Trapping and Manipulation of Isolated Atoms Using Nanoscale Plasmonic Structures

We propose and analyze a scheme to interface individual neutral atoms with nanoscale solid-state systems. The interface is enabled by optically trapping the atom via the strong near-field generated by a sharp metallic nanotip. We show that under realistic conditions, a neutral atom can be trapped with position uncertainties of just a few nanometers, and within tens of nanometers of other surfaces. Simultaneously, the guided surface plasmon modes of the nanotip allow the atom to be optically manipulated, or for fluorescence photons to be collected, with very high efficiency. Finally, we analyze the surface forces, heating and decoherence rates acting on the trapped atom.

Figure 1

(a) Schematic of a single atom tightly trapped near a conducting nanotip. The atom is strongly coupled to single surface plasmons guided by the nanotip, which can be efficiently converted to a single photon in a coupled optical fiber, allowing for efficient manipulation and readout. The atom can be brought within tens of nanometers of other surfaces, which allows it to be interfaced, e.g., with an optical microdisk cavity as shown here. (b) Illustration of a nanotip with $z_0=2\mathrm{nm}$ and normalized total field intensity $|E_{\mathrm{total}}/E_0{|}^2$. (c) Typical optical potential (red) and total potential (including van der Waals potential, black) for a Rb atom trapped near a $z_0=2\mathrm{nm}$ nanotip. The potentials are normalized by $U_0=\hslash {\Omega }_0^2/\delta$, the optical potential at infinity. The inset shows the potentials around the trap center in greater detail.

Figure 2

(a) Purcell factor $P$ (averaged over dipole orientations, blue curve) and trap distance to surface $d$ (green curve) for a ${}^{87}\mathrm{Rb}$ atom trapped near a silver nanotip, as a function of $z_0$, in absence of van der Waals forces. (b) Trap lifetime for various values of trapping frequency ${\omega }_{T,z}$ and tip curvature $z_0$. The incident trap laser intensity is plotted along the horizontal axis, while the detuning is varied to maintain a given value of ${\omega }_{T,z}$. The black dashed (solid) curve corresponds to $z_0=3\mathrm{nm}$ and trap frequency of ${\omega }_{T,z}=10(100)\mathrm{MHz}$, while the red curve corresponds to $z_0=1\mathrm{nm}$ and ${\omega }_{T,z}=100\mathrm{MHz}$.