It was shown that, in the strong-field limit, the two-particle collective dressed states are uniformly populated so the interference vanishes at strong driving. This restricts potential applications, e.g., in coherent backscattering from disordered structures of atoms, the generation of squeezed coherent light by scattering light off of a regular structure, the lithography, or precision measurements and optical information processing.

Researchers at China and State Key Laboratory of High Field Laser Physics——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) propose a different scheme to recover the spatial interference of resonance fluorescence from two duplicated two-level atoms via controlling the relative phase of driving fields.[ PHYSICAL REVIEW A 83, 023410 (2011)].

In their scheme, the atomic system is driven by two orthogonally polarized fields, and thus a closed-loop system is formed. As the same as the common statement, the spatial interference vanishes when atoms are driven by strong fields. In this loop system, the relative phase significantly impacts the populations and the atomic coherences of each atom. Thus with a proper relative phase, even driven by strong fields, the atoms are no longer equally populated. The interference pattern could be recovered accordingly. However, we find later that if the two fields have the same intensity and a relative phase π/2, which is equivalent to a circularly polarization, no resonance fluorescence could be detected. This restriction can be removed by adjusting the relative intensity or, alternatively, by replacing one driving field with a standing-wave field and then adjusting the distance between the atoms and the observing screen. Based on the technology of phase control, this scheme may provide experimental maneuverability.