  We demonstrate strong light-matter interaction at ambient conditions between
a ladder-type conjugated polymer and the individual modes of a vertical
microcavity with tunable resonance frequencies. Zero-dimensional
wavelength-scale confinement for the polaritons is achieved through a
sub-micron sized Gaussian defect, resulting in a vacuum Rabi splitting of the
polariton branches of 2g = 166 meV. By placing a second Gaussian defect nearby,
we create a polaritonic molecule with tunnel coupling strength of up to 2J ~ 50
meV. This platform enables the creation of tailor-made potential landscapes
with wavelength-scale dimensions and tunable coupling strengths beyond the
thermal energy, opening a route towards room-temperature polariton-based
quantum simulators.
