Identify the mechanism of quasiparticle breakdown in 2D Bose polarons

Determine whether, in two-dimensional Bose gases at strong impurity-boson coupling (approximately 0 < ln(k_F a) ≲ 3), the observed breakdown of the Bose polaron quasiparticle is governed by an orthogonality catastrophe of the impurity or by self-localization of the impurity, and establish the microscopic mechanism responsible for this regime.

Background

In 2D, quantum fluctuations are enhanced and theory (QMC, FRG, variational) predicts a sharp reduction of the quasiparticle residue at strong coupling, indicating breakdown of the polaron picture. The microscopic origin of this breakdown is unresolved.

Competing scenarios include orthogonality catastrophe (as in 1D and certain fermionic contexts) and self-localization due to strong dressing. Disentangling these mechanisms requires high-precision spectroscopy and controlled theoretical modeling that includes few-body and many-body correlations.

References

The regime between 0< \ln\left(k_{\mathrm{F} a\right)\lesssim3 remains poorly understood. It is believed that the formation of many-body bound states involving multiple excitations causes the observed breakdown. An open question concerns microscopic physics of this regime and whether the polaron leads to an orthogonality catastrophe or rather self-localization.

— Impurities and polarons in bosonic quantum gases: a review on recent progress (2410.09413 - Grusdt et al., 12 Oct 2024) in Subsection "Bose polaron in 2D"