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

TL;DR

This paper investigates the spontaneous emission spectra and decay rates of a two-qubit system in circuit QED, revealing superradiant and subradiant behaviors based on initial states and qubit configurations.

Contribution

It provides explicit formulas for emission spectra and decay rates of two artificial atoms in a waveguide, extending the transition operator method to circuit QED systems.

Findings

Identification of superradiant and subradiant decay regimes

Explicit expressions for emission spectra and decay rates

Analysis of effects of initial states and qubit distances

Abstract

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.