两组分BECs在光晶格中的隧穿动力学及其周期调制效应

研究了两组分玻色-爱因斯坦凝聚体(BECs)在一维光晶格中的隧穿动力学及周期调制效应.在两模近似下,运用数值分析的方法,讨论了两组分间相互作用对体系的隧穿动力学行为的影响.进一步讨论了两组分间相互作用在周期调制下系统的动力学特性,分析了随着调制振幅和频率的变化,系统发生隧穿、不稳定和自俘获的区域分布,发现在中低频调制下,系统的隧穿动力学发生了明显的改变.     

Landau-Zener Tunnelling of Two-Component Bose-Einstein Condensates inOptical Lattices

We investigate the Landau--Zener tunnelling of two-componentBose-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 twoself-interactions when the cross-interaction between the components exists. The result can not be found in the single component BECs.     

The dynamics of triple-well trapped Bose-Einstein condensates with atoms feeding and loss effects

In this paper, we consider the macroscopic quantum tunnelling and self-trapping phenomena of Bose-Einstein condensates （BECs） with three-body recombination losses and atoms feeding from thermal cloud in triple-well potential. Using the three-mode approximation, three coupled Gross-Pitaevskii equations （GPEs）, which describe the dynamics of the system, are obtained. The corresponding numerical results reveal some interesting characteristics of BECs for different scattering lengths. The self-trapping and quantum tunnelling both are found in zero-phase and ：r-phase modes. Furthermore, we observe the quantum beating phenomenon and the resonance character during the self-trapping and quantum tunnelling. It is also shown that the initial phase has a significant effect on the dynamics of the system.     

双模压缩真空场与Λ型三能级原子非共振作用

研究了双模压缩真空场与Λ型三能级原子非共振相互作用系统中,场模失谐量对原子布居概率和光场的双模互关联函数、二阶相干度的影响.结果表明：失谐量使原子Rabi振荡呈现周期性崩塌与复苏现象；当光场初始压缩因子r较小时,失谐量将削弱光子的反聚束效应；当r较大时,失谐量又将增强光场两模相关的稳定性.     

Moving Matter-Wave Solitons in Spin-Orbit Coupled Bose-Einstein Condensates

We investigate the moving matter-wave solitons in spin-orbit coupled Bose-Einstein condensates(BECs) by a perturbation method.Starting with the one-dimensional Gross-Pitaevskii equations,we derive a new KdV-like equation to which an approximate solution is obtained by assuming weak Raman coupling and strong spinorbit coupling.The derivation of the KdV-like equation may be useful to understand the properties of solitons excitation in spin-orbit coupled BECs.We find different types of moving solitons:dark-bright,bright-bright and dark-dark solitons.Interestingly,moving dark-dark soliton for attractive intra- and inter-species interactions is found,which depends on the Raman coupling.The amplitude and velocity of the moving solitons strongly depend on the Raman coupling and spin-orbit coupling.     

斯塔克效应对两模双光子J-C模型腔场谱的影响

研究了斯塔克(Stark)效应对两模双光子Jaynes-Cummings(J-C)模型腔场谱的影响,推导计算出了腔场处于光子数态时腔场谱的计算公式和数值结果,讨论了斯塔克效应和初始场强对腔场谱的影响。发现斯塔克效应在弱场条件下对腔场谱线的频率和强度都有明显的影响,破坏了谱结构的对称性,使两模的谱线更加丰富。初始场较强时斯塔克效应对谱线的影响较弱。模Ⅰ为真空场、模Ⅱ初始场强递增时,斯塔克效应使模Ⅱ的高频峰受到较强的抑制作用,其低频峰在初始场较弱时受到抑制,初始场较强时又有强化作用,初始场更强时,模Ⅱ的谱线退化为经典的共振荧光谱,与无斯塔克效应的情况基本相同。     

Preparation of steady-state entanglement via a laser-excited resonant interaction

In this paper we propose a scheme in which two-mode entanglement in a steady state is produced by using two lasers to resonantly drive a single four-level atom embedded inside a two-mode optical cavity.In this scheme,atomic coherence induced by a classical laser plays an important role in the process of preparing the entangled state.With the coupling of a strong control field,direct two-photon transition is generated and the relatively weak pump field induces the parametric interaction between two photons,which makes them entangle with each other.By numerical calculation,we find that the degree of entanglement depends strongly on the Rabi frequencies of the classical laser fields and the cavity losses.     

