Bloch oscillations in the absence of a lattice

We experimentally study the dynamics of strongly-correlated quantum many-body systems of ultracold atoms with particular focus on bosons confined to one-dimensional geometry. We have investigated the quantum motion of an impurity atom that is immersed in a strongly interacting Bose liquid and is subject to an external force [1]. We find that the momentum distribution of the impurity exhibits characteristic Bragg reflections at the edge of an emergent Brillouin zone. While Bragg reflections are typically associated with lattice structures, in our strongly correlated quantum liquid they result from the interplay of short-range crystalline order and kinematic constraints on the many-body scattering processes in the one-dimensional system. As a consequence, the impurity exhibits periodic dynamics that we interpret as Bloch oscillations. These arise even though the quantum liquid is translationally invariant. Our observations are supported by large-scale numerical simulations. [1] F. Meinert et al., arXiv:1608.08200 (2016).