Reference-frame-independent quantum key distribution with passive light source monitoring

The quantum key distribution (QKD) allows two legitimate parties, Alice and Bob, to share secure keys based on the laws of physics. security BB84 protocol was proven in theory by many scientists. In QKD protocol, X-basis Z-basis used for encoding at Alice's end Bob's constitute their respective reference frames. Normally, Bob need same frame. If frames are inconsistent, system will not function properly. most widely method today is active real-time calibration both communication using classical communication. However, calibrating frame consumes a lot time thus reduces efficiency whole process, increasing complexity cost system, may even have some risks.In order avoid operation frames, reference-frame-independent (RFI-QKD) proposed. RFI-QKD immune effects slowly changing drift, requiring that only one set bases should be aligned remaining sets can change channel. real basis vectors always found maintain stable alignment.However, assumptions made sources reported works, i.e., with trusted fixed photon-number (PND), which usually satisfied practical implementations. Those unreasonable inevitably compromise systems. To solve problem, this paper, we present passive light source monitoring (PLSM) scheme RFI-QKD, accomplished module consisting beam splitter detectors side. Through PLSM module, get four events local then precisely estimate bounds distributions. Specifically, employ three-intensity decoy-state-based as an example illustration. Compared original our passively monitor PND has more advantages when fluctuations, finite-size deflection angles taken into account.