Isometric tensor network optimization for extensive Hamiltonians is free of barren plateaus

Strongly correlated quantum many-body systems from condensed matter and particle physics are very hard to study classically and variational quantum algorithms (VQAs) may be hampered by barren plateaus, where energy gradients decay exponentially in the system size. The authors prove that this critical problem can be resolved by employing VQAs based on suitable isometric tensor network states, establishing a new route for the investigation of strongly correlated quantum matter on NISQ devices.