近日，日本RIKEN紧急物质科学中心的Michael D. Fraser等取得一项新进展。经过不懈努力，他们对激子-极化子Floquet光学晶格中的非互易能带结构进行研究。相关研究成果已于2024年4月23日在国际知名学术期刊《自然—光子学》上发表。

该研究团队利用两个激光器之间的干涉，构建了一个非共振光学晶格，其中的极化子凝聚体具有可调的位势深度和最近邻耦合强度。时间调制是通过泵浦激光器之间的千兆赫频率失谐引入的，构建了一个极化子“传送带”。这种时间反演对称性的破缺，使得能带结构呈现出非互易性，并获得了由普朗克常数和调制频率共同决定的普遍倾斜（hΔf）。

这种非互易倾斜与具有有限陈数的Floquet-Bloch能带的非平凡拓扑密切相关。晶格位势深度及其动力学的详细表征突出了，高能载流子在极化子光学势景观形成中的作用，证明了调制速度快于极化子寿命的可能性，并为极化子凝聚体的Floquet工程开辟了一条途径。

据悉，哈密顿量的周期时间调制可以引起量子态动力学中的几何和拓扑现象。

附：英文原文

Title: Non-reciprocal band structures in an exciton–polariton Floquet optical lattice

Author: del Valle Inclan Redondo, Yago, Xu, Xingran, Liew, Timothy C. H., Ostrovskaya, Elena A., Stegmaier, Alexander, Thomale, Ronny, Schneider, Christian, Dam, Siddhartha, Klembt, Sebastian, Hfling, Sven, Tarucha, Seigo, Fraser, Michael D.

Issue&Volume: 2024-04-23

Abstract: Periodic temporal modulation of Hamiltonians can induce geometrical and topological phenomena in the dynamics of quantum states. Using the interference between two lasers, we demonstrate an off-resonant optical lattice for a polariton condensate with controllable potential depths and nearest-neighbour coupling strength. Temporal modulation is introduced via a gigahertz frequency detuning between pump lasers, creating a polariton ‘conveyor belt’. The breaking of time-reversal symmetry causes band structures to become non-reciprocal and acquire a universal tilt given by Planck’s constant and the frequency of modulation (hΔf). The non-reciprocal tilting is connected to the non-trivial topology of the Floquet–Bloch bands, which have a finite Chern number. Detailed characterization of the lattice potential depth and its dynamics highlights the role of high-energy carriers in the formation of optical potential landscapes for polaritons, demonstrating the possibility of modulation faster than the polariton lifetime and opening a pathway towards Floquet engineering in polariton condensates.

DOI: 10.1038/s41566-024-01424-z

Source: https://www.nature.com/articles/s41566-024-01424-z