 quantum superposition is the foundation of quantum mechanics which allows for the interference of two identical particles through their indistinguishability. This phenomenon has been studied extensively since the 1980s to explore the complementary nature of quantum mechanics and its wave particle duality. In particular, Wheeler's delayed choice experiments have demonstrated this principle by showing how the violation of causal relations can be achieved with the use of a polarizing filter placed outside of the interferometer. We have experimentally demonstrated this effect using coherent photon pairs, where the violation of causality is due to the measurement of one particle's basis choice. This article was authored by Sang B Kim and B Young S Ham.