  Strong light-matter coupling manifested by vacuum Rabi splitting has
attracted tremendous attention due to its fundamental importance in cavity
quantum-electrodynamics research and great potentials in quantum information
applications. A prerequisite for practical applications of the strong coupling
in future quantum information processing and coherent manipulation is an
all-solid-state system exhibiting room-temperature vacuum Rabi splitting with
active control. Here we realized such a system in heterostructure consisting of
monolayer WS2 and an individual plasmonic gold nanorod. By taking advantage of
both of the small mode volume of the nanorod and large binding energy of the
WS2 exciton, giant vacuum Rabi splitting energies of 91 meV ~ 133 meV can be
obtained at ambient conditions, which only involve 5 ~ 18 excitons. The vacuum
Rabi splitting can be dynamically tuned either by electrostatic gating or
temperature scanning. These findings could pave the way towards active quantum
optic devices operating at room temperature.
