  The intrinsic optical nonlinearities of quasi-one dimensional structures,
including conjugated chain polymers and nanowires, are shown to be dramatically
enhanced by the judicious placement of a side group or wire of sufficiently
short length to create a large phase disruption in the dominant eigenfunctions
along the main path of probability current. Phase disruption is proposed as a
new general principle for the design of molecules, nanowires and any quasi-1D
quantum system with large intrinsic response and does not require charge
donors-acceptors at the ends.
