Individual-Ion Addressing with Microwave Field Gradients
  Individual-qubit addressing is a prerequisite for many instances of quantum information processing. We demonstrate this capability on trapped-ion qubits with microwave near-fields delivered by electrode structures integrated into a microfabricated surface-electrode trap. We describe four approaches that may be used in quantum information experiments with hyperfine levels as qubits. We implement individual control on two 25Mg+ ions separated by 4.3 micrometer and find spin-flip crosstalk errors on the order of 10^(-3). 
U. Warring, C. Ospelkaus, Y. Colombe, R. J\"ordens, D. Leibfried, and   D. J. Wineland
quant-ph physics.atom-ph