Chinese-German team builds ultra-sensitive ‘floating compass’ to hunt dark matter

Chinese researchers have developed a table-top magnetic sensor that operates at room temperature and can spot magnetic signals a billion times fainter than the Earth’s own field.

The Levitated Magnet Magnetometer (LeMaMa) functions like a compass with a needle that floats in mid-air with virtually no friction. By tracking the needle’s tiny deflections, the team can measure magnetic fields down to the femtotesla level – an advance that could widen the hunt for elusive dark matter particles or monitor brain signals.

“The combination of room-temperature operation, tiny components and high sensitivity makes LeMaMa promising for fundamental physics experiments,” Ji Wei, assistant professor at Peking University’s school of physics and corresponding author of the study, told Guangming Daily on August 17.

Magnetic fields are everywhere, ranging in strength from about 1.5 tesla for a hospital magnetic resonance imaging machine to the vanishingly weak femtotesla, or a quadrillionth of a tesla, generated by human brain activity. Measuring the tiniest magnetic fields has long been a challenge.

Now, scientists from China’s Peking University and Johannes Gutenberg University Mainz in Germany have built the world’s first room-temperature ultraprecise magnetometer based on a levitated magnet. Their work was published in the journal Science on August 6.

Until now, femtotesla-level measurements have mainly relied on two approaches. One is the superconducting quantum interference device (Squid) magnetometer, which offers excellent sensitivity but must operate at cryogenic temperatures near absolute zero, requiring bulky and expensive liquid-helium cooling.