Axion like particles multi-parameter sensing

How can we simultaneously estimate the mass and coupling constants of axion-like particles (ALPs) using quantum metrology, and how can we overcome the fundamental limitations imposed by the singularity of the Quantum Fisher Information Matrix (QFIM) in such multi-parameter estimation tasks?

The researchers propose a sensing setup based on a Fermi-Hubbard lattice of trapped fermionic spins. By exploiting the position-dependent nature of the exotic pseudoscalar spin-spin interaction between a source (polarized 3He nuclei) and the sensor (trapped 40K electron spins), the system generates a gradient field that encodes information about the axion mass and coupling constants. To resolve the singularity of the QFIM—which typically prevents the simultaneous estimation of multiple parameters—the authors employ a multi-probe strategy using two orthogonal lattice configurations. They then apply the quantum Cramér-Rao bound to derive the ultimate sensitivity limits and construct an exclusion region for ALP parameters.

The study demonstrates that the multi-probe strategy effectively removes the QFIM singularity, allowing for the simultaneous estimation of axion mass and coupling constants. Numerical simulations indicate that this setup can exclude axion coupling values (gep gnp) down to 10^-7 for axion masses up to 10^-3 eV. This performance surpasses current laboratory constraints, suggesting that quantum-enhanced sensing in optical lattices is a viable path for probing dark matter candidates.

Searching for axions is a central challenge in modern cosmology, as they are prime candidates for dark matter. Traditional experimental setups often struggle to distinguish between mass and coupling parameters simultaneously. By utilizing quantum metrology and multi-probe configurations, this work provides a rigorous framework to improve the sensitivity of fifth-force searches, potentially opening new windows into physics beyond the Standard Model.