Flat-band localization and interaction-induced delocalization of photons

Lattices with dispersionless, or flat, energy bands have attracted significant interest in part due to the strong dependence of particle dynamics on interactions. Using superconducting circuits, we experimentally study the dynamics of one and two particles in a single plaquette of a lattice whose band structure consists entirely of flat bands. We first observe strictly localized dynamics of a single particle, the hallmark of all-bands-flat physics. Upon initializing two particles on the same site, we see an interaction-enabled delocalized walk across the plaquette. We further find localization in Fock space for two particles initialized on opposite sides of the plaquette. These results mark the first experimental observation of a quantum walk that becomes delocalized due to interactions and establishes a key building block in superconducting circuits for studying flat-band dynamics with strong interactions., This data was collected by averaging 3000 single shot data points at each time evolution point. Data is bounded by 0 and 1 and was corrected for measurement errors using readout mitigation from the qiskit python library. The error bars for the data are 95% Clopper-Pearson confidence intervals. , , # Data from: Flat-band localization and interaction-induced delocalization of photons

[https://doi.org/10.5061/dryad.0cfxpnw80](https://doi.org/10.5061/dryad.0cfxpnw80)

The data included here was used to generate Figures 2, 3, and 4 in the main body of the text. Figure 2 characterizes single particle dynamics in the plaquette with zero and pi flux. In the pi flux device, we see localized dynamics where an initial excitation is localized to three of the four lattice sites. Figure 3 characterizes the dynamics of two particles initialized on the same site. Due to interactions, these particles hop as a pair and we find delocalized dynamics for the bound pair across the plaquette in both zero and pi flux devices. Figure 4 characterizes the dynamics of two particles initialized on opposite sides of the plaquette. Here, we find that when particles are initialized on the left and right sites (LR state), transfer to the TB state is prohibited in the pi flux plaquette.

## Description of the da...