Scalable optical quantum computer

A way of designing a scalable optical quantum computer based on the photon echo effect is proposed. Individual rare earth ions Pr³⁺, regularly located in the lattice of the orthosilicate (Y₂SiO₅) crystal, are suggested to be used as optical qubits. Operations with qubits are performed using coherent and incoherent laser pulses. The operation protocol includes both the method of measurement-based quantum computations and the technique of optical computations. Modern hybrid photon echo protocols, which provide a sufficient quantum efficiency when reading recorded states, are considered as most promising for quantum computations and communications.