A magnetic environment with reproducible spatio-temporal magnetic conditions at picotesla level
Walk-in, picotesla-scale environments are essential for measurements of biomagnetism and fundamental physics. However, conventional rooms require typical active dynamic compensation, which adds complexity and magnetic noise. Here, we present a solution that achieves an absolute residual field well below 100$\,$pT within its central measurement volume. Following magnetic equilibration, this environment achieves picotesla-scale reproducibility. Consequently, optically pumped magnetometers operate at their design noise and drift performance and remain operational during sensor motion without active feedback. A key technique is robotic mapping, which resolves the ultra-low residual field patterns and demagnetization stability. We demonstrate the platform's versatility through high-fidelity adult and fetal magnetocardiography, standing magnetoencephalography, and ultra-low field magnetic resonance with polarized noble gases in the limit of strongly coupled spins in a negligible holding field. The achieved passive reproducibility turns the ultra-low magnetic background into a predictable, correctable property, establishing a novel foundation for next-generation quantum sensing and precision physics.