The momentum-space entanglement properties of several quantum spin chains are investigated. More specifically, we study the entanglement spectra, i.e. the set of eigenvalues of the reduced density matrix, between left-and right-moving particles in bosonic and fermionic formulations of quantum spin chains. We elaborate on how momentum-space entanglement spectra may support the numerical study of phase transitions and classify certain critical systems. We also investigate the momentum-space entanglement spectrum after a quantum quench and show that the momentum-space entanglement spectrum of the XXZ spin-half chain possesses many universal features both in equilibrium and after a quantum quench.
References: Phys. Rev. Lett. 113, 256404 (2014), arXiv:1512.09030, arXiv:1603.01997