  An early approach to include pointers representing measurement devices into
quantum mechanics was given by von Neumann. Based on this idea, we model such
pointers by qubits and couple them to a free particle, in analogy to a
classical time-of-flight arrangement. The corresponding Heisenberg dynamics
leads to pointer observables whose expectation values allow us to reconstruct
the particle's momentum distribution via the characteristic function. We
investigate different initial qubit states and find that such a reconstruction
can be considerably simplified by initially entangled pointers.
