Research in Atomic, Ionic and Photonic Systems for Scalable Deterministic Quantum Logic

Abstract

The "pushing gate" that we intend to use to entangle ions was thoroughly studied theoretically (milestone 1 complete). We proposed a solution to a hidden weakness in the original proposal which led to extreme sensitivity to, for example, laser intensity noise. We demonstrate that fast gates of good fidelity are possible without ground-state cooling [1].We implemented and quantitatively studied photo-ionization ion loading and optimized the loading process so that we could trap and laser-cool all the naturally-occurring isotopes of calcium (including the 0.004%-abundant 46 Ca). We can load single ions or small crystals "on demand", from a background vapour pressure 4-5 orders of magnitude lower than with electron bombardment, and with negligible drift in static electric fields between loads; this gives increased environmental stability for the ion-qubits and should reduce deposition on electrodes to a negligible level. Most importantly for the implementation of qubits, we can reliably load small, pure, crystals of the 0.14%-abundant 43 Ca+ ion (milestone 2 complete). The ability to do this without an enriched isotopic source was beyond our expectations and represents a significant experimental simplification. Isotope-selection of specific even isotopes (e.g. We began the design process for our next-generation multiple trap (start of milestone 3), with studies of possible electrode structures. We designed and had built a high-power solid-state violet laser system in order to test its suitability for implementing the "pushing gate" (start of milestone 4).