A high-dimensional quantum frequency converter.

In high dimensional quantum communication networks, quantum frequency converter (QFC) is indispensable as an interface in the frequency domain. For example, Much QFCs have been built to link atomic memories and fiber channels. However, Almost all of QFCs work in two-dimensional space. It is still a key challenge to construct a high quality QFC for some complex quantum states, e.g., a high dimensional single-photon state that refers to a qudit. Here, we firstly propose a high-dimensional QFC for orbital angular momentum-based qudit via sum frequency conversion with a flat top beam pump. As a demonstration, we realize quantum frequency conversions for a qudit from infrared to visible. Based on the qudit quantum state tomography, we get the fidelities are 98.29\%, 97.42\% and 86.75\% for qudit in 2,3, and 5 dimensions, respectively. The demonstration is very promising for constructing a high capacity quantum communication network.