  The identification of environmental changes is crucial in many fields. The
present research is aimed at investigating the optimal performance for
detecting change points in a quantum system when its Hamiltonian suddenly
changes at a specific time. Assume that the Hamiltonians before and after the
change are known and that the prior probability of each prospective change
point is identical. These Hamiltonians can be time-dependent. The problem
considered in this study is an extension of the problem of discriminating
multiple quantum processes that consist of sequences of quantum channels.
Although it is often extremely difficult to find an analytical solution to such
a problem, we demonstrate that the maximum success probability for the
Hamiltonian change point problem can be determined analytically and has a
simple form.
