  Under appropriate conditions controllable two-level systems can be used to
detect the third moment of current fluctuations. We derive a Master Equation
for a quantum system coupled to a bath valid to the third order in the coupling
between the system and the environment. In this approximation the reduced
dynamics of the quantum system depends on the frequency dependent third moment.
Specializing to the case of a controllable two-level system (a qubit) and in
the limit in which the splitting between the levels is much smaller than the
characteristic frequency of the third moment, it is possible to show that the
decay of the qubit has additional oscillations whose amplitude is directly
proportional to the value of the third moment. We discuss an experimental setup
where this effect can be seen.
