• Measurement-device-independent quantum key distribution enhances the implementation security. In this tutorial talk, I shall review its security proof and various optical implementations, highlighting the twin-field and mode-pairing schemes that offer quadratic key-rate improvement.
Abstract Device-independent quantum key distribution (DI-QKD) provides the gold standard for secure key exchange. Not only does it allow for information-theoretic security based on quantum mechanics, but it also relaxes the need to physically model the devices, thereby fundamentally ruling out many quantum hacking threats to which non-DI QKD systems are vulnerable. In practice though, DI-QKD is very challenging. It relies on the loophole-free violation of a Bell inequality, a task that requires high quality entanglement to be distributed between distant parties and close to perfect quantum measurements, which is hardly achievable with current technology. Notwithstanding, recent theoretical and experimental efforts have led to proof-of-principle DI-QKD implementations. In this article, we review the state-of-the-art of DI-QKD by highlighting its main theoretical and experimental achievements, discussing recent proof-of-principle demonstrations, and emphasizing the existing challenges in the field.
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.
A recently proposed fully passive quantum key distribution (QKD) removes all source modulator side channels. In this work, we combine fully passive sources with measurement-device-independent (MDI) QKD to simultaneously remove side channels from source modulators and detectors. We show a numerical simulation of passive MDI QKD, and we obtain an acceptable key rate while achieving much better implementation security, as well as ease of implementation, compared with a recently proposed fully passive twin-field QKD, paving the way towards more secure and practical QKD systems. We prove that a fully passive protocol is compatible with MDI QKD and we propose a novel idea that can improve the sifting efficiency.