MULTIMODE DENSITY-MATRICES OF LIGHT VIA AMPLITUDE AND PHASE-CONTROL

A new method is described for determining the quantum state of correla ted multimode radiation by interfering the modes and measuring the sta tistics of the superimposed fields in four-port balanced homodyne dete ction. The full information on the N-mode quantum state is obtained by controlling both the relative amplitudes and the phases of the modes, which simplifies the reconstruction of density matrices to only N + 1 Fourier transforms. In particular, this method yields time-correlated multimode density matrices of optical pulses by superimposing the sig nal by a sequence of short local-oscillator pulses.