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Category: quantum physics

Can thermal noise train a computer? A new framework points to low-power AI

What if the thermal noise that hinders the efficiency of both classical and quantum computers could, instead, be used as a power source? What if computers could make use of the noise instead of suppressing or overcoming it? These are the goals of a relatively new branch of computing known as thermodynamic computing. A collaboration between researchers at the Molecular Foundry and the National Energy Research Scientific Computing Center (NERSC), both U.S. Department of Energy (DOE) user facilities located at Lawrence Berkeley National Laboratory (Berkeley Lab), is bringing them closer to reality.

In a paper published in Nature Communications, the researchers have proposed a design and training framework for a type of thermodynamic computer that mimics a neural network, which could drastically reduce the energy requirements of machine learning.

Modern computing requires energy: a single Google search, for example, consumes enough energy to power a six-watt LED for three minutes. This is partly because computers must contend with thermal noise—that is, the vibration of charge carriers, mostly electrons, within electronically conductive materials. In classical computers, even the smallest devices, such as transistors and gates, operate at energy scales thousands of times larger than that of this vibration.

Neutrons reveal magnetic signatures of chiral phonons

Physicists in China have uncovered new evidence that chiral phonons and magnons can interact strongly inside magnetic crystals. Using neutron spectroscopy, a team led by Song Bao at Nanjing University mapped magnetic signatures linked to chiral phonons in a ferrimagnetic material, revealing a previously elusive relationship between lattice vibrations and magnetic excitations. Reported in Physical Review Letters, the results could help researchers better understand how heat, sound and spin interact in quantum materials.

Phonons are collective vibrations of atoms in a crystal lattice which carry quantized packets of sound and heat through a solid. As quasiparticles, they behave somewhat like particles moving through the material and can interact with other excitations. In some cases, phonons also exhibit chirality: where some property of a particle differs from its mirror image.

For phonons, chirality arises when ions move in circular motions as the lattice vibrates, which imparts both an angular momentum and a tiny magnetic moment, which rotates in a plane perpendicular to the phonon’s direction of travel. Crucially, however, the phonon’s properties will vary depending on whether this rotation is clockwise or anticlockwise.

Researchers create a never-before-seen molecule and prove its exotic nature with quantum computing

An international team of scientists from IBM, The University of Manchester, Oxford University, ETH Zurich, EPFL and the University of Regensburg have created and characterized a molecule unlike any previously known—one whose electrons travel through its structure in a corkscrew-like pattern that fundamentally alters its chemical behavior. The work appears in Science.

This is the first experimental observation of a half-Möbius electronic topology in a single molecule. To the scientists’ knowledge, a molecule with such topology has never before been synthesized, observed, or even formally predicted.

Understanding this molecule’s behavior at the electronic structure level required something equally fundamental: a high-fidelity quantum computing simulation. The discovery advances science on two fronts. For chemistry, it demonstrates that electronic topology—the property governing how electrons move through a molecule—can be deliberately engineered, not merely found in nature.

Why Large Hadron Collider predictions can miss the mark, and a new way to fix it

Estimating things that exist is generally easy, but when it comes to estimating things that do not exist, it’s more difficult. This is something physicists from Poland and the UK are well aware of. To improve current simulations of high-energy particle collisions, they have developed a more accurate method for estimating the impact of calculations that are not performed.

Prediction can be difficult, especially when it comes to the future, as Niels Bohr—one of the fathers of quantum mechanics—once said. The fundamental problem with predicting the future lies in the simple fact that we just do not know it. A somewhat similar challenge arises in the calculations used to model high-energy particle collisions: For them to be useful, one must be able to estimate the impact of calculations that are not performed.

Physicists Matthew A. Lim from the University of Sussex in Brighton and Dr. Rene Poncelet from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow have presented a new approach to this issue in the journal Physical Review D.

Quantum Memory Isn’t What We Thought: Physicists Reveal a Hidden Duality

An international team of scientists has taken a closer look at how memory functions in quantum systems and their time evolution. Their study reveals that whether a quantum process appears to have memory depends on how it is examined. From one angle, the process may seem completely memoryless. From another, traces of past behavior remain visible. The findings open new paths for research in quantum science and emerging technologies.

In classical physics, memory is defined in a straightforward way. If a system’s future behavior depends only on its current condition, it is considered memoryless. If earlier states continue to influence what happens next, the system is said to have memory.

Quantum physics complicates this picture. Quantum systems can store and transmit information in ways that have no counterpart in classical science. In addition, measurement is not just a passive observation. It plays an active and fundamental role in how quantum systems evolve.

What’s going on inside quantum computers? New method simplifies process tomography

Quantum computers work by applying quantum operations, such as quantum gates, to delicate quantum states. Ideally, quantum computers can solve complex equations at staggeringly fast speeds that vastly outpace regular computers. In real hardware, the operations of quantum computers often deviate from the ideal behavior because of device imperfections and unwanted noise from the environment. To build reliable quantum machines, researchers need a way to accurately determine what a quantum device is actually doing.

Quantum process tomography (QPT) is a standard method for this. However, traditional QPT becomes very costly as the system grows, because the number of required measurements and calculations increases rapidly with the number of qubits.

To address this challenge, a research team from Tohoku University, the Nara Institute of Science and Technology (NAIST), and the University of Information Technology (Vietnam National University, Ho Chi Minh City) has introduced a new framework called compilation-based quantum process tomography (CQPT). The work is published in Advanced Quantum Technologies.

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