Deterministic enhancement for bright-seeded Mach–Zehnder interferometer using low-noise feed-forward amplifiers

Abstract

We propose to use low-noise feed-forward amplifiers (LFAs) to enhance the phase sensitivity of a bright-seeded Mach–Zehnder interferometer (MZI). LFAs are performed on the two arms inside the MZI, which are based entirely on linear optics, off-line squeezed ancillary states, and homodyne detectors. We demonstrate the necessity of LFA-based topology in achieving sensitivity improvement beyond the standard quantum limit, compared with the deterministic linear amplification scheme. Remarkably, we find that the LFA-based MZI is advantageous over the standard MZI in robustness against the internal losses of the interferometer.