Max Planck Institute of Quantum Optics

Abstract:

Symmetry plays a central role in characterizing quantum phases. In open quantum systems, it arises in two distinct forms: weak symmetry, where charges are conserved only on average, and strong symmetry, with exact conservation laws. In this talk, I will explore their physical implications in 1D open systems using a tensor network framework. For weak symmetry, I will show that it enables a quantized response distinguishing mixed-state phases, including those without pure-state analogs, identifiable through string order parameters. For strong symmetry, I construct a broad class of renormalization fixed-point mixed states that exhibit zero correlation length and anomalous symmetry. Despite the absence of local correlations, these states cannot be efficiently prepared, indicating intrinsic long-range
entanglement.

Reference:

[1] ZM Huang, S Diehl, XQ Sun, arXiv:2504.02941

[2] XQ Sun, arXiv:2504.16985

About the speaker:

Dr. Xiao-Qi Sun is currently a Humboldt Postdoctoral Fellow at the Max Planck Institute of Quantum Optics. Before moving to Germany, he obtained his Ph.D. from Stanford University in 2020 and was a Gordon and Betty Moore Postdoctoral Scholar at the University of Illinois at Urbana-Champaign. His research lies at the intersection of quantum information and condensed matter physics, with a focus on topological phenomena in quantum many-body systems, both in and out of equilibrium.

Place: Room M830, IOP-CAS (中国科学院物理研究所M830)