Superradiant emission spectra of a two-qubit system in circuit quantum electrodynamics

  1. Ya. S. Greenberg,
  2. and O. A. Chuikin
In this paper we study the spontaneous emission spectra and the emission decay rates of a simplest atom system that exhibits sub- and superradiant properties: a system which consists
of two artificial atoms (superconducting qubits) embedded in a one-dimensional open waveguide. The calculations are based on the method of the transition operator which was firstly introduced by R. H. Lehmberg to theoretically describe the spontaneous emission of two-level atoms in a free space. We obtain the explicit expressions for the photon radiation spectra and the emission decay rates for different initial two-qubit configurations with one and two excitations. For every initial state we calculate the radiation spectra and the emission decay rates for different effective distances between qubits. In every case, a decay rate is compared with a single qubit decay to show the superradiant or subradiant nature of a two-qubit decay with a given initial state.

Non-Hermitian Hamiltonian approach to the microwave transmission through one- dimensional qubit chain

  1. Ya. S. Greenberg,
  2. and A. A. Shtygashev
We investigate the propagation of microwave photons in a one-dimensional waveguide interacting with a number of artificial atoms (qubits). Within the formalism of projection operators
and non-Hermitian Hamiltonian approach we develop a one-photon approximation scheme for the calculation of the transmission and reflection factors of the microwave signal in a waveguide which contains an arbitrary number \emph{N} of non-interacting qubits. It is shown that for identical qubits in the long-wave limit a coherent superradiance state is formed with the width being equal to the sum of the widths of spontaneous transitions of \emph{N} individual qubits.