Intensity product-based optical sensing to beat the diffraction limit in an interferometer

Abstract: The classically defined minimum uncertainty of the optical phase is known as the standard quantum limit or shot-noise limit (SNL) originating in the uncertainty principle of quantum mechanics. Based on SNL, the phase sensitivity is inversely proportional to the square root K, where K is the number of interfering photons or statistically measured events. Thus, using a high-power laser is advantageous to enhance sensitivity due to the square root K gain in the signal-to-noise ratio. In a typical interferometer, however, the resolution remains in the diffraction limit of the K=1 case unless the interfering photons are resolved as in quantum sensing. Here, a projection-measurement method in quantum sensing is adapted for an interferometer to achieve an additional square root K gain in resolution. For the projection measurement, the interference fringe of an interferometer can be Kth-powered to replace the Kth-order intensity product. To understand many-wave interference-caused enhanced resolution, several types of interferometers are numerically compared to draw corresponding resolution parameters. As a result, the achieved resolution by the Kth power to an N-slit interferometer exceeds the diffraction limit and the Heisenberg limit in quantum sensing.