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QI: Fachverband Quanteninformation

QI 9: Quantum Machine Learning and Classical Simulability

QI 9.1: Invited Talk

Tuesday, March 19, 2024, 09:30–10:00, HFT-FT 101

Does provable absence of barren plateaus imply classical simulability? Or, why we might need to rethink variational quantum computing — •Zoe Holmes — EPFL, Lausanne, Switzerland

A large amount of effort has recently been put into understanding the barren plateau phenomenon. Here we face the increasingly loud elephant in the room and ask a question that has been hinted at by many but not explicitly addressed: Can the structure that allows one to avoid barren plateaus also be leveraged to efficiently simulate the loss classically? We present strong evidence that commonly used models with provable absence of barren plateaus are also in a sense classically simulable, provided that one can collect some classical data from quantum devices during an initial data acquisition phase. This follows from the observation that barren plateaus result from a curse of dimensionality, and that current approaches for solving them end up encoding the problem into some small, classically simulable, subspaces. This sheds serious doubt on the non-classicality of the information processing capabilities of parametrized quantum circuits for barren plateau-free landscapes and on the possibility of superpolynomial advantages from running them on quantum hardware. We end by discussing caveats in our arguments, the role of smart initializations, and by highlighting new opportunities that our perspective raises.

Keywords: Variational quantum algorithms; Barren plateaus; Quantum advantage; Classical simulability