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Category: quantum physics – Page 3

Quantum Neural Networks Face the Hardware Test

Artificial neural networks have become powerful tools for finding patterns in complex data, from classifying images to predicting protein structures and assisting mathematical discovery. Yet their success has so far relied almost entirely on classical hardware. Recent developments in quantum-computing technologies make it timely to ask whether trainable models can also make use of quantum effects such as superposition and the intrinsic uncertainty associated with quantum measurements. What’s more, running neural networks on real quantum processors could potentially turn these networks into probes, revealing how different hardware architectures shape networks’ behaviors.

Why Flowing Spins Polarize Up or Down

One of the goals of spintronics is to flip the magnetization of ferromagnetic domains solely via an electrically controlled spin current flowing in a layer underneath. The antiferromagnet manganese germanide (Mn3Ge) is a prime candidate for providing that control thanks to the out-of-plane polarization of its spin currents. Now Mingxing Wu of the University of Tokyo and his colleagues have identified which of two mechanisms proposed by theorists is responsible for the polarization [1]. The answer is both.

The triangular lattice of Mn3Ge causes groups of three adjacent spins to orient themselves at 120° with respect to each other. That noncolinear arrangement engenders so-called Weyl points in the crystal’s band structure. Thanks to a quantum geometry property called Berry curvature, Weyl points act like internal magnetic fields that deflect electrons in a spin-dependent way.

Until the work of Wu and his colleagues, just how the deflection leads to out-of-plane polarization was unclear. It could conceivably arise either via a mechanism called spin swapping (SSW) or via the magnetic spin Hall effect (MSHE). To settle the question, the researchers subjected single-crystal strips of Mn3Ge topped with layers of permalloy (a nickel–iron alloy) to a technique called spin-torque ferromagnetic resonance (ST-FMR). The ST-FMR signal from MSHE depends on the orientation of the Mn3Ge lattice with respect to the spin current, whereas the signal from SSW does not. By creating differently oriented samples, Wu and his colleagues found that both mechanisms contribute to the out-of-plane spin polarization with comparable magnitudes. Now that the mystery has been solved, the next step is to harness both mechanisms for the magnetic-field-free switching of magnetization.

Researchers expand simulation tool to help design the next generation of photonic and quantum devices

Many modern technologies, from optical communications and artificial intelligence (AI) hardware to advanced sensors and medical imaging, depend on photonic and semiconductor devices that precisely control the interaction between light and electrons. Designing these devices, however, remains a major challenge because existing simulation tools often require researchers to choose between modeling an entire device or capturing the detailed behavior of electrons. Few can do both within the same model.

Researchers from the Singapore University of Technology and Design (SUTD) and National University of Singapore (NUS) have developed a new computational approach that extends the widely used open-source particle-in-cell (PIC) method with condensed-matter physics. The result is a single platform that can simulate a much broader range of light-matter interactions in metals, semiconductors and emerging quantum materials.

Published in Computer Physics Communications, the research, “Particle-in-cell simulations of quantum plasmas,” demonstrates how an established plasma physics tool can be adapted to study condensed-matter systems, opening new possibilities for designing photonic and quantum technologies.

Quantum internet leaves the lab with first real-world entanglement over busy telecom fiber

Quantum information is notoriously fragile. Internet traffic is anything but. Yet Northwestern University scientists have demonstrated they can peacefully coexist inside the same fiber-optic cable.

In a new study, researchers successfully sent entangled photons through a 24.4-kilometer (15.2-mile) fiber-optic cable connecting Evanston and downtown Chicago while the same cable simultaneously carried high-capacity internet traffic. Even amid the torrent of conventional data, the quantum signals remained remarkably intact—preserving entanglement with more than 94% fidelity.

By allowing fragile quantum signals and powerful classical data streams to share the same optical fiber, the work demonstrates a practical path toward building future quantum networks without requiring entirely new communications infrastructure.

New multiplexing scheme accelerates long-distance quantum communication

Quantum networks, systems consisting of multiple connected nodes or devices that can transmit quantum information to one another, have the potential to advance future communications. These networks typically leverage entanglement, a quantum phenomenon that prompts two or more distant particles to become highly correlated, so that measuring one instantly affects the state of the other.

To ensure that distant particles have become entangled and can transmit quantum states, some quantum scientists try to realize so-called heralded entanglement. This entails confirmation, from a detectable signal, that entanglement between nodes has been established.

Researchers at Tsinghua University and Hefei National Laboratory recently introduced a promising strategy to accelerate the generation of heralded entanglement between multiple ions (i.e., atoms with an electrical charge). Their proposed approach, outlined in a paper published in Physical Review Letters, relies on a so-called multiplexing scheme, a technique to send multiple signals through the same communication channel.

Neural networks unlock larger quantum simulations with lower computational costs

In recent years, research using artificial intelligence to predict material properties has advanced rapidly. Neural network quantum Monte Carlo methods have attracted attention as highly accurate simulation techniques. However, their extremely high computational cost has limited their application to small molecular systems. This study introduces a new computational method that overcomes this limitation.

Methods that simulate electron-level mechanisms on supercomputers are widely used to explore novel materials and understand biological phenomena. There is strong demand for new approaches that can deliver faster predictions while maintaining high accuracy.

Detecting the body’s magnetic fields with a low-power Ramsey-based magnetometer

Our bodies generate extremely weak magnetic fields as electric currents flow through the heart, brain and other tissues. These signals are used in magnetocardiography and magnetoencephalography to assess heart function and brain activity, respectively. These fields can be detected at room temperature using diamond sensors containing nitrogen-vacancy (NV) centers, in which a carbon atom is replaced by a nitrogen atom adjacent to an empty lattice site.

However, conventional NV-center sensors typically require watt-level lasers to detect the extremely weak biomagnetic fields, which are usually below the picotesla level. These high-power lasers generate significant heat, limiting how close the sensor can be placed to biological tissue. Since biomagnetic fields rapidly weaken with distance, overcoming thermal and close-proximity challenges is essential for practical biomagnetic sensing.

A research team led by Professor Takayuki Iwasaki from the Department of Electrical and Electronic Engineering, School of Engineering, Institute of Science Tokyo, Japan, has developed a diamond quantum magnetometer using a low-power laser of just 210 mW, a light-trapping diamond waveguide and a compact microwave antenna. The new sensor limits its temperature rise to only 13 K while allowing it to be placed just 2 mm (0.08 inches) from the sample, enabling close-proximity biomagnetic measurements without compromising thermal safety.

Australian scientists unveil first quantum battery that could one day charge devices in seconds

A new development from Australia’s national science agency is offering a glimpse of a future in which charging your phone, laptop, or even grid-scale storage systems could take a fraction of the time it does now.

Researchers in Australia say they have built the world’s first fully functioning proof-of-concept quantum battery.

Scientists from the CSIRO, the University of Melbourne, and RMIT announced that they had successfully developed and tested a quantum battery prototype, Lab Worldwide reported.

The First Room-Temperature Quantum Material of Its Kind Is Spun From Atoms of Gold

Materials in a quantum state come with exotic properties that bend the laws of physics and offer huge potential to scientists – but they’re usually also incredibly delicate, and require ultra-low temperatures to exist and function.

That presents a problem when it comes to making the most of these materials and their characteristics: they need to move out of large lab refrigerators.

We’re now another step towards that being possible.

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