Practical Long‐Distance Measurement‐Device‐Independent Quantum Key Distribution By Four‐Intensity Protocol

Abstract

Quantum key distribution (QKD) can provide unconditionally secure private communication between two remote parties. The measurement-deviceindependent (MDI) QKD can remove all security loopholes in measurement devices. However, the large value of the observed error rate in X basis has severely limited its key rate. The four-intensity protocol with fully optimized post data processing can improve the key rate and distance of MDI-QKD effectively. In this paper, the four-intensity MDI-QKD protocol is reviewed. In the four-intensity protocol, each of Alice and Bob uses one intensity in Z basis and three intensities in X basis (normally including one vacuum). This improves the number of effective bits in Z basis. The joint mathematical treatment for statistical fluctuation and the parameter scan pointing directly to the final key rate are applied to reduce the effect of statistical fluctuation. The double scanning method further improves the key rate and the secure distance of the four-intensity protocol. These have greatly improved the performance of the protocol with finite-key effects. So far, many MDI-QKD experiments are based on the four-intensity protocol. The successful results of these experiments have clearly shown the superiority of the four-intensity protocol in practical long-distance MDI-QKD.

Deploying an Inter‐European Quantum Network

“…Possible improvements include a real-time optical switch, which should be preferred for nodes where a transmitter serves more than one user instead of our beam-splitter, and a real-time quantum random number generator (QRNG), which should be used in all Alice's devices. Moreover, future implementations of the quantum network will be using more advanced quantum key distribution protocols, such as measurement device independent (MDI) [34] and/or twin-field quantum key distribution protocol, [35] which exploit an untrusted user, usually located in the middle of the communication link, to establish a secure key rate.…”

Analysis of the Effects of the Two-Photon Temporal Distinguishability on Measurement-Device-Independent Quantum Key Distribution

“…In practical situations, the length of the raw key is finite, which induces a statistical fluctuation in parameter estimation. Here, we refer to [22] to calculate the effect of finite size. The expected lower and upper bounds of ω…”

“…where cor  is the failure probability of error correction,   and  are the coefficients while using the chain rules of smooth min-and max-entropy, PA  is the failure probability of privacy amplification [22].…”

“…It should be noted that the calculation results we obtained are based on the three-intensity model. However, the fourintensity model [21,22] with better performance have been proposed and implemented. It was suggested in fourintensity model will improve the performance for smaller number of pulses.…”

“…References [13][14][15] analyzed decoy-state MDI-QKD with an infinite key length, and the decoy-state MDI-QKD of a finite key length with statistical fluctuation was also analyzed [15][16][17][18][19][20][21]. References [20][21][22] proposed more the efficient four-intensity with joint constraints for statistical fluctuation protocol. The MDI-QKD protocol has been successfully implemented in the laboratories and field [23][24][25][26][27][28].…”