  We propose a scheme to achieve a uniform cross phase modulation (XPM) for two
nonclassical light pulses and study its application for quantum non-demolition
measurements of the photon number in a pulse and for controlled phase gates in
quantum information. We analyze the scheme by quantizing a common
phenomenological model for classical XPM. Our analysis first treats the ideal
case of equal cross-phase modulation and pure unitary dynamics. This
establishes the groundwork for more complicated studies of non-unitary dynamics
and difference in phase shifts between the two pulses where decohering effects
severely affect the performance of the scheme.
