  The wave plate is a basic device for transforming and measuring the
polarization states of light. It is known that the transformation of light by
means of two wave plates makes it possible to measure the state of polarization
in an arbitrary basis. The finite spectral width of the light, however, leads
to a chromatic aberration of the polarization quantum transformation caused by
the parasitic dispersion of the birefringence of the plate material. This
causes systematic errors in the tomography of quantum polarization states and
significantly reduces its accuracy. This study is a development of our work1,
in which an adequate model for quantum measurements of polarization qubits
under chromatic aberration was first formulated. This work includes a
generalization of the results obtained earlier for the cases of two-qubit
states. Along with examples of random states those uniformly distributed over
the Haar measure are considered. Using a matrix of complete information, it is
quantitatively traced how the presence of chromatic aberrations under
conditions of a finite spectral width of light leads to the loss of information
in quantum measurements. It is shown that the use of the developed model of
fuzzy measurements instead of the model of standard projection measurements
makes it possible to suppress systematic errors of quantum tomography even when
using high-order wave plates. It turns out that the fuzzy measurement model can
give a significant increase in the reconstruction accuracy compared to the
standard measurement model.
