  Quantum entanglement is a stunning consequence of the superposition
principle. This universal property of quantum systems has been intensively
explored with photons, atoms, ions and electrons. Collective excitations such
as surface plasmons exhibit quantum behaviors. For the first time, we report an
experimental evidence of non-local control of single plasmon interferences
through entanglement of a single plasmon with a single photon. We achieved
photon-plasmon entanglement by converting one photon of an entangled photon
pair into a surface plasmon. The plasmon is tested onto a plasmonic platform in
a Mach-Zehnder interferometer. A projective measurement on the polarization of
the photon allows the non-local control of the interference state of the
plasmon. Entanglement between particles of various natures paves the way to the
design of hybrid systems in quantum information networks.
