Serrodyne transceiver for entangled quantum and coherent co-transmission on a single frequency channel

Fiber optic networks are essential for managing global data traffic, and future telecommunications will require integrating quantum information for applications like quantum key distribution. Encoding quantum information in the frequency domain offers a scalable solution to quantum information transmission. Although the integration of frequency-entangled photons with coherent information transmission is possible through spectral multiplexing, more resource-efficient methods are necessary. We present and experimentally validate a transceiver concept that transmits coherent and frequency-entangled photons within a single frequency channel using the serrodyne technique via electro-optic phase modulation. This approach exploits distinct photon dynamics to enable temporal multiplexing and signal separation. We demonstrate preserved entanglement through the serrodyne transceiver despite coherent light, showing potential for efficient bandwidth use in hybrid quantum-coherent networks.