  A theory of electron counting statistics in quantum transport is presented.
It involves an idealized scheme of current measurement using a spin 1/2 coupled
to the current so that it precesses at the rate proportional to the current.
Within such an approach, counting charge without breaking the circuit is
possible. As an application, we derive the counting statistics in a single
channel conductor at finite temperature and bias. For a perfectly transmitting
channel the counting distribution is gaussian, both for zero-point fluctuations
and at finite temperature. At constant bias and low temperature the
distribution is binomial, i.e., it arises from Bernoulli statistics. Another
application considered is the noise due to short current pulses that involve
few electrons. We find the time-dependence of the driving potential that
produces coherent noise-minimizing current pulses, and display analogies of
such current states with quantum-mechanical coherent states.
