NONDEGENERATE 2-PHOTON DOWN-CONVERSION - COHERENT INPUTS AND NONCLASSICAL EFFECTS

We study the nondegenerate two-photon down conversion described by a q uantum trilinear Hamiltonian. The idler mode is initially prepared in the vacuum while the pump (laser) and the signal mode are prepared in coherent states which at high intensities resemble classical inputs. S uch setup with a coherent signal mode allows us to scan the dynamics f rom the regime of the down conversion (empty signal) up to the frequen cy conversion (highly excited signal). The analysis concentrates on th e entanglement properties of the modes which are compared with their o ther statistical properties such as squeezing and antibunching to give a more complete characterization of the modes. We show that the singl e mode nonclassical effects (squeezing and antibunching) disappear whe n an initial signal intensity highly exceeds that of the pump. In this regime the numerical results are confirmed by approximate analytical calculations. We point out that initially comparable intensities of th e signal and pump mode lead to the effect of the ''spontaneous disenta nglement'' of the signal mode from others and to the production of its squeezed and sub-Poissonian state which is pure to a good approximati on.