Interferometric technique for density matrix reconstruction by on/off detectors

The density matrix provides the most complete description of a quantum optical state and a scheme addressed to its reconstruction for arbitrary sources can be fundamental for several applications, ranging from quantum information to the foundations of quantum mechanics and quantum optics. We demonstrate an innovative state reconstruction technique, which provides the density matrix of a field mode and requires only avalanche photodetectors (coupled with phase modulation with respect to a local oscillator), without any phase or amplitude discrimination power. It represents an alternative of simpler implementation to quantum homodyne tomography.