High-Efficiency Lightweight Quantum Key Agreement Scheme Based on Bell State Entanglement

To address the low qubit efficiency and high user-side operational complexity in existing quantum key agreement schemes, this paper proposes a high-efficiency and lightweight quantum key agreement scheme based on Bell states. The scheme is constructed upon a time-reversed EPR architecture, in which a quantum server performs entangled-state preparation and Bell state measurement. Furthermore, a bidirectional decoy photon mechanism is incorporated into the architecture to achieve eavesdropping detection. By exploiting the completeness and orthogonality of the Bell basis, the scheme introduces an encoding mechanism based on local Pauli operations, enabling a single Bell state to carry 2 bits of key information and thereby realizing dense coding, which improves qubit efficiency. Meanwhile, users are only required to perform single-qubit operations, which reduces the quantum operational requirements on the user side. Based on the properties of Bell states, this paper derives the mapping relationship between local Pauli operations and Bell state measurement outcomes. Experimental results on the SpinQ Gemini quantum computing platform are consistent with the theoretical analysis, verifying the feasibility of the proposed scheme. In addition, security analysis shows that, owing to the bidirectional decoy photon mechanism, the scheme can resist various quantum attacks. The proposed scheme combines high efficiency with a lightweight implementation, reducing quantum hardware requirements on the user side and network deployment costs, thereby providing a cost-effective solution for practical quantum key agreement.