Photon noise from chaotic and coherent millimeter-wave sources measured with horn-coupled, aluminum lumped-element kinetic inductance detectors

TL;DR

This study demonstrates photon-noise limited performance of millimeter-wave detectors using a source with variable power and coherence, confirming theoretical noise models and achieving a NEP around 2×10⁻¹⁷ W/Hz¹/².

Contribution

First measurement of photon noise in millimeter-wave detectors with controlled broadband and coherent sources, validating simple quasiparticle models across a wide power range.

Findings

Photon noise dominates at powers >1 pW with NEP ≈ 2×10⁻¹⁷ W/Hz¹/².

NEP scales linearly with power for broadband (chaotic) illumination.

NEP scales with the square root of power for continuous-wave (coherent) illumination.

Abstract

We report photon-noise limited performance of horn-coupled, aluminum lumped-element kinetic inductance detectors at millimeter wavelengths. The detectors are illuminated by a millimeter-wave source that uses an active multiplier chain to produce radiation between 140 and 160 GHz. We feed the multiplier with either amplified broadband noise or a continuous-wave tone from a microwave signal generator. We demonstrate that the detector response over a 40 dB range of source power is well-described by a simple model that considers the number of quasiparticles. The detector noise-equivalent power (NEP) is dominated by photon noise when the absorbed power is greater than approximately 1 pW, which corresponds to $\mathrm{NEP} \approx 2 \times 10^{-17} \, \mathrm{W} \, \mathrm{Hz}^{-1/2}$, referenced to absorbed power. At higher source power levels we observe the relationships between noise and power expected from the photon statistics of the source signal: $\mathrm{NEP} \propto P$ for broadband (chaotic) illumination and $\mathrm{NEP} \propto P^{1/2}$ for continuous-wave (coherent) illumination.