A New Angle on Quantum Impurities

Understanding how impurities interact with a quantum environment is an important problem with widespread implications in physics [1, 2]. An impurity has complex quantum-mechanical interactions with its host environment, and it can acquire properties that differ greatly from those of the impurity in isolation. However, such many-body effects are formidably challenging to describe with theory. A new theoretical approach introduced by Mikhail Lemeshko at the Institute of Science and Technology in Austria [3] provides a simple and elegant way to describe an important type of impurity: a molecule immersed in a quantum solvent. Analyzing experimental data collected by various groups over two decades, Lemeshko has shown that molecules in one such solvent, superfluid helium, form quasiparticles called angulons. This finding may lead to a substantial simplification of theories that describe a broad range of molecules and solvents.