Splitting indistinguishable photons: Using linear optics to exceed the limit of photon blockade

Photon-photon interactions are an essential requirement of quantum photonic information processing. One way to generate these interactions is to utilize an atom strongly coupled to an optical cavity. This system exhibits the photon blockade effect which enables single photon switching and creation of non-classical light. But the nonlinear effects enabled by this system suffer from a fundamental time-bandwidth constraint. For the the simple case of splitting an input pulse of two indistinguishable photons, this constraint imposes a limit on the efficiency of routing photons to different output ports. We show that this limit can be exceeded by combining the strongly-coupled atom with linear optics. By optimizing the unitary of the linear optical transformation, we achieve improved splitting efficiency for both un-entangled and entangled photons. Our results suggest that it may be possible to improve the efficiency of nonlinear optical processes at the single photon level by making suitable use of linear optics. These results could have implications for quantum information processing with photons