Abstract
Quantum key distribution (QKD) promises provably secure communications. In order to improve the secret key rate, combining a biased basis choice with the decoy-state method is proposed. Concomitantly, there is a basis-independent detection efficiency condition, which usually cannot be satisfied in a practical system, such as the time-phase encoding. Fortunately, this flaw has been recently removed theoretically and experimentally in the four-intensity decoy-state BB84 QKD protocol using the fact that the expected yields of single-photon states prepared in two bases stay the same for a given measurement basis. However, the security proofs do not fully consider the finite-key effects for general attacks. In this work, we provide the rigorous finite-key security bounds in the universally composable framework for the four-intensity decoy-state BB84 QKD protocol. We build a time-phase encoding system with 200 MHz clock to implement this protocol, in which the real-time secret key rate is more than 60 kbps over 50 km single-mode fiber.
Highlights
Encryption is an important foundation for ensuring information security
To further increase the key rate, combining a biased basis choice with the decoystate method is proposed [19,20,21] by an additional basisindependent detection efficiency condition that usually cannot be satisfied and brings security loopholes in the practical system
A four-intensity decoy-state BB84 Quantum key distribution (QKD) [22] uses a subtle fact, the expected yields of single-photon component prepared in two bases are the same for a given measurement basis, to remove basisindependent detection efficiency condition and provide a higher key rate
Summary
Encryption is an important foundation for ensuring information security. With the rapid development of quantum computing technology, current public-key encryption systems will be seriously threatened. To further increase the key rate, combining a biased basis choice with the decoystate method is proposed [19,20,21] by an additional basisindependent detection efficiency condition that usually cannot be satisfied and brings security loopholes in the practical system. A four-intensity decoy-state BB84 QKD [22] uses a subtle fact, the expected yields of single-photon component prepared in two bases are the same for a given measurement basis, to remove basisindependent detection efficiency condition and provide a higher key rate. We exploit the autonomous time-phase encoding system to experimentally realize this protocol and continuously distribute secret keys for two months, where there is a 1.8 dB difference between the efficiency of two bases at the receiver. The real-time extracted secret key rate is more than 60 kbps over 50 km single-mode fiber and can be secure against coherent attacks in the universally composable framework [27]
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