Topic: The spacetime density matrix formalism and entropy-related quantities
Speaker: Assoc. Prof. Wuzhong Guo
Coordinates: PCFT C1124, 16:00, Thursday, October 16
Abstract: The spacetime density matrix formalism provides a natural generalization of the standard density matrix—from a single Cauchy surface to multiple Cauchy surfaces. This framework captures correlations across different times and regions and can be systematically constructed for general quantum systems. There are several reasons why we are interested in this formalism. First, it provides the foundation for defining and evaluating timelike entanglement, a new concept that plays an important role in QFTs and holography. Second, it offers a unified treatment of timelike and spacelike correlations and is closely related to the dynamical processes of the system. In this talk, I will briefly discuss how timelike entanglement can be made well-defined through the spacetime density matrix and how to evaluate corresponding entanglement measures in QFTs. By studying the moments of the (reduced) density matrix, we find that entropy-related quantities are sensitive to couplings between subsystems. This sensitivity provides a potential probe for detecting interactions between subsystems, which may have interesting implications for scattering processes and open quantum systems. I will also present some illustrative examples and comment on a systematic method for computing entropy-related quantities in the weak-coupling limit.