Quantum Entanglement of Many Particles in Spinor Bose–Einstein Condensates

We present a theoretical treatment of the proposal for creating maximally entangled states of many particles in spin-1 Bose–Einstein condensates (BECs) by applying a single atom Raman transition [You. L. (2003). Physical Review Letters 90, 030402]. It is shown that the three-mode model suggested by You can be further reduced to an efficient two-mode one by a simple method. We also suggest a scheme for generating the atom-atom continuous-variable entangled states in this system. PACS number: 03.75.Gg, 03.75.Mn, 05.30.JP, 03.75.Hh     

Entanglement transfer from two-mode squeezed vacuum light to spatially separated mechanical oscillators via dissipative optomechanical coupling

In this paper, we propose a scheme to generate an entangled state between two spatially separated movable mirrors by injecting the two-mode squeezed optical reservoir to the dissipative optomechanics, in which the movable mirrors can modulate the linewidth of the cavity modes. When the coupling between the mirrors and the corresponding cavity modes is weak, the two driven cavity fields can respectively behave as the squeezed-vacuum reservoir for the two movable mirrors by utilizing the effect of completely destructive interference of quantum noise. Thus the mechanical modes are prepared in a two-mode squeezed vacuum state. Moreover,when the coupling between the two mirrors and the cavities modes is strong, the entanglement between the two movable mirrors decreases because photonic excitation can preclude the completely destructive interference of quantum noise, but the movable mirrors are still entangled.     

Hyperchaos of two coupled Bose--Einstein condensates with a three-body interaction

We investigate the dynamics of two tunnel-coupled Bose--Einstein condensates (BECs) in a double-well potential. The effects of the three-body recombination loss and the feeding of the condensates from the thermal cloud are studied in the case of attractive interatomic interaction. An imaginary three-body interaction term is considered and a two-mode approximation is used to derive three coupled equations which describe the total atomic numbers of the two condensates, the relative population and relative phase respectively. Theoretical analyses and numerical calculations demonstrate the existence of chaotic and hyperchaotic behaviour by using a periodically time-varying scattering length.     

Stability and Chaos of Two Coupled Bose-Einstein Condensates with Three-Body Interaction

We study the dynamics of two Bose-Einstein condensates (BECs) tunnel-coupled by a double-well potential.A real three-body interaction term is considered and a two-mode approximation is used to derive two coupled equations,which describe the relative population and relative phase. By solving the equations and analyzing the stability of the system, we find the stable stationary solutions for a constant atomic scattering length. When a periodically time-varying scattering length is applied, Melnikov analysis and numerical calculation demonstrate the existence of chaotic behavior and the dependence of chaos on the three-body interaction parameters.     

Generation of entanglement via atomic coherence in a two-mode three-level cascade atomic system

The generation of continuous variable entanglement via atomic coherence in a two-mode three-level cascade atomic system is discussed according to the entanglement criterion proposed by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)]. Atomic coherence between the top and bottom levels is induced with two photons of a strong external pump field. It shows that entanglement for the two-mode field in the cavity can be generated under certain conditions. Moreover, by means of the input-output theory, we show that the two-mode entanglement could also be approached at the output.     

Amplitude-squeezed emission from a transverse single-mode vertical-cavity surface-emitting laser with weakly anticorrelated polarization modes

We discuss the polarization-resolved intensity noise characteristics of a transverse single-mode vertical-cavity surface-emitting laser (VCSEL). Measurements by a sensitivity-enhanced lock-in amplifier detection scheme yield only an imperfect anticorrelation between the strong and the weak orthogonally polarized fundamental modes. Yet the total emission shows amplitude squeezing of 0.4 dB below the shot-noise level. Unlike for transverse two-mode emission, a perfect anticorrelation between the two polarization modes is not necessary for generation of amplitude-squeezed emission in a transverse single-mode VCSEL, in agreement with theoretical predictions.     

