Ground-state instabilities and entanglement in the spin-boson model

Abstract

Ground state instabilities of the spin-boson model is studied in this work. The existence of sequential ground state instabilities is shown analytically for arbitrary detuning in the two-spin system. In this model, extra discontinuities of concurrence(entanglement measure) are found in the finite system, which do not appear in the on-resonant model. The above results remain intact by including extra boson modes. Moreover, by including extra modes, it is found that ground state entanglement can be obtained and enhanced even in the weak coupling regime.

Quantum phase transitions of light in the Dicke-Bose-Hubbard model

“…Consequently the subspace of N i excitations spanned by N i + 1 vectors is given by the direct product of atom and field states, i.e. |atom |photon [15,16].…”