Atom trap and waveguide using a two-color evanescent light field around a subwavelength-diameter optical fiber

We suggest using a two-color evanescent light field around a subwavelength-diameter fiber to trap and guide atoms. The optical fiber carries a red-detuned light and a blue-detuned light, with both modes far from resonance. When both input light fields are circularly polarized, a set of trapping minima of the total potential in the transverse plane is formed as a ring around the fiber. This design allows confinement of atoms to a cylindrical shell around the fiber. When one or both of the input light fields are linearly polarized, the total potential has two local minimum points in the transverse plane. This design allows confinement of atoms to two straight lines parallel to the fiber axis. Due to the small thickness of the fiber, we can use far-off-resonance fields with substantially differing evanescent decay lengths to produce a net potential with a large depth, a large coherence time, and a large trap lifetime. For example, a 0.2-μm-radius silica fiber carrying 30 mW of 1.06-μm-wavelength light and 29 mW of 700-nm-wavelength light, both fields circularly polarized at the input, gives for cesium atoms a trap depth of 2.9 mK, a coherence time of 32 ms, and a recoil-heating-limited trap lifetime of 541 s.

Figure 1

Schematic of atom trapping and guiding around an optical fiber.

Figure 2

van der Waals potential $V$ of a ground-state cesium atom near a thin cylindrical silica fiber.

Figure 3

Ratio between the van der Waals potentials $V$ and $V_{\text{flat}}$ of a ground-state cesium atom near a thin cylindrical silica fiber and a flat-surface bulk silica dielectric, respectively.

Figure 4

Contributions to the total trapping potential $U_{\mathrm{tot}}$ of a ground-state cesium atom outside a vacuum-clad subwavelength silica fiber with two circularly polarized input light fields. The radius of the fiber is $a=0.2\mu \mathrm{m}$. The absolute value of the red-detuned component $U_1$ (dotted line) subtracts from the blue-detuned component $U_2$ (dashed line) to give the net optical potential $U$ (thin solid line). This is modified by the van der Waals surface interaction, giving the total potential $U_{\mathrm{tot}}$ (thick solid line). The laser wavelengths are ${\lambda }_1=1.06\mu \mathrm{m}$ and ${\lambda }_2=700\mathrm{nm}$. The laser powers are $P_1=30\mathrm{mW}$ and $P_2=29\mathrm{mW}$.

Figure 5

Transverse-plane profile of the total potential $U_{\mathrm{tot}}$ produced by laser beams that are circularly polarized at the input. All the parameters are the same as for Fig. 4.

Figure 6

Effect of the power $P_1$ of the red-detuned light on the total potential $U_{\mathrm{tot}}$. The power of the blue-detuned light is fixed at $P_2=29\mathrm{mW}$. All the other parameters are the same as for Fig. 4.

Figure 7

Effect of the power $P_2$ of the blue-detuned light on the total potential $U_{\mathrm{tot}}$. The power of the red-detuned light is fixed at $P_1=30\mathrm{mW}$. All the other parameters are the same as for Fig. 4.

Figure 8

Bound states for the first six levels ($n=0$, 1, 2, 3, 4, and 5) of the radial motion of a cesium atom in the effective potential $U_{\mathrm{eff}}=U_{\mathrm{tot}}+{\hslash }^2(m^2-1∕4)∕2M{r}^2$. The rotational quantum number is $m=0$. All the other parameters are the same as for Fig. 4.

Figure 9

Transverse-plane profile of the total potential $U_{\mathrm{tot}}$ produced by laser beams that are linearly polarized at the input. The laser powers are $P_1=30\mathrm{mW}$ and $P_2=35\mathrm{mW}$. All the other parameters are the same as for Fig. 4.

Figure 10

Total potential $U_{\mathrm{tot}}$ as a function of $x$ at $y=0$ (a) and as a function of $y$ at $x=0$ (b). All the parameters are the same as for Fig. 9.

Figure 11

Azimuthal dependence of the total potential $U_{\mathrm{tot}}$ for $r=0.4\mu \mathrm{m}$. All the parameters are the same as for Fig. 9.