Quantum Engineering of Superdark Excited States in Arrays of Atoms
We suggest a regular method of achieving an extremely long lifetime of a collective singly excited state in a generic small-size ensemble of N identical atoms. The decay rate Γ_N of such a `superdark' state can be as small as Γ_N \propto Γ(r/λ)^{2(N-1)} (Γis the radiative decay rate of an individual atom, r and λare the system size and the wavelength of the radiation, respectively), i.e., considerably smaller than in any of the systems suggested up to now. The method is based on a special fine tuning of the atomic Hamiltonian: namely, on a proper position-dependent adjustment of atomic transition frequencies. So chosen set of the control parameters is sufficient to ensure the minimum of the spontaneous decay rate of the engineered state in a generic ensemble of atoms (`qubits').