Exponential speed-up of quantum annealing via n-local catalysts

The quantum speedup in solving optimization problems via adiabatic quantum annealing is often hindered by the closing of the energy gap during the anneal, especially when this gap scales exponentially with system size. In this work, we address this by demonstrating that for the Maximum Weighted Independent Set (MWIS) problem, an informed choice of n-local catalysts (operators involving n qubits) can re-open the gap or prevent it from closing during the anneal process. By analyzing first-order phase transitions in toy instances of the MWIS problem, we identify effective forms of catalysts and also show that non-stoquasticity is not essential to avoid such phase transitions. While some of the toy problems studied might not be classically NP-hard, they reveal that n-local catalysts exponentially improve gap scaling and need to be connected across unfrustrated loops in the problem graph to be effective. Our analysis suggests that non-local quantum fluctuations entangling multiple qubits are key to achieving the desired quantum advantage.