Quantum particles behave like social creatures, Monash physicists find
Professor Meera Parish and Associate Professor Jesper Levinsen
Quasiparticles, the building blocks of many quantum materials, interact in surprisingly social ways, with their behaviour depending on how “in sync” they are within a quantum system, a new study led by Monash University has found.
The findings, published today in Physical Review Letters, could reshape how scientists design quantum technologies and understand exotic states of matter.
Led by Professor Meera Parish and Associate Professor Jesper Levinsen from the School of Physics and Astronomy, the research investigates how bosonic impurities, known as polarons, interact inside a dilute Bose gas at ultra-cold temperatures. Their work challenges long-standing theories by showing that the surrounding medium can actually enhance repulsion between these quasiparticles, rather than inducing attraction as previously thought.
“People often imagine forces in physics as fixed and mysterious,” said Professor Parish. “But we’ve shown that these forces are dynamic, they depend on whether the quasiparticles are condensed into the same quantum state. It’s a bit like how people behave differently in a crowd versus alone.”
Quasiparticles are particle-like entities that emerge from the collective behaviour of quantum particles. They’re essential to understanding complex systems like metals, semiconductors, and even the behaviour of atoms in ultra-cold gases. Yet until now, scientists couldn’t agree on whether polaron quasiparticles attract or repel each other, a fundamental question with major implications.
“Our work resolves a long-standing puzzle,” said Associate Professor Levinsen. “We found that polarons with matching momentum repel each other, while those with differing momentum attract. This aligns with experimental results across different platforms, from trapped atoms to atomically thin semiconductors.”
The study also connects polaron interactions to other exotic quantum phenomena, such as phase separation and droplet formation, behaviours that occur when impurity-boson interactions become strong enough to destabilize the system.
Understanding these interactions is crucial for designing quantum devices, especially those that rely on entanglement and coherence between particles. The research offers a new framework for predicting and controlling quasiparticle behaviour in a wide range of materials.
“This is a big step forward in our understanding of quantum matter,” said Professor Parish. “It’s not just about particles, it’s about the relationships between them.”
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