  Interlayer excitons (IXs) in 2D semiconductors have long lifetimes and
spin-valley coupled physics, with a long-standing goal of single exciton
trapping for valleytronic applications. In this work, we use a nano-patterned
graphene gate to create an electrostatic IX trap. We measure a unique
power-dependent blue-shift of IX energy, where narrow linewidth emission
exhibits discrete energy jumps. We attribute these jumps to quantized increases
of the number occupancy of IXs within the trap and compare to a theoretical
model to assign the lowest energy emission line to single IX recombination.
