  Realizing nonlinear optical response in the low photon density limit in
solid-state systems has been a long-standing challenge. Semiconductor
microcavities in the strong coupling regime hosting exciton-polaritons have
emerged as attractive candidates in this context. However, the weak interaction
between these quasiparticles has been a hurdle in this quest. Dipolar excitons
provide an attractive strategy to overcome this limitation but are often
hindered by their weak oscillator strength. The interlayer dipolar excitons in
naturally occurring homobilayer MoS$_2$ alleviates this issue owing to their
hybridization of interlayer charge transfer exciton and intralayer B exciton.
Here we demonstrate the formation of dipolar exciton polaritons in bilayer
MoS$_2$ resulting in unprecedented nonlinear interaction strengths. A ten-fold
increase in nonlinearity is observed for the interlayer dipolar excitons
compared to the conventional A excitons. These highly nonlinear dipolar
polaritons will likely be a frontrunner in the quest for solid-state quantum
nonlinear devices.
