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Category: quantum physics – Page 134

Harvard researchers have shown that quantum coherence can survive chemical reactions at ultracold temperatures. Using advanced techniques, they demonstrated this with 40K87Rb bialkali molecules, suggesting potential applications in quantum information science and broader implications for understanding chemical reactions.

Zoom in on a chemical reaction to the quantum level and you’ll notice that particles behave like waves that can ripple and collide. Scientists have long sought to understand quantum coherence, the ability of particles to maintain phase relationships and exist in multiple states simultaneously; this is akin to all parts of a wave being synchronized. It has been an open question whether quantum coherence can persist through a chemical reaction where bonds dynamically break and form.

Now, for the first time, a team of Harvard scientists has demonstrated the survival of quantum coherence in a chemical reaction involving ultracold molecules. These findings highlight the potential of harnessing chemical reactions for future applications in quantum information science.

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Imagine a two-dimensional flatland, instead of our three-dimensional world, where the rules of physics are turned on their head and particles like electrons defy expectations to reveal new secrets. That’s exactly what a team of researchers, including Georgia State University Professor of Physics Ramesh G. Mani and recent Ph.D. graduate U. Kushan Wijewardena, has been studying at Georgia State’s laboratories.

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The operation of a quantum computer relies on encoding and processing information in the form of quantum bits—defined by two states of quantum systems such as electrons and photons. Unlike binary bits used in classical computers, quantum bits can exist in a combination of zero and one simultaneously—in principle allowing them to perform certain calculations exponentially faster than today’s largest supercomputers.

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Researchers have uncovered new phenomena in the study of fractional quantum Hall effects.

Their experiments, conducted under extreme conditions, have revealed unexpected states of matter, challenging existing theories and setting the stage for advancements in quantum computing and materials science.

Exploring the enigmatic world of quantum physics.

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A new device converts a stream of microwave photons into an electric current with high efficiency, which will benefit quantum information technologies.

Technologies for quantum computing, sensing, and communication process information stored in quantum bits (qubits) by using microwave photons. But detecting such photons accurately and at high rates—to read out the changing states of a quantum computer, for example—is a challenge, since they have much less energy than visible or infrared photons. Now researchers have demonstrated a detection method based on the fact that a photon can assist in the quantum tunneling of an electron through a superconducting junction [1]. The technique converts a stream of microwave photons into a flow of electrons far more effectively than other methods, showing an efficiency of 83%, and it will be of immediate use in quantum technologies.

Building good detectors of microwave photons is inherently difficult, says Julien Basset of the University of Paris-Saclay, because such photons lack the energy needed to excite electrons in semiconductors into the conduction band, thereby generating a current that can be measured. Researchers have been pursuing several techniques, but none works well for a continuous stream of photons, in which multiple photons may arrive simultaneously. For such continuous operation, as would likely be required in many practical quantum information devices, the best efficiency demonstrated so far has been only a few percent, Basset says.

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Quantum technology relies on qubits, the fundamental units of quantum computers, whose operation is influenced by quantum coherence time. Scientists believe that moiré excitons — electron-hole pairs trapped in overlapping moiré interference fringes — could serve as qubits in future nano-semiconductors. However, previous limitations in focusing light have caused optical interference, making it difficult to measure these excitons accurately.

Kyoto University researchers have developed a new technique to reduce moiré excitons, allowing for accurate measurement of quantum coherence time. Their findings, published in Nature Communications, reveal that the quantum coherence of a single moiré exciton remains stable for over 12 picoseconds at −269°C, significantly longer than that of excitons in traditional two-dimensional semiconductors. The confined moiré excitons in interference fringes help maintain quantum coherence, advancing the potential of quantum technology.

“We combined electron beam microfabrication techniques with reactive ion etching. By utilizing Michelson interferometry on the emission signal from a single moiré exciton, we could directly measure its quantum coherence time,” said Kazunari Matsuda of KyotoU’s Institute Advanced Energy.

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