Spatial–spectral mapping to prepare frequency entangled qudits

Abstract

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-to-operate 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 phase-matching 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.

Controllable transitions among phase-matching conditions in a single nonlinear crystal

“…This wavelength range, particularly around 405 nm, holds significant importance for entangled photon sources, being widely utilized not only in the laboratory [33][34][35] but also in satellite-based endeavors [36] . The popularity of this wavelength range can be attributed to the maturity of blue-violet laser technology, which allows the production of high-power blue lasers at relatively affordable costs [37][38][39][40][41][42] . The identification of three phase-matching conditions in this study holds the potential to advance the quantum applications of entangled photon sources utilizing blue lasers and PPKTP crystals.…”