Measurement of the Wavefunction for a Biphoton State with Homodyne Detection Using Least Squares Estimation

We report the measurement of wave function for a biphoton state with continuous variables (CV) by homodyne detection. The biphoton interference occurs on an optical parametric oscillator, which is seeded with a coherent state. A set of second-order correlation function values for the output field are recorded when the intensity coherent state is varied. The wave function, which includes both magnitude and argument for a complex parameter of the biphoton state, is reconstructed using the least square estimation method. This may introduce another approach to characterizing a biphoton state in the regime of CV.