# Estimation of nonclassical independent Gaussian processes by classical interferometry

## TL;DR

This paper introduces a classical interferometry method using low-intensity thermal radiation to estimate nonclassical Gaussian processes in materials, demonstrating robustness against noise and loss without requiring active optical elements.

## Contribution

It presents a novel interferometric approach for estimating Gaussian processes that is robust, does not need active elements, and works with limited radiation sources.

## Key findings

- Passive optical elements suffice for estimation accuracy.
- Method is robust against noise and loss.
- Suitable even with limited radiation sources.

## Abstract

We propose classical interferometry with low-intensity thermal radiation for the estimation of nonclassical independent Gaussian processes in material samples. We generally determine the mean square error of the phase-independent parameters of an unknown Gaussian process, considering a noisy source of radiation the phase of which is not locked to the pump of the process. We verify the sufficiency of passive optical elements in the interferometer, active optical elements do not improve the quality of the estimation. We also prove the robustness of the method against the noise and loss in both interferometric channels and the sample. The proposed method is suitable even for the case when a source of radiation sufficient for homodyne detection is not available.