The Quantum Rabi model (QRM) describes a two-level system (qubit) coupled to a cavity electromagnetic mode (an oscillator) [1], a minimalist paradigm of matter-light interactions with applications in numerous fields ranging from quantum optics to quantum information science and condensed-matter physics. The last decade has witnessed the development of experimental techniques which allow the implementation of the quantum Rabi model in enhanced parameter regimes [2]. Although even simpler than the hydrogen atom, the solution of the QRM is nontrivial and it was not clear whether it can be obtained analytically. Recently it was shown that the QRM is not only exactly solvable but integrable [3], using Bargmann-space methods. A transcendental functions was derived, whose zeros yield the so-called regular spectrum. By using extended coherent states, we can recover this exact solution in an alternative simpler and more physical way[4]. In the same framework, the two-photon and two mode QRMs [5] are solved exactly by treating extended squeezed states on an equal footing. The so-called Bogoliubov operators approach can be also applied to the multi-qubit case [6].

[1]  I. I. Rabi, Phys. Rev., 49, 324 (1936) ; 51, 652 (1937) .
[2]  T. Niemczyk et al., Nat. Phys. 6, 772 (2010).
[3]  D. Braak, Phys. Rev. Lett. 107, 100401 (2011).
[4]  Q. H. Chen et al.,  Phys.  Rev.  A 86, 023822 (2012).
[5]  L. W. Duan et al.,  Europhys. Lett. 112, 34003  (2015).
[6]  S. He et al.,  New Journal of Physics 17,  043033 (2015).

陈庆虎浙江大学教授，1994年在中国科技大学获理学博士学位。1996年在浙江大学物理系工作，任副教授。2000年晋升教授和博士生导师。从事凝聚态物理理论和量子光学理论研究，发表和合作发表SCI 收录学术论文百余篇。