  A measurement is deemed successful, if one can maximize the information gain
by the measurement apparatus. Here, we ask if quantum coherence of the system
imposes a limitation on the information gain during quantum measurement. First,
we argue that the information gain in a quantum measurement is nothing but the
coherent information or the distinct quantum information that one can send from
the system to apparatus. We prove that the maximum information gain from a pure
state, using a mixed apparatus is upper bounded by the initial coherence of the
system. Further, we illustrate the measurement scenario in the presence of
environment. We argue that the information gain is upper bounded by the entropy
exchange between the system and the apparatus. Also, to maximize the
information gain, both the initial coherence of the apparatus, and the final
entanglement between the system and apparatus should be maximum. Moreover, we
find that for a fixed amount of coherence in the final apparatus state the more
robust apparatus is, the more will be the information gain.
