Dynamical Control of Quantum Photon-Photon Interaction with Phase Change Material

Quantum interference can produce pivotal effective photon-photon interactions, enabling the exploration of various quantum information technologies that are beyond the possibilities of classical physics. While this effective interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, loss-induced nonunitary operations provide an alternative degree of freedom to control quantum interference. Here, we propose and experimentally demonstrate a concise yet powerful tool to unravel the essential features of quantum interference based on the phase change material vanadium dioxide. Since the insulator-metal transition in an elaborate vanadium dioxide thin film can create any desired particle exchange phase response, harnessing its phase transition would allow the dynamical control of photon-photon interaction such that the conventional coalescence and the anomalous anti-coalescence of photons can be continuously tuned. These results highlight an alternative approach for investigating quantum light-matter interactions, and facilitate nonunitary quantum interference for various quantum information processing tasks.