High fidelity quantum networking of trapped atomic ions

Abstract

Trapped-ion processors constitute a leading platform for quantum computing,and quantum networking due to qubits that exhibit exceptional coherence and high- fidelity logic. Scaling these systems to larger registers, however, remains non-trivial. A scalable architecture can be realized by linking smaller computing modules with photonic interconnects, forming a modular network that is agnostic to the underlying hardware design. In an earlier work we generated remote ion–ion entanglement at 250 s´1 using the photon’s polarization degree of freedom. However, uncontrolled birefringence in optical elements imposed fidelity limits on the entangled states. Here we replace polarization with time-bin encoding, where we distribute entan- glement via time-binned photons that are immune to polarization rotations. This strategy enables heralding of Bell states with a fidelity of 97%, the highest reported for photon-mediated ion-ion entanglement. During these experiments, we identified and quantitatively characterized an unexpected decoherence channel arising from re- coil of the emitting ion, marking the first direct observation of this effect. Finally, we generalize this protocol by using higher-dimensional time-bin photons to distribute entanglement across the levels of an atomic qudit.