Tip-enhanced imaging and control of infrared strong light-matter interaction

Optical antenna resonators provide for the control of light-matter interaction on the nanoscale with electron-photon hybrid states in strong coupling. Mid-Infrared plasmonic antennas have been shown to strongly couple to intersubband transitions in multi-quantum-well semiconductor heterostructures which are then tunable in coupling strength by driving field intensity and antenna resonance. Here, we demonstrate ground state depletion-induced modification of oscillator strength in a femtosecond nano-FTIR spectroscopic nano-imaging experiment. This allows for nano-scale spatial control of the coupling strength. We observe nanotip-induced interference of excitation pathways through the phase-dependent optical interactions of the tip with the infrared resonant IR nano-antenna. This leads to, e.g., the ability to realize strong and weak coupling and their switching localized at opposite antenna terminals, respectively. We model the behavior via a coupled three-oscillator model as electromagnetically induced scattering. These results present a new regime of nonlinear IR light-matter control based on the dynamic manipulation of quantum hybrid states for switching and signal processing, power limiter, or saturable absorbers on the nanoscale.