Tip Nano-Cavity Control, Imaging, and Spectroscopy of Infrared Polaritonic Heterostructures

Infrared polaritonic heterostuctures based on a multi-quantum-well intersubband transition coupled to a gold antenna exhibit record-high nonlinear optical responses and optical power limiting behavior. However, the collective response of an ensemble of these structures are limited to static passive performance depending on fabrication parameters. Here, we use broadband and ultrafast infrared nano-probe imaging and spectroscopy of single antenna quantum well heterostructures to actively tune quantum-well saturation, coupling strength, and quantum path interference through manipulation of the nanocavity mode volume between the tip and sample. We show how the tip acts as coupled antenna resonator and how the tip-sample nano-cavity enhances far-field coupling to control photon emission, electric field orientation, and nanoscopic field heterogeneity. We further extend our previous picosecond laser far-field optical power limiting and pump-probe characterization to probe and control the ultrafast near-field optical response, where the positioning of the tip, polarization of incident light, and sample orientation can be tuned to give quantum state hybridization control and to perform qubit phase rotation operations.