Abstract
Twin-field quantum key distribution (TF-QKD) is proposed to achieve a remote key distribution with a maximum secure transmission distance up to over 500 km. Although the security of TF-QKD in its detection part is guaranteed, there are some remaining problems in the source part. The sending-or-not-sending (SNS) protocol is proposed to solve the security problem in the phase post-selection process; however, the light source is still assumed to be an ideal coherent state. This assumption is not satisfied in real-life QKD systems, leading to practical secure issues. In this paper, we discuss the condition that the photon number distribution (PND) of the source is unknown for the SNS protocol, demonstrate that the security analysis is still valid under a source with unknown PND, and show that with light source monitoring, the performance of the SNS protocol can remain almost unchanged.
Highlights
Quantum key distribution (QKD) provides a way for different communication parties to share a set of identical security keys [1,2]
Since the SNS protocol and the MDI protocol have the same structure in the intensity modulation part, the same light source monitoring (LSM) module can be added to the SNS protocol as shown in Figure 1, and with the extra LSM module, the same results can be obtained in the SNS protocol as follows [38]: single photon detector (SPD)
We analyze the security of the SNS protocol under UPC, and propose an LSM scheme to solve the unknown photon number distribution (PND) problem in the source part
Summary
Quantum key distribution (QKD) provides a way for different communication parties to share a set of identical security keys [1,2]. An exciting experimental work has shown that the transmission distance for TF-QKD can reach over 500 km in practice [28], showing that TF-type protocols can significantly improve the transmission distance with the currently available technology Among those TF-type protocols, the sending-or-not-sending (SNS) protocol proposed by. By analyzing the form of the prepared state in Eve’s view, it is shown that the security analysis in the SNS protocol is still valid without the coherent state assumption, and the final secret key rate can be derived naturally. By applying a light source monitoring (LSM) method proposed previously [37,38], all relevant parameters can be estimated compactly, the secret key rate of the SNS protocol under UPC can be obtained.
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