Parametric down-conversion with coherent pulse pumping and quantum interference between independent fields

The process of parametric down-conversion pumped by a short coherent pulse is analysed. The coherence properties of the down-converted field are investigated. It is found that the spectrum of the down-conversion is mostly determined by the nonlinear medium and is independent of the width of the short pumping pulse and that it is impossible to realize a transform-limited two-photon state. Fourth-order interference between a weak coherent pulse and the down-converted pulse is considered. It is found that high visibility near 100% is achievable by means of narrow optical filtering. It is shown that by gating the detection on one of the down-converted photons, a transform-limited single-photon pulse is achievable in the other conjugate field, but its pulse width is shorter than that of the down-converted pulse and its peak position is uncertain within the pulse width of the down-converted light. However, with narrow optical filtering on the gating detection process, a transform-limited single-photon state can be obtained in the gated field with its peak position synchronized to the pump pulse. The possibility for the realization of a multi-photon interference experiment is explored for the quantum state measurement of the single-photon state.