1. L. D. Landau and E. M. Lifshitz, Quantum Mechanics: Non-relativistic Theory, 3rd ed., Pergamon Press, Oxford (1977).
2. B. M. Smirnov and M. I. Chibisov, Zh. Éksp. Teor. Fiz. 49, 841 (1965) [Sov. Phys. JETP 22, 585 (1966)].
3. A. M. Perelomov, V. S. Popov, and M. V. Terent’ev, Zh. Éksp. Teor. Fiz. 50, 1393 (1966) [Sov. Phys. JETP 23, 924 (1966)]; 51, 309 (1966) [24, 207 (1967)].
4. V. S. Popov, V. P. Kuznetsov, and A. M. Perelomov, Zh. Éksp. Teor. Fiz. 53, 331 (1967) [Sov. Phys. JETP 26, 222 (1968)].
5. T. Yamabe, A. Tachibana, and H. J. Silverstone, Phys. Rev. A 16, 877 (1977).