Quantum key distribution:

The aim of quantum key distribution is to allow Alice and Bob to generate a secure private key that can be used for the one-time pad without having to meet privately. They will be able to accomplish this task by using quantum information. There are a few different schemes for doing this, and among them one of them is: BB84,which is Easy to implement, relatively hard to prove security.

For detailed explanation: https://arxiv.org/ftp/arxiv/papers/1409/1409.1452.pdf