Novel Ion Trap for Efficient Fluorescence Collection from Trapped Ion Qubits

Efficient ion fluorescence collection is critical for fast reliable qubit state detection and higher photon collection rates from single trapped ions or atoms would lead to more efficient single-photon sources and ion-photon entanglement. By integrating a high N.A. spherical mirror into a linear Paul trap, we recently achieved $10\%$ photon collection efficiency from a single $Ba^+$ qubit. Based on the current successful trap, we designed and built a novel trap in which the reflective optical surface serves as the RF electrode. The new trap geometry is very open and almost 30\% of the photons emitted by the ion will be intercepted. Additionally, the axial symmetry of the trap provides means for self-alignment of the ion trapping position and the optical axis of the spherical mirror. Its smaller size will proportionally reduce the spherical aberration so that we can achieve diffraction-limited ion image, and attempt to couple ion fluorescence into a single mode optical fiber for remote ion entanglement. Compared to refractive optics systems, our solution has the advantage of simplicity, low cost, flexibility and scale-up potential.