Christoph Eigen (University of Cambridge)
Bose polarons in a box
Emergent polaronic quasiparticle descriptions underpin our understanding of conventional quantum many-body systems, a paradigm first introduced by Landau and Pekar to describe the mobility of an electron impurity in a dielectric crystal. Nowadays, the concept is relevant in diverse contexts, from condensed matter to surface chemistry and quantum computation.
Here I will showcase a series of recent experiments studying Bose polarons [1], which form when impurities are immersed in a Bose-Einstein condensate. We measure the spectral properties and real-time dynamics of mobile impurities injected into a homogeneous 39K Bose-Einstein condensate, offering reduced inhomogeneous-density broadening and widely tuneable interparticle interactions using Feshbach resonances. We map out both attractive and repulsive branches of polaron quasiparticles, resolving the repulsive polaron and the molecular branch associated with the Feshbach resonance in the strongly interacting regime, and show that the latter also has a many-body character. Our measurements reveal remarkably universal behavior, controlled by the bath density and a single dimensionless interaction parameter; for near-resonant interactions the polarons are no longer well defined, but the universality persists. Finally, we study the fate of the quasiparticle branches as we heat the system and cross the BEC transition temperature of the bath.
References:
[1] J. Etrych, G. Martirosyan, A. Cao, C. J. Ho, Z. Hadzibabic, C. Eigen, arXiv:2402.14816.