The first AMO/QI 290F seminar of the semester will take place Wednesday, February 9 from 11-12 p.m. PDT in Physics 375 North. Our speaker is Christie Chiu (Princeton). Details are below.

Line-graph lattices: models inspired by quantum simulation

Given any periodic lattice of sites and the bonds between them, we can construct the line graph of this lattice in just two steps. First, we make a lattice site for every bond in the original lattice. Second, we connect pairs of sites if their corresponding bonds in the original lattice are neighbors. Strikingly, in two dimensions and above, all of these lattices host exactly flat bands in the band spectra. These dispersionless bands indicate a quenching of kinetic energy and diverging effective mass, making flat-band lattices a rich playground for exploring strongly interacting many-body physics. For example, theoretical work has explored phenomena including ferromagnetism, flat-band many-body localization, unconventional superconductivity, and zero-magnetic-field fractional quantum Hall states. Experimentally, flat bands have been realized in photonics, superconducting circuits, and ultracold atoms, as well as in materials such as magic-angle twisted bilayer graphene and twisted bilayer transition metal dichalcogenides.

Line-graph lattices, in particular, arise naturally from superconducting circuits of microwave resonators. In this talk, we will explore properties of these lattices and their flat bands. This will allow us to tackle the question, "Are line-graph-lattice flat bands topological?" and catch a glimpse into the world of topological materials [1]. Our set of theoretical results makes experimental studies of line-graph-lattices with superconducting circuits highly promising. At the same time, new directions in strongly interacting many-body flat-band systems are also entirely within reach.

[1] C. S. Chiu, et al. Fragile Topology in Line-Graph Lattices with 2, 3, or 4 Gapped Flat Bands. Physical Review Research 2, 043414 (2020).