Simulating quantum systems on the Bethe lattice by translationally invariant infinite-tree tensor network

We construct an algorithm to simulate imaginary time evolution of translationally invariant spin systems with local interactions on an infinite, symmetric tree. We describe the state by symmetric infinite-Tree Tensor Network (iTTN) and use translation-invariant operators for the updates at each time step. The contraction of this tree tensor network can be computed efficiently by recursion without approximations and one can then truncate all the iTTN tensors at the same time. The translational symmetry is preserved at each time step that makes the algorithm very well conditioned and stable. The computational cost scales like O(Dq+1)O(Dq+1) with the bond dimension DD and coordination number qq, much favorable than that of the iTEBD on trees [D. Nagaj, E. Farhi, J. Goldstone, P. Shor, I. Sylvester, Phys. Rev. B 77 (2008) 214431]. Studying the transverse-field Ising model on the Bethe lattice, the numerics indicate a ferromagnetic-paramagnetic phase transition, with a finite correlation length even at the transition point.

► Finding ground states of interacting spin systems by imaginary time evolution.
► Translation-invariant iTTN description kept at every time step.
► Phase diagram of the Ising model on the Bethe lattice, finite correlation length.