  Rectification of microwave radiation by asymmetric, ballistic quantum dot is
observed. The directed transport is studied at different frequency (1-40 GHz)
temperatures (0.3K-6K)and magnetic field. Dramatic reduction of the
rectification is found in magnetic fields at which the cyclotron (Larmor)
radius of the electron orbits at Fermi level is smaller than the size of the
quantum dot. It strongly suggests the ballistic nature of the observed
nonlinear phenomena. Both symmetric and anti-symmetric with respect to the
magnetic field contributions to the directed transport are presented. We have
found that the behavior of the symmetric part of the rectified voltage with the
magnetic field is different significantly for microwaves with different
frequencies. A ballistic model of the directed transport is proposed.
