  One of the most puzzling consequences of interpreting quantum mechanics in
terms of concepts borrowed from classical physics, is the so-called
wave-particle duality. Usually, wave-particle duality is illustrated in terms
of complementarity between path distinguishability and fringe visibility in
interference experiments. In this work, we instead propose a new type of
complementarity, that between the continuous nature of waves and the discrete
character of particles. Using the probabilistic methods of quantum field
theory, we show that the simultaneous measurement of the wave amplitude and the
number of photons in the same beam of light is, under certain circumstances,
prohibited by the laws of quantum mechanics. Our results suggest that the
concept of ``interferometric duality'' could be eventually replaced by the more
general one of ``continuous-discrete duality''.
