THz-photon generation due to electrons injected via quantum-Hall edge channels

We report THz radiation originating from encounter of quantum-Hall edge states. The measurements are implemented by using a photon-counting microscope with quantum-dot single THz-photon detectors. Inter-Landau-level photon emission is found to occur on the confluence of unequally populated edge states in a quantum-Hall effect plateau (filling factor ν=4), where potential barriers across a Hall-bar are introduced. It is revealed that the confluence of edge states on the lower-potential sample boundary for electrons (with positive Hall voltage) is significantly more emissive than the other. This emission phenomenon is unique in the point that electrons are injected by coherent transport channels to a microscopic area where radiation takes place, suggesting a potential platform for studying the interplay between quantum electron transport and quantum optics.