Energy density and squeezing
Physics
We have studied the squeezing properties of arbitrary numbers of superpositions of various squeezed states such as squeezed vacuum state, photon-added coherent states, and two mode squeezed vacuum state. We have considered two superpositions: the first kind and the second kind. In the case of the first kind, the superpositions of squeezed states do not show both squeezing and higher-order squeezing of all orders. This is found to be true for any state which has quadrature squeezing and multi-mode squeezed states. However, in the case of the superpositions of the second kind (also called generalized superpositions), it has been shown that the superposition states show significant amounts of quadrature and higher-order squeezing. This is achieved by choosing the proper weight factors in the superpositions; this method also enables us to control over the amount of squeezing produced.
The vanishing and appearance of squeezing in a superposition state are explained based on expectation values of energy density or stress-energy tensor. States with squeezing are shown to have a negative expectation value for the stress-energy tensor for some values of spacetime-dependent phase. In the case of states with no squeezing, the expectation values of energy density is always positive.
Figure:- Contour plot of <:T00:> for squeezed number state with number squeezing (a) n=2 and (b) n=3 (K00=1)
- Ref: Squeezing and nonclassicality of q-deformed superposition states, S. Anupama, S. Kannan, C. Sudheesh, Eur. Phys. J. D 76, 11 (2022), https://doi.org/10.1140/epjd/s10053-021-00337-8.
- Ref: Disappearance of squeezing in superposition states and its manifestation in the energy density, S. Kannan, C. Sudheesh, J. Phys. B: At. Mol. Opt. Phys. 55, 095403 (2022), https://doi.org/10.1088/1361-6455/ac6846.