Lifeboat Foundation

Around age six, we start learning how to tie our shoelaces, making knots that look like ribbons—or possibly more complex forms, if we are a little clumsy. We use knots every day, but the type of knots we generally use are associated with physical objects, things we can touch.

Although it can be hard to image, light can also be shaped in ways that form knotted configurations, whose shape depends on the orbital angular momentum of the light. This parameter is responsible for making the beam of light twist around its own axis, generating different knot shapes, and expanding to a new degree of freedom that can carry valuable information.

Learning and mastering how to generate twisted light—light with orbital angular momentum—has been a thriving field of study for the past 20 years. Unlike spin angular momentum, which is associated with the polarization of light, orbital angular momentum is associated with the spatial distribution of the electric field. These two types of angular momentum can also be coupled, which results in a variety of light fields of different shapes with polarizations that change from point to point.

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A color smartwatch that never needs charging.

A team of researchers from the University of California at Berkeley and Lawrence Berkeley National Laboratory has found a way to make the Casimir effect attract or repulse depending on the size of the gap between two objects. In their paper published in the journal Science, the group describes their technique and possible applications.

The Casimir effect, first proposed by Hendrik Casimir back in 1948, is the phenomenon in which two tiny surfaces in close proximity experience a force that pulls them closer together. Quantum fluctuations inside and outside of the gap push against the plates, but because those pushing from the outside are stronger, they create an attractive force between the two plates. The Casimir effect is more than a curiosity, because it can create problems in nanotechnology applications.

Just two years after Casimir first proposed the effect, others in the field began making predictions about ways to counter it—making it repulsive rather than attractive, for example, in the case of fluids and plates made of lower refractive metals. Then, in 2010, a team at MIT suggested that it should be possible to counter both attractive and repulsive effects to create a state of equilibrium between the two plates. In this new effort, the researchers report that they have done just that.

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In “Avengers: Endgame,” Tony Stark warned Scott Lang that sending him into the quantum realm and bringing him back would be a “billion-to-one cosmic fluke.”

In reality, shrinking a light beam to a nanometer-sized point to spy on quantum-scale light-matter interactions and retrieving the information is not any easier. Now, engineers at the University of California, Riverside, have developed a new technology to tunnel light into the quantum realm at an unprecedented efficiency.

In a Nature Photonics paper, a team led by Ruoxue Yan, an assistant professor of chemical and environmental engineering, and Ming Liu, an assistant professor of electrical and computer engineering, describe the world’s first portable, inexpensive, optical nanoscopy tool that integrates a glass optical fiber with a silver nanowire condenser. The device is a high-efficiency round-trip light tunnel that squeezes visible light to the very tip of the condenser to interact with molecules locally and send back information that can decipher and visualize the elusive nanoworld.

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Dielectric laser accelerators (DLAs) provide a compact and cost-effective solution to this problem by driving accelerator nanostructures with visible or near-infrared (NIR) pulsed lasers, resulting in a 10,000 times reduction of scale. Current implementations of DLAs rely on free-space lasers directly incident on the accelerating structures, limiting the scalability and integrability of this technology. Researchers present the first experimental demonstration of a waveguide-integrated DLA, designed using a photonic inverse design approach. These on-chip devices accelerate sub-relativistic electrons of initial energy 83.4 keV by 1.21 keV over 30 µm, providing peak acceleration gradients of 40.3 MeV/m. This progress represents a significant step towards a completely integrated MeV-scale dielectric laser accelerator.

Dielectric laser accelerators have emerged as a promising alternative to conventional RF accelerators due to the large damage threshold of dielectric materials the commercial availability of powerful NIR femtosecond pulsed lasers, and the low-cost high-yield nanofabrication processes which produce them. Together, these advantages allow DLAs to make an impact in the development of applications such as tabletop free-electron-lasers, targeted cancer therapies, and compact imaging sources.

They have designed and experimentally verified the first waveguide-integrated DLA structure. The design of this structure was made possible through the use of photonics inverse design methodologies developed by the team members. The fabricated and experimentally demonstrated devices accelerate electrons of an initial energy of 83.4 keV by a maximum energy gain of 1.21 keV over 30 µm, demonstrating acceleration gradients of 40.3 MeV/m. In this integrated form, these devices can be cascaded to reach MeV-scale energies, capitalizing on the inherent scalability of photonic circuits. Future work will focus on multi-stage demonstrations, as well as exploring new design and material solutions to obtain larger gradients.

Continue reading “Laser-driven Particle Accelerator Made Ten Thousand Times Smaller” »

Research by neuroscientists at the University of Chicago shows how short-term, working memory uses networks of neurons differently depending on the complexity of the task at hand.

The researchers used modern artificial intelligence (AI) techniques to train computational neural networks to solve a range of complex behavioral tasks that required storing information in short term memory. The AI networks were based on the biological structure of the brain and revealed two distinct processes involved in short-term memory. One, a “silent” process where the brain stores short-term memories without ongoing neural activity, and a second, more active process where circuits of neurons fire continuously.

The study, led by Nicholas Masse, Ph.D., a senior scientist at UChicago, and senior author David Freedman, Ph.D., professor of neurobiology, was published this week in Nature Neuroscience.

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Will Europe’s Human Brain Project simulate a human brain?

Opinion: Progress in deep learning research will come from the convergence of engineering and neuroscience.