Generation of hybrid entanglement of light

Entanglement between quantum and classical objects is of special interest in the context of fundamental studies of quantum mechanics and potential applications for quantum information processing. In quantum optics, single photons are treated as light quanta while coherent states are considered the most classical of pure states. Recently, entanglement between a single photon and a coherent state in a free-travelling field was identified as a useful resource for optical quantum information processing. However, the extreme difficulty involved in generating such states was highlighted, as it requires clean cross-Kerr nonlinearities. Here, we devise and experimentally demonstrate a scheme to generate such hybrid entanglement by implementing a superposition of two distinct quantum operations. The generated states clearly show entanglement between the two different types of states. Our work opens the way to the generation of hybrid entanglement of greater size and the development of efficient quantum information processing using a new type of qubit.