  Combining miniaturization and good operating speed is a compelling yet
crucial task for our society. Plasmonic waveguides enable the possibility of
carrying information at optical operating speed while maintaining the dimension
of the device in the nanometer range. Here we present a theoretical study of
plasmonic waveguides extending our investigation to structures so small that
Quantum Size Effects (QSE) become non negligible, namely quantum plasmonic
waveguides. Specifically, we demonstrate and evaluate a blue-shift in Surface
Plasmon (SP) resonance energy for an ultra-thin gold nanowire.
