The ZZ-Entangling Feature Map

The secret ingredient of the QSVM

Curious why some quantum kernels soar while others stumble? This post sheds light onto a fundamental quantum kernel: the ZZ-entangling feature map.

Of course, there is not just one map that applies to all. If your task requires global interweaving—that is, if features that are far apart in the index need to talk to each other—or if you are looking for third- or higher-order correlations, you need to build in additional interweaving passages or explore richer feature map architectures. But these very additions carry the risk of barren plateaus and collapsing kernels if not carefully managed.

The elegance of the ZZ-map lies in its modesty: it shows us how far we can go with first- and second-order terms before hardware noise and optimization problems arise.