Fig. 1: Quantum sensor network.
From: Long-baseline quantum sensor network as dark matter haloscope
a A network of 15 atomic magnetometers situated in two separate shield rooms in Suzhou and Harbin, China, with a distance of 1692 km between them. Such magnetometers are synchronized with the global positioning system. The underlying map is from Google Earth. b Schematic for dark photon dark matter (DPDM) induced radio signal inside a shielded room. Each room is made of five-layer mu-metal and its innermost layer has the dimension of 2 × 2 × 2 m3. A magnetic field can be produced by the DP radio current \({\overrightarrow{{{{{{{{\bf{J}}}}}}}}}}_{{{{{{{{\rm{eff}}}}}}}}}\) (dashed line) along z. Miniaturized atomic magnetometers (QuSpin Inc.) are installed on the surface of the shield room and detect the DP induced magnetic field (green circle) along the y direction parallel to the wall. c Schematic illustration of atomic magnetometer based on zero-field resonance. Top, operation in zero field; bottom, operation with a measured field that causes alkali-metal spin precession and reduces the transmitted light intensity.
