Reliable Monte Carlo simulation of T-gate cultivation circuits without twirling artifacts

Develop a fast Monte Carlo simulation technique for large magic state cultivation circuits containing many T gates that avoids Pauli-twirling artifacts which convert benign stabilizer errors into malignant ones, enabling accurate logical error-rate estimation without resorting to S/Z proxy circuits.

Background

Previous work simulated large cultivation circuits by tracking Pauli error propagation and twirling non-Pauli errors across T gates back to Pauli errors. The authors report that, in their circuits, twirling makes benign errors malignant, leading to spuriously high logical error rates and undermining the approach.

They attempted fixes but were unsuccessful, leaving a gap for a scalable simulation method that faithfully handles T-gate non-Pauli error propagation in the presence of stabilizer unfolding and postselection.