Axion polarimetry with parametric readout: photon-number conversion and sensitivity limits
Abstract
We propose a bias-assisted active photon-number conversion scheme for axion-induced polarization rotation in a four-port optical ring cavity with parametric readout. A calibrated real polarization rotation applied \emph{before} the final optical parametric oscillator (OPO) converts the otherwise quadratic response of the summed output photon number into a linear signal. We derive the resulting photon moments and the extracted-field covariance, retaining the four-port optical transfer, finite axion coherence and linewidth. Our principal phenomenological result is a prospective low-mass sensitivity window at ma=10−18--10−16 eV, extending below the published exclusion bounds included in our comparison, notably the NuSTAR M82 limits. This is a conditional noise-equivalent projection, using the adopted A/σA=1 stochastic-power criterion and a parameterized technical-noise budget, not a confidence-level exclusion forecast. As a separate readout result, OPO-based total counting reduces the noise-equivalent coupling by approximately 5% relative to matched selective attenuation in a favorable higher-frequency band; 5% internal loss together with a $0.10$-rad pump-phase offset leaves a 3.5% advantage in the stated example. A coherent input with only the final OPO retains this high-frequency benefit, whereas optimized coherent polarimetry remains more sensitive in the baseline. Our results identify both the operating principle of active number conversion and the stability requirements for a future implementation.
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BibTeX
@misc{capolupo2026axion,
title = {{Axion polarimetry with parametric readout: photon-number conversion and sensitivity limits}},
author = {Antonio Capolupo and Gabriele Pisacane and Raoul Serao},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.03340},
eprint = {2611.03340},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.03340},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Axion polarimetry with parametric readout: photon-number conversion and sensitivity limits
AU - Antonio Capolupo
AU - Gabriele Pisacane
AU - Raoul Serao
PY - 2026
DA - 2026/11/02
PB - arXiv
DO - 10.48550/arxiv.2611.03340
UR - https://arxiv.org/abs/2611.03340
AB - We propose a bias-assisted active photon-number conversion scheme for axion-induced polarization rotation in a four-port optical ring cavity with parametric readout. A calibrated real polarization rotation applied \emph{before} the final optical parametric oscillator (OPO) converts the otherwise quadratic response of the summed output photon number into a linear signal. We derive the resulting photon moments and the extracted-field covariance, retaining the four-port optical transfer, finite axion coherence and linewidth. Our principal phenomenological result is a prospective low-mass sensitivity window at m_a=10^−18--10^−16 eV, extending below the published exclusion bounds included in our comparison, notably the NuSTAR M82 limits. This is a conditional noise-equivalent projection, using the adopted A/σ_A=1 stochastic-power criterion and a parameterized technical-noise budget, not a confidence-level exclusion forecast. As a separate readout result, OPO-based total counting reduces the noise-equivalent coupling by approximately 5% relative to matched selective attenuation in a favorable higher-frequency band; 5% internal loss together with a $0.10$-rad pump-phase offset leaves a 3.5% advantage in the stated example. A coherent input with only the final OPO retains this high-frequency benefit, whereas optimized coherent polarimetry remains more sensitive in the baseline. Our results identify both the operating principle of active number conversion and the stability requirements for a future implementation.
ER -