The security of quantum secret sharing based on entanglement swapping is revisited and a participant attack is presented. In this attack two dishonest agents together can illegally recover the secret quantum state without the help of any other controller, and it will not be detected by any other users. Furthermore, by modifying the distribution process of particles and adding a detection step after each distribution process, we propose an improved protocol which can resist this kind of attack.
A new protocol for the anonymous communication of quantum information is proposed. The anonymity of the receiver and the privacy of the quantum information are perfectly protected except with exponentially small probability in this protocol. Furthermore, this protocol uses single photons to construct anonymous entanglement instead of multipartite entangled states, and therefore it reduces quantum resources compared with the pioneering work.
The discrimination of quantum operations plays a key role in quantum information and computation. Unlike discriminating quantum states, it has some special properties which can be carried out in practice. In this paper, we provide a general description of discriminating quantum operations. Concretely speaking, we describe the distinguisha- bility between quantum operations using a measure called operator fidelity. It is shown that, employing the theory of operator fidelity, we can not only verify some previous results to discriminate unitary operations, but also exhibit a more general discrimination condition. We further apply our results to analysing the security of some quantum cryptographic protocols and discuss the realization of our method using well-developed quantum algorithms.