非线性三能级体系的绝热朗道-齐纳隧穿

研究了绝热条件下非线性三能级体系的朗道-齐纳隧穿.通过研究体系的本征值和本征态，发现当非线性不是很强时，三个能级的结构与线性情况相似，但中间能级所对应本征态的性质分段，这种分段导致绝热定理被破坏，引起所谓的绝热隧穿现象.由于本征态的不稳定性，造成隧穿率的混乱.当非线性较强时，能级结构发生非常复杂的扭曲，使绝热定理被更加严重地破坏.还讨论了这个模型在三势阱波色-爱因斯坦凝聚体系中的可能应用. 关键词： 三能级 朗道-齐纳隧穿 隧穿率     

Rotational tunnelling splitting of a chain of four coupled methyl groups

It is our goal to obtain a reliable prediction of the rotational tunnelling spectrum to be expected for a long chain of coupled one-dimensional quantum rotors. The problem is intractable by the simple methods used so far for up to three coupled methyl groups. Therefore, an efficient, nevertheless sufficiently precise method for solving the stationary Schrödinger equation of interacting methyl groups is developed first; it proves to be valid for a broad range of not too weak potential strengths. Then, three scenarios are investigated: they differ with respect to the relative strength of the single-rotor potential and the interaction potential. For each scenario, we illustrate the dependence of the energy level scheme on the number of coupled groups. For strong coupling and weak single-particle potential, the characteristic features of the energy level scheme of interacting methyls are most clearly observable: For as few as four coupled methyl groups we predict tunnelling spectra which are hardly distinguishable from single-methyl spectra. However, the collective behaviour is still important for the value of the tunnelling splitting. Therefore, the interpretation of such a spectrum in terms of single-methyl tunnelling is obvious but misleading with respect to the potential seen by a methyl group in the crystal.     

克尔介质中双原子与场拉曼作用系统的腔场谱

研究了含克尔介质腔中两个耦合二能级原子与双模光场拉曼相互作用过程的腔场谱。通过求解本征方程导出了腔场谱的计算公式,给出了双模初始光场均处于数态时的数值计算结果。发现在两模初始场均为弱场时,克尔效应不仅使峰位右移,还使峰的强度、个数和频率发生改变,破坏峰结构的对称性。在克尔效应较强时,原子之间的耦合对腔场的影响被抑制,谱结构主要由克尔效应决定。在强场条件下,无克尔介质加入时,原子间的耦合作用使各峰的强度都得到加强;随克尔效应的增强,靠近中心频率的主峰迅速增长并很快达到饱和,而远离中心频率的边峰则被抑制并产生劈裂。     

Energy sharing induced by the nonlinear interaction

Strong energy sharing is shown by numerically investigating coupled multi-component Bose–Einstein condensates(BECs) with a harmonic trap to simulate the Fermi–Pasta–Ulam model(FPU). For two-component BECs, the energy exchanging between each part, from regular, quantum beating to complete energy sharing, is explored by simulating their Husimi distributions, the time evolution of energies and the statistical entropy. Meanwhile, in the three-component case, a more complex energy sharing behavior is reported and a strong energy sharing is found.     

非等同双原子与双模腔场拉曼相互作用模型的腔场谱

研究了非等同双原子与双模腔场拉曼相互作用模型的腔场谱,分析了谱结构随原子与腔场相对耦合常数R=g2/g1的变化规律,发现R对真空场、弱场、强场谱结构都有不同程度的影响.当R=1或R=0时,一般呈现简并的谱结构,而当R介于0与1之间时,腔场谱一般呈现复杂的非对称多峰结构.同时还发现,当R固定不变时,低频腔场初始场强对高频真空场谱结构也有较明显的影响. 关键词： 量子光学 腔场谱 拉曼相互作用 双模腔场     

Quantum phase transition and dynamics induced by atom-pair tunnelling of Bose-Einstein condensates in a double-well potential

We investigate the quantum phase transition (QPT) and dynamics induced by atom-pair tunnelling of Bose-Einstein condensates in a symmetric double well under the mean-field approximation. We find the system undergoes a new QPT towards phase-locking state when atom-pair tunnelling is strong enough, and the critical point of self-trapping QPT is shifted by atom-pair tunnelling. As for the dynamics, the system displays localized dynamical behaviour: phase-locking motion and self-trapping motion. We further study the correlation between this localized dynamics and QPT, and find that the area of the localized trajectories in the phase space can serve as an order parameter for both QPTs. The critical exponent of this order parameter is also discussed.