Scientists have discovered a way to transform a long-standing limitation in Earth-field range atomic magnetometry into a quantum advantage. The NonLinear Zeeman (NLZ) effect has historically restricted the sensitivity and accuracy of atomic magnetometers operating in Earth’s magnetic field range. Rather than trying to eliminate this effect, researchers have identified that it naturally generates intrinsic Spin Squeezed States (SSS) within individual atoms through nuclear-electron spin coupling.
The challenge has been that these quantum states oscillate in both degree and axis orientation, making them difficult to observe and utilize. The research team developed an innovative “quantum locking” technique using dynamic decoupling sequences optimized by machine learning to stabilize these oscillating states, effectively harnessing their quantum properties.
This breakthrough enables Earth-field-range magnetometers to operate beyond the Standard Quantum Limit (SQL) that constrains conventional sensors. By applying differential evolution algorithms—inspired by natural selection strategies—the researchers created a model-free approach that could potentially benefit various quantum technologies struggling with decoherence issues.
The implications extend far beyond theoretical physics. Sensitive magnetic field measurements in the Earth-field range (approximately 50 μT) are vital for geological surveys, biomedical applications, fundamental physics experiments, and magnetic navigation systems. While alkali-metal atomic magnetometers can achieve femtotesla sensitivity, they’ve been hampered by the NLZ effect’s tendency to split and distort magnetic-resonance lines.
Previous approaches focused on eliminating the NLZ effect while preserving spin coherence. However, this research reveals that embracing and controlling the quantum states naturally created by this “problematic” effect provides greater benefits than attempting to suppress it.
This intelligent magnetometry approach, which automatically exploits intrinsic quantum advantages to surpass conventional measurement limits, opens new avenues for quantum metrology, Earth-field sensing applications, and quantum control techniques. The work represents a paradigm shift in converting what was once considered a fundamental limitation into a resource for enhanced measurement capabilities.
npj Quantum Information, Published online: 03 March 2025; doi:10.1038/s41534-025-00971-9
