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Category: quantum physics

A robust new telecom qubit identified in silicon

Quantum technologies are anticipated to transform computing, communication, and sensing by harnessing the unusual behavior of matter at the atomic scale. Translating quantum’s promise into practical devices will require physical systems that have desirable quantum properties and can be easily manufactured. Silicon, the material behind today’s computer chips, is highly attractive as a platform because it plays to the strengths of the trillion-dollar semiconductor industry that has already been built. Identifying quantum building blocks—qubits—in silicon is, therefore, an important frontier research area.

In a new study, researchers in UC Santa Barbara materials professor Chris Van de Walle’s Computational Materials Group identified a robust new qubit in silicon, called the CN center. The work is published in the journal Physical Review B.

Qubits can be based on atomic-scale defects in a crystal. A prototype example is the NV center, which consists of a nitrogen (N) atom sitting next to a vacancy (V, a missing carbon atom) in a diamond crystal. These defects can interact with both electrons and light, allowing them to emit single photons (quanta of light) that can transmit quantum information or be processed in quantum networks.

Ion bombardment triggers a reliable quantum switch in tantalum disulfide crystals

When you toss a coin, you put it into a higher-energy state until it falls back down again. It can then end up in one of two possible states: heads or tails. No matter which state the coin was in before, after the toss both outcomes are equally likely. A team at TU Wien has analyzed a quantum system that also has two equivalent ground states. By supplying energy through ion bombardment, this state can be changed.

Remarkably, however, the system behaves very differently from a coin toss: it switches every single time. After ion impact, it reliably ends up in the opposite state. For the experiment, the ion-beam equipment of TU Wien was transported to DESY in Hamburg. The crystals studied were provided by Kiel University (CAU), which also participated in the experiments at DESY. The research is published in the journal Nano Letters.

A protocol to realize near-perfect atom-photon entanglement

Quantum technologies, devices and systems that operate leveraging quantum mechanical effects, could tackle some tasks more reliably and efficiently than any classical technology could. In recent years, some researchers have been trying to realize quantum networks to scale up the size of quantum computers, which essentially consist of several connected smaller quantum processors.

The devices in a quantum network are connected via entanglement, a quantum effect via which distant quantum particles become inextricably linked and share a single correlated state. One way to create entanglement between different atomic quantum computers is to use an atom-cavity interface, a system in which atoms interact with light inside an optical cavity.

Over two decades ago, two physicists at the University of Aarhus introduced a protocol designed to produce high-quality entangled states, reliably connecting devices in a network. Despite its potential, this framework, known as the state-carving (SC) protocol, was found to only succeed in 50% of cases, which has so far prevented its application on a large scale.

Quantum effect could power the next generation of battery-free devices

A new study has revealed how tiny imperfections and vibrations inside a promising quantum material could be used to control an unusual quantum effect, opening new possibilities for smaller, faster, and more efficient energy-harvesting devices.

The international team, led by Professor Dongchen Qi from the QUT School of Chemistry and Physics and Professor Xiao Renshaw Wang from Nanyang Technological University in Singapore, studied the mechanism governing the so-called nonlinear Hall effect (NLHE). The research is published in the journal Newton.

Unlike the classical Hall effect, this quantum version allows alternating electrical signals, like those found in wireless or ambient energy sources, to be converted directly into usable direct current without the need for traditional diodes or bulky components.

When light ‘thinks’ like the brain: The connection between photons and artificial memory

An international study has revealed a surprising connection between quantum physics and the theoretical models underlying artificial intelligence. The study results from a collaboration between the Institute of Nanotechnology of the National Research Council (Cnr-Nanotec), the Italian Institute of Technology (IIT), and Sapienza University of Rome, together with international research institutions. The research paper was published recently in the journal Physical Review Letters.

Italian researchers show that identical photons propagating within optical circuits spontaneously behave like a Hopfield Network, one of the best-known mathematical models used to describe the associative memory mechanisms of the human brain.

“Instead of using traditional electronic chips, we exploited quantum interference —the phenomenon that occurs in photonic chips when particles of light overlap and interact with one another to encode and retrieve information,” explains Marco Leonetti, coordinator and corresponding author of the study, senior researcher at Cnr-Nanotec and affiliated with the Center for Life Nano-and Neuro-Science at the Italian Institute of Technology (IIT) in Rome. “In this system, photons are not merely carriers of data, but themselves become the ‘neurons’ of an associative memory.”

AI develops easily understandable solutions for unusual experiments in quantum physics

Researchers at the University of Tuebingen, working with an international team, have developed an artificial intelligence that designs entirely new, sometimes unusual, experiments in quantum physics and presents them in a way that is easily understandable for researchers. This includes experimental setups that humans might never have considered. The new AI doesn’t just create a single design proposal; instead, it writes computer code that generates a whole series of physical experiments, that is, groups of experiments with similar outputs. The study has been published in the journal Nature Machine Intelligence.

The newly developed AI uses a programming language that researchers can easily understand. This allows them to figure out the underlying idea behind the AI’s processes much more easily than before. “AI systems usually deliver their solutions without explaining how they work,” says Mario Krenn, Professor of Machine Learning in Science at the University of Tuebingen and senior author of the study. “We scientists have to try to understand the solutions afterward. This often took us days or weeks—if we understood them at all.”

Clearing the path for turbulence-free quantum communication

A University of Ottawa team has developed a new way to protect free-space quantum key distribution (QKD) from atmospheric turbulence, one of the main causes of distortion and errors when sending quantum information through air. Their paper, “All-optical turbulence mitigation for free-space quantum key distribution using stimulated parametric down-conversion,” appears in the journal Optica.

Instead of relying on complex, expensive digital adaptive optics, the researchers use a nonlinear optical process called “stimulated parametric down-conversion (StimPDC).” The technique leverages StimPDC’s phase-conjugation property to correct spatial-mode distortions dynamically without requiring prior knowledge of the turbulent channel.

“We found the idea of using a fundamental optical process to correct the effects of turbulence in real time to be both innovative and largely unexplored,” said Aarón Cardoso, lead author and Quantum Optics Student Researcher at uOttawa. “Our results show we can reduce quantum error rates below the security threshold even under strong turbulence.”

7,000 GPUs Simulate Quantum Microchip in Unprecedented Detail

Using the Perlmutter supercomputer, researchers achieved a record-scale simulation of a quantum microchip to refine and validate next-generation quantum hardware designs. Researchers from Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley have complete

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