Modifying atom-surface interactions with optical fields

The ability to control matter on the nanometer scale is greatly influenced by the van der Waals (vdW) interaction. Therefore, understanding and manipulating the vdW interaction is of interest to the fields of nanotechnology and atom optics. We show that near-resonant light can significantly modify atom-surface vdW interactions in the nonretarded regime. A theory based on quantized electromagnetic fields is used to calculate (1) the ordinary vdW interaction, (2) corrections to the ordinary vdW interaction due to thermal radiation, and (3) modifications to the ordinary vdW interaction that result from monochromatic (laser) radiation. Near-resonant laser light with an intensity of $5\text{W}/{\text{cm}}^2$ is predicted to double the vdW interaction strength for sodium atoms, and possible experiments to detect this effect are discussed.

Figure 1

Depiction of the field-modified atom-surface interaction. An external field ${\mathbf{E}}_{\text{ext}}$ induces a dipole moment $\mathbf{p}$ in an atom some distance $z$ from a surface. The atom also experiences a field from its image dipole ${\mathbf{p}}_i$ within the surface, leading to a force between the atom and surface.

Figure 2

Searching for a field-modified vdW interaction with atomic diffraction from a material grating. The intensity (a) and phase (b) of atom-wave diffraction orders $n$ are plotted as a function of the intensity of an applied laser field, using Eq. (28) and the diffraction theory from Ref. [35] for typical experimental parameters [36]. As the atoms pass by the grating walls their de Broglie wave phase is influenced by the vdW interaction with the grating surface, altering the far-field atom-wave diffraction pattern [35, 36, 37]. The grating surface is assumed to be perfectly conducting so that when the laser field is off (zero intensity) Na atoms will experience a vdW coefficient of $C_3=6.3\text{meV}{\text{nm}}^3$, which is doubled when the laser intensity is $5\text{W}/{\text{cm}}^2$.

Figure 3

Simulated laser-modified atom diffraction patterns. Light is predicted to change the diffraction patterns because of modified atom-surface interactions and also photon scattering. Plot (a) shows the effect of a laser beam, with intensity $I=5\text{W}/{\text{cm}}^2$ and detuning $\Delta =100\text{MHz}$, illuminating the atoms inside a nanograting. Plot (b) shows the effect of the same laser illuminating atoms after passing through a nanograting. In each simulation atoms exposed to the laser have an equal probability of spontaneously scattering 1 or 0 photons.