Kinked linear response from non-Hermitian cold-atom pumping

Abstract: It is well known that non-Hermitian, non-reciprocal systems may harbor exponentially localized skin modes. However, in this work, we find that, generically, non-Hermiticity gives rise to abrupt and prominent kinks in the semi-classical wave packet trajectories of quantum gases, despite the absence of sudden physical impulses. This physically stems from a hitherto underappreciated intrinsic non-locality from non-Hermitian pumping, even if all physical couplings are local, thereby resulting in enigmatic singularities in the band structure that lead to discontinuous band geometry and Berry curvature. Specifically, we focus on the realization of the kinked response in an ultracold atomic setup. For a concrete experimental demonstration, we propose an ultracold atomic setup in a two-dimensional optical lattice with laser-induced loss such that response kinks can be observed without fine-tuning in the physical atomic cloud dynamics. Our results showcase unique non-monotonic behavior from non-Hermitian pumping beyond the non-Hermitian skin effect and suggest new avenues for investigating non-Hermitian dynamics on ultracold atomic platforms.