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
context.
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).