Reducing of the Uncertainty Product of Coherent Light through Multi-Photon Interference

TL;DR

This paper shows that multi-photon interference can reduce the diffraction and resolution limits of coherent light, enabling more precise interferometry without the need for entangled or squeezed states.

Contribution

It introduces a method to surpass the standard quantum limit in resolution using multi-photon interference with coherent light, demonstrated both theoretically and experimentally.

Findings

Fringe width reduced by up to 1/√(2N) with N=2,3,4 photons

Achieved resolution beyond the diffraction limit without entangled light

Experimental validation of theoretical predictions

Abstract

We demonstrate theoretically and experimentally how the diffraction and interferometric resolution limit for single-mode coherent cw laser light can be overcome by multi-photon interference. By use of a Mach-Zehnder interferometer, operated in the single input and single or double output port geometries, we observe a fringe width reduction of the conventional interference pattern, predicted by the wave or single photon quantum theory, by a factor of up to $1/\sqrt{2N}$ through coincident detection of $N=2,3,4$ photons. Our scheme does not require squeezed or entangled light to overcome the standard quantum limit and greatly facilitates precision interferometry experiments.