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Category: computing – Page 400

Toward a Complete Theory of Crystal Vibrations

A new set of equations captures the dynamical interplay of electrons and vibrations in crystals and forms a basis for computational studies.

Although a crystal is a highly ordered structure, it is never at rest: its atoms are constantly vibrating about their equilibrium positions—even down to zero temperature. Such vibrations are called phonons, and their interaction with the electrons that hold the crystal together is partly responsible for the crystal’s optical properties, its ability to conduct heat or electricity, and even its vanishing electrical resistance if it is superconducting. Predicting, or at least understanding, such properties requires an accurate description of the interplay of electrons and phonons. This task is formidable given that the electronic problem alone—assuming that the atomic nuclei stand still—is already challenging and lacks an exact solution. Now, based on a long series of earlier milestones, Gianluca Stefanucci of the Tor Vergata University of Rome and colleagues have made an important step toward a complete theory of electrons and phonons [1].

At a low level of theory, the electron–phonon problem is easily formulated. First, one considers an arrangement of massive point charges representing electrons and atomic nuclei. Second, one lets these charges evolve under Coulomb’s law and the Schrödinger equation, possibly introducing some perturbation from time to time. The mathematical representation of the energy of such a system, consisting of kinetic and interaction terms, is the system’s Hamiltonian. However, knowing the exact theory is not enough because the corresponding equations are only formally simple. In practice, they are far too complex—not least owing to the huge number of particles involved—so that approximations are needed. Hence, at a high level, a workable theory should provide the means to make reasonable approximations yielding equations that can be solved on today’s computers.

Could your daily routine lead to dementia? New research points to sedentary lifestyle as potential risk factor

In a recent study published in JAMA, researchers investigated whether accelerometer-assessed sedentary behavior was associated with incident dementia.

The global population is engaging in more sedentary-type activities such as sitting while using the computer, watching television, and driving. Studies have reported associations between sedentary behavior and cardiometabolic diseases and related mortality; however, its relationship with new-onset dementia is not clear.

Motion of stars near Milky Way’s central black hole is only predictable for a few hundred years

The orbits of 27 stars orbiting closely around the black hole at the center of our Milky Way are so chaotic that researchers cannot predict with confidence where they will be in about 462 years. This finding emerges from simulations by three astronomers based in the Netherlands and the United Kingdom. The researchers have published their findings in two papers in the International Journal of Modern Physics D and in the Monthly Notices of the Royal Astronomical Society.

Simulating 27 stars and their interactions with each other and with the black hole is easier said than done. For centuries, for example, it was impossible to predict the motions of more than two interacting stars, planets, rocks, or other objects. It was only in 2018 that Leiden researchers developed a computer program in which rounding errors no longer play a role in the calculations. With this, they were able to calculate the motions of three imaginary stars. Now the researchers have expanded their program to deal with 27 stars that, by astronomical standards, move close to the black hole at the center of the Milky Way.

The simulations of the 27 and the black hole resulted in a surprise. Although the stars remain in their orbits around the black hole, the interactions between the stars show that the orbits are chaotic. This means that small perturbations caused by the underlying interactions change the orbits of the stars. These changes grow exponentially and, in the long run, make the star orbits unpredictable.

How Tiny Schrödinger’s Cats Could Upend Quantum Again

The building blocks of quantum computers are often thought to imitate the famous thought experiment known as Schrödinger’s cat, in which quantum physics essentially suspends a cat in a box in a nebulous state between life and death: The cat only definitely becomes alive or dead when someone looks in the box. Now, by mimicking Schrödinger’s cats as closely as possible, a French startup reveals it could help make extraordinarily powerful quantum computers a reality sooner than previously thought—a strategy Amazon is also pursuing.

Classical computers generally switch transistors either on or off to symbolize data as ones or zeroes. In contrast, quantum computers use quantum bits— qubits —that, because of the surreal nature of quantum physics, can exist in a state of superposition where they are both 1 and 0 at the same time. This essentially lets each qubit carry out two calculations simultaneously. The more qubits are quantum-mechanically linked, or entangled, the more calculations they can perform at once, to an exponential degree.

The new strategy depends on so-called “cat states,” pairs of very different quantum states as diametrically opposed to one another as the “alive” and “dead” feline once famously postulated by Erwin Schrödinger.

Defying Conventional Wisdom — Scientists Push the Boundaries of Photonics

Defying conventional wisdom, scientists have discovered a novel coupling mechanism involving leaky mode, previously considered unsuitable for high-density integration in photonic circuits.

This surprising discovery paves the way for dense photonic integration, transforming the potential and scalability of photonic chips in areas such as optical computing quantum communication, light detection and ranging (LiDAR), optical metrology, and biochemical sensing.

In a recent Light Science & Application publication, Sangsik Kim, associate professor of electrical engineering at Korea Advanced Institute of Science and Technology (KAIST), and his students at Texas Tech University demonstrated that an anisotropic leaky wave can achieve zero crosstalk between closely spaced identical waveguides using subwavelength grating (SWG) metamaterials.

Researchers take first step to de-freezing quantum computing

Koto_feja/iStock.

Quantum computing is the next frontier of computation, potentially allowing for calculations that are impossible for classic computers to even process. As researchers around the world work to optimize the computations with an increasing number of quantum bits or qubits, the biggest hurdle they face is the need for ultra-cool environments to run these computers themselves.

A strategy to fabricate highly performing tin perovskite-based transistors

Metal halide perovskites are semiconducting materials with advantageous optoelectronic properties, low defects and low costs of production. In contrast with other emerging semiconductors, these materials can be easily synthesized via affordable solution processing methods.

In recent years, some engineers have been exploring the potential of for creating highly solar cells and light emitting diodes (LEDs). Their favorable characteristics, however, could also facilitate their use for fabricating next-generation , including .

Researchers at Pohang University of Science and Technology in South Korea, the Chinse Academy of Sciences and the University of Electronic Science and Technology of China recently introduced a new strategy to develop transistors based on a metal perovskite, specifically tin perovskite. In their paper, published in Nature Electronics, they showed that the resulting tin perovskite-based transistors could attain performances comparable to those of existing .

Precise control of qubits using new quantum computing method

Instead of designing their own qubits for study, the team used nature-made ones and focused on ways to control them.

Researchers at the University of Waterloo in Canada have developed a novel and robust way to control individual qubits. This ability is a crucial step as humanity attempts to scale up its computational capacities using quantum computing, a press release said.

Much like silicon-based computers use bits as the basic unit of storing information, quantum computers use quantum bits or qubits. A number of elemental particles, such as electrons and photons, have been used to serve this purpose, wherein the charge or polarization of the light is used to denote the 0 or 1 state of the qubit.

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