Sub-half-wavelength atom localization via bichromatic phase control of spontaneous emission

We show that the bichromatic phase control of the spontaneous emission spectrum leads to the sub-half-wavelength atom localization. We consider a three-level Λ-type atom interacting with a bichromatic coupling field and a bichromatic probe field with equal frequency difference. One component of the bichromatic coupling field is a standing-wave field with position dependent Rabi frequency. When the spontaneous emitted photons are detected, the atom is localized in either of the two half-wavelength regions with 50% probability by the variation of the difference between the relative phases of the two bichromatic fields.