Understanding how complex behaviour emerges from simple interactions is a central goal of many-particle quantum physics. A particularly powerful approach is to study the quantum impurity problem, where a small number of particles interact with and become "dressed" by a surrounding quantum medium, forming quasiparticles known as polarons. While originally introduced to describe electrons moving through a crystal lattice, the impurity problem has now become a versatile framework for understanding a wide range of systems, from cold atomic gases to neutron stars. 

In this talk, I will show how insights gained from quantum impurities can be used to understand the collective behaviour of quantum mixtures, where more than one type of quantum particle coexists. I will first discuss recent work on interactions between polarons, demonstrating how the nature of these interactions depends on both the quantum statistics of the impurities and the response of the surrounding medium. I will then introduce a novel theoretical framework that naturally connects the impurity picture to a strongly interacting quantum mixture of bosons and fermions. In particular, I will show that a strong attraction between bosons and fermions leads to the emergence of self-bound quantum droplets — the quantum analogue of a classical liquid.

Meera Parish is a Professor in theoretical physics and an ARC Future Fellow at Monash University in Melbourne, Australia. Since obtaining her Ph.D. from the University of Cambridge, she has been a PCTS postdoctoral fellow at Princeton University, and a Lecturer and EPSRC research fellow at University College London. She is also a recipient of the IOP Maxwell medal and prize. Her research focuses on strongly correlated phenomena at the interface between ultracold atomic gases and condensed matter physics.