Remotely entangling trapped ions using trap-integrated optics for photon collection and interference

Large-scale quantum processors will likely require connecting modules, and photon-mediated entanglement generation is an attractive method for achieving high-fidelity interconnection using trapped ions. Current demonstrations rely on bulk photon-collection and manipulation optics that suffer from mode-matching challenges and system-to-system variability—factors that impede scaling to the large numbers of entangled pairs needed for quantum information processing. To address these limitations, we demonstrate remote entanglement using a collection method that enables passive phase stability, straightforward photonic manipulation, and intrinsic reproducibility. Specifically, we engineer waveguide-integrated gratings to couple photons emitted from a trapped ion into single optical modes that are interfered on a multi-mode interferometer based beam splitter within a microfabricated ion-trap chip. We detect these interfered photons from separate ions in different zones of the chip to generate photon-mediated entanglement heralded by a single photon detection. The integrated nature of the collection gratings will allow for straightforward multiplexing of remote entanglement in future devices. This demonstration could thus lay the foundation for scalably creating high-rate, high-fidelity interconnects between modules of a distributed trapped ion quantum computer.