Special states in quantum many-body spectra

While quantum many-body systems typically thermalize, exceptions to thermalization provide interesting opportunities, e.g. with respect to information storage. One possibility is that all states in the spectrum many-body localize. Another is a weak violation of thermalization, in which a few special states in the spectrum do not thermalize, while the rest do. This phenomenon is known as quantum many-body scars.

Here, we propose and demonstrate that one can similarly have a weak violation of many-body localization, in which one or a few states in a spectrum have above area law entanglement, while the rest of the states are many-body localized. We show that this can be achieved through a mechanism, in which emergent symmetry of the special states prevents many-body localization in these states. In addition, we provide two examples of normal quantum many-body scars, in which the special states are topological.

References: arXiv:2002.07824, arXiv:2009.03923, arXiv:2009.00022