Requirements on strong chi-2 nonlinearity for parametric conversion and using optical nonlinearity for Bell measurement

Optical chi-2 nonlinearity has broad applications in optical technology. Although current materials only provide weak nonlinearity, there has been improvements towards producing materials with stronger strength. However, strong nonlinearity means higher order interactions between photons are significant and we show that the frequency response of a bulk chi-2 medium may induce spectral entanglement between photons that lowers the conversion rate. We prove that one way of reducing the spectral entanglement is to utilize periodically poled media. Here we also show how one may use currently available optical nonlinearity to do Bell measurements that can outperform the linear optical partial Bell measurement scheme.