Subradiant States of a 1D Qubit Chain

Subradiance is the phenomenon that the spontaneous emission from an atomic ensemble is inhibited cooperatively. Excitations in subradiant states have lifetime longer than an individual atom coupled to the same light fields. For a finite chain of two-level atoms coupled to a 1D waveguide, and being based on a non-Hermitian Hamiltonian formalism, we analytically revealed the wave functions of the one-excitation subradiant states and their lifetimes. For atom chains with multiple excitations, we identified two families of subradiant states. One has fermionic behaviours that can be explained through Lieb-Liniger model at the Tonks-Girardeau limit. The other is the bound state of two atomic excitations, where one excited atom effectively constitutes a defect (a site blocking further excitation) and establishes a localized mode for the other excitation. The results can be extended to atom chains coupled to 3D free space.