Abstract
As a variant of the twin-field quantum key distribution (TF-QKD), the sending-or-not twin-field quantum key distribution (SNS TF-QKD) is famous for its higher tolerance of misalignment error, in addition to the capacity of surpassing the rate–distance limit. Importantly, the free-space SNS TF-QKD will guarantee the security of the communications between mobile parties. In the paper, we first discuss the influence of atmospheric turbulence (AT) on the channel transmittance characterized by the probability distribution of the transmission coefficient (PDTC). Then, we present a method called prefixed-threshold real-time selection (P-RTS) to mitigate the interference of AT on the free-space SNS TF-QKD. The simulations of the free-space SNS TF-QKD with and without P-RTS are both given for comparison. The results showed that it is possible to share the secure key by using the free-space SNS TF-QKD. Simultaneously, the P-RTS method can make the free-space SNS TF-QKD achieve better and more stable performance at a short distance.
Highlights
Even with a malicious third party, Eve, the quantum key distribution (QKD) can provide theoretically secure secret keys between two legitimate users, Alice and Bob, based on the mechanics of quantum physics
The former one drops more sharply than the latter one after 190 km. The reason for this should be that after a certain point, as the channel transmittance increases with the transmission distance, it becomes more difficult to find the experiment round that satisfies the condition of the prefixed-threshold real-time selection (P-RTS), making the secure key rate (SKR) decrease more quickly
We presented a prefixed-threshold selection for the free-space SNS TFQKD, where we demonstrated the more accurate observable model for the free-space channel to calculate the SKR in the case of atmospheric turbulence (AT)
Summary
Even with a malicious third party, Eve, the quantum key distribution (QKD) can provide theoretically secure secret keys between two legitimate users, Alice and Bob, based on the mechanics of quantum physics. The QKD through free-space channels has become a hot topic, since it allows the users to communicate on mobile platforms, which is inconvenient for optical fiber quantum communication. It became more attractive when the Micius quantum experiment science satellite was launched [27,28]. The model of the free-space channel is required in order to mathematically describe the SKR performance of the free-space protocols with and without transmittance post-selection. Assume the two channels in the SNS TF-QKD protocol (Alice to Charlie and Bob to Charlie) are free-space channels and the fluctuations of their transmittances can be described by the log-normal model.
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