Williamson Dominic J, Dua Arpit, Cheng Meng
Department of Physics, Yale University, New Haven, Connecticut 06520-8120, USA.
Yale Quantum Institute, Yale University, New Haven, Connecticut 06520, USA.
Phys Rev Lett. 2019 Apr 12;122(14):140506. doi: 10.1103/PhysRevLett.122.140506.
We demonstrate that linear combinations of subregion entropies with canceling boundary terms, commonly used to calculate the topological entanglement entropy, may suffer from spurious nontopological contributions even in models with zero correlation length. These spurious contributions are due to a specific kind of long-range string order and persist throughout certain subsystem symmetry-protected phases. We introduce an entropic quantity that measures the presence of such order, and hence should serve as an order parameter for the aforementioned phases.
