Measuring the world’s tiniest magnetic fields

A novel magnetometer that achieves an energy resolution per energy bandwidth that goes far beyond this limit.


Some magnetic fields are fragile, hence require extremely sensitive magnetometers to detect them. Until now, scientists have invented many such technologies for this purpose, but they all stalled at about the same level, meaning that some magnetic signals were too faint to detect.

Magnetometers measure the direction, strength, or relative changes of magnetic fields, at a specific point in space and time. They can help doctors see the brain through medical imaging or archaeologists to reveal underground treasures without excavating the ground.

Scientists from ICFO and Aalto University have detected magnetic signals undetectable by any other existing sensor technology using atoms only a few billionths of a degree above absolute zero. To do so, they come up with a novel magnetometer that achieves an energy resolution per energy bandwidth that goes far beyond this limit.

Scientists used a single-domain Bose-Einstein condensate to create this exotic sensor. This condensate was made of rubidium atoms, cooled to nano-Kelvin temperatures by evaporative cooling in a near-perfect vacuum, and held against gravity by an optical trap.

At these ultracold temperatures, the atoms form a magnetic superfluid. This superfluid responds to magnetic fields like a compass needle. Plus, it can reorient itself with zero friction or viscosity. Because of this, a genuinely tiny magnetic field can cause the condensate to reorient, making the tiny field detectable.

The novel bose-condensate magnetometer achieved an energy resolution per bandwidth of ER= 0.075 ħ, 17 times better than any previous technology.

Scientists noted“The sensor is capable of detecting previously undetectable fields. This sensitivity could be improved further with a better readout technique or by using Bose-Einstein condensates made of other atoms. The Bose-Einstein condensate magnetometer may be directly useful in studying the physical properties of materials and in hunting for the dark matter of the Universe.”

“Most importantly, the finding shows that ħ is not an unpassable limit, and this opens the door to other extremely-sensitive magnetometers for many applications. This breakthrough is interesting for neuroscience and biomedicine, where detection of extremely weak, brief and localized magnetic fields could enable the study of new aspects of brain function.”

Journal Reference:

  1. Silvana Palacios Alvarez et al. Single-domain Bose condensate magnetometer achieves energy resolution per bandwidth below ℏ. DOI: 10.1073/pnas.2115339119
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