Atom microscopy via two-photon spontaneous emission spectroscopy

We study subwavelength position measurement via spontaneous emission spectroscopy with two photons. Our model systems are a single Λ-type three-level atom, in which a dual interaction generates two independent photons, and an M-type five-level atom, which emits two photons in a double-Raman process. The difference is that the M-type system emits correlated pairs of photons, while the photon pairs from the Λ system are uncorrelated. In order to evaluate the performance of the position measurement, we introduce an analysis scheme motivated by a possible experimental measurement procedure. We find characteristic differences in the spontaneous emission spectra of the two systems arising from the photon correlation in the M-type system. But interestingly, the effect of this photon pair correlation on the conditional position probability distribution does not lead to an increase in the position information of the single atom. Nevertheless, both schemes allow for an efficient measurement of the particle position with unambiguous position determination over a wide range of parameters.