Experimental passive round-robin differential phase-shift quantum key distribution.

In quantum key distribution (QKD), the bit error rate is used to estimate the information leakage and hence determines the amount of privacy amplification-making the final key private by shortening the key. In general, there exists a threshold of the error rate for each scheme, above which no secure key can be generated. This threshold puts a restriction on the environment noises.

Experimental demonstration of counterfactual quantum communication.

Quantum effects, besides offering substantial superiority in many tasks over classical methods, are also expected to provide interesting ways to establish secret keys between remote parties. A striking scheme called "counterfactual quantum cryptography" proposed by Noh [Phys. Rev.