A protocol of quantum key distribution without relying on information-disturbance trade off

Abstract

We propose a new scheme of quantum key distribution (QKD) called the round-robin differential-phase-shift (RRDPS) protocol, which is based on a principle entirely different from the conventional QKD protocols based on the information-disturbance trade off. In the RRDPS protocol, the amount of privacy amplification is essentially constant and there is no need to change it according to the observed amount of disturbance. This means that it is hard for an eavesdropper to guess the bit value regardless of the amount of disturbance she has caused. The new scheme has a better tolerance on bit errors and is free from the cost of monitoring eavesdropping attempts. In contrast to the conventional QKD schemes, the amount of privacy amplification is the same even if the quality of the transmission channel becomes poorer and the bit error rate increases. This leads to a higher bit error threshold, typically over 30% and with no theoretical bound less than 50%. The fact that the protocol does not require precise estimation of the amount of signal disturbance is advantageous when the finite-key effect is taken into account; the RRDPS protocol can produce a key even when the total number of transmitted bits is small.