  Finite resolution quantum nondemolition (QND) measurements allow a
determination of light field properties while preserving some of the original
quantum coherence of the input state. It is thus possible to measure
correlations between the photon number and a quadrature component of the same
light field mode. Nonclassical features emerge as photon number quantization is
resolved. In particular, a strong anti-correlation of quantization and
coherence is observable in QND measurements of photon number, and a correlation
between measurement induced quantum jumps and quadrature component measurement
results is obtained in QND measurements of quadrature fluctuations in the
photon vacuum. Such nonclassical correlations represent fundamental quantum
properties of the light field and may provide new insights into the nature of
quantization itself.
