Positive energy density leads to no squeezing

Abstract

We consider two kinds of superpositions of squeezed states of light. In the case of superpositions of first kind, the squeezing and all higher order squeezing vanishes. However, in the case of the second kind, it is possible to achieve a maximum amount of squeezing by adjusting the parameters in the superposition. The emergence and vanishing of squeezing for the superposition states are explained on the basis of expectation values of the energy density. We show that expectation values of energy density of quantum states which show no squeezing will be always positive and that of squeezed states will be negative for some values of spacetime-dependent phase.