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We study a superfluid Bose system with single-particle and pair condensateson the basis of a half-phenomenological theory of a Bose liquid not involvingthe weakness of interparticle interaction. The coupled equations describing theequilibrium state of such system are derived from the variational principle forentropy. These equations are analyzed at zero temperature both analytically andnumerically. It is shown that the fraction of particles in the single-particleand pair condensates essentially depends on the total density of the system. Atdensities attainable in condensates of alkali-metal atoms, almost all particlesare in the single-particle condensate. The pair condensate fraction grows withan increasing total density and becomes dominant. It is shown that at densityof liquid helium, the single-particle condensate fraction is less than 10%,which agrees with experimental data on inelastic neutron scattering, MonteCarlo calculations and other theoretical predictions. The ground state energy,pressure, and compressibility are found for the system under consideration. Thespectrum of single-particle excitations is also analyzed.

Role of single-particle and pair condensates in Bose systems with arbitrary intensity of interaction