Observing the quantum interference using phase-sensitive amplification

We show that a coherent superposition of coherent states remains highly non classical when it is amplified through a linear phase-sensitive or phase-in sensitive amplifier. The nonclassicality persists for arbitrarily large gai n. We also propose a scheme for the observation of quantum interference via phase-sensitive amplification. The basic idea is to amplify a Schrodinger- cat state through a phase-sensitive two-photon CEL amplifier such that ther e is no added noise in the quadrature of interest and all the noise is fed into the conjugate quadrature. This scheme allows us to avoid the problem o f detector efficiency in balanced homodyne detection. (C) 2000 Elsevier Sci ence B.V. All rights reserved.