Probing Quantum Nature of Quasi-Classical States in an Interferometric setting.

Using quasi-classical states (coherent states) from a continuous wave (CW) source, we have been able to observe purely quantum mechanical effects. Our approach is based on the uniform randomization of the temporal phase of these states in an interferometric setting. We call such states as Phased Randomized Coherent States (PRCSs). First, we experimentally realized two-photon bunching and its complementary Hong-Ou-Mandel (HOM) effect. Then, after this quantum signature, we extend the idea to the probe of the Bell inequality. We successfully observed the violation from the CHSH form of the inequality and hence confirmed the existence of entanglement through our approach. In these works, the only degree of freedom involved was polarization. However, we aimed afterwards to add orbital angular momentum (OAM) to this toolbox and examine if we can transfer quantum information using OAM through coherent states from a CW source. Once again, this approach correctly matched with theoretical predictions resulting in two-photon bunching experimentally. Therefore, we believe that quasi-classical states can be utilized to a more diverse set of experiments in the domain of quantum optics and quantum information. One main benefit of these states is their photon rate. They do not have any shortage in photon numbers and thus they do not face scalability problem as much as the other single-photon sources do.