  Strain engineering of perovskite quantum dots (pQDs) enables widely-tunable
photonic device applications. However, manipulation at the single-emitter level
has never been attempted. Here, we present a tip-induced control approach
combined with tip-enhanced photoluminescence (TEPL) spectroscopy to engineer
strain, bandgap, and emission quantum yield of a single pQD. Single
CsPbBr$_{x}$I$_{3-x}$ pQDs are clearly resolved through hyperspectral TEPL
imaging with $\sim$10 nm spatial resolution. The plasmonic tip then directly
applies pressure to a single pQD to facilitate a bandgap shift up to $\sim$62
meV with Purcell-enhanced PL quantum yield as high as $\sim$10$^5$ for the
strain-induced pQD. Furthermore, by systematically modulating the tip-induced
compressive strain of a single pQD, we achieve dynamical bandgap engineering in
a reversible manner. In addition, we facilitate the quantum dot coupling for a
pQD ensemble with $\sim$0.8 GPa tip pressure at the nanoscale. Our approach
presents a new strategy to tune the nano-opto-electro-mechanical properties of
pQDs at the single-crystal level.
