Optimal Calibration-Free Observable for the Nucleon-Coupling Ratio in a Dual-Alkali Comagnetometer for Dark Matter Searches
Abstract
A dual-alkali single-cell 87Rb-39K-3He comagnetometer can read an axion-like dark matter signal through two optical rotation channels, encoding the ratio ℛ=ξn/ξp of the field's neutron and proton spin couplings in their relative response. The inter-species phase difference Δφ has been proposed as a calibration-free readout that is sensitive to ℛ. Treating the extraction of ℛ as a statistical estimation problem, we show that the estimate of ℛ depends on the two channels only through their complex ratio, which splits into Δφ and an amplitude ratio, of which only Δφ is insensitive to the relative gain and hence calibration free. For our choice of comagnetometer parameters, above ∼ 100 Hz the phase difference alone captures most of the coupling-ratio information. At lower frequencies Δφ is no longer near-sufficient. Below ∼ 40 Hz, the amplitude ratio would improve the precision on ℛ by a factor of ≳2. Recovering that information, however, requires the relative gain to be known sufficiently accurately, so Δφ remains the robust observable even where it is not the most informative one.
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BibTeX
@misc{rosenzweig2026optimal,
title = {{Optimal Calibration-Free Observable for the Nucleon-Coupling Ratio in a Dual-Alkali Comagnetometer for Dark Matter Searches}},
author = {Yossi Rosenzweig and Yevgeny Kats and Eli Sarid and Menachem Givon and Yonathan Japha and Ron Folman},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.07456},
eprint = {2608.07456},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.07456},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Optimal Calibration-Free Observable for the Nucleon-Coupling Ratio in a Dual-Alkali Comagnetometer for Dark Matter Searches
AU - Yossi Rosenzweig
AU - Yevgeny Kats
AU - Eli Sarid
AU - Menachem Givon
AU - Yonathan Japha
AU - Ron Folman
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2608.07456
UR - https://arxiv.org/abs/2608.07456
AB - A dual-alkali single-cell ^87Rb-^39K-^3He comagnetometer can read an axion-like dark matter signal through two optical rotation channels, encoding the ratio ℛ=ξ_n/ξ_p of the field's neutron and proton spin couplings in their relative response. The inter-species phase difference Δφ has been proposed as a calibration-free readout that is sensitive to ℛ. Treating the extraction of ℛ as a statistical estimation problem, we show that the estimate of ℛ depends on the two channels only through their complex ratio, which splits into Δφ and an amplitude ratio, of which only Δφ is insensitive to the relative gain and hence calibration free. For our choice of comagnetometer parameters, above ∼ 100 Hz the phase difference alone captures most of the coupling-ratio information. At lower frequencies Δφ is no longer near-sufficient. Below ∼ 40 Hz, the amplitude ratio would improve the precision on ℛ by a factor of ≳2. Recovering that information, however, requires the relative gain to be known sufficiently accurately, so Δφ remains the robust observable even where it is not the most informative one.
ER -