  The advancement of quantum photonic technologies relies on the ability to
precisely control the degrees of freedom of optically active states. Here, we
realize real-time, room-temperature tunable strong plasmon-exciton coupling in
2D semiconductor monolayers enabled by a general approach that combines strain
engineering plus force- and voltage-adjustable plasmonic nanocavities. We show
that the exciton energy and nanocavity plasmon resonance can be controllably
toggled in concert by applying pressure with a plasmonic nanoprobe, allowing in
operando control of detuning and coupling strength, with observed Rabi
splittings >100 meV. Leveraging correlated force spectroscopy,
nano-photoluminescence (nano-PL) and nano-Raman measurements, augmented with
electromagnetic simulations, we identify distinct polariton bands and dark
polariton states, and map their evolution as a function of nanogap and strain
tuning. Uniquely, the system allows for manipulation of coupling strength over
a range of cavity parameters without dramatically altering the detuning.
Further, we establish that the tunable strong coupling is robust under multiple
pressing cycles and repeated experiments over multiple nanobubbles. Finally, we
show that the nanogap size can be directly modulated via an applied DC voltage
between the substrate and plasmonic tip, highlighting the inherent nature of
the concept as a plexcitonic nano-electro-mechanical system (NEMS). Our work
demonstrates the potential to precisely control and tailor plexciton states
localized in monolayer (1L) transition metal dichalcogenides (TMDs), paving the
way for on-chip polariton-based nanophotonic applications spanning quantum
information processing to photochemistry.

Optics;Quantum Physics