Coherent optical control of quantum Hall edge states

Current-carrying chiral edge states in quantum Hall systems exhibit fascinating properties typically studied using electron spectroscopy and interferometry. Here we demonstrate that electron occupation, current, and coherence in the chiral edge states can be selectively probed and controlled by low-energy electromagnetic radiation in the microwave to infrared range, without affecting electron states in the bulk or disrupting the quantum Hall effect conditions within the sample. Both linear and nonlinear optical controls are feasible due to the inevitable violation of adiabaticity and inversion symmetry breaking for electron states near the edge. Moreover, valley-selective excitation of edge states is possible in graphene-based systems. This opens up new pathways for frequency- and polarization-selective spectroscopy and the control of individual edge states.