Środowiskowe Seminarium z Informacji i Technologii Kwantowych

Quantum-classical hybrid theories describe scenarios where quantum degrees of freedom interact with classical degrees of freedom. The need for such theories becomes particularly clear in feedback control, where classical measurement outcomes are fed back to a quantum system to influence its dynamics. Additionally, quantum-classical hybrid theories can be used to model a quantum system interacting with a large but finite-sized environment. In this case, the classical degree of freedom can be the magnetization of the environment.I will present two examples of quantum-classical hybrid theories. The quantum Fokker-Planck master equation (QFPME) that describes continuous feedback control and the extended microcanonical master equation (EMME) that describes a qubit coupled to a bath of two-level systems. The QFPME allows for obtaining analytical results for feedback scenarios that previously were only accessible using numerical methods. The EMME allows for keeping track of the magnetization of the bath, as well as the classical correlations between system and bath. These methods will be illustrated with simple but relevant examples.