The Cirac-Zoller gate is one of the key tools in the manipulation of quantum information on a string of trapped ions, and its proposal was a huge step in the path of quantum computing from abstract algorithms towards actual hardware in the lab, particularly because the ability to interface and entangle the internal electronic states of multiple ions in the trap was both scalable and reasonably protected from decoherence.
Nevertheless, despite the fact that it was clearly a very promising way forward, and the , it took eight years between the proposal of the gate in 1995,
- Quantum Computations with Cold Trapped Ions. J.I. Cirac and P. Zoller. Phys. Rev. Lett. 74, 4091 (1995); eprint.
and its realization in 2003,
- Realization of the Cirac–Zoller controlled-NOT quantum gate. F. Schmidt-Kaler et al. Nature 422, 408 (2003); eprint.
for reasons that theorist-folklore tends to brush nowadays as simply "it turned out to be technically challenging", but which have never been quite clear to me.
So: what were the main technical obstacles that had to be overcome for the Cirac-Zoller gate to get implemented?
