Jan Tuziemski (Stockhom University ): Out-of-time-ordered correlation functions in open systems
Channel: Centrum Fizyki Teoretycznej PAN
Date: 2021-04-10

Jan Tuziemski (Stockhom University )
Out-of-time-ordered correlation functions in open systems.
Recent theoretical and experimental studies have shown significance of quantum information scrambling (i.e. a spread of quantum information over a system degrees of freedom) for problems encountered in high-energy physics, quantum information, and condensed matter. Due to complexity of quantum many-body systems it is plausible that new developments in this field will be achieved by experimental explorations. Since noise effects are inevitably present in experimental implementations, a better theoretical understanding of quantum information scrambling in systems affected by noise is needed. To address this problem I will discuss indicators of quantum scrambling -- out-of-time-ordered correlation functions (OTOCs) in open quantum systems. As most experimental protocols for measuring OTOCs are based on backward time evolution, two possible scenarios of joint system-environment dynamics reversal will be considered: In the first one the evolution of the environment is reversed, whereas in the second it is not. Derivation of general formulas for OTOCs in those cases as well as a study of the spin chain model coupled to the environment of harmonic oscillators will be presented. In the latter case I derive expressions for open systems OTOCs in terms of Feynman-Vernon influence functional. Subsequently, assuming that dephasing dominates over dissipation, I provide bounds on open system OTOCs and illustrate them for a spectral density known from the spin-boson problem. In addition to being significant for quantum information scrambling, this results also advance understating of decoherence in processes involving backward time evolution. Based on Phys. Rev. A 100, 062106. 
CTP Quantum Information Days (online), 22-24 February 2021.
Center for Theoretical Physics PAS (Warsaw, Poland)