Decay of metastable excited states of two qubits in a waveguide
Elena S. Redchenko, Vladimir I. Yudson · Physical Review A · 2014
For a system of two spatially separated qubits (two-level atoms) coupled to a one-dimensional waveguide we have described the time evolution of singly or doubly excited states of the atomic subsystem. When the interatomic distance $l$ takes special (``resonant'' or ``antiresonant'') values, the singly excited system of resonant atoms can form metastable (dark) states. If $l$ slightly deviates from one of the special values or the atomic frequencies do not coincide, the dark states slowly decay and we have calculated the decay rate. Also, we have found that the doubly excited state of two resonant atoms located at the special positions does not completely decay but, with a finite probability, can evolve (with the emission of a single photon) to one of the metastable singly excited states. Metastable states of pairs of qubits may find applications (e.g., as memory elements) in information processing or as detectors sensitive to external perturbations.