Application of quantum Hall edge channels

Three remarkable effects of edge channels are described. The first is the coherent control of nuclear spins in GaAs/AlGaAs Hall bars. Nuclear spins are (i) electrically polarized by unequally populated spin–split integer-quantum Hall edge channels via the hyperfine interaction, (ii) coherently controlled via pulsed nuclear magnetic resonance induced by local RF-magnetic fields, and (iii) finally detected by the edge channels through resistance change of the Hall device via the hyperfine interaction. The controlled nuclear spins are limited to those along the edge channels, on the order of 109. The second is the study of spin polarization of fractional-quantum Hall edge channels by utilizing the hyperfine interaction. The third is the single-photon detection in the terahertz wave spectral region, which is carried out by incorporating an integer-quantum Hall electron system into a quantum dot. Individual events of single-terahertz-photon absorption within the quantum dot via cyclotron resonance cause the quantum dot to electrically polarize. The polarization, in turn, is detected as respective telegraph-like switches of the tunnel conductance through the quantum dot. The effective sensitivity of detection is better than that of conventional detector by a factor about 104.