Quantum Phase Transitions in Spin-Boson Systems: Dissipation and Light Phenomena

Spin-boson models are essentially useful in the understanding of quantum optics, nuclear physics, quantum dissipation, and quantum computation. We discuss quantum phase transitions in various spin-boson Hamiltonians, compare, and contrast them. We summarize the theoretical concepts and results, open questions and implementations of those ideas in cold atomic and QED cavity systems are also addressed.