“…The effect of the structure of the cost function on the appearance of barren plateaus was also investigated in other works [14,15], and it was shown that global cost functions are more prone to exhibit barren plateaus. Note that shallow models such as quantum kernel machines [36][37][38][39][40] and reservoir computing models [41][42][43][44], while often easier to train than variational quantum algorithms, might also suffer from trainability issues of a similar nature [45].…”