Variational Polaron Theory for Ground States of Strongly Coupled Light-Matter and Electron-Phonon Systems.
- 1Department of Chemical Science and Engineering, Graduate School of Engineering, Kyoto University, Kyoto615-8510, Japan.
Abstract
Strong light-matter and electron-phonon coupling generate ground states dressed by virtual bosonic excitations, making bare-state truncations and perturbative treatments unreliable in the ultrastrong-coupling regime. We introduce a nonperturbative variational ground-state framework based on a state-dependent polaron transformation, combined with a product-state ansatz and a second-order perturbative correction for residual matter-boson entanglement. We show that the optimized transformed frame becomes asymptotically decoupled at infinite coupling, because the leading linear coupling is canceled while off-diagonal matter transitions are suppressed by displaced-oscillator overlaps. The approach is asymptotically correct in both weak- and strong-coupling limits and remains accurate in the intermediate regime, where fixed polaron transformations are least reliable. Dicke-model benchmarks reproduce ground-state energies, fidelities, and the superradiant transition, with second-order energy errors below 0.2%. Holstein-model benchmarks yield errors below 0.5% and clarify how translational symmetry affects wave function quality. This dressed-basis framework enables nonperturbative modeling of strongly coupled light-matter and electron-phonon systems.
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BibTeX
@article{phuc2026variational,
title = {{Variational Polaron Theory for Ground States of Strongly Coupled Light-Matter and Electron-Phonon Systems.}},
author = {Nguyen Thanh Phuc},
journal = {The journal of physical chemistry letters},
year = {2026},
month = oct,
doi = {10.1021/acs.jpclett.6c02011},
url = {https://europepmc.org/article/MED/42917164},
note = {CC BY},
}
RIS
TY - JOUR
TI - Variational Polaron Theory for Ground States of Strongly Coupled Light-Matter and Electron-Phonon Systems.
AU - Nguyen Thanh Phuc
PY - 2026
DA - 2026/10/01
JO - The journal of physical chemistry letters
DO - 10.1021/acs.jpclett.6c02011
UR - https://europepmc.org/article/MED/42917164
AB - Strong light-matter and electron-phonon coupling generate ground states dressed by virtual bosonic excitations, making bare-state truncations and perturbative treatments unreliable in the ultrastrong-coupling regime. We introduce a nonperturbative variational ground-state framework based on a state-dependent polaron transformation, combined with a product-state ansatz and a second-order perturbative correction for residual matter-boson entanglement. We show that the optimized transformed frame becomes asymptotically decoupled at infinite coupling, because the leading linear coupling is canceled while off-diagonal matter transitions are suppressed by displaced-oscillator overlaps. The approach is asymptotically correct in both weak- and strong-coupling limits and remains accurate in the intermediate regime, where fixed polaron transformations are least reliable. Dicke-model benchmarks reproduce ground-state energies, fidelities, and the superradiant transition, with second-order energy errors below 0.2%. Holstein-model benchmarks yield errors below 0.5% and clarify how translational symmetry affects wave function quality. This dressed-basis framework enables nonperturbative modeling of strongly coupled light-matter and electron-phonon systems.
SN - 1948-7185
ER -