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Quantum phase transition of sub-Ohmic spin-boson models: An approach by the multiple Davydov D2Ansatz.

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Bibliographic Details
Title: Quantum phase transition of sub-Ohmic spin-boson models: An approach by the multiple Davydov D2Ansatz.
Authors: Tan, Justin Zhengjie, Zhou, Nengji, Zhao, Yang
Source: Journal of Chemical Physics; 11/7/2025, Vol. 163 Issue 17, p1-9, 9p
Subject Terms: QUANTUM phase transitions, GROUND state (Quantum mechanics), VARIATIONAL principles, COMPUTATIONAL complexity, DAVYDOV splitting
Abstract: The ground state properties and quantum phase transitions of sub-Ohmic spin-boson models are investigated using the multiple Davydov D2Ansatz 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 D2Ansatz 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 the von Neumann exhibiting 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. [ABSTRACT FROM AUTHOR]
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Description
Abstract:The ground state properties and quantum phase transitions of sub-Ohmic spin-boson models are investigated using the multiple Davydov D<subscript>2</subscript>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 D<subscript>2</subscript>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 the von Neumann exhibiting 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. [ABSTRACT FROM AUTHOR]
ISSN:00219606
DOI:10.1063/5.0286482