The Fourth Seminar on Quantum Optics, from May 12 to 14, 1992 in Raubichi was held after the disintegration of the USSR. This was embodied in its title -- it became international. The Belarus Foundation for Basic Research appeared as a sponsor of SQO-IV. However, the scope of the seminar remained the same. It was determined by special features of the development of quantum optics and, of course, by the scientific interests of its participants, including the permanent organizers and participants (Yu.M. Golubev, A.S. Chirkin, A.S. Troshin, A.V. Masalov, S.Ya. Kilin, and A.P Nizovtsev); scientists actively working in the field of quantum optics; and young scientists and post-graduate students, who were given a chance to report and discuss their scientific works.

Reports reflecting refined understanding of quantum states of light as a complicated object, which cannot be adequately described by means of simplified ideas, were presented at SQO-IV. The report by V. Buzek (Bratislava) and P. Knight (Imperial College, London) was devoted to the dynamics of superposition states formed of coherent states in a microwave cavity. A.Ya. Orlovskii (Warsaw University) discussed the superposition principle and its relation to the notion of squeezing. The concept of squeezing was extended to the polarization variables in the report by V.P Karasev and A.V. Masalov (FIAN). New results on the quantum representation of multimode (pulsed) fields were presented in the reports by A.S. Chirkin, N.V. Korolkova. and A.V. Belinskii (MSU). A number of reports were devoted to phase properties of quantized fields [B.K. Burzakhmetov (UINR), B.B. Govorkov (UINR), and Ya.A. Fofanov (IAP RAS)].

Experimental evidence for the conservation of the generalized phase in the process of SRS leading to solitonlike spikes in the intensity of depleted pumping was the subject of the report by S.Ya. Kilin, V.A. Orlovich, A.S. Grabchikov, and D.E. Gakhovich (IP BAS).

Problems, whose importance for quantum optics would be realized two years later, were the subjects of the reports by E.A. Zubova (MSU), about single-electron reversible logical elements for a quantum-mechanical computer; D.S. Mogilevtsev (IP BAS), about the effect of "freezing" of spontaneous decay of atoms placed in a medium with a gap in the density of photon states (so-called photon crystals); and T.B. Karlovich (IP BAS), about the multistability of the radiation field of a system of atoms in a coherently-excited high-quality cavity.

New possibilities in the generation of sub-Poissonian light were discussed in the reports by Yu.M. Golubev and A.S. Troshin.

The ideas of controlling dephasing of the transition frequencies of impurity centers in ruby crystals by external electromagnetic radiation received further development in the reports by A.P. Nizovtsev (IP BAS) and V.S. Malinovskii (NSU).

A number of new phenomena in coherent quantum optics was discussed in reports by E.E. Fradkin (St. Petersburg State University, SPSU), A.V. Gorokhov (SSU), A.M. Basharov (MEPI), B.A. Samson (IP BAS), Z. Gaizhauskas (Vilnius University), V.R Kozich and A.l. Vodchits (IP BAS), and V.A. Savva (IP BAS).

A poster section was organized at SQO-IV. Sixteen reports were presented there, including reports by Kho Chung Zung and N.S. Shumovskii (JINR) on decay in the Jaynes-Cummings model, T.M. Maevskaya (IP BAS) on continuous variations of fields with sources, and D.B. Horoshko (IP BAS) on simulation of feedback on the basis of the theory of continuous quantum measurements.

A part of the reports presented at SQO-IV was published in Optika i Spektroskopiya (Optics and Spectroscopy), 1993, vol. 74, no. 5.