  In this article, we use spatially modulated control fields to increase the
four-wave mixing efficiency in a four-subband semiconductor asymmetric double
quantum well, motivated by similar works in atomic systems. Using a simplified
version of the propagation equations, we show analytically that for control
fields with constant amplitude and linearly varying mixing angle with the
propagation distance, a conversion efficiency close to unity can be achieved
even for relatively short propagation distances. Subsequently, we confirm these
results by numerically simulating the full set of propagation equations.
