Abstract
Twin-field quantum key distribution (TF-QKD) can beat the linear bound of repeaterless QKD systems. After the proposal of the original protocol, multiple papers have extended the protocol to prove its security. However, these works are limited to the case where the two channels have equal amount of loss (i.e. are symmetric). In a practical network setting, it is very likely that the channels are asymmetric due to e.g. geographical locations. In this paper we extend the ‘simple TF-QKD’ protocol to the scenario with asymmetric channels. We show that by simply adjusting the two signal states of the two users (and not the decoy states) they can effectively compensate for channel asymmetry and consistently obtain an order of magnitude higher key rate than previous symmetric protocol. It also can provide 2–3 times higher key rate than the strategy of deliberately adding fibre to the shorter channel until channels have equal loss (and is more convenient as users only need to optimize their laser intensities and do not need to physically modify the channels). We also perform simulation for a practical case with three decoy states and finite data size, and show that our method works well and has a clear advantage over prior art methods with realistic parameters.
Highlights
Quantum key distribution (QKD) is proven to provide information-theoretic security to two communicating parties
(2) The X basis QBER will increase with channel asymmetry, and greatly reduce the key rate of Twin-Field quantum key distribution (TF-QKD) if no compensation is performed - on the other hand, the Z basis gain is little affected by channel asymmetry
Asymmetry will only affect the performance of the protocol - asymmetric channels will result in higher QBER and subsequently lower key rate, and asymmetric intensities can compensate for channel asymmetry and enable high key rate for the protocol even when channels are highly asymmetric
Summary
Quantum key distribution (QKD) is proven to provide information-theoretic security to two communicating parties. Instead of using two-photon interference like in measurement-device-independent (MDI) QKD [2], TFQKD makes use of single-photon interference to generate keys, and on average only one photon passes through either Alice’s or Bob’s channel - which allows to key rate to scale with transmittance over only half the distance between Alice and Bob. does TF-QKD surpass the repeaterless bound, it provides security against attacks on measurement devices [3] similar to MDI-QKD. We will apply our method to TF-QKD and show that it is possible to obtain good key rate through asymmetric channels by adjusting Alice’s and Bob’s intensities - we will show that, Alice and Bob only need to adjust their signal intensities to obtain optimal performance. We provide a detailed discussion about the physics behind the security of our asymmetric protocol
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Published Version
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