The Physical Implementation of the Two-Qubit Logical Operator CNOT

Abstract

The optical properties of a system of two identical two-level atoms in collective (symmetric \Psi_s and antisymmetric \Psi_a) Bell states are studied for arbitrary interatomic distances. The closed-form analytical expressions for shifts and widths of considered states are obtained taking into account the retarded dipole-dipole interaction between atoms. It is shown that under certain conditions the retarded interaction of atoms of this quantum diatomic system can lead to both additional widening of energy levels of atoms compared to radiation width, and the opposite effect – narrowing of the natural width of atomic levels. We can identify three types of quantum information transfer processes associated with either a resonant (non-resonant) absorption of a photon by one of the atoms of the system or with variation of interatomic distance.