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中国物理学会期刊

超冷原子光晶格体系中束缚态的拓扑泵浦

Topological pumping of bound states in ultracold atomic optical lattice

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  • 拓扑泵浦是受拓扑保护的定向粒子输运,近年来在超冷原子、光子晶体等实验平台中已被广泛实现. 粒子间相互作用无处不在,为拓扑泵浦带来了新的调控自由度. 为进一步探究相互作用系统中的拓扑输运规律,本文研究了一维相互作用广义 Aubry-André-Harper 模型中两粒子束缚态的拓扑泵浦行为. 只考虑在位相互作用,除同位束缚态拓扑泵浦外,还存在一种新奇的邻位束缚态泵浦模式,即两粒子始终保持相邻占据并作为整体进行拓扑泵浦. 在绝热周期驱动下,两类束缚态均可作为复合准粒子实现量子化泵浦,经过一个泵浦周期,其质心位移取决于对应能带的陈数. 在开边界条件下,系统中存在这两类束缚态的边缘模式,其可以通过边缘态-体态混合泵浦模式从系统一侧边缘输运到另一侧边缘. 本研究揭示了邻位束缚对拓扑泵浦这一新颖的输运模式,丰富了两体拓扑泵浦的物理图像,为相互作用系统中的拓扑输运研究提供了新的视角.

     

    Topological pumping, as topologically protected unidirectional transport of particles, has been widely realized in experimental platforms such as ultracold atoms and photonic crystals in recent years. Since interactions between particles are ubiquitous in realistic systems, they provide additional degrees of freedom for controlling topological transport. To further explore the role of interactions in topological pumping, we investigate topological pumping of two-particle bound states in a one-dimensional interacting generalized Aubry-André-Harper model. The Hamiltonian consists of modulated onsite potentials, alternating tunneling amplitudes, and onsite interactions. Such a Hamiltonian can be realized by superimposing three optical lattice with different lattice constants d 2d, and 3d. The periodic driving is introduced through a time-dependent phase in the optical lattice with lattice constant 3d, generating an adiabatic pumping cycle. We identify two types of bound states, the usual on-site bound pair, and a nearest-neighbor bound pair. For repulsive interactions, the onsite bound pair lies in the high-energy sector and exhibits dominant diagonal correlations in the two-body density correlation function, while the nearest-neighbor bound pair lies in the lower-energy region, with dominant off-diagonal correlations. The nearest-neighbor bound states emerge from the interplay between onsite interactions and the spatial modulation of tunneling amplitudes. Under adiabatic evolution, both types of bound states behave as composite quasiparticles and exhibit quantized pumping. In the case of nearest-neighbor bound state, the two particles predominantly occupy adjacent lattice sites and are transported collectively during the pumping cycle. In the case of onsite bound state, the two particles occupying the same site are transported as a whole. In both cases, the center-of-mass displacements over one pumping cycle are determined by the Chern numbers of the corresponding two-body energy bands. Under open boundary conditions, edge modes associated with both types of bound states are observed. These states can be transported from one boundary to the other through an edge-bulk hybrid pumping process. Our work shows that the topological pumping of nearest-neighbor bound pair, distinct from conventional pumping of onsite bound pair, enriches the physical picture of few-body topological pumping.

     

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