Density-matrix reconstruction by unbalanced homodyning

Abstract
Recently a method for measuring quasidistributions of single-mode optical fields in unbalanced homo- dyne detection has been proposed [S. Wallentowitz and W. Vogel, Phys. Rev. A 53, 4528 (1996); K. Bana- szek and K. Wódkiewicz, Phys. Rev. Lett. 76, 4344 (1996)]. We show that the scheme can be used for direct sampling of the signal-mode density matrix in the Fock basis. In this case it is sufficient to vary only the phase of the local oscillator, keeping its amplitude constant.