Nonclassical states: An observable criterion

An observable criterion is derived that allows one to distinguish nonclassical states of the harmonic oscillator from those having a classical counterpart. A quantum state is shown to have no classical counterpart if and only if the characteristic functions of the quadrature distributions or the s-parametrized phase-space distributions exhibit a slower decay than for the ground state of the oscillator. This renders it possible to experimentally check the failure of the P function to be a probability measure.     

Nonclassical properties of coherent states

It is demonstrated that a weak measurement of the squared quadrature observable may yield negative values for coherent states. This result cannot be reproduced by a classical theory where quadratures are stochastic c-numbers. The nonclassicality of coherent states can be associated with negative values of the Terletsky–Margenau–Hill distribution.     

Nonclassical states generated via four-wave mixing

The nonclassical properties of quantum fields generated by four- or three-wave mixing are investigated on the basis of assumptions of two-photon coherent (squeezed) input states and the approximation of strong pumping. The influence of losses is shown supposing the model of mutually independent phonon reservoirs. The possibility of producing squeezed and sub-Poisson light outputs is demonstrated in single or superposed modes using computer solutions.The author wishes to acknowledge helpful discussions with Dr. J. Peina and Dr. M. Kárská.     

Comment on "Corresponding states of periodic structures in nematic liquid crystals"

Palangana, Sim?es, Evangelista, and Arrotéia [Phys. Rev. E 56, 4282 (1997)] (PSEA) propose a general scaling model for periodic wall patterns in the magnetic twist Fréedericksz transition of nematics, performing an elastic energy analysis. We demonstrate that this model is incorrect because it does not consider consistently the hydrodynamic wavelength selection of the observed structures, but is based on the assumption of inappropriate model functions instead. It is shown that experimental data actually contradict the proposed theory. The approach of PSEA is particularly not suited to determine elastic constant ratios of nematic liquid crystals.