Using the universe's coldest material to measure the world's tiniest
magnetic fields

Date:
February 8, 2022
Source:
ICFO-The Institute of Photonic Sciences
Summary:
Using atoms only a few billionths of a degree above absolute zero,
a team of researchers has detected magnetic signals undetectable
by any other existing sensor technology.



FULL STORY ========================================================================== Using atoms only a few billionths of a degree above absolute
zero, a team of researchers from ICFO and Aalto University have
detected magnetic signals undetectable by any other existing
sensor technology. Magnetometers measure the direction, strength or
relative changes of magnetic fields, at a specific point in space and
time. Employed in many research areas, magnetometers can help doctors
to see the brain through medical imaging, or archaeologists to reveal underground treasures without excavating the ground.


==========================================================================
Some magnetic fields of great interest, for example those produced by
the brain, are extraordinarily weak, a billion times weaker than the
field of the Earth, and therefore, extremely sensitive magnetometers
are required to detect these weak fields. Many exotic technologies have
been invented for this purpose, including superconducting devices and laser-probed atomic vapors. Even the impurities that give some diamonds
their color have been used as magnetic sensors. Until now, however, the sensitivity of all of these technologies has stalled at about the same
level, meaning that some magnetic signals were simply too faint to detect.

Physics describes this limitation with a quantity called the energy
resolution per bandwidth, written ER, a number that combines the spatial resolution, the duration of the measurement, and the size of the sensed
area. In about 1980, superconducting magnetic sensors reached the level
ER = ħ and since then, no sensor has been able to do better (ħ, pronounced "h bar," is the fundamental Planck's constant, also called
the quantum of action).

Surpassing the energy resolution limit In a study published at PNAS,
ICFO researchers Silvana Palacios, Pau Go'mez, Simon Coop and Chiara
Mazzinghi, led by ICREA Prof. Morgan Mitchell, in collaboration with
Roberto Zamora from Aalto University, report a novel magnetometer that
for the first time achieves an energy resolution per energy bandwidth
that goes far beyond this limit.

In the study, the team 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 that responds to magnetic fields in the same way as an ordinary compass needle,
but can reorient itself with zero friction or viscosity. Because of
this, a truly tiny magnetic field can cause the condensate to reorient,
making the tiny field detectable. The researchers showed that their Bose condensate magnetometer has achieves an energy resolution per bandwidth
of ER= 0.075 ħ, 17 times better than any previous technology.

A qualitative advantage With these results, the team confirms that their
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.

========================================================================== Story Source: Materials provided by
ICFO-The_Institute_of_Photonic_Sciences. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Silvana Palacios Alvarez, Pau Gomez, Simon Coop, Roberto
Zamora-Zamora,
Chiara Mazzinghi, Morgan W. Mitchell. Single-domain Bose condensate
magnetometer achieves energy resolution per bandwidth below ℏ.

Proceedings of the National Academy of Sciences, 2022; 119 (6):
e2115339119 DOI: 10.1073/pnas.2115339119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220208105202.htm
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