Exact large deviations and emergent long-range correlations in sequential quantum East circuits

Abstract: Exploiting quantum measurements is a promising route for preparation of correlated quantum states. We use methods from large deviation theory to solve this problem exactly for a specific system: the deterministic quantum East circuit with boundary measurements. We show that conditioning on measurement outcomes generates a long-range correlated state, despite typical trajectories being trivial. We derive the channel that optimally realizes the rare measurement trajectories, and establish a formal connection with the Petz recovery (time-reversal) map. We compute one- and two-point correlation functions in the conditioned state, revealing finite two-body correlations at arbitrarily large separations, and an underlying fractal structure, related to the Sierpi\'nski triangle. These results demonstrate explicitly how boundary measurements can be used to control bulk properties of a quantum system.