Characterization of Quantum and Classical Critical Points for an Integrable Two-Qubit Spin–Boson Model
Roberto Grimaudo,
Antonino Messina,
Hiromichi Nakazato,
Alessandro Sergi,
Davide Valenti
Affiliations
Roberto Grimaudo
Dipartimento di Fisica e Astronomia “E. Majorana", Università degli Studi di Catania, Via S. Sofia 64, I-95123 Catania, Italy
Antonino Messina
Dipartimento di Matematica e Infrormatica, Università degli Studi di Palermo, Via Archirafi 34, I-90123 Palermo, Italy
Hiromichi Nakazato
Department of Physics, Waseda University, Tokyo 169-8555, Japan
Alessandro Sergi
Dipartimento di Scienze Matematiche e Informatiche, Scienze Fisiche e Scienze della Terra, Università degli Studi di Messina, Viale F. Stagno d’Alcontres 31, I-98166 Messina, Italy
Davide Valenti
Dipartimento di Fisica e Chimica “Emilio Segrè", Università degli Studi di Palermo, Viale delle Scienze, Ed. 18, I-90128 Palermo, Italy
The class of two-interacting-qubit spin–boson models with vanishing transverse fields on the spin-pair is studied. The model can be mapped exactly into two independent standard single-impurity spin–boson models where the role of the tunneling parameter is played by the spin–spin coupling. The dynamics of the magnetization are analyzed for different levels of (an)isotropy. The existence of a decoherence-free subspace, as well as of different classical regimes separated by a critical temperature, and symptoms of quantum (first-order and Kosterlitz–Thouless type) phase transitions in the Ohmic regime are brought to light.
