▎ 摘　　要

Graphene-a naturally occurring two-dimensional material with unique optical and electronic properties-serves as a platform for novel terahertz applications and miniaturized systems with new capabilities. Recent discoveries of unusual quantum magneto-transport and high magneto-optical activity in strong magnetic fields make graphene a potential candidate for nonreciprocal photonics. Here we propose a paradigm of a flatland graphene-based metasurface in which an extraordinary and quantized magneto-optical activity at terahertz and infrared is attained at low, on-chip-compatible, magnetizations (similar to 0.2-0.3 T). The proposed system essentially breaks the tight linkage between the strength of the magnetic biasing and the resulting magneto-optical response. We design a system extremely sensitive to the quantized spectrum of graphene Landau levels and predict up to 90 degrees of Faraday rotation with just a single sheet of graphene. We also demonstrate how to resolve the quantum resonances at the macroscopic level in the far-field. Our results not only are of a fundamental interest, but, as we discuss, pave a way to conceptually new capabilities in a range of applications, including sensing, terahertz nanophotonics, and even cryptography.