Physics Colloquium

System of cold trapped atomic ions has all key features necessary for implementing quantum computation, and many demonstrations of high fidelity quantum logic gates, high fidelity information storage and readout have been made in recent years. However, scalability remains an elusive goal. I will describe one possible avenue to a scalable ion trap quantum computing architecture known as the MUSIQC architecture, in which an expandable number of Elementary Logic Units (ELUs), microfabricated traps holding linear chains of 10 to 100 ions, are linked together using photonic interface to form a modular large-scale system. Local quantum gates are performed using motional coupling between ions in the same trap. One or two ions in each chain are reserved for performing a slower entanglement operation between ions in different ion traps coupled by optical fibers. This long distance entanglement will be accomplished using photon-mediated ion-ion entanglement, in which pairs of ions are projected into an entangled Bell state by a combined measurement of their emitted single photons. It is beneficial to separate the fast motional coupling and the slower remote ion entanglement to different ion species, ytterbium and barium respectively, whose atomic transitions are widely separated in frequency, yet atomic masses are relatively similar. I will comment on the current state of the art of this architecture, and briefly mention our work on two-dimensional trapped ion crystals, and an effort towards linking trapped ion qubits and solid state spins.