The earth is a magnet – but unfortunately not a very symmetrical one. The magnetic poles move constantly relative to the fixed geographical poles. Over long periods of time, the earth’s magnetic field sometimes becomes stronger, sometimes weaker, and can even completely reverse its polarity. These changes affect Earth’s magnetic shield from particle streams from the Sun and reliable compass navigation. The most accurate and frequent measurements possible are necessary in order to update the World Magnetic Model (WMM) as quickly as possible. The National Geospatial Intelligence Agency in the USA is therefore organizing the MagQuest competition, in which the world‘s best magnetometers – installed on satellites – compete against each other.
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MagQuest is now entering a decisive round with only three finalists left. In addition to a scaler vector magnetometer from the University of Colorado in Boulder and a vector fluxgate magnetometer from Iota Technology, the Canadian company SBQuantum is using a new type of quantum magnetometer. All three are now building small, compact systems that, according to current plans, are scheduled to begin taking measurements in Earth orbit in mid-2025.
The heart of the quantum magnetometer is an artificial diamond. During the cultivation of diamond crystals from a hot carbon-containing cloud, defects in the crystal structure, so-called nitrogen gaps, are deliberately created. Two electrons are essentially freed at each of these defects. Therefore, their own angular momentum, the spin, can be influenced by a magnetic field via the Zeeman effect. A splitting of spectral lines occurs due to the different shifts in the energy levels of individual states. Using a combination of a precisely adjusted laser, a microwave transmitter and a photodetector, this splitting can be measured as an exact measure of the magnetic field.
With their quantum magnetometer, the developers at SBQuantum hope to be able to measure the strength and orientation of a magnetic field more reliably and precisely than the other two finalists. Tests in the coming years will show whether this actually works. The winner of MagQuest could then replace the three satellites Alpha, Bravo and Charlie of the European Space Agency (ESA)’s Swarm mission. The Swarm satellites, which were launched at the end of 2013, have been measuring the earth’s magnetic field for much longer than intended – the mission was designed for four years – and are essentially waiting to be replaced.
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