  Ballistic transport of hot electrons in a quantum Hall edge channel is
attractive for studying electronic analog of quantum optics, where the edge
potential profile is an important parameter that governs the charge velocity
and scattering by longitudinal-optical (LO) phonons. Here we use a parallel
double gate to control the electric field of the edge potential, and
investigate the ballistic length of the channel by using hot-electron
spectroscopy. The ballistic length is significantly enhanced by reducing the LO
phonon scattering rate in the tailored potential.
