Study of CP(N-1) θ-Vacua by Cluster Simulation of SU(N) Quantum Spin Ladders

D-theory provides an alternative lattice regularization of the 2D CP(N-1) quantum field theory in which continuous classical fields emerge from the dimensional reduction of discrete SU(N) quantum spins. Spin ladders consisting of n transversely coupled spin chains lead to a CP(N-1) model with a vacuum angle θ=nπ. In D-theory no sign problem arises and an efficient cluster algorithm is used to investigate θ-vacuum effects. At θ=π there is a first order phase transition with spontaneous breaking of charge conjugation symmetry for CP(N-1) models with N>2.