On matrix product states for periodic boundary conditions
Klaus Krebs
Abstract
The possibility of a matrix product representation for eigenstates with energy and momentum zero of a general m–state quantum spin Hamiltonian with nearest neighbour interaction and periodic boundary condition is considered. The quadratic algebra used for this representation is generated by 2m operators which fulfil m 2 quadratic relations and is endowed with a trace. It is shown that not every eigenstate with energy and momentum zero can be written as matrix product state. An explicit counter–example is given. This is in contrast to the case of open boundary conditions where every zero energy eigenstate can be written as a matrix product state using a Fock–like representation of the same quadratic algebra.