  White-light interferometry is one of today's most precise tools for
determining optical material properties. Achievable precision and accuracy are
typically limited by systematic errors due to a high number of interdependent
data fitting parameters. Here, we introduce spectrally-resolved quantum
white-light interferometry as a novel tool for optical property measurements,
notably chromatic dispersion in optical fibres. By exploiting both spectral and
photon-number correlations of energy-time entangled photon pairs, the number of
fitting parameters is significantly reduced which eliminates systematic errors
and leads to an absolute determination of the material parameter. By comparing
the quantum method to state-of-the-art approaches, we demonstrate the quantum
advantage through 2.4 times better measurement precision, despite involving 62
times less photons. The improved results are due to conceptual advantages
enabled by quantum optics which are likely to define new standards in
experimental methods for characterising optical materials.
