Crossover from few-to many-body physics: Breakdown of the Bose polaron due to Efimov physics

Simple few-body physics can give rise to interesting emergent many-body effects. One such emergent effect arising at small particle number is the Efimov effect [1], where three particles with pairwise interactions form a special type of Borromean three-body bound state due to cooperative binding. In our work we study which role the Efimov effect plays in many-body systems. To this end, we theoretically study the role of Efimov physics in the paradigmatic model of the Bose polaron [2], an impurity immersed in a BEC. We use a variational method based on Gaussian States in the reference frame of the impurity [3]. This Ansatz allows for an arbitrary number of bosonic excitations with pairwise interboson correlations and three-body correlations involving the impurity. We show that the formation of large Efimov-like bound states can lead to the breakdown of the polaron for light impurities. Our results can be probed in experiments with cold atom mixtures using currently available state-of-the-art techniques.

 

[1] P. Naidon and S. Endo, Rep. Prog. Phys. 80, 056001 (2017)

[2] Y. E. Shchadilova, R. Schmidt, F. Grusdt, and E. Demler, Phys. Rev. Lett. 117, 113002  (2016)

[3] T. Shi, E. Demler, J.I. Cirac, Ann. Phys. 390, 245 (2018)