Towards Practical and Secure Quantum Communication

Objective

Cryptography is vital in the digital age, underpinning secure communication and random number generation. Traditional methods, however, cannot guarantee security against adversaries with sufficient computational power. Quantum information science offers a paradigm shift through quantum random number generators (QRNGs) and quantum key distribution (QKD), enabling security based on the physical laws of nature rather than technological limitations. In particular, device-independent approaches ensure ultimate security without requiring detailed knowledge of the internal workings of the devices. However, designing quantum cryptographic systems that are both ultimately secure and practical under real-world conditions still remains a critical challenge. This proposal addresses this challenge by bridging ultimate security frameworks based on device independence with practical implementations. The key idea is to tailor security assumptions to the strengths of specific platforms, while retaining strong security guarantees. For example, photonic platforms offer high precision in photon-number statistics, which justifies relaxing device-independent assumptions for state preparations. Instead, the protocol can incorporate well-motivated energetic assumptions, enabling a more realistic yet still secure implementations. This two-year project begins addressing ultimate security of QRNGs, quantifying the threat of quantum attacks and developing novel numerical tools to certify the amount of randomness in their presence. The second phase addresses the balance between security and implementability of QKD protocols, introducing key elements such as multiple preparation choices and energetic assumptions, for practical long-distance secure communication. By leveraging accessible physical systems and realistic assumptions, the project aims to deliver feasible QRNG and QKD solutions, bridging theory and experiment towards practical and secure quantum cryptography.