We demonstrate that conditional as well as unconditional basic operations
which are prerequisite for universal quantum gates can be performed with almost
100% fidelity within a strongly interacting two-electron quantum ring. Both
sets of operations are based on a quantum control algorithm that optimizes a
driving electromagnetic pulse for a given quantum gate. The demonstrated
transitions occur on a time scale much shorter than typical decoherence times
of the system.Comment: 4 pages, 4 figures, copyright 2010 The American Physical Societ