  The determination of the density matrix of an ensemble of identically
prepared quantum systems by performing a series of measurements, known as
quantum tomography, is minimal when the number of outcomes is minimal. The most
accurate minimal quantum tomography of qubits, sometimes called a tetrahedron
measurement, corresponds to projections over four states which can be
represented on the Bloch sphere as the vertices of a regular tetrahedron. We
investigate whether it is possible to implement the tetrahedron measurement of
double slit qubits of light, using measurements performed on a single plane.
Assuming Gaussian slits and free propagation, we demonstrate that a judicious
choice of the detection plane and the double slit geometry allows the
implementation of a tetrahedron measurement. Finally, we consider possible sets
of values which could be used in actual experiments.
