title: Degenerate ground states and multiple bifurcations in a two-dimensional q-state quantum Potts model.
abstract: We numerically investigate the two-dimensional q-state quantum Potts model on the infinite square lattice by using the infinite projected entangled-pair state (iPEPS) algorithm. We show that the quantum fidelity, defined as an overlap measurement between an arbitrary reference state and the iPEPS ground state of the system, can detect q-fold degenerate ground states for the Z_{q} broken-symmetry phase. Accordingly, a multiple bifurcation of the quantum ground-state fidelity is shown to occur as the transverse magnetic field varies from the symmetry phase to the broken-symmetry phase, which means that a multiple-bifurcation point corresponds to a critical point. A (dis)continuous behavior of quantum fidelity at phase transition points characterizes a (dis)continuous phase transition. Similar to the characteristic behavior of the quantum fidelity, the magnetizations, as order parameters, obtained from the degenerate ground states exhibit multiple bifurcation at critical points. Each order parameter is also explicitly demonstrated to transform under the Z_{q} subgroup of the symmetry group of the Hamiltonian. We find that the q-state quantum Potts model on the square lattice undergoes a discontinuous (first-order) phase transition for q=3 and q=4 and a continuous phase transition for q=2 (the two-dimensional quantum transverse Ising model).
authors.affiliation: Centre for Modern Physics and Department of Physics, Chongqing University, Chongqing 400044, People's Republic of China.
authors.forename: Yan-Wei
authors.initials: YW
authors.lastname: Dai
authors.affiliation: Centre for Modern Physics and Department of Physics, Chongqing University, Chongqing 400044, People's Republic of China.
authors.forename: Sam Young
authors.initials: SY
authors.lastname: Cho
authors.affiliation: Centre for Modern Physics and Department of Physics, Chongqing University, Chongqing 400044, People's Republic of China and Department of Theoretical Physics and Mathematical Science Institute, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Murray T
authors.initials: MT
authors.lastname: Batchelor
authors.affiliation: Centre for Modern Physics and Department of Physics, Chongqing University, Chongqing 400044, People's Republic of China.
authors.forename: Huan-Qiang
authors.initials: HQ
authors.lastname: Zhou
mesh_terms: D000465:Algorithms; D060526:Magnetic Fields; D008962:Models, Theoretical; D044367:Phase Transition; D011789:Quantum Theory