Hybrid Optical–Atom Interferometer Nodes for Robust Mid-Band Burst Detection

The AION prototype (Baynham et al. 2025) demonstrates SQL-limited atom interferometry robust to injected laser phase noise—a key mid-band advantage. We pair such an atom interferometer with a small-scale cryogenic silicon optical interferometer (Adhikari et al. 2020) to form a co-located “hybrid node.” The optical arm brings high optical bandwidth and strain readout; the atom arm acts as a noise reference with intrinsically different susceptibility to laser and platform noise. The new piece is the real-time, engineered correlation: we actively subtract shared laser phase and gravity-gradient noise using the atom readout as a differential witness, enabling detection of unexpected mid-band GW bursts and nonstandard signals. We further explore polarization Sagnac speedmeter topologies (Spencer et al. 2021) on the optical side for quantum backaction suppression, and test sensitivity to alternative-gravity polarizations (Konoplya & Zhidenko 2016), which mid-band detectors could uniquely probe. This hybrid approach (i) leverages AION’s demonstrated robustness to laser phase anomalies, (ii) adds cryogenic optical strain sensitivity, and (iii) creates a discriminant for unmodeled or exotic bursts—an especially valuable capability in a band where terrestrial interferometers are noise-limited and LISA is less sensitive. The networked deployment of such nodes could form an early-warning and anomaly-triage layer bridging ground-based and space-based observatories.

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