Interactions between light and matter lie at the heart of optical communication and information processing. Nanophotonic devices enhance light-matter interactions by confining photons to small mode volumes, enabling devices to operate at significantly lower energies.  In the strong coupling regime these interactions are sufficiently large to generate a nonlinear response with a single photon, an essential component for quantum information processing applications.  In this talk I will describe our effort to generate strong photon-photon interactions by coupling spin to light using nanophotonics. I will discuss an experimental demonstration of a quantum transistor, a fundamental building block for quantum computers and quantum networks, using a single electron spin that strongly interact with light through a nanophotonic cavity.  This device enables the spin to switch a single photon, and a single photon to flip the spin. Using the spin as an ancilla memory, we are able to switch a strong optical field with more than 20 photons using just a single photon as a control signal. Finally, I will discuss our recent effort to extend our results into the telecommunication wavelengths, and to improve the efficiency and scalability of the structure in order to attain integrated multi-dot devices on a single chip.