Polarization properties of long-lived stimulated photon echo

The polarization properties of the long-lived stimulated photon echo formed on the transition j_a → j_b with the atomic levels degenerate in the projections of the angular momenta are studied theoretically. The two particular transitions j_a = 1 → j_b = 0 and j_a = 1 → j_b = 1 with degenerate ground state j_a = 1 are discussed. For the transitions j_a = 1 → j_b = 1 the polarizations and areas of the first (‘write’) and the third (‘read’) excitation pulses are found when the echo polarization faithfully reproduces the arbitrary polarization of the weak (single-photon) second (‘information’) pulse, so that this echo scheme may implement the quantum memory for a single-photon polarization qubit, while for the transitions j_a = 1 → j_b = 0 it is shown, that the echo polarization differs from that of the second pulse at any conditions. (letter)