Spin operator matrix elements in the quantum Ising chain: fermion approach

Abstract

Using some modification of the standard fermion technique we derive factorized formulasfor spin operator matrix elements (form factors) between general eigenstates of theHamiltonian of the quantum Ising chain in a transverse field of finite length. Thederivation is based on the approach recently used to derive factorized formulas forZN-spin operator matrix elements between ground eigenstates of the Hamiltonian of theZN-symmetric superintegrable chiral Potts quantum chain. The obtained factorized formulasfor the matrix elements of the Ising chain coincide with the corresponding expressionsobtained by the separation of variables method.