Efficient collection of single photons emitted from a trapped ion into a single-mode fiber for scalable quantum-information processing

Interference and coincidence detection of two photons emitted by two remote ions can lead to an entangled state, which is a critical resource for scalable quantum-information processing. Currently the success probabilities of experimental realizations of this protocol are mainly limited by low coupling efficiency of a photon emitted by an ion into a single-mode fiber. Here we consider two strategies to enhance the collection probability of a photon emitted from a trapped Yb+ ion, using analytic methods that can be easily applied to other types of ions or neutral atoms. Our analysis shows that we can achieve fiber coupling efficiency of over 30% with an optical cavity made of a flat fiber tip and a spherical mirror. We also investigate ways to increase the fiber coupling efficiency using high-numerical-aperture optics, and show that collection probability of over 15% is possible with proper control of aberration.