I've been look at this Notebook from
qiskit and trying to understand whats happening, but can't quite figure it out.
From my understanding, rotations around the Z Axis do not influence the probabilities of measuring $|0\rangle$ and $|1\rangle$. So, with my Knowledge, I would assume that the
ZZFeatureMap has no direct influence.
After that, the
RealAmplitudesis applied which corresponds more to my knowledge. We use weights inside of RY gates to play with the importance of single features and their contribution to the probability of measuring 0/1.
I would assume that given the circuit, my measurements should be a perfect 1/4 split across all 4 possible states, yet that is not the case.
Maybe I'm missing key information/relation between the global phase and measurements. I'm quite intrigued by it, as my circuits that incorporate RY/CRY gates for features and weights barely manage to hit 60% accuracy, where with the same training and problem the ZZFeatureMap + RealAmplitudes achieves a perfect 100% accuracy