Phys.org February 14, 2023 Plasmon modes are treated as quasiparticles, and they are considered essential for the realization of future nanoscale quantum functionality. Implementing and demonstrating such functionality requires access to the quasiparticle’s quantum state to monitor and manipulate its corresponding quantum wave packet dynamics in Hilbert space. Researchers in Germany succeeded in detecting such superposition states of light directly in a nanostructure using plasmon-assisted electron emission as a signal in coherent two-dimensional nanoscopy. The observation of a quantum coherence oscillating at the third harmonic of the plasmon frequency was traced back to the superposition of energetically non-adjacent plasmon occupation […]