Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer

We describe an ultrasensitive atomic magnetometer based on optically pumped potassium atoms operating in a spin-exchange relaxation free regime. We demonstrate magnetic field sensitivity of 160 aT/Hz1/2 in a gradiometer arrangement with a measurement volume of 0.45 cm3 and energy resolution per unit bandwidth of 44ℏ. As an example of an application enabled by such a magnetometer, we describe measurements of weak remnant rock magnetization as a function of temperature with a sensitivity on the order of 10−10 emu/cm3/Hz1/2 and temperatures up to 420°C.