The shadow of a single atom
Abstract: We have implemented single-atom imaging with unprecedented resolution using phase Fresnel lenses. This scalable imaging solution will enable parallel quantum repeaters based on ion-photon entanglement in spontaneous emission. Using this technology, we have performed absorption imaging of a single atomic ion for the first time with 5.6% contrast. Defocused absorption images provide spatial interferograms of the scattered light, permitting accurate retrieval of the amplitude and phase of the scattered wave. We have measured a phase shift of >1 radian in the scattered light as a function of laser detuning, verifying the microscopic origin of the refractive index for the first time. We have constructed, and are now testing, a monolithically integrated Fresnel mirror array for large arrays of trapped ions on a microfabricated chip for a highly parallel quantum repeater. We are also preparing for experiments with high-repetition-rate ultrafast lasers that can potentially increase trapped-ion logic gate speeds by two orders of magnitude.