Try a piston trap that will make them fall into a 1x1 pit, with a pressure plate at the bottom, rigged to
1. Self destruct immediatly by breaking the block beneath it.
2. Activate an electrified force-field trap (make a 2 second delay between hitting the plate and activating the field).
The block on which the pressure plate rests should be directly above a large pit, and, while they're still falling, the force field will activate, and they will be stuck inside, getting zapped constantly. It should eventualy kill even a quantum armored player, provided it's powered using a renewable power source.
Sorry for rezzing a two month dead thread, but I really couldn't resist.