Heat flow from a measurement apparatus monitoring and feedbacking a dissipative qubit*

  Quantum measurement is a fundamental operation in quantum information processing and plays a crucial role in the operation of quantum computers. Unlike classical measurements, quantum measurements have the unique property of altering the state of the measured quantum system. Furthermore, the changes induced by quantum measurements in the quantum state give rise to the generation of heat. This intersection of quantum measurements and thermodynamics has led to the development of the field of quantum thermodynamics, prompting extensive research into intriguing problems such as Maxwell's demon and the Szilard engine.

  Direct heat exchange between the measurement apparatus and the quantum system being measured is inherently driven by quantum measurements. The question of how much heat can be extracted from the quantum system or stored within it is of paramount importance. However, when it comes to dissipative quantum systems subjected to continuous quantum measurements, the fundamental question of the direction of heat flow remains unexplored. This issue is not only critical for advancing our understanding of information thermodynamics but also holds potential applications in the development of measurement-based thermal devices.

  In this talk, we focus on the most fundamental quantum system, the qubit, as the measuring system. We clarify the heat flow between a qubit and a measurement apparatus when the qubit is coupled to bosonic heat baths under continuous quantum measurements and feedback.