Temporal heterodyne detector for multitemporal mode quantum state measurement

We propose a novel method for measuring the multitemporal mode quantum stat e of repetitive radiation fields with ultrafast temporal resolution. The te chnique incorporates spectrometers at the output ports of a DC-balanced fou r-port apparatus. The signal field to be measured is delayed in time with r espect to an ultrashort local oscillator pulse which is taken to be in a la rge-amplitude single temporal mode coherent state. A quantum-mechanical ana lysis shows that the Fourier transform of the spectrally resolved differenc e counts is proportional to the multitemporal mode Q-function describing th e signal field statistics. We apply the technique to reconstruct the multit emporal mode Q-function from simulated data of repetitive broadband chaotic light from which we calculate the photon number correlations between pairs of temporal modes.