Eur. Phys. J. D (2013) 67: 91
https://doi.org/10.1140/epjd/e2013-40015-8

Regular Article

Emission spectrum of a qubit in Rabi model in strong coupling regime

¹ Department of Physics, Huazhong Normal University, Wuhan 430079, P.R. China
² Institute of Photonics and Photo-Technology, Hubei University of Science and Technology, Xianning 437100, P.R. China

^a e-mail: gaox@phy.ccnu.edu.cn

Received: 7 January 2013
Received in final form: 12 March 2013
Published online: 30 April 2013

Abstract

The analytical eigenenergies and eigenstates of the Rabi model are obtained approximately based on a unitary transformation and a generalized rotating-wave approximation (GRWA). Using these analytical expressions without the rotating wave approximation (RWA), we generalize the definition of the physical emission spectrum valid with the RWA in order to meet without the RWA with some modifications. Taking into account the counter-rotating wave terms and the intercrossing of energy level in the strong coupling regime, the physical emission spectrum of qubit is investigated. Different from the case with RWA, the multi-peak vacuum Rabi splitting, even when the qubit initially in its ground state and the bosonic field initially in vacuum, can emerge. These new features of physical emission spectrum originate from the effect of counter-rotating wave terms. Moreover, the intercrossing of energy level can also be observed in the strong coupling regime.