Superposition states identical atoms

In the general case of Ti / T2, the superposition states +) and —) are non-maximally entangled states. However, the states +) and —) can be represented by linear superpositions of the maximally entangled states of two identical atoms... 

However, the preparation of the superposition state requires that the atoms have different transition frequencies. Beige et al. [32] have proposed a scheme in which the superposition state <1>) can be prepared in a system of two identical atoms placed at fixed positions inside an optical cavity. 

Here, we discuss an alternative scheme where the superposition state <1>) can be generated in two identical atoms driven in free space by a coherent laser field. This can happen when the atoms are in nonequivalent positions in the driving field, where the atoms experience different intensities and phases of the driving field. The populations of the collective states of the system can be found from the master equation (31). We use the set of the collective states (35) as an appropriate representation for the density operator... 

Thus, the condition V 2 = /1 1I2 for suppression of spontaneous emission from the antisymmetric state is valid for identical as well as nonidentical atoms, whereas the coherent interaction between the superpositions appears only for nonidentical atoms with different transition frequencies and/or spontaneous damping rates. 

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