Method for implementation of universal quantum logic gates in a scalable   Ising spin quantum computer
  We present protocols for implementation of universal quantum gates on an arbitrary superposition of quantum states in a scalable solid-state Ising spin quantum computer. The spin chain is composed of identical spins 1/2 with the Ising interaction between the neighboring spins. The selective excitations of the spins are provided by the gradient of the external magnetic field. The protocols are built of rectangular radio-frequency pulses. The phase and probability errors caused by unwanted transitions are minimized and computed numerically. 
G. P. Berman, D. I. Kamenev, R. B. Kassman, C. Pineda, and V. I.   Tsifrinovich