  Individual addressing of qubits is essential for scalable quantum
computation. Spatial addressing allows unlimited numbers of qubits to share the
same frequency, whilst enabling arbitrary parallel operations. We demonstrate
addressing of long-lived $^{43}\text{Ca}^+$ "atomic clock" qubits held in
separate zones ($960\mu$m apart) of a microfabricated surface trap with
integrated microwave electrodes. Such zones could form part of a "quantum CCD"
architecture for a large-scale quantum information processor. By coherently
cancelling the microwave field in one zone we measure a ratio of Rabi
frequencies between addressed and non-addressed qubits of up to 1400, from
which we calculate a spin-flip probability on the qubit transition of the
non-addressed ion of $1.3\times 10^{-6}$. Off-resonant excitation then becomes
the dominant error process, at around $5 \times 10^{-3}$. It can be prevented
either by working at higher magnetic field, or by polarization control of the
microwave field. We implement polarization control with error $2 \times
10^{-5}$, which would suffice to suppress off-resonant excitation to the $\sim
10^{-9}$ level if combined with spatial addressing. Such polarization control
could also enable fast microwave operations.
