We study the spontaneous emission of an excited atom close to an optical nanofiber and the resulting scattering forces. For a suitably chosen orientation of the atomic dipole, the spontaneous emission pattern becomes asymmetric and a resonant Casimir-Polder force parallel to the fiber axis arises. For a simple model case, we show that such a lateral force is due to the interaction of the circularly oscillating atomic dipole moment with its image inside the material. With the Casimir--Polder energy being constant in the lateral direction, the predicted lateral force does not derive from a potential in the usual way. Our results have implications for optical force measurements on a substrate as well as for laser cooling of atoms in nanophotonic traps.
We study the spontaneous emission of an excited atom close to an optical nanofiber and the resulting scattering forces. For a suitably chosen orientation of the atomic dipole, the spontaneous emission pattern becomes asymmetric and a resonant Casimir-Polder force parallel to the fiber axis arises. For a simple model case, we show that such a lateral force is due to the interaction of the circularly oscillating atomic dipole moment with its image inside the material. With the Casimir--Polder energy being constant in the lateral direction, the predicted lateral force does not derive from a potential in the usual way. Our results have implications for optical force measurements on a substrate as well as for laser cooling of atoms in nanophotonic traps.
This study proposes a nanophotonic structure that supports the generation and enhancement of the lateral Casimir-Polder (CP) force acting on atoms. By applying the two-dimensional anisotropic material, we demonstrate that both the spontaneous decay rate and the emission pattern of the atom exhibit distinct features by manipulating the parameters of the system. In particular, the exact numerical solutions of population dynamics reveal the occurrence of Rabi oscillations in the strong atom-field coupling case, where the Markovian results fail to describe this phenomenon. We also show that the asymmetric spatial distribution of the in-plane dipole radiation into surface plasmon modes is achievable for the system under consideration. Based on these intriguing properties, we predict the generation of the lateral CP force, where the transient evolution of the force indicates the periodical variation in both the direction and the amplitude under strong light-atom interaction conditions. Our findings have potential applications for novel optical nanotechnologies and devices, which provide a method for atom manipulation and trapping.
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.
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.
Influence of the Casimir-Polder force on a slowly moving atom near a left-handed slab is discussed.We focus on an initially excited atom and its dynamic evolution during the spontaneous decay process.The left-haned slab is adopted based on two factors:(1) It provides a relatively stronger Casimir-Polder force on the excited atom far away from the interface,and(2) it can lead to an inhibited spontaneous decay rate within such a region.Therefore,we can discuss the dynamic evolution of atoms acted only by the Casimir-Polder force.The dynamic evolution discussed here includes both the evolution of atomic population and the atomic displacement.As the Casimir-Polder force depends on the atomic population,while the decay rate is related to the atomic positions,the atomic dynamic evolution is determined by its initial conditions,i.e.its position and volecity.We choose two initial positions for discussion,i.e.(1) the position with the maximum resonant Casimir-Polder force,and(2) the edge of the resonant Casimir-Polder force of the atom with dipole parallel to the interface.Furthermore,we also consider two kinds of orientations of atomic dipole,i.e.parallel and normal to the interface.It is found that the atom can be repulsed away from a surface by the Casimir-Polder force with a proper initial velocity in certain dipole orientaion during the sponatneous decay process.As the atomic dynamics depends on the orientation of the atom dipole momentum,our result can be used as a reference to distinguish atoms with different dipole momenta.Though the force discussed here exists during the spontaneous decay process,it is much different from the recoil force of the atom when it emits a photon during the spontaneous decay.The statistical average of the recoil force is null,but that of the resonant Casimir-Polder force is not.After reasonable estimation,such a Casimir-Polder force can counteract the thermal fluctuation of temperature of 15 μK during sponatneous decay.If combined with other constraint methods,it is helpful to control the dynamics of an atom more efficiently.
Influence of the Casimir-Polder force on a slowly moving atom near a left-handed slab is discussed. We focus on an initially excited atom and its dynamic evolution during the spontaneous decay process. The left-haned slab is adopted based on two factors: (1) It provides a relatively stronger Casimir-Polder force on the excited atom far away from the interface, and (2) it can lead to an inhibited spontaneous decay rate within such a region. Therefore, we can discuss the dynamic evolution of atoms acted only by the Casimir-Polder force. The dynamic evolution discussed here includes both the evolution of atomic population and the atomic displacement. As the Casimir-Polder force depends on the atomic population, while the decay rate is related to the atomic positions, the atomic dynamic evolution is determined by its initial conditions, i.e. its position and volecity. We choose two initial positions for discussion, i.e. (1) the position with the maximum resonant Casimir-Polder force, and (2) the edge of the resonant Casimir-Polder force of the atom with dipole parallel to the interface. Furthermore, we also consider two kinds of orientations of atomic dipole, i. e. parallel and normal to the interface. It is found that the atom can be repulsed away from a surface by the Casimir-Polder force with a proper initial velocity in certain dipole orientaion during the sponatneous decay process. As the atomic dynamics depends on the orientation of the atom dipole momentum, our result can be used as a reference to distinguish atoms with different dipole momenta. Though the force discussed here exists during the spontaneous decay process, it is much different from the recoil force of the atom when it emits a photon during the spontaneous decay. The statistical average of the recoil force is null, but that of the resonant Casimir-Polder force is not. After reasonable estimation, such a Casimir-Polder force can counteract the thermal fluctuation of temperature of 15 μupK during sponatneous decay. If combined with other constraint methods, it is helpful to control the dynamics of an atom more efficiently.
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 8S1/2 of a rubidium atom achieves a positive peak value of about $17\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$ 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.