Magnetometers measure the direction, strength, or relative changes of magnetic fields at a given point in space and time. Used in many research fields, magnetometers can also help doctors see the brain through medical imaging or help archaeologists uncover underground treasures without digging the ground. Some magnetic fields of great interest, such as those produced by the brain, are extraordinarily weak. It is a billion times weaker than Earth's field. Therefore, highly sensitive magnetometers are required to detect these weak areas. For this purpose, superconducting devices were invented. Many exotic technologies were even invented, in which measurements of atomic vapors probed with lasers could be made. In the latest study, we can say that "The Smallest Magnetic Field Was Measured With The Coldest Material" with quantitative values.
Even the impurities that give some diamonds their color have been measured using magnetic sensors. But so far, the precision of all these technologies has stood at about the same level. This means that some magnetic signals are too weak to be detected.
In physics, this limitation defines a number called energy resolution per bandwidth. This is denoted as “ER”. The “ER” defines the spatial resolution, the duration of the measurement, and the size of the detected area.
Around 1980, superconducting magnetic sensors reached ER = ħ, and no sensor has done better since.
What is Used in Measurement Standards?
(ħ, pronounced “h bar”, is the fundamental Planck constant, also called the effect quantum).
Researchers Silvana Palacios, Pau Gómez, Simon Coop, Prof. Morgan Mitchell, Chiara Mazzinghi, and Roberto Zamora of Aalto University achieved a very good first time in their work together. Of course, we have to give you the quantitative values. The values obtained were a magnetometer measurement providing resolution per energy bandwidth far beyond the limit.
Exceptionally Precise Magnetometer
In the research, the team used a single-domain system to build this exotic sensor. Bose-Einstein condensation used. This condenser 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 temperatures, atoms responded to magnetic fields in the same way as an ordinary compass needle. It created a magnetic superfluid that could reorient itself with zero friction or viscosity.
Therefore, a really small magnetic field would cause the condensate to reorient, making the small field detectable. Now let's give you the quantitative values regarding the results obtained.
Planck's Constant Is Not An Insurmountable Limit
The researchers demonstrated that Bose condensation magnetometers achieve an energy resolution of ER= 17 ħ per bandwidth, 0.075 times better than any previous technology.
With these results, the team confirms that their sensors are able to detect previously undetected areas.
This sensitivity can be further improved by a better reading technique or by using Bose-Einstein condensates made of other atoms.
The Bose-Einstein condensation magnetometer could also be directly useful in studying the physical properties of materials and in searching for the dark matter of the Universe.
Most importantly, the finding shows that ħ is not an insurmountable limit.
This work opens the door to other highly sensitive magnetometers for many applications. It is expected that the detection of extremely weak, short and localized magnetic fields will also open a wide field of study for neuroscience and biomedicine, where it makes it possible to investigate new aspects of brain function.