  We propose a scheme to realize quantum controlled phase flip (CPF) between
two rare earth ions embedded in respective microsphere cavity via interacting
with a single-photon pulse in sequence. The numerical simulations illuminate
that the CPF gate between ions is robust and scalable with extremely high
fidelity and low error rate. Our scheme is more applicable than other schemes
presented before based on current laboratory cavity-QED technology, and it is
possible to be used as an applied unit gate in future quantum computation and
quantum communication.
