Non-Gaussian Phase Transition and Cascade of Instabilities in the Dissipative Quantum Rabi Model
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| Main Authors: | , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866914282355032064 |
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| author | Kang, Mingyu Zhang, Yikang Brown, Kenneth R. Barthel, Thomas |
| author_facet | Kang, Mingyu Zhang, Yikang Brown, Kenneth R. Barthel, Thomas |
| contents | The open quantum Rabi model describes a two-level system coupled to a harmonic oscillator. A Gaussian phase transition for the nonequilibrium steady states has been predicted when the bosonic mode is soft and subject to damping. We show that oscillator dephasing is a relevant perturbation, which leads to a non-Gaussian phase transition and an intriguing cascade of instabilities for $k$-th order bosonic operators, as well as a jump in the steady-state qubit polarization. For the soft-mode limit, the equations of motion form a closed hierarchy and spectral properties can be efficiently studied. To this purpose, we establish a fruitful connection to non-Hermitian Hamiltonians. The results for the phase diagram, stability boundaries, and relevant observables are based on mean-field analysis, exact diagonalization, perturbation theory, and Keldysh field theory. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_07092 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Non-Gaussian Phase Transition and Cascade of Instabilities in the Dissipative Quantum Rabi Model Kang, Mingyu Zhang, Yikang Brown, Kenneth R. Barthel, Thomas Quantum Physics Atomic Physics The open quantum Rabi model describes a two-level system coupled to a harmonic oscillator. A Gaussian phase transition for the nonequilibrium steady states has been predicted when the bosonic mode is soft and subject to damping. We show that oscillator dephasing is a relevant perturbation, which leads to a non-Gaussian phase transition and an intriguing cascade of instabilities for $k$-th order bosonic operators, as well as a jump in the steady-state qubit polarization. For the soft-mode limit, the equations of motion form a closed hierarchy and spectral properties can be efficiently studied. To this purpose, we establish a fruitful connection to non-Hermitian Hamiltonians. The results for the phase diagram, stability boundaries, and relevant observables are based on mean-field analysis, exact diagonalization, perturbation theory, and Keldysh field theory. |
| title | Non-Gaussian Phase Transition and Cascade of Instabilities in the Dissipative Quantum Rabi Model |
| topic | Quantum Physics Atomic Physics |
| url | https://arxiv.org/abs/2507.07092 |