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Category: quantum physics – Page 500

Physicists May Have Found a Hard Limit on The Performance of Large Quantum Computers

A newly discovered trade-off in the way time-keeping devices operate on a fundamental level could set a hard limit on the performance of large-scale quantum computers, according to researchers from the Vienna University of Technology.

While the issue isn’t exactly pressing, our ability to grow systems based on quantum operations from backroom prototypes into practical number-crunching behemoths will depend on how well we can reliably dissect the days into ever finer portions. This is a feat the researchers say will become increasingly more challenging.

Whether you’re counting the seconds with whispers of Mississippi or dividing them up with the pendulum-swing of an electron in atomic confinement, the measure of time is bound by the limits of physics itself.

Model Correctly Predicts High-Temperature Superconducting Properties

A first-principles model accounts for the wide range of critical temperatures (Tc’s) for four materials and suggests a parameter that determines Tc in any high-temperature superconductor.

Since the first high-temperature superconducting materials, known as the cuprates, were discovered in 1986, researchers have struggled to explain their properties and to find materials with even higher superconducting transition temperatures (Tc’s). One puzzle has been the cuprates’ wide variation in Tc, ranging from below 10 K to above 130 K. Now Masatoshi Imada of Waseda University in Japan and his colleagues have used first-principles calculations to determine the order parameters—which measure the density of superconducting electrons—for four cuprate materials and have predicted the Tc’s based on those order parameters [1]. The researchers have also found what they believe is the fundamental parameter that determines Tc in a given material, which they hope will lead to the development of higher-temperature superconductors.

For each material, Imada and his colleagues applied the basic principles of quantum mechanics, focusing on the planes of copper and oxygen atoms that are known to host the superconducting electrons. They used a combination of numerical techniques, including one supplemented by machine learning, and did not require any adjustable parameters.

Quark Picture Put to the Test

A measurement of the charge radius of an aluminum nucleus probes the assumption that there are only three families of quarks.

In the standard model of particle physics, matter is made of elementary particles called quarks and leptons. Quarks are the heavy constituents that form, for example, protons and neutrons, whereas leptons are the light constituents, such as the electron. The six known quarks—up, down, charm, strange, top, and bottom—are split into three families. But could there be a fourth family? Answering that question would require hundreds of different measurements in particle and nuclear physics. However, not all these measurements are yet available or precise enough, and many parameter values are only inferred or extrapolated. Now Peter Plattner at CERN in Switzerland and his colleagues show how a single one of these measurements can shift our understanding of this fundamental question [1].

In the quantum-mechanical framework of the standard model, quarks can oscillate among their different flavors. The best-known example occurs in the beta decay of radioactive nuclei: a proton is transformed into a neutron (or vice versa) when one of its quarks oscillates from up to down (or down to up). The rate of beta decay depends on many factors involving both nuclear and atomic physics, but the rate at which the quarks oscillate is described by a single quantity: Vud, the so-called matrix element of the transformation of an up quark into a down quark.

How AI and quantum physics link up to consciousness

Will artificial intelligence serve humanity — or will it spawn a new species of conscious digital beings with their own agenda?

It’s a question that has sparked scores of science-fiction plots, from “Colossus: The Forbin Project” in 1970, to “The Matrix” in 1999, to this year’s big-budget tale about AI vs. humans, “The Creator.”

The same question has also been lurking behind the OpenAI leadership struggle — in which CEO Sam Altman won out over the nonprofit board members who fired him a week earlier.

The Universe in a lab: Testing alternate cosmology using a cloud of atoms

In the basement of Kirchhoff-Institut für Physik in Germany, researchers have been simulating the Universe as it might have existed shortly after the Big Bang. They have created a tabletop quantum field simulation that involves using magnets and lasers to control a sample of potassium-39 atoms that is held close to absolute zero. They then use equations to translate the results at this small scale to explore possible features of the early Universe.

The work done so far shows that it’s possible to simulate a Universe with a different curvature. In a positively curved universe, if you travel in any direction in a straight line, you will come back to where you started. In a negatively curved universe, space is bent in a saddle shape. The Universe is currently flat or nearly flat, according to Marius Sparn, a PhD student at Kirchhoff-Institut für Physik. But at the beginning of its existence, it might have been more positively or negatively curved.

Diamond-stretching technique makes qubits more stable and controllable

Researchers are claiming a breakthrough in quantum communications, thanks to a new diamond-stretching technique they say greatly increases the temperatures at which qubits remain entangled, while also making them microwave-controllable.

Quantum networking is an emerging field that uses weird quantum phenomena to send and receive information. These networks will be impossible to hack, and will use quantum entanglement to cover large distances, creating pairs of qubits which mirror each other’s quantum state without any physical connection.

Diamond-based qubits are capable of maintaining their state of entanglement for a decent length of time – but only provided they’re kept incredibly cold – just a hair above absolute zero. That limits their usefulness, because it’d mean you’d need a giant, energy-intensive cooling apparatus at every node of your quantum network.

Researchers invent new way to stretch diamond for better quantum bits

A future quantum network may become less of a stretch thanks to researchers at the University of Chicago, Argonne National Laboratory and Cambridge University.

A team of researchers announced a breakthrough in quantum network engineering. By “stretching” thin films of diamond, they created that can operate with significantly reduced equipment and expense. The change also makes the bits easier to control.

The researchers hope the findings, published Nov. 29 in Physical Review X, can make future quantum networks more feasible.

Quantum Squeeze: MIT Unlocks New Dimensions in Precise Clocks

More stable clocks could measure quantum phenomena, including the presence of dark matter.

The practice of keeping time relies on stable oscillations. In grandfather clocks, the length of a second is marked by a single swing of the pendulum. In digital watches, the vibrations of a quartz crystal mark much smaller fractions of time. And in atomic clocks, the world’s state-of-the-art timekeepers, the oscillations of a laser beam stimulate atoms to vibrate at 9.2 billion times per second. These smallest, most stable divisions of time set the timing for today’s satellite communications, GPS systems, and financial markets.

A clock’s stability depends on the noise in its environment. A slight wind can throw a pendulum’s swing out of sync. And heat can disrupt the oscillations of atoms in an atomic clock. Eliminating such environmental effects can improve a clock’s precision. But only by so much.

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