Exact multiple complex mobility edges and quantum state engineering in coupled 1D quasicystals

Abstract: The key concept of mobility edge, which marks the critical transition between extended and localized states in energy domain, has attracted significant interest in the cutting-edge frontiers of modern physics due to its profound implications for understanding localization and transport properties in disordered systems. However, a generic way to construct multiple mobility edges (MME) is still ambiguous and lacking. In this work, we propose a brief scheme to engineer both real and complex exact multiple mobility edges exploiting a few coupled one-dimensional quasiperiodic chains. We study the extended-localized transitions of coupled one-dimensional quasiperiodic chains along the chain direction. The model combines both the well-established quasiperiodicity and a kind of freshly introduced staggered non-reciprocity, which are aligned in two mutually perpendicular directions, within a unified framework. Based on analytical analysis, we predict that when the couplings between quasiperiodic chains are weak, the system will be in a mixed phase in which the localized states and extended states coexist and intertwine, thus lacking explicit energy separations. However, as the inter-chain couplings increase to certain strength, exact multiple mobility edges emerge. This prediction is clearly verified by concrete numerical calculations of the Fractal Dimension and the scaling index $\beta$. Moreover, we show that the combination of quasiperiodicity and the staggered non-reciprocity can be utilized to design and realize quantum states of various configurations. Our results reveal a brief and general scheme to implement exact multiple mobility edges for synthetic materials engineering.