Decorrelated PDC source at telecom wavelengths with identical signal and idler

Parametric downconversion (PDC) in waveguides offers compact setups and high design flexibility in terms of the temporal-spectral properties of the generated photon pairs. It is thus a versatile source for a large number of quantum states with applications in quantum communication or quantum networks. One key element of those systems is the interference of quantum states from different, independent sources at e.g. beamsplitters with high visibility. Those sources should therefore not only meet demands of brightness and efficiency but also generate pure photons with identical properties, in particular in the frequency degree of freedom. In the context of PDC, such states are called decorrelated as there are no spatio-temporal correlations between signal and idler. They can be realized in bulk materials and waveguides by tailoring the pump and dispersion properties. The first source of this kind was demonstrated in bulk KDP at near-infrared wavelengths. For telecom wavelengths a bright, decorrelated source in a waveguide structure was realized in periodically poled KTP. However, in these sources the spectral properties of the signal and idler photons are still dissimilar.