  In several settings of physics and chemistry one has to deal with molecules
interacting with some kind of an external environment, be it a gas, a solution,
or a crystal surface. Understanding molecular processes in the presence of such
a many-particle bath is inherently challenging, and usually requires
large-scale numerical computations. Here, we present an alternative approach to
the problem - that based on the notion of the angulon quasiparticle. We show
that molecules rotating inside superfluid helium nanodroplets and Bose-Einstein
Condensates form angulons, and therefore can be described by straightforward
solutions of a simple microscopic Hamiltonian. Casting the problem in the
language of angulons allows not only to tremendously simplify it, but also to
gain insights into the origins of the observed phenomena and to make
predictions for future experimental studies.
