Quantum tunneling of ultracold atoms in optical traps

We review our theoretical advances in quantum tunneling of BoseEinstein condensates in optical traps and in microcavities. By employing a real physical system, the frequencies of the pseudo Goldstone modes in different phases between two optical traps are studied respectivdy, which are tile crucial feature of the non-Abelian Joseptmon effect. When the optical lattices are under gravity, we investigate the quantum tummling in the ＂Wannier-Stark localization＂ regime and ＂Lan（lau Zener tunneling＂ regime. We finally get the total decay rate and the rate is valid over the entire range of temperatures. At high temperatures, we show how the decay rate reduces to the appropriate results for the classical thermal activation. At hltermediate temperatures, the results of tile total decay rate are consistent with the thermally assisted tunneling. At low temperatures, we obtain the pure quantmn tunneling ultimately. And we study the alternating-current and direct-current （ac and de） photonic 3osephson effects in two weakly linked microcavities containing ultracold two-level atones, which allows for direct observation of the effects. This enables new investigations of the effect of maw-body physics in strongly coupled atom-cavity systems and provides a strategy for constructing novel interference devices of coherent photons. In addition, we propose the experimental protocols to observe these quantmn tunneling of Bose- Einstein condensates.     

Generation of Entangled State and Entanglement Swapping

A scheme is proposed for the generation of entangled atomic states and a method is presented to produce entangled photon states. It is shown that entanglement can be swapped from atoms to cavities via atom-cavity interaction.     

Generation of maximally entangled state from a single-photon state in fiber-connected cavities

Starting from the physical model consisting of two remotely located atoms trapped in high finesse fiber-connected cavities, generation of maximally entangled state is firstly realized theoretically from a initial single-photon state. Result shows that under the regime of strong atom-cavity coupling strength, the averaged fidelity can remarkably exceed 0.9980. The distant creation of maximally entangled state may provides certain opportunities and be helpful in the accomplishment of scalable quantum networks.     

Generation of Entangled State and Entanglement Swapping

A scheme is proposed for the generation of entangled atomic states and a method is presented to produce entangled photon states. It is shown that entanglement can be swapped from atoms to cavities via atom-cavity interaction.     

Teleportation of a bipartite entangled coherent state via cavity QED

Based on the atom--cavity--field interaction, this paper proposes a scheme for the teleportation of a bipartite entangled coherent state (ECS) with high fidelity as long as $\left| \alpha \right|$ is not too small. In this proposal, only four cavities and a three-level cascade atom are needed. The fidelity of the ECS is calculated and analysed in detail.     

Collapse–revival of squeezing of two atoms in dissipative cavities

Based on the time-convolutionless master-equation approach, we investigate the squeezing dynamics of two atoms in dissipative cavities. We find that the atomic squeezing is related to initial atomic states, atom–cavity couplings, nonMarkovian effects and resonant frequencies of an atom and its cavity. The results show that a collapse–revival phenomenon will occur in the atomic squeezing and this process is accompanied by the buildup and decay of entanglement between two atoms. Enhancing the atom–cavity coupling can increase the frequency of the collapse–revival of the atomic squeezing.The stronger the non-Markovian effect is, the more obvious the collapse–revival phenomenon is. In particular, if the atom–cavity coupling or the non-Markovian effect is very strong, the atomic squeezing will tend to a stably periodic oscillation in a long time. The oscillatory frequency of the atomic squeezing is dependent on the resonant frequency of the atom and its cavity.