  With the aid of a quantum memory, the uncertainty about the measurement
outcomes of two incompatible observables of a quantum system can be reduced. We
investigate this measurement uncertainty bound by considering an additional
quantum system connected with both the quantum memory and the measured quantum
system. We find that the reduction of the uncertainty bound induced by a
quantum memory, on the other hand, implies its increasing for a third
participant. We also show that the properties of the uncertainty bound can be
viewed from perspectives of both quantum and classical correlations, in
particular, the behavior of the uncertainty bound is a result of competitions
of various correlations between different parties.
