A magnet smaller than a grain of rice, suspended in a vacuum chamber, can read magnetic fields TEN BILLION TIMES weaker than the Earth's. Wei Ji, Chang Xu, Guoqing Qu and Dmitry Budker at Peking University published it in Science on 6 August. It was reported in Nature on the same day. The device is a sub-millimetre permanent magnet suspended between a lifting magnet above and a diamagnetic stabiliser below, with a laser watching how it moves. Fields at the femtotesla scale shift it, and the laser picks that up. I mean sure, other instruments reach femtotesla sensitivity, but they just need a great deal of apparatus to do it. A SQUID, for example - SQUID being Superconducting Quantum Interference Device So a SQUID will do the job, but needs temperatures near absolute zero - meaning cryogenics - meaning the whole apparatus that goes with cryogenics. A SERF - Spin-Exchange Relaxation-Free magnetometer - also works, but needs near-perfect magnetic shielding. This NEW device needs neither, and it can sit a few hundred micrometres from whatever you're measuring. Another approach - using diamond magnetometers - also doesn't need huge amounts of apparatus, but is orders of magnitude less sensitive. Ji, on how unforgiving the regime is: "When you're probing the femtotesla scale, even a thin film of aluminium foil can introduce 100 femtoteslas of noise." #Physics #Sensors #Nature
