Seminar

We show, via explicit computation on a constrained bosonic model born from Hilbert Space Fragmentation, that the presence of subsystem symmetries can lead to a quantum phase transition where the critical point exhibits an emergent enhanced symmetry. Such a transition separates a unique gapped ground state from a gapless one; the latter phase exhibits a broken symmetry. The intermediate critical point separating these phases exhibits an additional emergent symmetry which we identify; this emergence leads to a critical theory in the Ashkin-Teller, instead of the expected Ising, universality class. We verify this scenario via explicit exact-diagonalization computations. We reach fairly large system sizes (28-plaquettes) in this quasi-1d system due to the constraints on the Hilbert space. We compute among other things, the critical exponents and using finite size scaling, and also the central charge of the underlying CFT. We connect the values of these parameters to the Ashkin-Teller critical line and summarize our results.