  We present a numerical method to simulate a system of multiple emitters
coupled to a non-interacting bath, in any parameter regime. Our method relies
on a Block Lanczos transformation that maps the whole system onto a strip
geometry, whose width is given by the number of emitters. Utilizing the spatial
symmetries of the problem and identifying the relevant range of energies of the
bath we achieve a more efficient simulation, which we perform using tensor
network techniques. As a demonstration, we study the collective emission from
multiple emitters coupled to a square lattice of bosons and observe how the
departure from Markovianity as coupling strength and emitter number is
increased prevents collective radiation. We also simulate the dynamic
preparation of an excitation in a bound state from a multi-excitation initial
state. Our work opens new possibilities for the systematic exploration of
non-Markovian effects in the dynamics and equilibrium properties of
multi-emitter systems. Furthermore, it can easily be extended to other setups,
including finite bath temperature or impurities coupled to fermionic
environments.
