Levitating sensor detects ultrafaint magnetic fields with simple design

Researchers have developed a magnetic field sensor based on a microscopic disc levitated in a vacuum chamber by magnetic fields.

The levitated microdisc acts as a mechanical oscillator whose motion can be measured with high precision using optical techniques.

Because the disc is suspended without physical contact, it avoids the thermal noise and mechanical dissipation that limit conventional solid-state sensors.

The device achieves sensitivity to magnetic field gradients at the level of femtotesla per square root hertz, comparable to much more complex superconducting quantum interference devices (SQUIDs) and optically pumped magnetometers.

The simple design consists of a commercially available magnetic particle, a magnetic trap, and an optical readout system, requiring no cryogenic cooling.

The researchers suggest the sensor could detect the extremely weak magnetic fields produced by neural activity in the brain, offering a potential alternative to existing magnetoencephalography (MEG) systems.

Beyond biophysics, the sensor's high sensitivity to tiny forces makes it a candidate for experiments searching for axion-like dark matter particles, which would exert minute forces on the levitated disc.

The work demonstrates that levitated optomechanical systems can reach fundamental quantum limits for force and magnetic field detection using relatively accessible equipment.