Quantum effects detected in collisions between hydrogen and noble gases

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VMI images of ions and electrons, Ne-H2 PI collisions. First row: all ions. Second row: h2+ coincidence ions and electrons. Third row: cropped images. Credit: Science (2023). DOI: 10.1126/science.adf9888

A research group from the Freie University of Berlin led by quantum physics professor Christiane Koch has demonstrated how hydrogen molecules behave when they collide with atoms of noble gases such as helium or neon. In an article published in the magazine Sciencethe researchers describe how they used simulations to draw connections between experimental data and theoretical models of quantum physics.

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The study includes theoretical calculations and data collected in experiments with atoms and molecules conducted at TU Dortmund University and the Weizmann Institute of Science in Israel. The team was able to show that the collisions change the way molecules vibrate and rotate according to the laws of quantum mechanics. Research in the field of quantum mechanics continues to gain prominence in today’s world. Findings like these can be applied to the development of cell phones, televisions, satellites, and in medical diagnostic technology.

The quantum effect observed here is known as the Feshbach resonance. “For a short moment after the collision, the hydrogen molecule and the noble gas atom form a chemical bond and then separate again,” explains Professor Koch of Freie Universitt Berlin.

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However, despite extremely detailed measurements and calculations for a relatively small and simple system, researchers are still a long way from being able to reconstruct the full quantum mechanical characteristics of the hydrogen-noble gas collision. “This is due to one of the fundamental phenomena of quantum mechanics: when it comes to measurements, there is no getting around the basic principles of classical physics. This creates a dilemma: we are able to mathematically describe certain quantum mechanical phenomena in abstract terms , but you still need to use the concepts of classical physics to fully understand them,” explains Koch.

Quantum effects, or types of behavior that cannot be explained by the rules of classical physics, appear when atoms and molecules can no longer be sufficiently described by the place they occupy and the speed with which they move. “They show characteristics that we associate with wave dispersion, such as interference, which is the constructive or destructive layering of waves,” says Koch. Furthermore, there are other phenomena such as entanglement, which occurs when quantum mechanical objects exert an immediate influence on each other despite being spatially distant.

Quantum effects typically appear in the realm of very small objects such as atoms and molecules, and when these objects are little affected by their environment. The latter is achieved for very short periods of time or at extremely low temperatures close to absolute zero (-273.15°C). “Under these circumstances, only a small amount of so-called quantum states are available to these particles. The system basically behaves in an ordered way,” says Koch.

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Higher temperatures allow for a greater number of quantum states in the particles, and quantum mechanical effects tend to smooth out when distributed as a statistical average across various states, and thus essentially disappear from view. In this state, the system behaves more randomly and can be described using statistics. So far, even the coolest atom-molecule collisions have exhibited this statistically predictable behavior. “This made it almost impossible to draw conclusions about the interaction between atoms and molecules, which meant that we could not establish a direct connection between real-life experimental data and theoretical models,” explains Koch.

More information:
Baruch Margulis et al, Feshbach Resonance State Tomography, Science (2023). DOI: 10.1126/science.adf9888

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About the magazine:
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