Heterogenous quantum interfaces for metropolitan-scale quantum networks

Currently, entanglement between different stationary qubits is mostly restricted to qubits of the same type in close proximity. While this simplifies the interconnection substantially and allows implementation of more complex quantum information processing protocols, it cannot bridge the larger distances, which requires photons with a wavelength matched to the transparency windows of optical fibers. First demonstrations of such transfers have been reported, but the interconnection of different species is still outstanding. One part of the challenge here is to not only match the wavelengths of photons emitted by different systems, but also to adapt their coherence time or bandwidth. In this study, we aim to transfer quantum information between two distinct stationary qubits: Silicon Vacancy (SiV) centers and neutral Rubidium atoms trapped in an optical dipole trap. The initial step in this transfer process involves a spontaneous emission, which entangles a photon with the respective stationary systems. A wavelength conversion process then converts the visible-range wavelengths to the telecom band, enabling frequency match between the different systems. We present the results of the wavelength conversion using PPLN waveguides, followed by tests for coherence and entanglement preservation.