Efficient semiquantum key distribution without entanglement

Abstract

Semiquantum cryptography was proposed to deal with the issue that some players require only partial quantum power, such as preparing or measuring quantum states in the classical basis, which simplifies the implementations of quantum cryptography. However, the efficiency of the existing semiquantum cryptographic protocols was relatively low from a practical point of view. In this paper, we devise improved semiquantum key distribution (SQKD) protocols to improve the efficiency of SQKD protocols. Our improved SQKD protocols utilize the discarded X-SIFT bits in the previous SQKD protocols for improving the efficiency of previous SQKD protocols (Boyer et al. in Phys Rev Lett 99:140501, 2007; Zou et al. in Phys Rev A 79:052312, 2009). Besides, the efficiency of our new protocols can be made asymptotically close to 100% by letting players select their actions asymmetrically. We prove the information theoretical secure of the proposed SQKD protocols against the most general attacks. Our security proof is suitable for the single-state SQKD protocol (Zou et al. in Phys Rev A 79:052312, 2009).