Phase-measurement sensitivity beyond the standard quantum limit in an interferometer consisting of a parametric amplifier and a beam splitter

摘要

We analyze a nonconventional interferometer that is formed with a parametric amplifier and a beam splitternfor beam splitting and recombination. Because the outputs from a parametric amplifier are entangled and theirnquantum noise is correlated, the employment of the beam splitter will superimpose the two quantum fields andnthe destructive interference will lead to the subtraction of the quantum noise and to noise reduction in the outputnof the interferometer and hence an improvement of the signal-to-noise ratio (SNR) beyond the standard quantumnlimit or the shot noise limit. Furthermore, the injection of a squeezed state into the idler port of the parametricnamplifier will lead to further improvement of the SNR.We will discuss the possibility of reaching the Heisenbergnlimit in such an interferometer. We find that the injection of a coherent state will degrade the performance innreaching the Heisenberg limit, whereas a squeezed state injection can improve it by a factor of 2 at best.