Quantum coherence of spin-boson model at finite temperature

Meng Qin, Tian-Yu Hou, Yan-Biao Li +2 more

Wen Chen, Zhide Chen

The dynamics of the spin-boson model with an Ohmic bath at finite temperature is studied by a variational calculation. Numerical solution of the self-consistent equation derived from the variational method shows that the transition from incoherent to coherent phases is discontinuous. It indicates that ( T = 0, s = 1) is a tricritical point, i.e. the transition changes from continuous to discontinuous by tuning from T = 0 to T ≠0. The discontinuous transition at finite temperature is analysed by Landau theory and the relation to the experimental observation on the coherent state is also discussed.

M. Fannes

Olga Goulko, Hsing-Ta Chen, Moshe Goldstein +1 more

We present numerically exact inchworm quantum Monte Carlo results for the real-time dynamics of the spin polarization in the sub-Ohmic spin-boson model at finite temperature. We focus in particular on the localization and coherence behavior of the model, extending our previous study at low temperature [Phys. Rev. Lett. 134, 056502 (2025)]. As the temperature increases, the system becomes less localized and less coherent. The loss of coherence, which is controlled by two independent mechanisms -- a smooth damping-driven crossover and a sharp frequency-driven transition -- exhibits a nontrivial temperature dependence. While both types of coherence loss occur at lower coupling in the high temperature regime, the frequency exhibits a sharper drop at high temperatures and this drop is observed for all values of the sub-Ohmic exponent, in contrast to the zero-temperature case. We discuss the full temperature-dependent dynamical phase diagram of the system and the interplay between coherence and localization across a wide range of physical parameters.

J. Oitmaa, Chris J. Hamer, Weihong Zheng