Near-field optical potential for a neutral atom

We study an effective interaction potential between a neutral atom and a nanometric probe tip in optical near-field systems. The wave-number dependence of the coupling coefficients of exciton polaritons is described with the effective-mass approximation, where massive virtual photons are exchanged between the atom and the probe tip. The near-field optical potential is shown as the sum of the Yukawa functions with several kinds of effective masses or interaction ranges, and is characterized in terms of detuning for the resonance energies of the atom and the probe tip. Consequently, we find that a potential minimum is produced for a blue detuning case. This result indicates that an atom can be trapped in the near-field optical potential well. Furthermore, we numerically investigate deflection and trapping of a single atom by means of optical near fields generated from a nanometric probe tip. The dependence on the probe-tip size, the kinetic energy of the cold atom, and the excitation energies of both probe tip and atom is clarified.