IQIM Postdoctoral and Graduate Student Seminar

Abstract: We identify a three-dimensional system that exhibits long-range entanglement at sufficiently small but nonzero temperature—it therefore constitutes a quantum topological order at finite temperature, the first known example of such order in physically realistic dimensions. The model of interest is known as the fermionic toric code, a variant of the usual 3D toric code, which admits emergent fermionic pointlike excitations. The fermionic toric code, importantly, possesses an anomalous two-form symmetry, associated with the spacelike Wilson loops of the fermionic excitations. We argue that it is this symmetry that imbues low-temperature thermal states with a novel topological order and long-range entanglement. Interestingly, the classification of three-dimensional topological orders suggests that the low-temperature thermal states of the fermionic toric code belong to a phase of matter that, in the context of equilibrium phases of matter, only exists at nonzero temperatures. Relatedly, despite its long-range quantum entanglement, the system only exhibits a classical memory.

Following the talk, lunch will be provided on the lawn outside East Bridge.