  Dense array of ions in microfabricated traps represent one possible way to
scale up ion trap quantum computing. The ability to address individual ions is
an important component of such a scheme. We demonstrate individual addressing
of trapped ions in a microfabricated surface-electrode trap using a magnetic
field gradient generated on-chip. A frequency splitting of 310(2) kHz for two
ions separated by 5 um is achieved. Selective single qubit operations are
performed on one of two trapped ions with an average of 2.2+/-1.0% crosstalk.
Coherence time as measured by the spin-echo technique is unaffected by the
field gradient.
