Quantum Information Processing with Trapped 43Ca+ Ions; Final progress rept. 1 Jul 2003-31 Dec 2007

摘要

We report on experiments with strings of laser-cooled Ca+ ions for quantum information processing. An experiment using the isotope 43Ca+ was set up from scratch. We devised techniques for loading and laser-cooling 43Ca+ ion strings, initializing the ions in the hyperfine clock states and reading out the quantum state with high efficiency. Coherence times of the qubits are about 1 s. The single-qubit gates were implemented using microwave and Raman excitation, and coupling to the motional state was demonstrated. Very recently, a pair of 43Ca+ ions were entangled for the first time. In a second line of experiments, we demonstrated simple quantum algorithms with few 40Ca+ ions as well as the implementation of a high-fidelity gate operation entangling a pair of ions with a fidelity of 99.3(1)%. Among the milestone experiments are the demonstration and quantum process tomography of a Cirac-Zoller gate with mean fidelity of about 93%, the demonstration of entanglement in a decoherence-free sub space lasting for 20s, the demonstration of deterministic quantum teleportation, a Toffoli gate, deterministic entanglement swapping a partial measurement of a GHZ state preserving entanglement in the remaining qubits, creation and analysis of an 8-ion W-state, the application of entangled ions for precision spectroscopy.