  We have measured a quantum ratchet effect for vortices moving in a
quasi-one-dimensional Josephson junction array. In this solid-state device the
shape of the vortex potential energy, and consequently the band structure, can
be accurately designed. This band structure determines the presence or absence
of the quantum ratchet effect, as observed in the presented experiments. In
particular, asymmetric structures possessing only one band below the barrier do
not exhibit current rectification at low temperatures and bias currents. The
quantum nature of transport is also revealed in a universal/non-universal
power-law dependence of the measured voltage-current characteristics for
samples without/with rectification.
