – about 1,000 times larger than anything previously discovered.
In this way, the team was able to confirm the hexagonal structure’s unusual characteristics. Salek says that now that they have larger crystals, they can get a better understanding of how they form and maybe replicate that process. Scientists are interested in Lonsdaleite since it might have even more industrial potential as a result of its theoretical hardness being stronger than a regular diamond. High-end saw blades, for instance, already contain regular diamonds.