Towards a complete toolbox for implementing the QCCD architecture with mixed species trapped ions crystals

Matteo Simoni, Francesco Lancellotti, Tanja Behrle, Thanh Long Nguyen, Jonathan Home
ETH Zurich, Switzerland

Trapped ions constitute one of the most promising platforms for quantum computing thanks for example to their high fidelities and to long range interactions. Nonetheless, long strings of ions seem difficult to scale up because because the complexity of the physical system under control increases, reducing control. One promising alternative is provided by the so called QCCD architecture: in this framework, the quantum computer is broken down into multiple modules, each occupied by a small number of ion; the modules are then connected by moving selected ions between the crystals. In order for the scheme to work, it is necessary to obtain reliable shuttling, merging and splitting of ion crystals, while not introducing excessive energy to the ion chains such that cooling to temperatures required for multi-ion gates does not take too long. I will describe work on implementing these tasks with mixed species ion crystals composed by Beryllium and Calcium ions to demonstrate proofs of principle of QCCD architecture schemes. While one species is used to store information, the other can be used either as an ancilla for syndrome readout in error correction or for re-cooling. Thanks to the optical isolation between the species, cooling can be performed without scattered light destroying stored quantum information. To optimise control, a better understanding of the potentials in our trap is required, particularly close to the crossing point of oscillation modes. The work contributes towards a fully formed toolbox for implementing the QCCD architecture, for which all other elements exist in our experimental apparatus. Other research directions we are pursuing are the study of dissipative quantum systems of mixed species ions crystals and the application of QEC schemes by encoding quantum information in the motional state of a Calcium ion.