Speaker
Description
Feedback cooling plays a critical role in stabilizing quantum systems and achieving low temperatures, where a key question is to determine the fundamental thermodynamic limits on cooling performance. In this talk, we discuss a fundamental bound on quantum feedback cooling in Gaussian systems, by deriving a generalized second law of thermodynamics involving the kinetic temperatures of the system and a measure of quantum information flow obtained by continuous measurement. In contrast to previously known bounds, the obtained bound can be saturated by experimentally feasible situations using the quantum Kalman filter with a large feedback gain, where the cooling efficiency approaches its maximum. We further analyze the attainability of maximum cooling efficiency at finite cooling power by deriving a thermodynamic uncertainty relation (TUR) for feedback cooling in classical underdamped systems. From the obtained TUR, we find that divergence of the fluctuation of the reversible local mean velocity (i.e., taking a sufficiently large feedback gain) is the key to achieve such situations. Our theory provides a general framework for understanding the cooling limit from the perspectives of information thermodynamics.
