Research On Quantum Entanglement Based On Strongly Coupled Cavity Quantum Electrodynamics

Quantum entanglement is a distinct feature for quantum physics different from classical one. It can not only provide the possibility for testing quantum mechanics against a local hidden variable theory, but also plays an important role in quantum information processing and quantum communications, which makes quantum entanglement intensely attractive. So far, most of properties for two-particle entanglement have been known by quantum scientists. Thus, one of the current motives for the investigation of quantum entanglement is to obtain an appropriate physical system to generate high-efficiency, high-fidelity, and long-decoherence entangled states, which are used for scale, integrated computation, remote quantum communications, high-precision quantum metrology, and so on.Cavity quantum electrodynamics (cavity QED) focuses on the interaction between matter (such as atoms, molecules, ions and quantum dots, etc.) and electromagnetic field in a confined space. One of cavity QED systems is to study the atom-cavity interaction, i.e. atom-cavity systems. When the coupling rate between atoms and cavities is much stronger than the one induced by environments, quantum system achieves the strong region. Strongly coupled cavity QED which can control the state of single atoms and single photons efficiently and determinably, is a potential candidate for quantum information processing and quantum communications. Up to now, the generation of atom-atom entanglement, photon-atom entanglement is realizable based on cavity QED. However, the individual control of single atoms in multi-atoms systems is still very difficult with current technologies. Furthermore, how to reduce the effect of various decoherence such as spontaneous emission and photon loss on the quantum system to construct large quantum computer and quantum internet is still a problem for cavity QED systems and other physical systems.Considering these problems, we will focus on the preparation and dynamics of quantum entanglement with strongly coupled cavity QED. The main works shown in the thesis are follows:1) Study the atomic W prepared in one cavity. We consider many A-type atoms interact with a single-mode cavity. In the whole procedure, one of two atomic transitions is resonant with cavity mode, and the other transition is driven by a weak laser pulse with an appropriate detuning, reducing the change of the system vacuum. Furthermore, numerical simulation shows that our proposal can reduce the effect of atomic spontaneous emission and photon loss on fidelity, leading the prepared W states to be robust.2) Study the generation of distributed NOON states in two coupled cavities for Heisenberg-limit quantum metrology. We consider two models based on atom-fiber-cavity system (two level atoms) and three-level A-type atoms interacting with two directly coupled cavities. Compared with two schemes, the first one can distribute NOON states much farther than the second one but it's decoherence is much shorter. Though both of the two protocols have flaws, they are meaningful in quantum computation and quantum internet.3) Quantum Zeno effect is studied during the evolution of quantum states. After that, we will prepare atomic entangled states in two directly coupled cavities. We take two A-type atoms (or atomic ensembles) interacting with two coupled cavities into account. In the whole procedure, both atoms and cavities still remain ground (or vacuum) states, making the system robust against atomic spontaneous emission and photon loss. Besides, the system is insensitive to the imperfection of the initial atomic states.4) Quantum entanglement dynamics is investigated with various circumstances for the aim of studying the storage of quantum entanglement, and furthermore quantum computer and quantum internet. In this part, we consider atomic entanglement dynamics for two Tavis-Cummings atoms simultaneously interacting with squeezed vacuum states. Numerical simulation tells us the atomic concurrence can disappear in in a finite time and then relive, which depends on the initial atomic states and the properties of squeezed states. We also find that there are two decoherence-free states in squeezed vacuum fields:one is the singlet state, and the other entangled state is the state that combines both excited states and ground states with a relative phase being equal to the phase of the squeezed state.