Valid conditions of the reference-frame-independent quantum key distribution

Abstract

Reference-frame-independent quantum key distribution (RFI QKD) has been experimental demonstrated to be robust for slowly varying reference frames. However, the protocol fails when reference frame varies rapidly. Furthermore, the rigorous definition of ``slowly varying'' is still not clear. Here we analyze the relationship of the related parameters and show how to adjust these parameters to make RFI QKD to be valid. This work provides a clear valid condition for the RFI QKD protocol and opens a way for researchers and users to handle the RFI QKD process practically.