Time-resolved detection of photon–surface-plasmon coupling at the single-quanta level

The interplay of nonclassical light and surface plasmons has attracted considerable attention due to fundamental interests and potential applications. To gain more insight into the quantum nature of the photon--surface-plasmon coupling, time-resolved detection of the interaction is invaluable. Here we demonstrate the time-resolved detection of photon--surface-plasmon coupling by exploiting single and entangled photons with long coherence time to excite single optical plasmons. We examine the nonclassical correlation between the single photons and single optical plasmons in such systems using the time-resolved Cauchy-Schwarz inequality. We also realize single optical plasmons with a programmable temporal wave packet by manipulating the waveform of incident single photons. The time-resolved detection and coherent control of single optical plasmons may offer new opportunities to study and control the light-matter interaction at the nanoscale.