Qubits based on spectrally selected groups of Pr$^{3+}$ ions in a LaF$_3$ crystal

Spectral selection, i.e., the separation of a group of particles with a spread in resonance frequencies smaller than the hyperfine splitting of working levels has been implemented by the method of burning of long-lived spectral dips in the inhomogeneously broadened absorption line of Pr$^{3+}$ in a LaF$_3$ crystal. The possibility of implementing qubits (basic elements of quantum computations) on ensembles of spectrally selected particles and the main operations with them, including the manipulation of the populations of hyperfine (qubit) levels and the controlled shift of the absorption line of one spectrally selected group of ions upon excitation of another group (two-qubit operations), has been demonstrated. The decay rates of the population of hyperfine sublevels of the ground state of the spectrally selected group of particles have been measured.