Directed transport of ultracold atoms in a Hamiltonian quantum ratchet

We report on the successful experimental realization of a quantum ratchet for ultracold atoms in a driven spatially asymmetric optical lattice. Ratchets are usually considered as a tool, which rectify an otherwise undirected, for instance oscillating or fluctuating, motion of particles or objects. In order to observe a directed transport of atoms one has to break the space-time symmetry of the system. Here, we report on the realization of a quantum ratchet in the absence of dissipative processes (Hamiltonian regime) within the interaction time.