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  Copyright: © Lehrstuhl für Lasertechnik LLT, RWTH Aachen University Overview of the planned heterogeneous quantum network between the RWTH Aachen University and the Fraunhofer ILT .

Currently, multiple physical platforms for the implementation of quantum devices are investigated. To make use of the individual advantages of each qubit type, they need to be connected in a heterogeneous quantum network. However, the frequency of the emitted photons is highly qubit-specific which violates the requirement for entanglement-generation. Furthermore, most qubits emit photons in the visible domain whereas optical fibers show minimal transmission losses at the telecom bands. Quantum frequency converters (QFCs) transform the frequency of the emitted photons without destroying their quantum state. This can be done by using three-wave mixing in nonlinear materials, e.g., in a waveguide. The aim is to minimize losses and noise whilst maximizing the conversion efficiency of the converter.

One focus of the quantum photonics group is building a heterogeneous fiber-based quantum network with entanglement between two qubits located at different buildings using a new, ultra-low loss waveguide-based QFC, as shown in figure 1. Furthermore, it is imperative to understand the relevant effects of fiber transmission on the qubit state. Therefore, entangled photon states will be sent over telecom fibers in future experiments at LLT and ILT. A dual fiber between the two institutes was provided by the RWTH to do further pre-testing for quantum communication in real-world conditions. One focus of the group is building a heterogeneous fiber-based quantum network with entanglement between two qubits located at different buildings using a new, ultra-low loss waveguide-based QFC, as shown in figure 1. Furthermore, it is imperative to understand the relevant effects of fiber transmission on the qubit state. Therefore, entangled photon states will be sent over telecom fibers in future experiments at LLT and ILT. A dual fiber between the two institutes was provided by the RWTH to do further pre-testing for quantum communication in real-world conditions.