Source-independent quantum key distribution without pre-sending entanglement

Quantum key distribution (QKD) theoretically offers information-theoretic security. The prevailing approach is the prepare-and-measure BB84 protocol, which implements QKD using a conventional laser rather than a single-photon source via the decoy-state method. However, side-channel attacks targeting sources severely threaten system security. Despite extensive efforts, including a fully passive scheme, this vulnerability persists even with a perfect single-photon source. Here, we propose a source-independent (SI) QKD protocol that resolves all known and unknown source-side attacks without pre-sending an entanglement source. Aligning with advances in quantum light sources, our protocol simultaneously doubles the transmission distance while remaining robust against imperfection of source. Theoretical analysis shows that non-classical light source provides practical security advantages unattainable with a conventional laser.