Abstract
In the region of Quantum information, some scientists focus on how to extend the lifetime and the Quantum coherence of the photon. Because of the dissipation during the teleportation,we have to extend the lifetime of the photon in order to make it propagate much longer. On the other hand, Quantum computing and Quantum teleportation strongly depend on the Quantum coherence of the photon. As long as the Quantum coherence of the photon dissipates, Quantum computing and Quantum teleportation are invalid. However, the scientists have found some methods to extend the lifetime and the Quantum coherence of the photon such as EIT, Subradiant array or Quantum zeno effect .etc. In our research,we work on the Quantum zeno effect which is the suppression of Hamiltonian evolution of the system by continuous measurements to extend the lifetime and the Quantum coherence of the system . According to QED, an electron in excited state must decay to its ground state as time passes by. However, if we apply rapid and continuous measurements to the system, the system stop evolving with time. That’s, the system never decays because of the Quantum zeno effect. Besides, if our system stays in the open quantum system, the Quantum coherence of our system dissipates due to the decoherence from the environment. By means of the Quantum zeno effect, we can still slow down the decay rate of Quantum coherence, because continuous measurements suppress the decoherence from the environment. We purpose to measure the N Two-level emitters(N-LTE) system and suppose that the N-LTE system is in the Superradiance state. As mentioned above, the extending of the coherence time of the system is mainly focused, so we intend to choose the Superradiance state which contains strong Quantum coherence. By classifying several special phenomenons of the Superradiance state under different parameters, the Quantum coherence of the N-TLE system and the results of the Quantum zeno effect can be predicted. There are many ways to observe the Quantum coherence, such as LG inequality, Bell inequality,CHSH inequality and Quantum witness. We observe the time evolution of the Quantum coherence in our system mainly by Quantum witness . Compared with other inequalities, Quantum witness provides us a simpler way to observe the Quantum coherence not only in experimental realization but in theoretical analysis. In this dissertation, we start from studying the time evolution of N-TLE system in Superradiance state in different parameters. Then observing its time evolution of Quantum coherence by Quantum witness in different parameters. Finally, demonstrating the final result of variance in Quantum coherence and the decay rate of N-TLE system under Quantum zeno effect.