Quantum phase transitions and frustration in a three-spin-boson model with independent baths
Phys. Rev. A 113, 042202 – Published 1 April, 2026
DOI: https://doi.org/10.1103/s8fy-51qp
Abstract
We investigate a generalized three-spin-boson model in which three spins interact via an Ising-type coupling and are each coupled to an independent bosonic bath. Using the variational matrix product state method with an optimized boson basis, we compute the ground-state phase diagram and identify three distinct phases: a delocalized phase, a permutationally symmetric localized phase, and a symmetry-broken frustrated phase. The nature of the quantum phase transitions depends strongly on the sign of the spin-spin interaction, with second-order transitions into the delocalized and localized phases, and a first-order transition between the localized and frustrated phases. In the strong-coupling regime, we find that bosonic observables exhibit a universal scaling behavior across different phases, suggesting that the environment remains insensitive to symmetry breaking in the spin sector. We further analyze spin-resolved quantities such as correlation functions, mutual information, and genuine multipartite entanglement to characterize the influence of the bosonic baths, and observe the emergence of an asymmetric correlation pattern among the three spins, reflecting a tendency toward bipartite separability in the frustrated regime.
