Temporal heterodyne detector for multitemporal mode quantum state measurement

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Abstract
We propose a novel method for measuring the multitemporal mode quantum state of repetitive radiation fields with ultrafast temporal resolution. The technique incorporates spectrometers at the output ports of a DC-balanced four-port apparatus. The signal field to be measured is delayed in time with respect to an ultrashort local oscillator pulse which is taken to be in a large-amplitude single temporal mode coherent state. A quantum-mechanical analysis shows that the Fourier transform of the spectrally resolved difference counts is proportional to the multitemporal mode Q-function describing the signal field statistics. We apply the technique to reconstruct the multitemporal mode Q-function from simulated data of repetitive broadband chaotic light from which we calculate the photon number correlations between pairs of temporal modes.