  We describe a technique to measure the position of a dipolar scatterer based
on self-homodyne detection of the scattered light. The method can theoretically
reach the Heisenberg limit, at which information gained about the position is
constrained only by the back-action of the scattered light. The technique has
applications in the fields of levitated optomechanics and trapped ions and is
generally applicable to the position determination of confined light
scatterers.
