Multiboundary generalization of thermofield double states and their realization in critical quantum spin chains

We propose a multi-boundary generalization of thermofield double states (TFD) two-dimensional conformal field theory (CFT) and show, through map to the complex plane, that they are closely related multi-point correlation functions. then also describe how approximately realize these TFD numerically on lattice, starting from critical quantum spin chain Hamiltonian. In addition, finite size corrections lattice seen be significantly reduced by use \textit{smoothers} -- optimized unitary transformations locally re-arrange degrees freedom. One merit realization is it allows us probe properties proposed numerical experiments, including characterization their entanglement structure. As an illustration, we explicitly construct generalized with three four boundaries for Ising CFT compute quantities using novel free fermion techniques. find ranges parameters where multipartite significant or negligible.