Distributed quantum sensors tighten ultralight axion dark-matter bounds
A multi-city network of hyperpolarized noble-gas spin sensors correlates five lab setups to search for transient, defect-induced axion signals. Through amplified signals and optimized noise filtering, the experiment constrains axion–nucleon coupling across 10 peV to 0.2 μeV, achieving 4.1×10^10 GeV at 84 peV. These bounds surpass some astrophysical limits under different model assumptions and illustrate a path toward detecting transient axion phenomena (waves, axion stars, strings, Q-balls) with distributed quantum sensors.