  Surface plasmon polaritons (plasmons) have the potential to interface
electronic and optical devices. They could prove extremely useful for
integrated quantum information processing. Here we demonstrate on-chip
electrical detection of single plasmons propagating along gold waveguides. The
plasmons are excited using the single-photon emission of an optically emitting
quantum dot. After propagating for several micrometers, the plasmons are
coupled to a superconducting detector in the near-field. Correlation
measurements prove that single plasmons are being detected.
