In Grover’s Algorithm, the oracle gate flips the amplitude of the target value. If the Oracle gate already knows the target value then why do we have to proceed further with the Algorithm?
I think it’s because it is in superposition. So, all possible values are treated at the same time in the Oracle, and only the target is marked… so you have a superposition state with one of the values marked.
I understand it thinking of a bunch of marbles falling down on a device that have a blue color detector. The input is the bunch of marbles, and the device detect blue ones and at the end of the device you have the blue ones at the bottom right of the device, and the rest at the bottom left.
Hope it helps