  We look at certain thought experiments based upon the 'delayed choice' and
'quantum eraser' interference experiments, which present a complementarity
between information gathered from a quantum measurement and interference
effects. It has been argued that these experiments show the Bohm interpretation
of quantum theory is untenable. We demonstrate that these experiments depend
critically upon the assumption that a quantum optics device can operate as a
measuring device, and show that, in the context of these experiments, it cannot
be consistently understood in this way. By contrast, we then show how the
notion of 'active information' in the Bohm interpretation provides a coherent
explanation of the phenomena shown in these experiments.
  We then examine the relationship between information and entropy. The thought
experiment connecting these two quantities is the Szilard Engine version of
Maxwell's Demon, and it has been suggested that quantum measurement plays a key
role in this. We provide the first complete description of the operation of the
Szilard Engine as a quantum system. This enables us to demonstrate that the
role of quantum measurement suggested is incorrect, and further, that the use
of information theory to resolve Szilard's paradox is both unnecessary and
insufficient. Finally we show that, if the concept of 'active information' is
extended to cover thermal density matrices, then many of the conceptual
problems raised by this paradox appear to be resolved.
