Entangled Photon-Pair Emission in Waveguide Circuit QED from a Cooper Pair Splitter

As a waveguide circuit QED architecture, we investigate theoretically the single-photon pair emission of a Cooper pair splitter composed of two double quantum dots, each coupled to a microwave transmission line. We find that this system can generate frequency-entangled photon pairs in the left and right transmission lines, specifically a superposition of two photon wave packets at different frequencies. The frequency entanglement of the two photons arises from the particle-hole coherent superposition (i.e., Andreev bound states) involving the delocalized entangled spin singlet. We also estimate a lower bound for the efficiency of entangled photon-pair generation, accounting for the presence of nonradiative processes such as phonon emissions. Our proposal is realistic and achievable with state-of-the-art techniques in quantum microwave engineering with electostatically defined semiconducting quantum dots.