Coherent optical control of quantum Hall edge states

Current carrying chiral edge states in quantum Hall systems have fascinating properties that are usually studied by electron spectroscopy and interferometry. Here we demonstrate that electron occupation, current, and electron coherence in 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 destroying quantum Hall effect conditions in the bulk of the sample. Both linear and nonlinear optical control is possible due to inevitable violation of adiabaticity and inversion symmetry breaking for electron states near the edge. This opens up new pathways for frequency- and polarization-selective spectroscopy and control of individual edge states.