Photon noise correlations in millimeter-wave telescopes

TL;DR

This paper investigates how photon noise correlations, due to the Hanbury Brown & Twiss effect, affect the sensitivity of millimeter-wave telescopes with densely packed detectors, providing a quantum optics-based calculation method.

Contribution

It introduces a general quantum optics formalism to calculate HBT photon noise correlations and assesses their impact on telescope sensitivity and focal-plane design.

Findings

HBT photon noise correlations reduce array sensitivity when pixel pitch is small.

The formalism extends to polarization-sensitive detectors.

Sensitivity scaling is less favorable than the uncorrelated limit under certain conditions.

Abstract

Many modern millimeter and submillimeter (``mm-wave'') telescopes for astronomy are deploying more detectors by increasing detector pixel density, and with the rise of lithographed detector architectures and high-throughput readout techniques, it is becoming increasingly practical to overfill the focal plane. However, when the pixel pitch $p_{\rm pix}$ is small compared to the product of the wavelength $\lambda$ and the focal ratio $F$, or $p_{\mathrm{pix}} \lesssim 1.2 F \lambda$, the Bose term of the photon noise correlates between neighboring detector pixels due to the Hanbury Brown & Twiss (HBT) effect. When this HBT effect is non-negligible, the array-averaged sensitivity scales with detector count $N_{\mathrm{det}}$ less favorably than the uncorrelated limit of $N_{\mathrm{det}}^{-1/2}$. In this paper, we present a general prescription to calculate this HBT correlation based on a quantum optics formalism and extend it to polarization-sensitive detectors. We then estimate the impact of HBT correlations on the sensitivity of a model mm-wave telescope and discuss the implications for focal-plane design.