Quantum calculations usually have to be completed within the coherence time of the corresponding qubit. Current phase gates in ion qubits are limited in length by the trap frequency and take at least several microseconds to complete. This means it is only possible to complete hundreds of gates within the coherence time. We want to implement a different approach that is independent of the trap frequency and relies on short, counter propagating pulse pairs .
Daniel Heinrich, Óscar Andrey Herrera, Christian Roos, Rainer Blatt
 J. J. García-Ripoll, P. Zoller, and J. I. Cirac. “Speed Optimized Two-Qubit Gates with Laser Coherent Control Techniques for Ion Trap Quantum Computing”, Phys. Rev. Lett. 91, 157901 (2003).