Quantum optical interferometry via the mixing of coherent and photon-subtracted squeezed vacuum states of light

Hofmann and Ono [Phys. Rev. A 76, 031806, (2007)] showed that the mixing of coherent light and single-mode squeezed light at a beam splitter gives good approximation results in a superposition of path-entangled photon number states (so-called N00N states), which can be used for phase-shift measurements by coincident detections at the output of an interferometer. They showed that N00N states for arbitrary photon number N could be produced by this procedure. Afek et al. [Science 328, 879 (2010)] have implemented the Hofmann-Ono proposal in the laboratory. In this paper, we show that, for a given coherent state amplitude and a given squeezing parameter, the mixing of coherent states and photon-subtracted squeezed vacuum states at the first beam splitter of an interferometer leads to improved phase-shift measurement sensitivity when using the photon-number detection technique on one of the output beams of the device. We also show that the phase-shift measurements will also be super-resolved to a greater degree than is possible by mixing coherent and squeezed vacuum light of the same field parameters. (C) 2014 Optical Society of America