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.
Categories: quant-ph cond-mat.mtrl-sci