Measuring the brightness of classical noise dominated light at the shot noise limit?

TL;DR

This paper critically reexamines a claim that certain measurement techniques can detect thermal light brightness at the shot noise limit, confirming that the claim was based on incorrect assumptions about thermal noise correlations.

Contribution

It clarifies the limitations of previous claims by correcting the assumptions about thermal noise correlations in brightness measurements.

Findings

The claim by Lieu et al was falsified due to incorrect assumptions.

The analysis confirms the importance of proper noise correlation modeling.

The measurement technique does not achieve shot noise limited detection as previously claimed.

Abstract

A recent claim by Lieu et al that beam splitter intensity subtraction (or homodyne with one vacuum port) followed by high resolution sampling can lead to detection of brightness of thermal light at the shot noise limit is reexamined here. We confirm the calculation of Zmuidzinas that the claim of Lieu et al was falsified by an incorrect assumption about the correlations in thermal noise.