SPECIAL SEMINAR: Detecting fractional Chern insulators using circular dichroism

Fractional Chern insulators (FCIs) are topological phases of strongly interacting particles on a lattice. In the simplest case, FCIs share their universal properties with fractional quantum Hall (FQH) states in Landau levels, including emergent excitations with fractional statistics, but they could also host new phases with no equivalent in Landau level physics. The engineering of FCIs progresses in parallel in solid state systems (where they have been realized in 2D layered materials but still require a magnetic field) and ultracold atomic gases. Indeed, recent achievements in the realization of topological Bloch bands, together with the possibility of tuning inter-particle interactions, suggest that FCIs could soon be generated in ultracold atomic gases. In this experimental framework, where transport measurements are limited, identifying unambiguous signatures of FQH-like states constitutes a challenge on its own. Here, we demonstrate that the fractional nature of the quantized Hall conductance, a fundamental characteristic of FQH states, can be detected in ultracold gases through a circular-dichroic measurement, namely, by monitoring the energy absorbed by the atomic cloud upon a circular drive. We validate this approach by numerically comparing the circular-dichroic signal to the Hall conductance, and discuss how such measurements could be performed to distinguish FQH-type states from competing states. Our scheme offers a practical tool for the detection of topologically-ordered states in quantum-engineered systems, with potential applications in solid state.