Spatial-spectral mapping to prepare frequency entangled qudits

Entangled qudits, the high-dimensional entangled states, play an important role in the study of quantum information. How to prepare entangled qudits in an efficient and easy-tooperate manner is still a challenge in quantum technology. Here, we demonstrate a method to engineer frequency entangled qudits in a spontaneous parametric downconversion process. The proposal employs an angle-dependent phasematching condition in a nonlinear crystal, which forms a classical-quantum mapping between the spatial (pump) and spectral (biphotons) degrees of freedom. In particular, the pump profile is separated into several bins in the spatial domain, and thus shapes the down-converted biphotons into discrete frequency modes in the joint spectral space. Our approach provides a feasible and efficient method to prepare a high-dimensional frequency entangled state. As an experimental demonstration, we generate a three-dimensional entangled state by using a homemade variable slit mask.

Automated summary

In this study, a method is proposed to prepare frequency entangled qudits through spontaneous parametric downconversion. The method utilizes an angle-dependent phasematching condition in a nonlinear crystal, establishing a classical-quantum mapping between the spatial and spectral degrees of freedom. By separating the pump profile into several bins in the spatial domain, discrete frequency modes are formed in the joint spectral space. This approach provides a feasible and efficient method to prepare high-dimensional frequency entangled states.