Symmetry is central to our understanding of natural phenomena. A Sagnac interferometer, first invented for the detection of the hypothetical “ether” a century ago, is intrinsically sensitive to broken time-reversal symmetry (TRS). In this talk, Jing Xia of UC Irvine describes a loop-less version of the Sagnac interferometer and microscope that has achieved unprecedented nanoradian level Kerr and Faraday sensitivity even at DC. He will discuss his group’s studies of 2D magnetism and superconductivity, as well as research indicating the existence of a chiral edge state that may be useful for robust quantum computing.