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In molecules, the atoms vibrate with characteristic patterns and frequencies. Vibrations are therefore an important tool for studying molecules and molecular processes such as chemical reactions. Although scanning tunneling microscopes can be used to image individual molecules, their vibrations have so far been difficult to detect.

Physicists at Kiel University (Christian-Albrechts-Universität zu Kiel, CAU) have now invented a method with which the vibration signals can be amplified by up to a factor of 50. Furthermore, they increased the frequency resolution considerably. The new method will improve the understanding of interactions in molecular systems and further simulation methods. The research team has now published the results in the journal Physical Review Letters.

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Neutronium was the material used in the hull of the doomsday machine in Star Trek.

Now I’m not terribly sure what the mechanical properties of neutronium would be like. It certainly is very dense (about a billion tons per cm3, about the volume of the end of your little finger), but it interacts with matter only weakly. I would expect both it to be pretty inefficient at stopping both electromagnetic radiation (neutrons only have a magnetic moment), and matter.

Continue reading “The Doomsday Explosive! (The Neutronium Bomb)” »

Imagine a world where super-strong, super-light, flexible, durable new materials, which don’t exist in nature could be made to order. New breakthroughs in the understanding of “spin”, a characteristic of subatomic particles — like mass and charge — mean we are on the brink of such a revolution.

“The ability to control spin, one of the fundamental properties of particles, is crucial to us being able to design advanced new materials that will change the world,” says Prof Alessandro Lunghi, a physicist at Trinity College Dublin, who heads up a team investigating the phenomenon.

The scientific concepts of particle mass and charge are widely understood and known, but the third property of particles — that of spin — remains mysterious to most. It’s a concept that even many scientists struggle to understand.

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When Mohammad Javad Khojasteh arrived at MIT’s Laboratory for Information and Decision Systems (LIDS) in 2020 to begin his postdoc appointment, he was introduced to an entirely new universe. The domain he knew best could be explained by “classical” physics that predicts the behavior of ordinary objects with near-perfect accuracy (think Newton’s three laws of motion). But this new universe was governed by bizarre laws that can produce unpredictable results while operating at scales typically smaller than an atom.

“The rules of quantum mechanics are counterintuitive and seem very strange when you first start to learn them,” Khojasteh says. “But the more you know, the clearer it becomes that the underlying logic is extremely elegant.”

As a member of Professor Moe Win’s lab, called the Wireless Information and Network Sciences Laboratory, or WINS Lab, Khojasteh’s job is to straddle both the classical and quantum realms, in order to improve state-of-the-art communication, sensing, and computational capabilities.

How can the mindless microscopic particles that compose our brains ‘experience’ the setting sun, the Mozart Requiem, and romantic love?

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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.

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.

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.

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.

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