Theoretical Study Of Foue-level Atom System Quantum Router Based On Coupled-resonator Wave Guides

The classical network promotes the progress of human society; allows everyone to stay at home while knowing everything in the world, which has brought great convenience to human life. However, the rapid development of quantum mechanics and quantum information urges people to set about to explore the unknown world, some scientists have focused on quantum network, because it plays an irreplaceable role in the future of information communication.Quantum network consists of quantum channel and quantum nodes, the quantum channel can be used as a channel for the transmission of quantum state, and the quantum node can store, process and transfer quantum information. In other words, the study of quantum node will be the first step to study the quantum network. As we all know, in a classical network, a router allows signal information to be correctly forwarded to a user. Similarly, a quantum router can also be used to send quantum information from one user to another. Recently,people in different systems have achieved the basic function of the quantum router, but a more perfect quantum router program is one of the urgent problems to be solved.In this paper, we mainly study the four-level atom system quantum router based on coupled-resonators waveguides. We use coupled-resonator waveguides as a quantum channel,and the four-level atom system is used as the medium to transmit the quantum information.Some of the main works are as follows:(1) We study the information-holding quantum router of single photons. In order to control the classical field, we utilize a four-level atom system that is embedded in two one-dimensional coupled-resonator waveguides, when the classical field is not absent, a single photon can transfer quantum information from one quantum channel to another; with a classical field opening, a single photon will be only reflected and transmitted in one channel.After that we calculate the fidelity of the atom before and after, we find that when the classical field is absent, the fidelity always is 1, when the classical field is not absent, the fidelity of the routing atom firstly decreases from the maximum value and then rises to the maximum value of 1 after a cycle of the time evolution. So, the quantum router showed by us can not only implement the routing functions but also retain the quantum information of the quantum state.(2) We study the spontaneous emission control of a single photon router based on a four level atomic system. Quantum information can be directed from one quantum channel into another by atomic spontaneous emission, and the difficulties of the router implementation inthe experiment have been lowered down due to the difficulties in the experiment for the classical field does not exist. Finally, we used Langevin equation and input/output relationship, we find that when coupling strength is equal, the fidelity reaches unit. This scenario demonstrates that quantum information can be retained after the quantum router.(3) We explore the single-photon router: realizing the fidelity of quantum state. Using our proposed method, we validate an article on a quantum router on the PRA in 2014. By calculating the fidelity, we can see that the fidelity curve from down to up, the change of the parameter only affects the change of the cycle as well, and has no effect on the other.Therefore, our method can be very good to verify whether the proposed quantum router can keep the quantum information, which also provides a good reference for the experimental implementation of quantum router.