期刊
PHYSICAL REVIEW A
卷 94, 期 2, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevA.94.023835
关键词
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资金
- Alexander von Humboldt Professorship
- EU Integrating Project DIADEMS
- EU STREP project EQUAM
- ERC
- Ministry of Science, Research and Arts and the Universities of the State of Baden-Wurttemberg, Germany
The Rabi model, a two-level atom coupled to a harmonic oscillator, can undergo a second-order quantum phase transition (QPT) [M.-J. Hwang et al., Phys. Rev. Lett. 115, 180404 (2015)]. Here we show that the Rabi QPT accompanies critical behavior in the higher-energy excited states, i.e., the excited-state QPT (ESQPT). We derive analytic expressions for the semiclassical density of states, which show a logarithmic divergence at a critical energy eigenvalue in the broken symmetry (superradiant) phase. Moreover, we find that the logarithmic singularities in the density of states lead to singularities in the relevant observables in the system such as photon number and atomic polarization. We corroborate our analytical semiclassical prediction of the ESQPT in the Rabi model with its numerically exact quantum mechanical solution.
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