Probing Surface-Bound Atoms with Quantum Nanophotonics

Quantum control of atoms at ultrashort distances from surfaces would open a new paradigm in quantum optics and offer a novel tool for the investigation of near-surface physics. Here, we investigate the motional states of atoms that are bound weakly to the surface of a hot optical nanofiber. We theoretically demonstrate that with optimized mechanical properties of the nanofiber these states are quantized despite phonon-induced decoherence. We further show that it is possible to influence their properties with additional nanofiber-guided light fields and suggest heterodyne fluorescence spectroscopy to probe the spectrum of the quantized atomic motion. Extending the optical control of atoms to smaller atom-surface separations could create opportunities for quantum communication and instigate the convergence of surface physics, quantum optics, and the physics of cold atoms.

Figure 1

Panel (a) shows the adiabatic potential as a function of the atom-surface separation. The yellow line represents the adsorption potential $V_{\mathrm{ad}}$, the red line a hybrid light- and surface-induced potential, and the red dashed line the contribution of the optical potential $V_{\mathrm{opt}}$. The dash-dotted line corresponds to a typical two-color optical trap for comparison. The inset illustrates some key experimental parameters. Panel (b) outlines the proposed setup for heterodyne fluorescence spectroscopy of the motional states.

Figure 2

Radial motional states of a cesium atom bound to a silica nanofiber. Panel (a) shows adsorbed states, panel (b) hybrid surface-bound states. We plot the corresponding potential $V$ (yellow) generated at power $P_r$ of the fiber-guided light beam, the spectrum ${\omega }_{\nu }/2\pi$ of motional states (dark blue), and two examples of the atom wave function (red) in arbitrary units. The gray area at $r-R<0$ marks the position of the nanofiber.

Figure 3

Spectrum of light inelastically scattered by nanofiber-bound atoms. We plot the power of the scattered light as a function of the frequency difference $\omega ={\omega }_s-{\omega }_p$ of the probe photon and the scattered photon. The scale $P_0$ is explained in the text. Panels (a) and (b) show sidebands due to transitions between the states in Figs. 2 and 2, respectively.