  Fluoride crystals doped with rare-earth ions (REI) and pair centers in
diamond for fast ($10^{-9}\rm{s}$) quantum computers (FQC) are proposed. As
specific systems for REI doping, we propose $Ca_{1-x}Sr_{x}F_{2}$ crystals and
their analogues. The $^{4}f$-states with different total orbital angular
moments of these ions serve as two-level systems (qubits). Suitable REIs are
proposed as well. It is established that the pair $SiV$ and $GeV$ centers in
diamond are promising systems for fast optical quantum computers operating at
elevated temperatures.
