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The quantum field Hamiltonian expressed in terms of density and current density variables has been employed together with the equal‐time commutation relations among these variables to find the ground state energy and the density fluctuation excitation spectrum of a system of interacting bosons at T = 0°K. The approximation involved consists in assuming that the density fluctuation in space is small compared with the average density. The results easily obtained in the lowest‐order approximation agree with those of Bogoliubov. However, in our treatment no condensation of particles in zero‐momentum state is assumed or apparent. A connection between the present treatment and the quantum hydrodynamic approach to the irrotational flow of a Bose liquid has been made

Density and Current Density as Coordinates for a System of Interacting Bosons at Absolute Zero