Asymmetric bidirectional controlled assisted cloning

Abstract

We first construct a seven-qubit maximally entangled state by using Hadamard gates and controlled-NOT gates, and its method is enlightening for generating other quantum entanglements. Then, using this entangled state as a quantum channel, we propose a bidirectional scheme for cloning an unknown two- and single-qubit states with help of the state preparer and the permission of the controller. The first stage of this scheme requires teleportation, where Alice transmits an unknown two-qubit state to Bob; at the same time, Bob conveys an unknown single-qubit state to Alice under the concession of the controller. In the second stage, based on the results of the preparer’s two- and single-qubit measurements, Alice is able to clone an original unknown two-particle state and its orthogonal complementary state; meanwhile, Bob can also clone an original unknown single-particle state and its orthogonal complementary state. By replacing the above unknown two-qubit state with an arbitrary unknown two-qubit state, we obtain a more general asymmetric controlled scheme for bidirectional assisted cloning. Furthermore, by replacing the above quantum channel with a seven-qubit non-maximally entangled state and replacing the Bell-state measurement in the aforementioned schemes with a generalized Bell-state measurement, we provide two extension schemes of the above two schemes. At last, by analyzing the measurement ways and adding the number of preparers and controllers, we obtain several evolutionary ideas for the proposed scheme, which not only displays the synchronization and flexibility of multi-party assisted cloning, but also provides multiple application scenarios for quantum communication.