Individual addressing of ions using magnetic field gradients in a surface-electrode ion trap

A dense array of ions in microfabricated traps represents 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 mu m 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 is reduced by the magnetic field gradient, but the spin-echo technique effectively restores the coherence time.