Measuring quantized circular dichroism in ultracold topological matter

TL;DR

This paper experimentally demonstrates a quantized spectroscopic response in ultracold topological matter, revealing a new way to probe the topology and geometry of quantum systems through circular dichroism measurements.

Contribution

First experimental observation of quantized circular dichroism in ultracold topological bands, linking spectroscopic response to the Chern number and estimating the Wannier-spread functional.

Findings

Quantized depletion rate difference matches Chern number predictions

First measurement of Wannier-spread functional in ultracold atoms

Establishes topological spectroscopic response as a versatile probing method

Abstract

The topology of two-dimensional materials traditionally manifests itself through the quantization of the Hall conductance, which is revealed in transport measurements. Recently, it was predicted that topology can also give rise to a quantized spectroscopic response upon subjecting a Chern insulator to a circular drive: Comparing the frequency-integrated depletion rates associated with drives of opposite orientations leads to a quantized response dictated by the topological Chern number of the populated Bloch band. Here we experimentally demonstrate this intriguing topological effect for the first time, using ultracold fermionic atoms in topological Floquet bands. In addition, our depletion-rate measurements also provide a first experimental estimation of the Wannier-spread functional, a fundamental geometric property of Bloch bands. Our results establish topological spectroscopic responses as a versatile probe, which could be applied to access the geometry and topology of many-body quantum systems, such as fractional Chern insulators.