Feedback Control of Continuously Monitored Qubits: An Action Formalism Perspective

Feedback control stabilizes quantum systems against noise and decoherence by adjusting dynamics in real time based on measurements. We investigate how feedback stabilizes a continuously monitored qubit using an action formalism approach, extending the Chantasri–Dressel–Jordan formalism to include feedback. Applying this framework to a transmon qubit under dispersive measurement, we analyze how optimized feedback parameters achieve ensemble-averaged stabilization and explore its stochastic phase-space structure.