"Quantum Fields and Quantum Information".

 The bridge between the quantum nature of the microscopic world and our classical daily life is a process called quantum decoherence, during which a quantum system gradually loses quantum information to the environment and becomes classical. The decoherence can also be viewed as the quantum system being weakly-measured by the environment. We apply quantum field theory techniques to understand quantum decoherence and weak measurement. This question can be mapped to a problem of boundary (or defect) of a quantum field theory, and many universal results can be obtained through standard quantum field theory techniques such as renormalization group. As examples, we investigate quantum critical points and topological states of matter, and their behaviors when they lose certain quantum features through decoherence.