I am relatively new to quantum computing and I feel like I don't fully understand the power of quantum computing due to a lack of understanding of how amplitude amplification works.
What is confusing me is that the amplitude of the qubit is the square root of the probability and so in amplitude amplification, how is the amplitude of the "correct answer" changed to negative (before then being reflected across the average)?
I understand that it is a gate and the gate is a series of complex operations but at the same time I fail to understand physically how do the gates change the amplitude of the qubit. I am referencing this in response to the webpage: IBM Q Experience Documentation - Grover's algorithm. Any help is greatly appreciated. Thank you!