Quantum enhancement of N-photon phase sensitivity by interferometric addition of down-converted photon pairs to weak coherent light

TL;DR

This paper demonstrates that adding down-converted photon pairs to weak coherent light enhances N-photon phase sensitivity through quantum interference, achieving sensitivities between the standard quantum limit and the Heisenberg limit.

Contribution

It introduces a more efficient method for generating non-classical N-photon states by combining down-converted photon pairs with coherent light, surpassing traditional approaches.

Findings

Achieves phase sensitivity of about 1/N^(3/2).

Enhancement is due to quantum interference effects.

Method is more efficient than using only down-converted photons.

Abstract

It is shown that the addition of down-converted photon pairs to coherent laser light enhances the N-photon phase sensitivity due to the quantum interference between components of the same total photon number. Since most of the photons originate from the coherent laser light, this method of obtaining non-classical N-photon states is much more efficient than methods based entirely on parametrically down-converted photons. Specifically, it is possible to achieve an optimal phase sensitivity of about delta phi^2=1/N^(3/2), equal to the geometric mean of the standard quantum limit and the Heisenberg limit, when the average number of down-converted photons contributing to the N-photon state approaches (N/2)^(1/2).