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arXiv · 2510.11130

Quantum phase transition of sub-Ohmic spin-boson models: An approach by the multiple Davydov D2 Ansatz

Justin Tan·Nengji Zhou·Yang Zhao
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Abstract

The ground state properties and quantum phase transitions of sub-Ohmic spin-boson models are investigated using the multiple Davydov D2 Ansatz in conjunction with the variational principle. Three variants of the model are studied: (i) a single bath with diagonal coupling, (ii) two independent baths with diagonal and off-diagonal couplings, and (iii) a single bath with simultaneous diagonal and off-diagonal couplings. For the purely diagonal model, the multiple Davydov D2 Ansatz yields critical coupling strengths that are consistent with other methodologies, validating its accuracy and efficiency. In the two-bath model, the competition between diagonal and off-diagonal couplings drives a first-order transition for both symmetric and asymmetric spectral exponents, with von-Neumann entropy showing a continuous peak only under exact symmetry. Finally, for a single bath with simultaneous diagonal and off-diagonal couplings, we demonstrate that a rotational transformation maps the system to an equivalent purely diagonal model, enabling simpler and intuitive physical interpretation and reduced computational complexity.

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Justin Tan, Nengji Zhou, Yang Zhao. 2025-10-13. Quantum phase transition of sub-Ohmic spin-boson models: An approach by the multiple Davydov D2 Ansatz. https://arxiv.org/abs/2510.11130

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