POSTER: From polarons to bipolarons in Bose-Einstein condensates.

Luis Ardila (ITP Hannover)

Dec 10. 2019, 17:00 — 19:00

 Mobile impurities in a Bose-Einstein condensate can form quasi-particles termed Bose polarons. Here

I show how these quasi-particles are originated when a single impurity is dressed by the excitations of

the quantum bosonic bath. The most striking advantage of these polarons is the huge degree of

controllability of the coupling strength between the impurity and the bosonic bath. Thus, one can

realize polarons from weak all the way up to the strong interacting regime [1,2] . For strong interactions

two polaron can bind together forming bound bipolarons states. They emerge due to the induced nonlocal

interaction mediated by density oscillations of the bath [3].  Polarons and bipolarons in ultra-cold

quantum gases could be used as a robust platform for quantum simulation in a condensed matter


It turns out that exploring low-dimensions, polarons can form many-body bound states even at

intermediate coupling. Here, we use exact QMC to study an impurity immersed in a 2D superfluid and

to compute the polaron energy, the effective mass and the quasiparticle residue for arbitrary coupling

strength. We find important deviations of the quasiparticle properties from perturbation theory even at

very weak coupling strengths. In the strongly interacting regime, the ground-state polaron loses the

quasiparticle nature characteristic of weak interactions and forms a many-body bound state featuring a

large effective mass, a vanishing wavefunction residue and a size that extends over many

healing lengths of the bath [4].




[1] N. B. Jørgensen, L. Wacker, K. T. Skalmstang, M. M. Parish, J. Levinsen, R. S. Christensen, G. M. Bruun, and J. J. Arlt.

Phys. Rev. Lett. 117 . 055302 (2016).

[2] M-G Hu, M. J. V. de Graaff, D. Kedar, J. P. Corson, E. A. Cornell, and D. S. Jin. Phys. Rev. Lett. 117, 055301 (2016)

[3] A. Camacho-Guardian, L. A. P Ardila, T. Pohl, G. M. Bruun, 121, 013401 (2018)

[4] L. A. P Ardila, Astrakharchik and S. Giorgini. ArXiv 1907.01533 (2019).

Further Information
ESI Boltzmann Lecture Hall
Associated Event:
Polarons in the 21st Century (Workshop)
Jozef Devreese (U Antwerpen)
Cesare Franchini (U of Vienna)
Georg Kresse (U of Vienna)
Jacques Tempere (U Antwerpen)