Preparation Of Entangled States Based On Atomic Spontaneous Emission

Quantum information science is a new interdisciplinary subject,which applies the unique properties of quantum system to modern information science and technology,thus making information science enter a new stage.As one of the unique properties of quantum physics,quantum entanglement is an indispensable and important resource for quantum information processing,so the preparation of quantum entanglement has become a research hotspot in quantum information science.However,the real quantum system will inevitably be affected by the external environment,which will lead to decoherence and destroy the preparation of entangled states.In recent years,by reexamining the interaction between the system and the environment,researchers have transformed quantum dissipation into a resource conducive to the preparation of entangled states,thus promoting the development of quantum state regulation in open systems.In this paper,the Bell states and multipartite GHZ state have been prepared by using the dissipative process of atomic spontaneous emission.Firstly,we propose a parallel quantum Zeno dynamic mechanism for the preparation of various Bell states in a cavity quantum electrodynamics(QED)system.The system trap two four-level atoms in an optical cavity,and each atom is driven by both a classical and a quantized cavity field.In the coupling strength of atoms and quantized cavity field is much larger than the atoms and the coupling strength of classic field,we propose a parallel quantum Zeno dynamics mechanism can provide two transition channels at the same time for the system,which can effectively shorten the time required for the system to evolve to the target state and suppress the adverse effects of photon leakage in the cavity.The achievement of the target state is independent of the choice of initial states,since the target state is the unique steady state of the system in the whole process.The numerical simulation results show that the proposed scheme can violate the Clauser-Horne-Shimony-Holt(CHSH)inequality within a certain parameter range in a finite temperature heat reservoir.The feasibility of the proposed scheme is discussed by referring to the experimental parameters of the current cavity QED system.The numerical simulation results show that the fidelity of the target state can reach about 99%.Secondly,we put forward two proposals to dissipatively prepare tripartite GreenbergerHorne-Zeilinger(GHZ)states in Rydberg atomic systems.In the first scheme,the tripartite GHZ state is successfully prepared by using the polychromatic driving fields and the spontaneous emission of atoms,and the original scheme is optimized by changing the driving field into the form of Gaussian pulse.Nevertheless,once the spontaneous emission of the Rydberg state is considered,the population of the tripartite GHZ state will steeply descend.In the second scheme,we convert the spontaneous emission of the Rydberg state into a favorable resource,and successfully obtain a stable tripartite GHZ state with a fidelity of about 98% by designing the switching driving of unconventional Rydberg pumping with the parity measurement.But the three Rydberg atoms in the two schemes the next-nearest neighbor interaction of Rydberg atoms cannot be neglected within the parameters they consider,unless the case of three Rydberg atoms arranged in an equilateral triangle.Finally,we extend the previous scheme to successfully prepare multipartite GHZ states with both odd and even numbers of particles in the presence of the next-nearest neighbor interaction.By appropriately adjusting the frequency of the driving fields and the relevant detuning,a stable GHZ state with high fidelity can be obtained.Without loss of generality,we discuss in detail the preparation of GHZ states in three-and four-partite systems.The numerical simulation results show that the population of the target state can reach more than99%.The introduction of quantum Lyapunov control can help us optimize the dissipative dynamics of the system so as to shorten the convergence time of the target state,improve the robustness against the spontaneous radiations of the excited Rydberg states,and release the limiting condition for the strengths of the polychromatic driving fields.