Twin-field quantum key distribution over 830-km fibre

Quantum key distribution surpassing the repeaterless rate-transmittance bound without global phase locking

“…The experiment detail is shown in Appendix F. Based on the experimental data, we find that the phase coherence can be maintained well in a time interval of 5 µs, correspond to l = 3000 ∼ 4000. If we apply the state-of-the-art optical communication system with the repetition rate of 4 GHz [36], we can realize a pairing interval over l = 20000. As an extra remark, our current discussion on the implementation of the mode-pairing scheme is based on the multiplexing of optical timebin modes.…”

“…From Figure 24, we can see that the error rate is stable when the pairing length is up to 3000 ∼ 4000. If we further enhance the system frequency to 4 GHz [36], we are able to achieve a maximal pairing length of 20000. In this way, the performance of the mode-pairing scheme can surpass the repeaterless key-rate bound.…”

“…In a typical 200-km fibre with a telecommunication frequency of 1550 nm, the phase of a coherent state is susceptible to small fluctuations in the optical transmission time (∼ 10 −15 s), optical length (∼ 200 nm) and light frequency ( ∼ 100 kHz). Recently, experimentalists have made great efforts to demonstrate high-performance in one-mode schemes, utilising high-end technologies to perform a precise control operation to stabilise the global phase by locking the frequency and phase of the coherent states [29][30][31][32][33][34][35][36]. However, this significantly increases the experimental difficulty and undermines the applicability of one-mode schemes in real life.…”

Universal approach to sending-or-not-sending twin field quantum key distribution

“…This makes it possible to greatly improve the performance of QKD at longer distance regimes. Following this protocol, many variants of TFQKD were proposed [34][35][36][37][38][39][40][41] and some experiments of TFQKD were demonstrated [42][43][44][45][46][47][48][49][50][51]. Among those protocols, the sending-or-not-sending (SNS) protocol [34] has the advantages of MDI security under coherent attacks and it can tolerate large misalignment error.…”

Experimental twin-field quantum key distribution with flawed and correlated sources

“…Another significant approach towards the security of practical QKD is measurement-device-independent QKD [17], as well as its single-photon interference version twin-field (TF) QKD [18], which closes all attacks on measurement devices, is practical [19][20][21][22][23][24][25][26], and breaks the transmission record using current technologies [27][28][29][30][31]. Thus, source flaws present a loophole towards securing QKD with imperfect devices.…”