Temporal coherence of surface plasmons in silver waveguides

Surface plasmon polaritons, in spite of being lossy, are known to preserve their coherence over long distances. In this paper, we investigate the coherence of surface plasmons propagating on a silver thin film surface using free-space optical Mach–Zehnder interferometry, where they are found to maintain their temporal coherence up to 80 µm, thus setting, for the first time to the best of our knowledge, a new limit. This can be important in applications integrating plasmonics with quantum information processing, where decoherence is a major challenge.