Quantum Speed Limit and Quantum Thermodynamic Uncertainty Relation under Feedback Control

Abstract: Quantum feedback control is a technique for controlling quantum dynamics by applying control inputs to the quantum system based on the results of measurements performed on the system. It is an important technique from both an applied and a fundamental theoretical point of view. There are two fundamental inequalities that describe trade-off relations in quantum mechanics, namely, the quantum speed limit and the quantum thermodynamic uncertainty relation. They characterize the operational limit of non-equilibrium quantum systems, making them essential for controlling such systems. Therefore, it is meaningful to formulate these trade-off relations within the framework of quantum feedback control. In this paper, we derive these inequalities based on the continuous matrix product state method. Additionally, we analytically derive the exact form of quantum dynamical activity under feedback control, which serves as the cost term in these inequalities. Specifically, we focus on the cases of Markovian feedback, i.e., the direct feedback of continuous measurement results. Our numerical analysis reveals that the presence of feedback control can improve the quantum speed limit time and the quality of continuous measurements. Furthermore, the relationship with quantum error correction, an important application of quantum feedback control, is discussed using numerical simulations. Thus, our work clarifies how feedback control affects these important trade-off relationships in quantum mechanics.