Speaker

Felipe Isaule
Postdoctoral Fellow, Pontifical Catholic University of Chile

Abstract

The progress in realising ultracold atomic mixtures has greatly revitalised the interest in studying impurities immersed in quantum mediums [1]. The past decade has seen the experimental realisation of the elusive Bose polaron, consisting of a quasiparticle formed from an impurity interacting with a Bose-Einstein condensate [2,3]. These developments have motivated extensive theoretical studies of Bose polarons and related systems, such as bipolarons [4], lattice polarons [5], amongst others.

In this talk, I will provide an overview of my research on polaron physics. This includes the examination of the behaviour of impurities in optical lattices interacting with a bath across the superfluid-to-Mott insulator transition. I will focus on harmonically confined optical lattices, where we have found that an impurity can form a correlated counterflow state with a bosonic bath [6]. This counterflow state shows long-range anti-pair order and displays non-trivial features, including a sudden orthogonality. In addition, I will briefly summarise the use of effective field theory to study strongly-interacting polarons [7], highlighting future directions.

[1] F. Grusdt, N. Mostaan, E. Demler and L. A. Peña Ardila, Rep. Prog. Phys. 88, 066401 (2025).
[2] M.-G. Hu et al., Phys. Rev. Lett. 117, 055301 (2016).
[3] N. B. Jørgensen et al., Phys. Rev. Lett. 117, 055302 (2016).
[4] A. Camacho-Guardian, L. A. Peña Ardila, T. Pohl, and G. M. Bruun, Phys. Rev. Lett. 121, 013401 (2018).
[5] V. E. Colussi, F. Caleffi, C. Menotti, and A. Recati, Phys. Rev. Lett. 130, 17, 3002  (2023).
[6] F. Isaule, A. Rojo-Francàs, L Morales-Molina, and B. Juliá-Díaz, Phys. Rev. Lett. 135, 023404 (2025).
[7] F. Isaule, I. Morera, P. Massignan, and B. Juliá-Díaz, Phys. Rev. A 104, 023317 (2021).

Looking forward to seeing many of you at the seminar!

Quantum Systems Unit (Busch U)