  Bloch oscillations are a phenomenon well known from quantum mechanics where
electrons in a lattice experience an oscillatory motion in the presence of an
electric field gradient. Here, we report on Bloch oscillations of hybrid
light-matter particles, called exciton-polaritons, being confined in an array
of coupled microcavity waveguides. To this end, we carefully design the
waveguides, widths and their mutual couplings such that a constant energy
gradient is induced perpendicular to the direction of motion of the propagating
exciton-polaritons. This technique allows us to directly observe and study
Bloch oscillations in real- and momentum-space. Furthermore, we support our
experimental findings by numerical simulations based on a modified
Gross-Pitaevskii approach. Our work provides an important transfer of basic
concepts of quantum mechanics to integrated solid state devices, using quantum
fluids of light.
