10 research outputs found
Force of light on a two-level atom near an ultrathin optical fiber
We study the force of light on a two-level atom near an ultrathin optical
fiber using the mode function method and the Green tensor technique. We show
that the total force consists of the driving-field force, the
spontaneous-emission recoil force, and the fiber-induced van der Waals
potential force. Due to the existence of a nonzero axial component of the field
in a guided mode, the Rabi frequency and, hence, the magnitude of the force of
the guided driving field may depend on the propagation direction. When the
atomic dipole rotates in the meridional plane, the spontaneous-emission recoil
force may arise as a result of the asymmetric spontaneous emission with respect
to opposite propagation directions. The van der Waals potential for the atom in
the ground state is off-resonant and opposite to the off-resonant part of the
van der Waals potential for the atom in the excited state. Unlike the potential
for the ground state, the potential for the excited state may oscillate
depending on the distance from the atom to the fiber surface
Repulsive Casimir-Polder potentials of low-lying excited states of a multilevel alkali-metal atom near an optical nanofiber
We study the Casimir-Polder potential of a multilevel alkali-metal atom near an optical nanofiber. We calculate the mean potential of the atom in a fine-structure state. We perform numerical calculations for the Casimir-Polder potentials of the ground state and a few low-lying excited states of a rubidium atom. We show that, unlike the potential of the ground state, which is negative and attractive, the potential of a low-lying excited state may take positive values, oscillate around the zero value with a decaying amplitude, and become repulsive in some regions of atom-to-surface distances. We observe that, for a nanofiber with a radius of 200 nm, the potential for the state 8S 1/2 of a rubidium atom achieves a positive peak value of about 17μK at a distance of about 150 nm from the fiber surface and becomes strongly repulsive in the region of distances from 150 to 400 nm. We also calculate the nanofiber-induced shifts of the transition frequencies of the atomic rubidium D2 and D1 lines. We find that the shifts are negative in the region of short distances, become positive, and oscillate around the zero value with a decaying amplitude in the region of large distances