Preservation of Quantum Coherence for Gaussian-State Dynamics in a Non-Markovian Process

Coherence is a key resource in quantum information science.Exactly understanding and controlling the variation of coherence are vital for implementation in realistic quantum systems.Using P-representation of density matrix,we obtain the analytical solution of the master equation for the classical states in the non-Markovian process and investigate the coherent dynamics of Gaussian states.It is found that quantum coherence can be preserved in such a process if the coupling strength between system and environment exceeds a threshold value.We also discuss the characteristic function of the Gaussian states in the non-Markovian process,which provides an inevitable bridge for the control and operation of quantum coherence.     

Effects of three-body interaction on collective excitation and stability of Bose--Einstein condensate

This paper investigates the collective excitation and stability of low-dimensional Bose--Einstein condensates with two- and three-body interactions by the variational analysis of the time-dependent Gross--Pitaevskii--Ginzburg equation. The spectrum of the low-energy excitation and the effective potential for the width of the condensate are obtained. The results show that: (i) the repulsive two-body interaction among atoms makes the frequency red-shifted for the internal excitation and the repulsive or attractive three-body interaction always makes it blue-shifted; (ii) the region for the existence of the stable bound states is obtained by identifying the critical value of the two- and three-body interactions.     

超冷原子向异核四聚物分子A3B的绝热转化

提出了利用Efimov共振辅助的受激拉曼绝热通道(ER-STIRAP) 过程实施超冷原子向异核四聚物分子A₃B转化的理论方案, 得到了转化过程中中间态分别为同核Efimov三聚物A₃和 异核Efimov三聚物A₂B两种途径下系统的暗态解, 证实了ER-STIRAP技术对超冷异核四聚物分子A₃B合成的可行性和有效性. 研究了外场参数, 包括缔合光脉冲的强度、脉宽、磁耦合强度及其失谐量等对A₃B形成的影响. 对两种不同中间态的转化途径进行比较发现, 与中间态为异核Efimov三聚物A₂B的途径相比, 经历中间态为同核Efimov三聚物A₃的途径时系统实现最终四聚物分子A₃B的产率更高. 另外, 还讨论了系统内禀的非线性和中间态的自发辐射损失对异核四聚物分子合成的影响.     

Landau-Zener Tunnelling of Two-Component Bose-Einstein Condensates in Optical Lattices

We investigate the Landau-Zener tunnelling of two-component Bose-Einstein condensates （BECs） in optical lattices. In the neighborhood of the Brillouin zone edge, the system can be reduced to two coupled nonlinear two-level models. From the models, we calculate the change of the tunnelling probability for each component with the linear sweeping rate. It is found that the probability for each component exhibits regular oscillating behavior for the larger sweeping rate, but for smaller rate the oscillation is irregular. Moreover, the asymmetry of the tunnelling between the two components can be induced by the unbalanced initial populations or the inequality of the two self-interactions when the cross-interaction between the components exists. The result can not be found in the single component BECs.     

Oscillating Guided Modes in Graphene-Based Asymmetric Waveguides

We investigate the guided modes in monolayer graphene-based waveguides with asymmetric quantum well structure induced by unequal dc voltages. The dispersion relation for the guided modes is obtained analytically, the structures of the guided modes are discussed under three distinct cases. For the cases of the classical motion and the Klein tunneling, the asymmetric structure does not influence the mode structures dramatically compared with that in the symmetric waveguide. But for the mixing case of the former two, the mode structures and the motion characteristics for the electron and the hole exhibit different behaviors at same condition. The results may be helpful for the practical application of graphene-based quantum devices.     

外场参数对超冷原子向异核三原子分子转化的影响

文章研究了利用双光子受激拉曼绝热暗通道技术实现超冷原子向异核三原子分子转化过程中,可控外场参量(包括拉比脉冲的强度,脉宽以及单光子失谐等)对系统绝热性和转化效率的影响. 结果发现,系统的转化效率随斯托克斯光强度的增大先减小,后振荡,最终趋于小于1的稳定值,而随抽运光强的增大先增大,然后很快趋于1,表明抽运光和斯托克斯光对超冷分子的形成具有不同的作用. 脉冲宽度既能决定最终转化效率的大小,也能反映达到稳定转化所需的时间. 单光子失谐为红失谐时,系统有比较高的稳定转化效率,而蓝失谐光脉冲则不利于超冷分子的形成. 另外,还讨论了超冷异核三原子分子转化系统在经历不同反应通道时绝热性和转化效率的差别. 关键词： 异核三原子分子 受激拉曼绝热暗通道 绝热参量 绝热保真度