  We introduce a novel concept which we call as potent value of system
observable for pre- and post-selected quantum states. This describes, in
general, how a quantum system affects the state of the apparatus during the
time between two strong measurements corresponding to pre- and post-selections.
The potent value can be realized for any interaction strength and for arbitrary
coupling between the system and the apparatus observables. Most importantly,
potent values generalize and unify the notion of the weak values and modular
values of observables in quantum theory. Furthermore, we define a potent
operator which describes the action of one system on the another and show that
superposition of time-evolutions and time-translation machines are potent
operators. These concepts may find useful applications in quantum information
processing and can lead to technological benefits.
