Conditional measurement of the photon number optical pulse collision

Summary form only given. The optical Kerr effect of fibers produced unique nonclassical correlations through intensity-dependent phase shifts in a variety of quadrature-amplitude squeezing and quantum-nondemolition (QND) experiments. Later, a new squeezing mechanism was observed with spectral filtering of fiber-optical pulses. Our novel QND approach applies spectral filtering to two interacting pulses in order to obtain a QND readout that is immune to phase noise. In a pulse collision the spectral separation between the center frequencies of the pulses is transiently enhanced, with the spectral shift of one (meter) pulse depending on the photon number of the other (signal) pulse. Thus photon-number fluctuations of one pulse are transferred to frequency fluctuations of the other pulse which are directly detectable after a spectral filter. The maximum frequency shift occurs in the center of the collision, where the pulses are well separated in frequency space, even if there is a spectral overlap before the collision.