Scalable ion–photon quantum interface based on integrated diffractive mirrors

Quantum networking links quantum processors through remote entanglement for distributed quantum information processing and secure long-range communication. Trapped ions are a leading quantum information processing platform, having demonstrated universal small-scale processors and roadmaps for large-scale implementation. Overall rates of ion–photon entanglement generation, essential for remote trapped ion entanglement, are limited by coupling efficiency into single mode fibers and scaling to many ions. Here, we show a microfabricated trap with integrated diffractive mirrors that couples 4.1(6)% of the fluorescence from a 174Yb+ ion into a single mode fiber, nearly triple the demonstrated bulk optics efficiency. The integrated optic collects 5.8(8)% of the π transition fluorescence, images the ion with sub-wavelength resolution, and couples 71(5)% of the collected light into the fiber. Our technology is suitable for entangling multiple ions in parallel and overcomes mode quality limitations of existing integrated optical interconnects. Building large-scale quantum computers or distributed networks of quantum computers requires small-scale nodes to be readily replicated and effectively connected. Atomic ions trapped above the surface of micro-fabricated chips are a leading method for implementing small, scalable, stationary quantum processing nodes. External communication between trapped ions has previously required bulky multi-element optics to create efficient photonic interconnections through single-mode optical fibers. Moji Ghadimi, with colleagues at Griffith University (Australia) and GeorgiaTech Research Institute, have overcome this hurdle with a demonstration of a chip trap with the primary optic integrated directly onto its surface. By patterning the flat reflective surface of the chip trap with a computer-generated hologram of a perfect focusing mirror they were able to image the ion’s fluorescence with nearly no distortions and couple that light efficiently into a single-mode fiber. This approach transfers optical complexity into the chip trap fabrication, where it can be more easily mass-produced.