Detection of a plasmon-polariton quantum wave packet
Nature Physics, (February 2023)DOI: 10.1038/s41567-022-01912-5
Abstract
Plasmon polaritons (plasmons, for simplicity) have become paramount
for tailored nanoscale light–matter interaction, and extensive research
has been conducted to monitor and manipulate their spatial3 and spatio-temporal dynamics. These dynamics result from the superposition of various plasmon modes, which are classical wave packets. Beyond this classical picture, 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. Here we report the local detection of nanoscale plasmon quantum wave packets 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 is
traced back to the superposition of energetically non-adjacent plasmon occupation number states and is therefore a direct fingerprint of the quantum wave packet. Beyond demonstrating the existence of a plasmon quantum wave packet via the coherence between certain occupation number states and providing an improved model for plasmon-assisted electron emission processes, the results may enable time-dependent
probing and manipulation of coupled quantum states and dynamics on the nanoscale.