Fig. 3
From: Barren plateaus in quantum neural network training landscapes
Exponential decay of variance. The sample variance of the gradient of the energy for the first circuit component of a two-local Pauli term \(\left( {\partial _{\theta _{1,1}}E} \right)\) plotted as a function of the number of qubits on a semi-log plot. As predicted, an exponential decay is observed as a function of the number of qubits, n, for both the expected value and its spread. The slope of the fit line is indicative of the rate of exponential decay as determined by the operator
