A Quantum-Bit Encoding Converter

To advance quantum information technologies, many quantum devices and protocols are being developed based on a variety of physical systems, including photons, atoms, mechanical oscillators, solidstate or superconducting devices. Implementations do not only choose between the vast landscape of platforms but also between favoured degrees of freedom and the advantages they can provide [1]. The capability to convert between different encodings is key to linking separate devices in a future heterogeneous quantum network [2]. Such a process is challenging as it requires one to preserve fragile quantum superpositions during the transcoding while functioning as a black box with propagating input and output qubits, a requisite that demands the process to be heralded and free of post-selection. Here we report the experimental realization of such a converter in the optical domain [3], [4], schematically shown in Fig. 1a.