  Fluctuations in the acoustoelectric current, induced by a surface acoustic
wave propagating along a ballistic quantum channel, are considered. We focus on
the large wave-amplitude case, in which it has been experimentally found that
the current is quantized, and analyze the noise spectrum. A phenomenological
description of the process, in terms of a random pulse sequence, is proposed.
The important ingredients of this description are the probabilities, p_n, for a
surface acoustic wave well to capture n electrons. It is found that from the
noise characteristics one can obtain these probabilities, and also estimate the
typical length scales of the regions in which the electrons are trapped.

Mesoscale and Nanoscale Physics