Abstract
The ultimate aim of quantum key distribution (QKD) is improving the transmission distance and key generation speed. Unfortunately, it is believed to be limited by the secret-key capacity of quantum channel without quantum repeater. Recently, a novel twin-field QKD (TF-QKD) is proposed to break through the limit, where the key rate is proportional to the square-root of channel transmittance. Here, by using the vacuum and one-photon state as a qubit, we show that the TF-QKD can be regarded as a measurement-device-independent QKD (MDI-QKD) with single-photon Bell state measurement. Therefore, the MDI property of TF-QKD can be understood clearly. Importantly, the universal security proof theories can be directly used for TF-QKD, such as BB84 encoding, six-state encoding and reference-frame-independent scheme. Furthermore, we propose a feasible experimental scheme for the proof-of-principle experimental demonstration.
Highlights
The longest transmission distance of quantum key distribution (QKD) has been implemented over 421 km with ultralow-loss optical fiber[4] and 1200 km satellite-to-ground[5]
We prove that twin-field QKD (TF-QKD) can be seen as a special type of measurement-device-independent QKD (MDI-QKD)
The TF-QKD inherits all positive features of MDI-QKD and increases the key rate a lot to break through the linear key rate bound
Summary
The longest transmission distance of QKD has been implemented over 421 km with ultralow-loss optical fiber[4] and 1200 km satellite-to-ground[5]. Improving the transmission distance and key rate are the most important tasks of QKD research. This task has been proven impossible beyond a certain limit without quantum repeaters[6,7]. In the TF-QKD, a pair of optical fields are generated respectively at locations of two remote parties and sent to the untrusted center to implement single-photon detection. One can consider that the untrusted center performs the single-photon Bell state measurement (BSM) while Alice and Bob prepare quantum state in the complementary bases. Combining the decoy-state method[25,26,27], we could acquire the tight key rate formula of TF-QKD with BB84 encoding[1], six-state encoding[28] and reference-frame-independent (RFI)[29] scheme
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