  We propose to encode a register of quantum bits in different collective
electron spin wave excitations in a solid medium. Coupling to spins is enabled
by locating them in the vicinity of a superconducting transmission line cavity,
and making use of their strong collective coupling to the quantized radiation
field. The transformation between different spin waves is achieved by applying
gradient magnetic fields across the sample, while a Cooper Pair Box, resonant
with the cavity field, may be used to carry out one- and two-qubit gate
operations.
