Recent Results in TrappedIon Quantum Computing
Abstract
We review recent experiments on entanglement, Bell's inequality, and decoherencefree subspaces in a quantum register of trapped \be ions. We have demonstrated entanglement of up to four ions using the technique of Mølmer and Sørensen. This method produces the state down down> + up up> for two ions and the state down down down down> + up up up up> for four ions. We generate the entanglement deterministically in each shot of the experiment. Measurements on the twoion entangled state violates Bell's inequality at the $8\sigma$ level. Because of the high detector efficiency of our apparatus, this experiment closes the detector loophole for Bell's inequality measurements for the first time. This measurement is also the first violation of Bell's inequality by massive particles that does not implicitly assume results from quantum mechanics. Finally, we have demonstrated reversible encoding of an arbitrary qubit, originally contained in one ion, into a decoherencefree subspace (DFS) of two ions. The DFSencoded qubit resists applied collective dephasing noise and retains coherence under ambient conditions 3.6 times longer than does an unencoded qubit. The encoding method, which uses singleion gates and the twoion entangling gate, demonstrates all the elements required for twoqubit universal quantum logic.
 Publication:

arXiv eprints
 Pub Date:
 February 2001
 arXiv:
 arXiv:quantph/0102086
 Bibcode:
 2001quant.ph..2086K
 Keywords:

 Quantum Physics
 EPrint:
 7 pages, 7 figures, proceedings for IQC01, Sydney, Australia