Simulating excitation spectra with projected entangled-pair states

We develop and benchmark a technique for simulating excitation spectra of generic two-dimensional quantum lattice systems using the framework of projected entangled-pair states (PEPS). The technique relies on a variational ansatz for capturing quasiparticle excitations on top of a PEPS ground state. Our method perfectly captures the quasiparticle dispersion relation of the square-lattice transverse-field Ising model and reproduces the spin-wave velocity and the spin-wave anomaly in the square-lattice Heisenberg model with high precision.