Impurities in degenerate quantum matter



Dr Jesper Levinsen, Monash University
This colloquium will be held 12 noon, 12th May, in Goddard 08-139

The behaviour of a mobile impurity particle interacting with a quantum-mechanical medium is of fundamental importance in physics. Ultracold atomic gases have greatly improved our understanding of the impurity problem owing to the high degree of control over experimental parameters such as interactions and atom population. I will discuss recent theoretical and experimental progress in exploring the properties of impurities interacting with bosonic and fermionic mediums. For the case of impurities in a degenerate Fermi gas, the dynamics following a quench of the impurity-medium interactions has recently been investigated [1]. Interferometric measurements have tracked the non-perturbative quantum evolution of the fermionic many-body system, revealing in real time the formation dynamics of quasiparticles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. For impurities interacting with a Bose-Einstein condensate, new experiments have demonstrated the existence of a well-defined quasiparticle state and a many-body continuum of excited states, with no significant effects of three-body losses observed [2]. This opens up new windows on the study of strongly interacting Bose systems.

[1] Cetina, Jag, Lous, Fritsche, Walraven, Grimm, Levinsen, Parish, Schmidt, Knap, and Demler, “Ultrafast many-body interferometry of impurities coupled to a Fermi sea”, Science 354, 96 (2016)
[2] Jørgensen, Wacker, Skalmstang, Parish, Levinsen, Christensen, Bruun, and Arlt, “Observation of Attractive and Repulsive Polarons in a Bose-Einstein Condensate”, Phys. Rev. Lett. 117, 055302 (2016)