  We consider a double-quantum-dot (DQD) qubit which contains six electrons
instead of the usual one or two. In this spin qubit, quantum information is
encoded in a low-lying singlet-triplet space much as in the case of a
two-electron DQD qubit. We find that initialization, manipulation, and read-
out can be performed similarly to the two-electron case, and that energy gaps
remain large enough that these operations can be performed robustly. We
consider DQD potentials with parameters chosen to be representative of current
experimental capabilities. Results are obtained using two complementary full
configuration interaction methods.
