  Optical cavities can enhance and control light-matter interactions. This has
recently been extended to the nanoscale, and with single emitter strong
coupling regime even at room temperature using plasmonic nano-cavities with
deep sub-diffraction-limited mode volumes. However, with emitters in static
nano-cavities, this limits the ability to tune coupling strength or to couple
different emitters to the same cavity. Here, we present tip-enhanced strong
coupling (TESC) spectroscopy, imaging, and control. Based on a nano-cavity
formed between a scanning plasmonic antenna-tip and the substrate, by
reversibly and dynamically addressing single quantum dots (QDs) we observe mode
splitting > 160 meV and anticrossing over a detuning range of ~100 meV, and
with sub-nm precision control over the mode volume in the ~1000 nm^3 regime.
Our approach, as a new paradigm of nano-cavity quantum-electrodynamics
near-field microscopy to induce, probe, and control single-emitter plasmon
hybrid quantum states, opens new pathways from opto-electronics to quantum
information science.
