Gapless quantum spin chains: multiple dynamics and conformal wavefunctions

作者：Chen Xiao^*; Fradkin Eduardo; Witczak Krempa William

来源：Journal of Physics A-Mathematical and Theoretical, 2017, 50(46): 464002.

DOI：10.1088/1751-8121/aa8dbc

• quantum spin chains
• quantum entanglement
• quantum dynamics
• conformal symmetry
• orbifolds
• Lifshitz quantum field theory
• non-equilibrium relaxation

We study gapless quantum spin chains with spin 1/2 and 1: the Fredkin and Motzkin models. Their entangled groundstates are known exactly but not their excitation spectra. We first express the groundstates in the continuum which allows for the calculation of spin and entanglement properties in a unified fashion. Doing so, we uncover an emergent conformal-type symmetry, thus consolidating the connection to a widely studied family of Lifshitz quantum critical points in 2d. We then obtain the low lying excited states via large-scale DMRG simulations and find that the dynamical exponent is z = 3.2 in both cases. Other excited states show a different z, indicating that these models have multiple dynamics. Moreover, we modify the spin-1/2 model by adding a ferromagnetic Heisenberg term, which changes the entire spectrum. We track the resulting non-trivial evolution of the dynamical exponents using DMRG. Finally, we exploit an exact map from the quantum Hamiltonian to the non-equilibrium dynamics of a classical spin chain to shed light on the quantum dynamics.

• 出版日期2017-11-17
• 单位中国科学院理论物理研究所