[Seminar] "Ultracold polarons and impurities: from lattice polarons to effective field theories" Dr. Felipe Isaule, Pontifical Catholic University of Chile

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)