  We report on progress towards implementing mixed ion species quantum
information processing for a scalable ion trap architecture. Mixed species
chains may help solve several problems with scaling ion trap quantum
computation to large numbers of qubits. Initial temperature measurements of
linear Coulomb crystals containing barium and ytterbium ions indicate that the
mass difference does not significantly impede cooling at low ion numbers.
Average motional occupation numbers are estimated to be $\bar{n} \approx 130$
quanta per mode for chains with small numbers of ions, which is within a factor
of three of the Doppler limit for barium ions in our trap. We also discuss
generation of ion-photon entanglement with barium ions with a fidelity of $F
\ge 0.84$, which is an initial step towards remote ion-ion coupling in a more
scalable quantum information architecture. Further, we are working to implement
these techniques in surface traps in order to exercise greater control over ion
chain ordering and positioning.
