  Experimental methods for laser-control of trapped ions have reached
sufficient maturity that it is possible to set out in detail a design for a
large quantum computer based on such methods, without any major omissions or
uncertainties. The main features of such a design are given, with a view to
identifying areas for study. The machine is based on 13000 ions moved via 20
micron vacuum channels around a chip containing 160000 electrodes and
associated classical control circuits; 1000 laser beam pairs are used to
manipulate the hyperfine states of the ions and drive fluorescence for readout.
The computer could run a quantum algorithm requiring 10^9 logical operations on
300 logical qubits, with a physical gate rate of 1 MHz and a logical gate rate
of 8 kHz, using methods for quantum gates that have already been experimentally
implemented. Routes for faster operation are discussed.
