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arXiv · 2603.06772

Fundamental Limits of Quantum Sensors for Gravitational Wave Detection

Sergio Gaudio
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Abstract

Recent advances in quantum sensing---optical clocks, frequency-dependent squeezing below the standard quantum limit, and quantum magnetometers---raise a natural question: can these technologies detect gravitational waves directly, or enhance existing detectors? We show that the answer is set primarily by the \emph{coupling mechanism} between wave and sensor. From the tidal Hamiltonian in Fermi normal coordinates we identify three physically distinct mechanisms by which a gravitational wave couples directly to a quantum system, and derive their transducer gains within linearized general relativity and non-relativistic quantum mechanics. Internal atomic coupling yields a transducer gain $G_A = 2.4\times 10^{-20}$, with vanishing first-order energy shifts for all $J=0$ clock states---a $\sim\!10^{35}$ deficit relative to laser interferometry. Center-of-mass (Doppler) coupling reaches strain sensitivities of $\sim\!10^{-18}$, still $10^4$ above LISA requirements. Only light-propagation coupling provides the enormous transducer gain that makes laser and atom interferometry viable. For detectors of this third kind we quantify the quantum enhancement accessible through the noise architecture: LISA's noise budget is predominantly classical, capping the combined enhancement at $\mathcal{E}\approx 1.04$, while ground-based detectors in the shot-noise-dominated regime achieve $\mathcal{E}=1.6$--$2.1$. Atom interferometers exploit the same mechanism to target the 0.01--10~Hz band.

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Sergio Gaudio. 2026-03-06. Fundamental Limits of Quantum Sensors for Gravitational Wave Detection. https://doi.org/10.1088/1361-6382%2Fae9449

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