Ground-state Riemannian metric, cyclic quantum distance, and the quantum   criticality in an inhomogeneous Ising spin chain
  We investigate the ground-state Riemannian metric and the cyclic quantum distance of an inhomogeneous quantum Ising spin-1/2 chain in a transverse field. This model can be diagonalized by using a general canonical transformation to the fermionic Hamiltonian mapped from the spin system. The ground-state Riemannian metric is derived exactly on a parameter manifold ring $S^1$, which is introduced by performing a gauge transformation to the spin Hamiltonian through a twist operator. The ground-state cyclic quantum distance and the second derivative of the ground-state energy are studied in different inhomogeneous exchange coupling parameter region. Particularly, we show that the quantum ferromagnetic phase in the uniform Ising chain can be characterized by an invariant cyclic quantum distance with a constant ground-state Riemannian metric, and this metric will rapidly decay to zero in the paramagnetic phase. 
Yu-Quan Ma, Deng-Shan Wang, Ya-Jiang Hao, Xiang-Guo Yin, Wu-Ming Liu
cond-mat.str-el quant-ph