Preservation of nonclassical character during the amplification of a Schrödinger cat state
Huaqing Huang, Shi-Yao Zhu, Muhammad Suhail Zubairy · Physical Review A · 1996
We examine the nonclassical property of a Schr\"odinger cat state, i.e., a superposition of two coherent states, when it is amplified by either a phase-sensitive or a phase-insensitive amplifier. In both cases the corresponding P representation remains nonpositive in some area of the complex plane, for any amplification factor. The contribution to the P function from these areas decreases exponentially with an amplification factor. With a phase-sensitive amplifier the onset of decay can be postponed to a larger amplification factor. Thus the nonclassical nature of the field can be preserved under a wide range of conditions, in spite of the noise introduced in the amplification process. \textcopyright{} 1996 The American Physical Society.