Efficient on-chip platform for coherent light-matter coupling using bound states in the continuum

Storing and retrieving photonic qubits are key functionalities in future optical quantum networks, and integrating scalable optical-memory units is crucial as these networks expand. However, attempts to combine silicon photonics and erbium ions for telecom memories, without losing the scalable and low-loss properties of silicon chips, face challenges because of limited light-matter interactions and potential extra decoherence. Here, we present an efficient silicon-chip platform using bound states in the continuum to overcome these limitations. In addition to a low propagation loss of 0.5 ± 0.5 decibels per centimeter, our experiments demonstrate an order-of-magnitude enhancement in light absorption compared to previous traditional silicon hybrid designs. Using these properties, we demonstrated photon echoes in our waveguide structures, revealing a coherence time of 2.6 ± 0.6 microseconds at zero magnetic field, closely matching that of bulk crystals. These characteristics make the bound state in the continuum platform a promising candidate for realizing integrated optical memories for quantum network applications.