Studies On Quantum Entanglement In Ultracold Rydberg Atoms

With the continuous development of economic globalization and information technology, quantum information technology based on quantum physics is drawing public interest increasingly. Entanglement is an important resource of applications in quantum information. It is extremely helpful in such tasks as the transmission and encryption of information, the reduction of classical communication complexity, entanglement-assisted orientation in space and clock synchronization. In the last few years, the promising application of Rydberg atoms in quantum information technology has been recognized, as well as in quantum simulation and quantum metrology. Especially in the preparation of quantum entanglement, Rydberg atoms have an advantage over other neutral atoms. With long radiative lifetimes and large dipole moments, it is easy to realize entanglement of more than two atoms in different scales. In this thesis, we study the preparation of entanglement in Rydberg atoms on account of such background.In this thesis, we focus on a sample of cold Rydberg atoms driven into a four-level configuration with two ground states, one intermediate state and one Rydberg state. We combine the Rydberg blockade mechanism with the stimulated Raman adiabatic passage(STIRAP), for realizing the population transfer from ground state to Rydberg state, so that we can achieve the preparation of quantum entanglement. The strong dipole-dipole interaction between Rydberg atoms will restrain the excitation of each other. By modulating the detuning of laser pulse sequence, the influence of dipole blockade will be compensated. As a result, the atoms will be efficiently transformed into the Rydberg states and we will get ideal entanglement only contained ground state and Rydberg state. Besides, the entanglement is highly dependent on the detuning of STIRAP laser pulse. Namely, the light pulses provide rich opportunities to prepare a variety of quantum entanglement.The research in this work has a considerable application prospect in the domain of quantum information and promotes the development of the theory. In addition, our results provide good resource for information coding, quantum cryptography as well as quantum logic.