Levitating magnet sensor achieves femtotesla sensitivity for brain-wave detection

A team led by physicist Wei Ji at Peking University has demonstrated a levitating magnetometer that can sense magnetic fields at the femtotesla level, sufficient to capture the brain's electrical activity. The sensor, smaller than one millimetre, is held aloft by a magnetic field above and a diamagnetic material below, creating a stable levitation gap of only a few hundred micrometres. A laser beam reflected off the magnet is monitored by a detector, which records minute orientation shifts when a nearby sample perturbs the field.

Housed in a Tupperware-sized vacuum chamber, the instrument avoids the extreme cooling required by SQUIDs and the heavy shielding needed for SERF devices. Additional magnetic coils and damping systems suppress interference from ambient fields and vibrations, achieving unprecedented sensitivity. This simpler, more compact design could broaden access to ultra-weak magnetic measurements in neuroscience and other fields.