IAS Physics Group Meeting

Abstract: Global symmetry and anomaly have long served as powerful organizing principles for understanding quantum phases of matter in ground states. In this talk I will discuss recent progress in extending these ideas to many-body mixed states. I will begin by reviewing the distinction between strong and weak symmetries, and introduce a novel form of spontaneous symmetry breaking (SSB) in which a strong symmetry is broken down to a weak one. I will show that such strong-to-weak SSB is a universal feature of mixed-state quantum phases. I will then turn to anomalous symmetries, whose strong-to-weak SSB gives rise to intrinsically mixed-state phases exhibiting long-range entanglement characterized by multi-partite inseparability.