Limits on quadrature variances and cross-correlations
P. D. Drummond · Quantum Optics Journal of the European Optical Society Part B · 1990
An arbitrary radiation field has limits on its quadrature variances and cross-correlations given by the positivity of the density matrix. These limits are derived and related to the optimisation of the squeezing measurements. The results are designed to deal with typical multimode squeezing experiments. In particular, the bounds indicate the necessity of achieving equal photon number intensities for optimal squeezing. A photon number imbalance can be compensated to some extent by using unequal gains. The optimal relative gain is obtained here.