Noise limits on two-photon interferometric sensing

TL;DR

This paper compares the noise resilience of Mach-Zehnder and Hong-Ou-Mandel two-photon interferometers for precise delay estimation, analyzing how different input states perform under phase noise.

Contribution

It provides a detailed analysis of noise limits on two-photon interferometric sensing and compares the robustness of Mach-Zehnder and Hong-Ou-Mandel setups under various conditions.

Findings

Mach-Zehnder interferometry is more sensitive to phase noise than Hong-Ou-Mandel interferometry.

Different two-photon input states have varying performance depending on noise levels.

Optimal input states depend on the specific noise regime and measurement goals.

Abstract

When a photon interferes with itself while traversing a Mach-Zehnder inteferometer, the output port where it emerges is influenced by the phase difference between the interferometer arms. This allows for highly precise estimation of the path length difference (delay) but is extremely sensitive to phase noise. By contrast, a delay between the arms of the two-photon Hong-Ou-Mandel interferometer directly affects the relative indistinguishability of the photon pair, affecting the rate of recorded coincidences. This likewise allows for delay estimation; notably less precise but with the advantage of being less sensitive to perturbations of the photons' phase. Focusing on two-photon input states, we here investigate to what degree of noise Mach-Zehnder interferometry retains its edge over Hong-Ou-Mandel interferometry. We also explore the competing benefits of different two-photon inputs for a Mach-Zehnder interferometer, and under what parameter regimes each input performs best.