image: Figure | Synthesizing topological atomic trimer array with tunable interaction. a, A topological trimer array is implemented in momentum lattices, based on the laser-driven Bragg transitions between the discrete atomic momentum states. The intra- and intercell hopping rates can be individually controlled by addressing each Bragg transition. Atoms are prepared at two leftmost sites with equal weight and a relative phase. b, Energy spectra of a trimer array in the noninteracting limit. The red lines represent topological edge states. c, Eigenmodes of topological trimer array correspond to the black dots in b. Two in-phase (out-of-phase) peaks characterize the modes 1 and 2 (modes 3 and 4). d, Illustration of the density-dependent, nonlinear energy induced by the atomic interactions.
Credit: Huiying Du et al.
Topological phases are the most exciting research topic in many branches of science, ranging from condensed matter to quantum simulators such as ultracold atoms and photonic waveguides. Exploring the interplay between topological band structures and tunable nonlinearities has led to an emerging field of nonlinear topological physics in photonics, which aims to extend the fascinating properties of topological states to a regime where interactions between the system constituents cannot be neglected. While the precisely-controlled ultracold atomic gas provides an excellent platform for exploring exotic topological phases, nonlinear effect on the engineered topological states have so far remained out of reach due to the raised fundamental and challenging questions.
In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Jie Ma from the Institute of Laser Spectroscopy, Shanxi University, China, and co-workers have report the observation of nonlinear edge states in a topological trimer array of interacting ultracold atoms. They synthesize a topological trimer array basing on the laser-driven couplings of discrete atomic momentum states, where the atomic interactions give rise to tunable nonlinearities. They observe the formation of nonlinear edge states in the density population evolution and participation ratio with increasing interaction, in contrast to the diffusive transport in a broad interaction range in nontopological arrays. Furthermore, they show the impact of interactions on the population distribution evolved from the initialized single-site population. This study will open new avenue for exploring emergent nonlinear topological behaviors in ultracold atomic gases.
In their experiment, a topological trimer array is synthesized by adopting the momentum-lattice technique in a 133Cs Bose-Einstein condensate, where the atomic interactions controlled via a broad Feshbach resonance lead to tunable nonlinearities. Combined with the precise control of the lattice parameters, the interplay between topology and nonlinearity is studied by measuring the impact of interactions on the density population and participation ratio in the quench dynamics of topological atomic trimer arrays. When the system is initialized at two types of edge states emerging in two topological band gaps, the formation of nonlinear edge states is observed by the localization of all atoms on two boundary sites with increasing interaction, whereas they cannot be formed in a broad interaction range in nontopological arrays. For the single-site injection, the population distribution obtained after an evolution time is consistent with that determined by the topological edge states in noninteracting or weakly interacting regimes, while all atoms become localized at the initial site for large interactions.
These scientists summarized the significant findings in their experiment:
“We study the impact of interactions on the population distribution in a topological trimer array of ultracold atoms, and observe the formation of nonlinear edge states. Our work provides a starting point for the study of nonlinear topological physics in ultracold atomic systems, which extends the domain of nonlinear topological photonics.”
Journal
Light Science & Applications
Article Title
Observation of nonlinear edge states in an interacting atomic trimer array