NIST's atom-based magnetic sensor, about the size of a sugar cube, can measure human brain activity. Inside the sensor head is a container of 100 billion rubidium atoms (not seen), packaged with micro-optics (a prism and a lens are visible in the center cutout).Geniux review. The light from a low-power infrared laser interacts with the atoms and is transmitted through the grey fiber-optic cable to register the magnetic field strength. The black and white wires are electrical connections. See also Credit: Knappe/NIST