Recent results in trapped-ion quantum
computing at NIST
(pp113-123)
David
Kielpinski, A. Ben-Kish,
Joe
Britton, V. Meyer, M.A.
Rowe, W.M. Itano, David .J. Wineland,
Charles
Sackett, and
Christopher
Monroe
doi:
https://doi.org/10.26421/QIC1.s-12
Abstracts:
We review recent experiments on entanglement, Bell's
inequality, and decoherence-free subspaces in a quantum register of
trapped {9Be+} ions. We have demonstrated entanglement of up to four
ions using the technique of Molmer and Sorensen. This method produces
the state ({|\uparrow\uparrow\rangle}+{|\downarrow\downarrow\rangle})/\sqrt{2}
for two ions and the state ({\downarrow}{\downarrow}{\downarrow}{\downarrow}
\rangle + | {\uparrow}{\uparrow}{\uparrow}{\uparrow} \rangle)/\sqrt{2}
for four ions. We generate the entanglement deterministically in each
shot of the experiment. Measurements on the two-ion 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 decoherence-free
subspace (DFS) of two ions. The DFS-encoded 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 single-ion gates and the two-ion entangling gate,
demonstrates all the elements required for two-qubit universal quantum
logic.
Key words: trapped ion
quantum computing |