Revealing the quantum nature of quasi-classical states carrying orbital angular momentum

The observation of the quantum nature of quasi-classical states is of utmost importance since these states are realistic sources of radiation and do not have any shortage in photon numbers. Therefore, they do not face the scalability problem as much as single-photon sources do, which makes them much more robust against photon loss. The physical dynamics of these states predict that the quantum aspects of a continuous source can be observed in the weak limit. Yet, since these states are superposition of different particle states of radiation, we need post-selection to achieve this result. Practically, even after the post-selection, this high photon rate has not been observed. In this manuscript, we attempt to demonstrate that quasi-classical states supplemented with orbital angular momentum (OAM) can deliver a significant high photon rate in producing quantum signature alluding to this fact that OAM is indeed an intrinsic property of light at the quantum level as well. Through our experiment, we realize two-photon bunching with the projection of OAM from a continuous wave source. We observe that this approach can produce the result from a single-photon source with the high accuracy after the post-selection. In fact, since there is no interaction with matter, the post-selected photon rate from this approach can be considered as an upper bound for the single-photon generation based on the input power. This work is a step forward toward a more diverse and practical use of quasi-classical states in the domain of quantum optics and quantum information.