



01657nas a2200205   4500008004100000245006800041210006700109260001500176300000900191490000700200520101600207100001701223700002001240700001501260700001801275700001601293700001901309700002301328856010001351       2021                        eng d00aNoise-induced barren plateaus in variational quantum algorithms0 aNoiseinduced barren plateaus in variational quantum algorithms  c11/29/2021  a69610 v123 a<p>Variational Quantum Algorithms (VQAs) may be a path to quantum advantage on Noisy Intermediate-Scale Quantum (NISQ) computers. A natural question is whether noise on NISQ devices places fundamental limitations on VQA performance. We rigorously prove a serious limitation for noisy VQAs, in that the noise causes the training landscape to have a barren plateau (i.e., vanishing gradient). Specifically, for the local Pauli noise considered, we prove that the gradient vanishes exponentially in the number of qubits n if the depth of the ansatz grows linearly with n. These noise-induced barren plateaus (NIBPs) are conceptually different from noise-free barren plateaus, which are linked to random parameter initialization. Our result is formulated for a generic ansatz that includes as special cases the Quantum Alternating Operator Ansatz and the Unitary Coupled Cluster Ansatz, among others. For the former, our numerical heuristics demonstrate the NIBP phenomenon for a realistic hardware noise model.</p>1 aWang, Samson1 aFontana, Enrico1 aCerezo, M.1 aSharma, Kunal1 aSone, Akira1 aCincio, Lukasz1 aColes, Patrick, J.  uhttps://quics.umd.edu/publications/noise-induced-barren-plateaus-variational-quantum-algorithms