We will model and analyze ultra-fast, all-optical switches operating at record low energy levels as well as few and single-photon switching with applications to quantum information technology (QIT). The analysis will be based on a powerful and versatile model for the description of lightmatter interaction in optical cavities and waveguides in photonic crystals (PCs), and we will test the model using advanced numerical methods as well as by direct comparison with experiments. In this way we will identify design trade-offs and calculate optimum device parameters.